Yaesu FT-8900R Repair – Part 01

While visiting family in Espanola, the three of us (Julie, Felix and I) stayed with one of Julie’s cousins (Denis), who as it happens is a fellow ham (VE3OOZ). Back in May, Denis showed me some of his radio gear and lamented that he had a nice quad-band radio which had the magic smoke escape. I asked Denis to save the radio from the scrap bin if he was planning to throw it away. In an attempt to save the radio, Denis sent it away to be assessed and if practical, have it repaired.

Work order for repair of FT-8900R

Work order for repair of FT-8900R

Well .. the radio came back from the repair shop with a ~$100 invoice saying that they were unable to repair the radio as the final amplifier requires a special soldering tool (which apparently the repair shop does not have access to). Looking at the FET, I am unable to imagine what kind of “special tool” is required.

At the conclusion of our visit in Espanola, Denis offered up the “box full of parts” for me to attempt my first modern radio repair!

The problem: the radio would key-up but would not produce any RF at the antenna port. The likely cause: a blown final amplifier.

Rigol DS2202 200MHz oscilloscope using home-made short ground lead and probe tip for high-frequency measurements.

Rigol DS2202 200MHz oscilloscope using home-made short ground lead and probe tip for high-frequency measurements.

My first order of business was to prepare my oscilloscope for high-frequency probing at an impedance of 50Ω. I rummaged through my box of connectors which a very generous ham (Ted) gave me a few years ago. My quest was for an in-line 50Ω termination. With the scope termination impedance matched to the radio, I turned my attention to the probe itself.

When working with high frequency waveforms, it is useful to keep the ground lead as short as possible which meant fabricating an on-probe ground leg out of some scrap wire.

200MHz probe with small wire wrapped around probe ground to provide short lead.

200MHz probe with small wire wrapped around probe ground to provide short lead.

Short ground legs are commercially available and have the advantage of being made of spring-steel which is a godsend. My poor rendition of a ground spring used a length of tinned copper wire wrapped multiple times around a golf-tee as a form. I then transferred the coil end onto the scope probe and bent up the long remainder of the wire into a lead form as shown in the image.

Having spring steel would have made life a whole lot better as it turns out. Too bad I am cheap!

Basic test setup with radio and a Bird 300W 50Ω dummy load.

Basic test setup with radio and a Bird 300W 50Ω dummy load.

With the oscilloscope ready for action, I prepared the radio which meant powering it up and reducing the RF output power to 5W on all bands.

Recall that VHF/UHF is quite bad for the eyes as they absorb the RF energy at a disproportionately higher rate than the rest of your body!

I also terminated the radio antenna port into a 50Ω dummy load to provide a resistive load for the RF to meet with both safety and regulatory requirements. My initial transmission included my callsign and “testing” just to be above-board with the whole process.

Yaesu FT-8900R guts showing primary area of interest for probing 2m and 70cm amplification stages (area shown in red box).

Yaesu FT-8900R guts showing primary area of interest for probing 2m and 70cm amplification stages (area shown in red box).

My initial test at 144.400MHz had the probe at the final FET and did not produce a waveform on the oscilloscope screen – it did however show the DC bias on the FET for normal operation. Time to change the probe inputs to AC coupling! (oops)

I then consulted the service manual for the radio in order to determine the signal path for 2m. The radio operates on four bands and so it would be important to check the output for all four bands as there are bound to be at least a few possible paths. The hope is to find a common fault which is ideally less involved and cheaper to repair.

Factory service manual showing 2m and 70cm signal paths.

Factory service manual showing 2m and 70cm signal paths.

As per the documentation:

144 MHz Signal
The adjusted speech signal from Q1054 is passed through the transistor switch Q1501 (BU4066BCFV) to varactor diodes D1076 and D1077 (both HVC365), which frequency modulate the transmitting VCO, made up of the VHF-VCO/B Q1109 (2SC5375) and D1078 (HSC277).

Probing the waveform at the gate of Q1139 (also confusingly shown as Q1039 in schematics).

Probing the waveform at the gate of Q1139 (also confusingly shown as Q1039 in schematics).

The modulated transmit signal is passed through buffer amplifiers Q1100 and Q1111 (both 2SC5374) and diode switches D1075 (HSC277) and D1128 (DAN235E) to the pre-drive amplifier Q1139 (2SK2596).

5W (intended) 144.400MHz waveform showing 1.5Vpp (500mV vertical scale) when probing the gate of Q1138 (also shown as Q1039).

5W (intended) 144.400MHz waveform showing 1.5Vpp (500mV vertical scale) when probing the gate of Q1139 (also shown as Q1039).

The amplified transmit signal from Q1139 is passed through the diode switch D1139/D1140 (both HSC277) and the driver amplifier Q1137 (2SK2975) to diode switch D1133 (RLS135), then finally amplifier by power amplifier Q1134 (RD70HVF1) up to 50 Watts of power output. These three stages of the power amplidier’s gain are controlled by the APC circuit.

The 50-Watt RF signal is passed through a low-pass filter network to the antenna switching relay RL1001 (G5A237P), then passed through a high-pass filter network and another low-pass filter network to the ANT jack.”

The results shown indicate that the modulated audio is making it as far as Q1139 (the pre-drive amplifier) which is taking a 1.5Vpp signal and effectively amplifying it to 28Vpp.

Probing the waveform at the drain of Q1139 (also confusingly shown as Q1039 in schematics).

Probing the waveform at the drain of Q1139 (also confusingly shown as Q1039 in schematics).

Checking the drain of Q1139, the 144.400MHz signal was observed to have a peak-to-peak voltage of 28.2V

This means that we can feel reasonably certain that the pre-driver amplifier is fine and is passing the appropriate signal level on to the next amplification stage.

5W (intended) 144.400MHz waveform showing 28.2Vpp (5v vertical scale) when probing the drain of Q1138 (also shown as Q1039).

5W (intended) 144.400MHz waveform showing 28.2Vpp (5v vertical scale) when probing the drain of Q1139 (also shown as Q1039).

Between the stages are a series of filter elements and diode switches. The easiest circuit element to check are the inductors as they should have a low in-circuit resistance and in the correct signal path, should pass the RF signal with some ease.

The diodes can be checked with a VOM in-circuit by using the (often) built-in diode check function. Being sure to test the diodes in both possible orientations, my first check would be for complete opens (that is no conductivity in either direction).

Before starting on the individual components, it is worthwhile to check the input side of the next amplification stage (the gate of Q1137) to see if we have a reasonable signal at that pin.

5W (intended) 144.400MHz waveform showing 28.6Vpp (5v vertical scale) when probing the left side of L1141

5W (intended) 144.400MHz waveform showing 28.6Vpp (5v vertical scale) when probing the left side of L1141

Upon scoping the gate of Q1137, it was found that there was no appreciable signal at that pin. Time to go back through the signal path and take some measurements at various points.

The first verification was the left side of L1141 to ensure that the same signal leaving Q1139 actually lands at the inductor. Sure enough, we have a good waveform and so to ensure that the

5W (intended) 144.400MHz waveform showing 28.0Vpp (5v vertical scale) when probing the right side of L1141

5W (intended) 144.400MHz waveform showing 28.0Vpp (5v vertical scale) when probing the right side of L1141

inductor is passing the signal, the right side was scoped and the output captured.

The voltage on the right side of L1141 was 28.0Vpp and the waveform looked very good. C1727 was the next component in the signal path, so it made sense to continue proving the signal as it progressed through the filtering / switching stage.

The results were interesting to say the least.

5W (intended) 144.400MHz waveform showing 27.2Vpp (5v vertical scale) when probing the bottom side of C1727

5W (intended) 144.400MHz waveform showing 27.2Vpp (5v vertical scale) when probing the bottom side of C1727

At the bottom side of C1727, a nice clean 27.2Vpp signal was observed. On the other side of C1727, there was a significant drop in voltage.The signal was measured to be 9.76Vpp. The voltage dropped across C1727 was 17.44V

5W (intended) 144.400MHz waveform showing 9.76Vpp (2v vertical scale) when probing the top side of C1727

5W (intended) 144.400MHz waveform showing 9.76Vpp (2v vertical scale) when probing the top side of C1727

Although my oscilloscope is rated (and calibrated) to 200MHz, it has been tested to be within the 3dB range beyond 350MHz and so I am fairly comfortable in the measured waveform voltage.

Does this decrease in voltage across C1727 concern me? Time to have a look at the value for C1727.

The service manual lists the capacitance to be 33pF with a 50V rating.

The expected current through a 50Ω resistor with a voltage drop of 17.44V is 0.35A (I = 17.44 / 50Ω) and thus, using this current, we can calculate the expected voltage drop across the capacitor and compare it against the measured value. First, we will need to calculate the impedance (capacitive reactance) of the capacitor.

Recall that capcitors improve in their ability to pass AC signals as capacitance and frequency increase, therefore, the reactance decreases. This informs us to use the following equation:

Xc = 1 / (2 π C) therefore Xc = 1 / (6.28 * 144E6 * 33E-9) = 0.033Ω

According to Ohm’s Law, the expected voltage drop should be: 0.01V (V = 0.35A x 0.033Ω) versus the observed 17.44V. With a voltage drop of 17.44V across an (expected) 0.033Ω the current would be 528A (I = 17.44v / 0.033Ω) which is impossible for this tiny capacitor. Looks like this capacitor is suspect!

… more to follow

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DSP232+ and the RTS / CTS fix

If you own a Timewave DSP-232+ TNC and are trying to connect to it using a USB to serial adapter, then you have likely come across issues when trying to operate in KISS mode. No matter what the settings, it appears that the DSP-232+ requires hardware flow control using the RTS (ready to send) and CTS (clear to send) control lines.

RS232 pinouts

RS232 pinouts

Most USB to serial adapters that I’ve worked with do not have the facility to use the RTS / CTS lines. One solution would be to replace the passive DB-9 serial plug with a DB9-USB-M which acts as a USB to serial converter that allegedly supports RTS / CTS.

DSP232+ RS232 schematic

DSP232+ RS232 schematic

In this case, I plan to short out RTS to CTS on the DSP232+ circuit board, fooling the DSP232+ into believing there is hardware flow control from the host. Looking on page 275 of the DSP232+ manual, the schematic for the RS232 port is shown.

Looking to make the hardware flow control fix a temporary measure, I would like to short out the RTS and CTS pins with a jumper wire. This is most easily accomplished by looking for convenient connection points in the circuit.

The RTS line (pin 7) and CTS line (pin 8) are shown as connecting to decoupling capacitors C11 and C15 respectively.

To short the RTS and CTS lines, we will look for the “high side” of the decoupling capacitors on the circuit board.

Location of C11 and C15 on DSP232+ circuit board

Location of C11 and C15 on DSP232+ circuit board

Looking at the PCB, the manufacturer was kind enough to label the components on the top-side. The red arrows in the accompanying image indicate the “high side” of the capacitors (note the thick ground-plane on the opposite side of the SMD caps?).

Using a thin piece of insulated wire, I will solder one leg to the capacitor C11 (lower right) and insert the other bare end into the via shown at C15.

C11 to C15 jumper soldered in to short RTS to CTS

C11 to C15 jumper soldered in to short RTS to CTS

With the jumper in place, we can test the DSP232+ with a USB to serial adapter, putting the TNC into KISS mode and waiting to see packets in the command line.

I will admit that my solder job at C11 is not the most beautiful sight to behold, but it will work for this test.

Notice also I’ve got some bodge wires – they connect the DB9 connector to their signal-appropriate nodes on the PCB. The old USB to serial style adapter which came with this DSP232+ was fried and the traces were lifted, necessitating a repair job to make the unit functional.

DS1216C and U5 stackedIn other news, I finally received the DS1216C that I’ve been waiting to try as a RTC for the DSP232+. The Dallas parts never did work when I tried to parallel them with the EPROM U5 shown in the above image. The DSP232+ boots normally with the DS1216C stack as shown and so I used some hot-glue to hold everything in place as the DS1216C has less than stellar mounting to the original socket.

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DSP-232+ and KISS operation

While I wait for my DS1243Y-120+ samples to arrive, I thought I would spend a bit of time working with my DSP-232+ and a Raspberry Pi. Although the DSP-232+ is capable of acting as a standalone system, I would like to press it into service as a simple TNC for VHF packet and APRS use. One plan is to have a Raspberry Pi acting as an iGate for APRS.

To begin, I connected a USB-to-RS232 adapter to the Pi and the TNC. This was a simple task and allows the Pi to communicate with the TNC at RS232 levels. The DSP-232+ does not communicate at TTL levels and so the USB to serial adapter bridges that gap nicely.

The distribution I am using on the Pi at the time of writing is Rasbian Jessie and uses kernel 4.1. After installing the distribution, I updated the packages by running the commands:

sudo apt-get update
sudo apt-get upgrade

After the updates are completed (which may take quite some time), I installed a number of AX.25 tools which are central to packet operation and the Raspberry Pi. This is done by issuing the command:

sudo apt-get install screen build-essential python-serial sqlite3 python-dev soundmodem libax25 libax25-dev ax25-tools ax25-apps libax25-dev

With the AX.25 packages installed, we are ready to start modifying the system to match our setup. To start, I edited the axports file to create a virtual radio port which will communicate with the radio via the DSP-232+ TNC.

sudo vi /etc/ax25/axports

One particular note – the axports file must not contain any blank lines! Be sure to keep this in mind when editing the file. My axports file simply contains the line:

0       VE3BUX-1        9600   128     4       TNC1

This creates a radio port (numbered zero) which has a data rate (to the TNC – not over the air) of 9600bps which matches my TNC settings. The next two values are “paclen” and “maxframe”.

“paclen” sets up the length of packets, smaller being used in more challenging (noisy) situations and on HF. As a general guide, it is suggested to use 128 as a default (particularly when using nodes or digipeaters). A value of 255 can be used for very low-noise environments and for direct connections. In my case, the DSP-232+ has a default paclen of 128 for 1200 baud VHF packet (p82 of the manual).

“maxframe” is one of the values which determines how data is sent in general. A good starting point is to use a maxframe of 4 as a default for VHF – perhaps as high as 7 for ideal conditions. For HF or marginal to poor conditions, a setting of 2 or even 1 is suggested.

With the axports file edited to our needs, we can now create the KISS port for the Pi to interface with. To create the interface, we need to know where the serial port exists in our /dev system. In my case, the USB device can be addressed as:

/dev/ttyUSB0

We will attach our KISS port 0 to the system and assign it an IP address of 44.128.0.2

Something to note is that you can assign a private IP4 address to the port – I selected the 44.0.0.0/8 network block as AMPRNet is specifically for Amateur Radio. You can request a 44 network IP address by using the AMPRNet portal.

sudo kissattach /dev/ttyUSB0 0 44.128.0.2

Until I can have an IP address assigned, I will “piggyback” on the network as 44.128.0.2 which should not be an issue as there is essentially zero packet activity in my area (aside from APRS).

If you run the command:

ifconfig

You should see an ax port in your network configuration list:

ifconfig sample output

ifconfig sample output

Next, we can test our configuration by tuning into the APRS frequency 144.390MHz and watching for packets:

sudo axlisten -a -c
axlisten sample output

axlisten sample output

A neat daemon which runs in the background is mheardd which listens for packet stations and stores the data in the file /var/ax25/mheard/mheard.dat which will store  the last 100 callsigns as well as the last heard date & time. To run the daemon, type:

sudo mheardd

At any time  you can use the mheard command to recall the callsigns your system has decoded from packet data.

mheard

The output of which will look like:

mheard test output

mheard test output

Once you are able to see packet data, you are in business! This opens up a world of possibilities for you – APRS iGate, Packet BBS, etc …

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Modifying a Timewave DSP-232+

Now that I have a feedline to the attic, I can really start to make use of my radio and its accessories. Some time ago I picked up a Timewave DSP-232+ TNC / full featured radio modem. I thought it might be fun to hook up the TNC and set up a packet / APRS station, so I started reading the DSP-232+ manual once again.

U5 EEPROM installed in DSP-232

U5 EEPROM installed in DSP-232

DS1216C real time clock

DS1216C real time clock

While perusing the manual, I noticed an entry in ch4 p10 which mentions that it would be possible to add a DS1216C SmartWatch clock chip from Dallas Semiconductor (now Maxim). The real-time clock would allow the DSP-232+ to operate without a computer and to keep accurate time. Interested in such a possibility, I looked up the part and found that it was discontinued. There are sources for these microchips out there but I was happy to try to use an alternative. According to the Maxim website, it is possible to replace the DS1216C with a newer realtime clock chip such as the DS1244Y-70+.

U5 and DS1244Y+70 microchips

U5 and DS1244Y+70 microchips

I ordered a couple of DS1244Y samples from Maxim and they arrived only a few days later. I have got to say that I am extremely grateful that the electronics industry provides engineering samples – this is a phenomenal resource and I often make us of it. It is a wise investment as many designers tend to use the parts which they sample and use in the prototyping phase of a project for their final design. I certainly do so whenever practical.

Chip stack dry-fit

Chip stack dry-fit

With the replacement RTC in-hand, I was ready to install the chip in the DSP-232. The old part (DS1216C) was a “pass-through” type where the existing EPROM (U5) would be inserted on top of the RTC and the RTC-U5 combo would be re-installed in the U5 socket. It is somewhat common to have a RTC and a RAM/ROM chip combo as the RTC often provides non-volatile ram in a design. The DS1244Y, while also a 600-mil DIP package, is not a pass-through design.

Reading U5 EPROM - M27C512

Reading U5 EPROM – M27C512

Prior to soldering the chips together, I thought it prudent to press my MiniPro TL866 programmer into service.

 

While tinkering in the past, I have let the magic smoke out of many microchips and I did not wish to repeat the experience. This ROM has data that I am unable to replace. As such, I like to keep binary files that contain a bit-wise copy of all data for the PROMS that I can get my hands on. You’d be amazed at the code / data that I have collected over the years.

MiniPRO programmer settings

MiniPRO programmer settings

I inserted the ST Microelectronics M27C512 one-time program EPROM into the reader and fired up the MiniPro.exe (v6.5). You may have to update the firmware on the programmer as I did – this is to improve stability and performance and is highly recommended.

 

Selecting “Select IC (S)” then “Search and Select”, I typed in the chip’s identification M27C512, selected ST on for the “manufactuory” and then the DIP28 device.

MiniPro TL866 read/write results

MiniPro TL866 read/write results

The read process proceeded very quickly and have the “Ok” result.

Being weary of the results, I often do a second read to confirm that there were no issues. In the past, I’ve saved corrupted data when a misleading read result was obtained.

The MiniPro TL866 is a very budget friendly programmer and is well worth buying on eBay, despite the obvious issues with translation, etc. The unit and software support a large number of manufacturers and chipsets.

MiniPro data screen for M27C513 PROM

MiniPro data screen for M27C513 PROM

Once you select “Cancel” from the read / write screen, the downloaded data is available for inspection and storage.

I always verify the data by selecting “Device (D)” and then “Verify (V)”. This performs a second read cycle and verifies that the displayed data matches the second data download.

Once the data verifies as good, I save it in both HEX and BIN formats.

MiniPro file load options

MiniPro file load options

One note – if you load the data later, it is important to know whether you should change the “Clear buffer when loading the file” drop-down box. In this case, when I loaded the HEX file to verify that the saved data is also valid (yes I am paranoid), I had to select “Clear buffer with 0x00” to ensure the data matched what was present on the PROM.

With the data safely stored on my NAS server, I was confident that I could proceed with the actual creation of the chip-stack. I had considered rolling out a PCB to house parallel sockets for the microchips but decided that I was too impatient to make the CAD drawing and knew of a much quicker (albeit less elegant solution).

Chip stack soldered together

Chip stack soldered together

A quick and dirty solution to running microchips in parallel (in the DIP package) is to simply stack them and solder the leads together. After slightly bending the leads outward on the top unit, you can sandwich the two (or more) microchips. Once bent and in position, it is a simple matter to solder the leads together to retain the stacked formation.

While I could have tested the chip stack as a dry-fit, I have run into problems doing so in the past. It is possible to have a poor connection which misleads you when you are working with the stack.

Chip stack installed in U5 socket of theDSP-232

Chip stack installed in U5 socket of the DSP-232

In hindsight, I should have at least tried the dry-fit method prior to soldering the chips together.

Very eager to fire up the DSP-232+ and set the RTC, I installed the chip-stack just as the PROM was previously installed and fired up the unit.

“Christmas tree lights”

That is an expression you never hope to utter, let alone see. The expression describes the unintended state of the display and diagnostic lights when something bad or unexpected happens.

The DSP-232+ would not boot with the chip stack installed. I tried moving the stack forward and still no luck. I decided that the addition of the “drop in equivalent” DS1244Y RTC was the culprit. Sadly, the only good method of de-installing the chip stack which was available to me was to cut off all of the leads of the DS1244Y and then remove the lead remnants from the U5 (M27C512) with a soldering iron one-by-one, destroying the DS1244Y.

Doh! Thankfully the kind people at Maxim Integrated agreed to send more than one DS1244Y RTC. With my spare RTC, I will be running the two chips in parallel on a breadboard so that I can determine:

  • is there a pin difference between the DS1244Y and the DS1216C which prevents operation?
  • can I bodge the DS1244Y and the M27C513 (U5) PROM together with a minimum of connections
U5 breadboarded to DSP-232

U5 breadboarded to DSP-232+

The bread-boarding process is slow and a bit clunky but it should work. I hope to compare both datasheets for the DS1244Y and DS1216C to see something that jumps out as an incompatibility.

I’ve already verified that the PROM is readable in its prototype (on a breadboard) state. In some cases, such a method would not work – mostly high frequency stuff and it generally fails due to distributed capacitance in the breadboard. High speed stuff requires special consideration about ground planes and minimizing capacitance between leads / components – something which is impossible with a conventional solderless bread-board.

Ribbon jumpers for solderless breadboard

Ribbon jumpers for solderless breadboard

I need to get more jumpers before I can proceed – I need 28 in total. Looks like a good time to scan Amazon for some ribbonized jumpers!

I’ve also got a slightly different RTC on the way. The only obvious difference between the DS1244Y and the part I have on order appears to be a difference in memory structure.

As I continue this project, I will be sure to post another update.

Stay tuned for more!

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Hidden attic dipole antenna installation

So it has been forever since I’ve posted anything, let alone made any serious attempts at “playing radio” so I figured that I should change that! I’ve had too many excuses not to get this project done; time to make good on a promise to myself.

Heliax cable (loose)

Heliax cable (loose)

A project which I’ve been meaning to complete for a very long time is to place a dipole antenna in the attic space of our house. This will provide me a means of reaching out to the world while I save my pennies and look for a good deal on a multi-band Yagi-Uda HF antenna (and possibly a different tower too).

One of the troubles with any antenna system is connecting the antenna to the radio (or vice versa depending on your stance). Many types of feed line are available, some with distinct advantages but they always come at a cost!

Having purchased what is usually a very expensive form of coax: Heliax, I wanted to finally make use of the cable. This is a perfect place to use such a specimen – I need to situate my transmitter some distance away from the eventual antenna location, so losses become an issue. This is where something like Heliax comes in handy.

When running the feed-line from my mechanical room to the attic, I wanted to offer physical protection for the coax. Using a conduit would accomplish this task as well as provide a future path for other cables to be run in the future.

Liquid tight conduit from mechanical room to attic

Liquid tight conduit from mechanical room to attic

I was fortunate enough to get my hands on quite a long piece of scrapped liquid tight flexible conduit. My original plan was to use PVC tubing, but the FR4 rated conduit which is a plastic coated metal armor (similar to BX wire) offered a much more elegant solution.

I installed the liquid tight conduit from my mechanical room to the attic of the house, fire-sealing all structural penetrations to ensure maximum safety while meeting code for electrical work (which is not technically required in this case, but is a best-practice approach).

Liquid tight conduit entering attic

Liquid tight conduit entering attic

Connector components laid out in reverse installation order

Connector components laid out in reverse installation order

With the conduit in place, the next step would be to run the feed line. In this case, I used a portion of the LDF2-50 (3/8″) Heliax cable I purchased back in Oct 2014.

The Heliax will allow me to have my shack virtually anywhere in the house while experiencing only 2.26dB of attenuation at 440MHz for every 100′ of cable and a measly 0.383dB per 100′ at 14MHz – talk about awesome for coaxial cable!!

Fishing the liquid tight conduit

Fishing the liquid tight conduit

Getting the Heliax cable through the conduit proved to be quite a challenge. I have fished large cables through conduit, etc many times but this proved to be particularly challenging as I was working alone.

Over the course of a few hours, I made a few trips up into the attic and then back into the basement, trying to pass the fish-tape through the conduit. Each time I would encounter a new challenge which would have my patience being tested. The worst part is that I knew that I should have passed the pull line through the conduit while it was on the ground and in a straight line.

Pull strings in buckets to keep from knotting up

Pull strings in buckets to keep from knotting up

Never the less, once I had the fish-tape through the conduit, I pulled two mule-tape pull strings through, one to be used as a reserve. To prevent the pull lines from becoming fouled with each other, I hand-fed them into separate buckets to act as a pull bag of sorts – this is a rock-climbing trick and it worked like a charm.

As it turned out, having two pull-lines in the conduit made it impossible to pull the Heliax. Doh! I could likely have managed if I were to use a conduit lube but I did not want to use such a product for a few reasons, personal preference being the primary consideration.

Fishing the liquid tight conduit

Fishing the liquid tight conduit

After much cursing and nearly a hernia from pulling so hard, I realized that I would have to pull both lines out and re-pull a single mule-tape instead. This meant another series of trips up to the attic and down to the basement – a routine which was getting old pretty quickly.

This was a perfect example of a project where having a second person helping would have cut the time by more than half. There are so many tasks that you take for granted when you have someone to help you – a project like this is a great way to remind yourself of some of those challenges which are overcome with assistance.

I would have asked my better half but she was kind enough to watch our newborn son while I spent hours alone in the attic and the basement.

Heliax cable on spool to pull through conduit

Heliax cable on spool to pull through conduit

When it came time to pull the Heliax, I ended up spooling it on a surplus wooden wire spool that I acquired (with the intention of turning it into furniture).

The spool was necessary because as I pulled the Heliax, it had a tendency to start kinking up and I would have to make many tens of trips to check the cable as I pulled. This was simply not acceptable and a better method had to be developed, hence the wire spool.

Spooling the cable was extremely helpful – I would recommend this to anyone attempting something similar.  I used a piece of 1/2″ black pipe to act as an axle and two tall automotive jack-stands to serve as a make-shift a-frame to hold the spool in place.

Heliax cable run for VHF/UHF to future tower

Heliax cable run for VHF/UHF to future tower

Once the feed-line was pulled through the conduit (which by the way would make even He-Man wince), I pulled enough slack to allow the cable to follow the ridge of the roof, all the way to the side of my garage.

This will be the future position of the Heliax feed-line once my tower is in place (presuming I do install it next to my garage).

For the current project, having the feed line above the antenna would cause all kinds of undesirable effects; one of which is a major distortion of the radiation pattern of the antenna.

Heliax run to garage side for future (tower) use

Heliax run to garage side for future (tower) use

I am not sure what I will be using for the feed-line for HF use in the future. I may very well use a pair of diplexers to take advantage of a single feed-line run. This is the lazy solution.

Being that I have more than enough Heliax to duplicate the same run, I may elect to run a second feed-line, taking the lessons I’ve learned from this exercise and applying them to any future work of this nature. This would allow for a multi-radio station without the worries associated with diplexer use: issues with guaranteeing at least 60dB of isolation between radios.

Dipole antenna balun / center

Dipole antenna balun / center

The dipole antenna I installed was cut roughly for 20m (14MHz) but the final tuning has not yet been performed, allowing for optimization for the in-situ configuration.

To facilitate installation, tuning, and future maintenance, the antenna supports were chosen to be ring-eyed lag bolts with pulleys attached. This method of connection would be more than strong enough for an antenna which will be protected from the harsh elements.

Antenna in place, looking over lived space

Antenna in place, looking over lived space

At either end of the dipole antenna, pulleys were once again used and lead weights tied to the supporting ropes to provide constant tension to the antenna system’s legs. Installing the antenna in such a manner will allow me to lower the middle section for tuning. In this case, the legs are shortened by loosening off the wire rope saddles and shortening the length of wire which attaches to the balun box.

It is possible to test-tune the antenna by folding the ends of the legs back on themselves but in my case, the antenna was built using copper weld wire and aircraft “anstad” type insulators which are apparently quite a pain in the butt to work with. I was advised by the gentleman who assembled this antenna that I would be best to tune from the middle so to speak. I picked this specimen up at the Carp Hamfest this past September as my G5RVjr did not hold up very well. I could certainly make an antenna but I tend to over-engineer things and don’t mind spending a little bit of money for something better built than I could manage with my limited parts.

Antenna in place, looking over lived space

Antenna in place, looking over lived space

For reasons of safety, I placed as much of antenna as possible away from the lived portion of the house. Canada’s Safety Code 6 outlines acceptable exposure limits for radio frequency radiation (at various frequencies) and it is important to consider safety when working within our hobby.

As you might see by reading over Safety Code 6, it does not take a whole lot of power to exceed the guidelines! Inverse square law and all, with an antenna less than 30 feet overhead, it is safe to say I would not be transmitting at very high power with this antenna system. My objective is low-power digital modes such as JT65 and QRSS.

Antenna in place, looking over lived space

Antenna in place, looking over lived space

The leg of the antenna which does intrude above the lived space does not penetrate very far (thankfully). All the same, such an antenna is most certainly a compromise and this needs to be considered when deciding on such an installation.

An attic installation was honestly not my first goal – it was born out of convenience and perhaps a bit of laziness. The whole project ended up being quite a bit more work than I had initially planned but I am glad to have it done.

Once the antenna was in place, I connected the feed line and fired up the spectrum analyzer so that I could have a quick peek at the return loss plot to check the resonant point of the antenna system now that it was in place. When an antenna is cut long, the resonant frequency will be lower than your anticipated frequency – this is extremely helpful knowledge when it comes time to make / tune an antenna.

Antenna in place, looking over lived space

Antenna in place, looking over lived space

As was expected, the resonant frequency was quite a bit lower than desired as the antenna legs were longer than the prescribed 16.63 feet for 14MHz (468 feet / 14.070 MHz / 2 = 16.63). This equation is only a jumping off point – it can not calculate the exact lengths needed for your installation as it does not consider the many interactions the antenna system has with its surroundings.

In the interim, I will be using my MFJ-902 travel tuner to provide a 50Ω impedance match from antenna system to the radio (FT-857D). This again is a compromise (for now) and will result in less than ideal performance but hey – at least I will be able to transmit now!!

 

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A future radio amateur is born ..

On Nov 24th my wife Julie and I delivered our first child (Felix) at home. It was quite a unique experience as we had not planned on delivering at home, however, Felix’s arrival was uncomplicated and very welcome.

Felix Marsden Buck

Felix Marsden Buck

Everyone is healthy and I look forward to sharing the magic of radio with the little guy. Turns out that the cosmic noise of the solar system as heard on a HT makes a great “white noise” generator!

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Heliax Cable

Back in October, I acquired 250 feet (~75m) of LDF2-50 (3/8″) Heliax cable for approximately $150. The cable also came with 9 x 41PW connectors which sadly are of no use to me presently as they are for the more common 1/4″ Heliax. The price of the 41PW connectors alone is higher than what I paid for the lot, so perhaps I will try to recover some of my funds by selling some of the less useful (to me) items.

250' of Heliax

250′ of Heliax

LT2NM-PL N-type Connector

LT2NM-PL N-type Connector

Connectors for the LDF2 cable which I acquired are not cheap, they cost $20/ea and are generally only of the “N” type (to maintain low-loss / constant impedance characteristics). I picked up four connectors to work with – saving two for future use.

The model number I purchased was: L2TNM-PL which is the so-called positive lock model. The connectors are large and heavy, hopefully their quality matches the aesthetic of the connectors.

Connector components

Connector components

Installation of these N-type connectors does not rely on soldering in any manner, instead, the connection is made via tight physical tolerances. There are some really nifty cable preparation tools available for the various sizes of Heliax, though as I am performing a limited amount of cable work, I opted to use a good sharp knife and some sand paper in lieu of fancy tools.

Heliax cable end cut

Heliax cable end cut

The instructions which come with the connectors indicate the lengths of the cable components required, including the number of “ridges” in the bond to expose. The first step is to cut the cable with a fine-tooth hack-saw, ensuring the end is as close to square as possible.

If you try to use a clamping cutter (i.e. linesman pliers) you may not be able to save the shield (bond) of the cable.

Removing polyethylene sheath

Removing polyethylene sheath

The first step is to remove a portion of the polyethylene sheathing from the cable. This is a simple operation which only requires you to cut a ring around the cable just deep enough to touch the copper shield.

Be sure to make this “ring cut” at the top of one of the shield’s ridges. This is explained in the instructions which come with the connector(s).

Lognitudinal cut of sheath

Longitudinal cut of sheath

Next, make a longitudinal cut to begin peeling back the sheath, exposing the beautiful heavy copper shielding beneath.

Again, try not to cut too deep – I scored the length a few times, peeling the polyethylene sheath back as it became possible. The goal is to avoid scoring the copper shield if at all possible.

A good sharp knife is a must for this!

Cable end prepared for connector

Cable end prepared for connector

Once the copper shield is exposed, the copper shield can be cut back to the specified length. This portion of the work was too difficult to document well (read: I was too lazy to set up the camera with interval shots, etc) so it will not be shown.

What you are looking to achieve is the removal of a small portion of the copper shield from the end of the cable. I simply scored the copper shield with a sharp knife, then I used a pair of side-cutters to nip away the copper, peeling it like a tin can, using the scored line to prevent removal of too much shield.

Connector components laid out in reverse installation order

Connector components laid out in reverse installation order

If the center conductor is too long, you can simply file it down (or sand it in my case) to match the specified length.

The actual installation of the connector components is extremely simple. The only trick would be to torque the connector to the specified value. I opted to go with just a snug fit for now – perhaps I will get out the old torque wrench to check the installation.

I hooked up the Heliax cable (all 250′) to my spectrum analyzer and found that the cable loss over the length is well within specifications (I saw just over 10db at 1.5GHz). I look forward to being able to use this extremely low-loss coax in the (hopefully) near future. This cable will allow me to situate my ham shack nearly anywhere in my house and still make it out to a modest tower.

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APRS / packet radio / TNC fun

Hi all,

I’ve had a crazy summer so far, and as a result I’ve had little time for tinkering and ham radio. Despite this fact, I’ve managed to acquire a new (to me) piece of kit: a Timewave DSP-232+ DSP radio modem.

DSP-232+ TNC / Radio Modem

DSP-232+ TNC / Radio Modem

I purchased this unit from Rob (VE3???) for a decent price – a little more than a standard stand-alone TNC, but this puppy can do Pactor and Amtor as well as a number of other functions.

The unit came with a USB-mini-b module already built-in which is pretty slick. I then proceeded to let the magic smoke out of it. The original “upgrade” is a U232 board from Timewave and carries a price tag of $70. Ouch! I know of a $20 solution – see below.

I wanted to ‘scope the output of the TNC so I hooked my trusty DS2202 up to the TX channel of “Radio 1”. Following best practices, I also connected the ground lead of the scope probe to the ground plane of the DSP-232+ which is what killed the USB to serial converter. A post-mortem of the situation revealed  that my Kenwood PS-30 power supply is happily producing 60Vac on both the (+) and (-) leads [reference to ground]. Not good.

RS232 to USB adapter module.

RS232 to USB adapter module.

To remedy the situation, I finally ordered a DB9-USB-F from Digikey. I spoke of this before in a prior blog posting, and I can say that this little unit is fantastic! You must be sure to order the correct module as it is offered in three flavours: RS232 levels (± 15v), TTL (5v) and 3v3 levels and two “pinouts”: male / female. In my case, I ordered the female RS232 level version as the pinout matched the schematic diagram of my DSP-232+. Installation was simple and the module performs very well.

To interface the DSP-232+ to my Yaesu FT-857D I had to fabricate a cable which is a male 5-pin DIN connector to a 6-pin mini-DIN connector. Referring to the manual, I made the appropriate connections.

Inline soldering using hook method of joining wires.

Inline soldering using hook method of joining wires.

To make the solder joint as small as possible, I use a method where I first tin the tips of the exposed wires, allowing me to form a solid “j” hook on each end. I then slide a piece of hear-shrink tubing on all of the wires, except for the one which will be the ground. Notice that in the photo, I’ve split the original insulation on the beige cord – this will allow me to slide the heat-shrink tubing away from the solder joint, but to re-envelop the wires after soldering.

Heat shrink detail

Heat shrink detail

I like to use clear heat-shrink tubing on my solder joints to ensure good visual inspections – this is however just a personal preference. I can’t tell you how many times I’ve finished a solder job like this only to discover that I forgot the last layer of heat-shrink tubing. I make a point of placing a length of tubing over one of the wires as soon as I’ve cut it, ensuring that I will be able to neatly finish the job every time.

Completed cable union

Completed cable union

Once all of the joints are complete, and the cable has been tested, I finish the splice by slipping the outer tube over the entire splice and shrink it down. In this case, it would have been nice to use a glue-lined (some times referred to as double-wall) heat shrink to add some mechanical rigidity. This is not strictly necessary but is advised for situations where vibration or other repetitive mechanical stresses may be present.

Notice how the diameter of the completed splice is only slightly larger than the smallest cable. This method leaves a really nice professional appearance.

In the end, I’ve got my DSP-232+ working nicely, pulling in APRS packets with ease. There are a ton of features in this unit – many of which will require some good-old manual time. Once I’ve got some good operating experience with this unit, I will be sure to post my thoughts. First I need to repair / replace my darn power supply – there should never be any AC on the DC outputs – this is most definitely a concern. Until then, I am operating my radio on battery power for testing purposes.

More to follow …

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FM Transmitter analysis

It has been far too long since my last update and so I decided to do a cursory analysis of an FM radio transmitter (the kind you would use to listen to your MP3 player in a vehicle which lacks an input port).

FM Transmitter Model: JH-CMWT104

FM Transmitter Model: JH-CMWT104

The transmitter under test is one which I purchased many years ago and bears the model number: JH-CMWT104. It is a 12v device and so I am using my converted ATX PSU to power the unit with a clean (verified by oscilloscope) +12v. The test bench included a Rigol DSA815-TG spectrum analyzer and a DG1022 arbitrary function generator.

Local test-bench background radio noise for comparison

Test-bench establishing local background radio noise for signal comparison

The first step was to establish local RF background measurements / spectrogram for later comparison. As an antenna, the test bench used a 1m collapsible whip antenna connected via BNC-to-N adapter with a 90° elbow.

A quick look at the resulting spectrogram (50Mhz to 550MHz span, RBW/VBW 3kHz) shows the FM broadcast band indicated in the lower portion of the display.

FM transmitter 100MHz unmodulated showing multiple odd harmonics

FM transmitter 100MHz unmodulated showing multiple harmonics

With the background parameters established, the FM transmitter was powered on with no signal at the device’s input. The transmitter was set to 100MHz for ease of demonstration.

Shown in the spectrogram, it is clear that there are multiple harmonics of the 100MHz fundamental. As the harmonics will be n-integer values, they will land nicely on the graticule lines of the display.

FM transmitter 100MHz unmodulated showing multiple odd harmonics w/ peak table

FM transmitter 100MHz unmodulated showing multiple harmonics w/ peak table

Using peak markers, the offending harmonics are shown in the spectrogram, labeled as 1 through 4.

No harmonics were visible (amplitude > 1dB above background level) beyond 500MHz and so the span was intentionally set from 50MHz to 550MHz to optimize signal display.

FM transmitter 100MHz unmodulated showing 3rd harmonic at 200MHz -27db

FM transmitter 100MHz unmodulated showing 2nd harmonic at 200MHz -27dBc

The 3rd harmonic (300MHz, -60dB relative to fundamental) was observed and has approximately 35dB of suppression from the fundamental which is pretty good.

What is intriguing is the 2nd harmonic at 200MHz which is only 27dBc (dBc = relative to the carrier) weaker than the fundamental. Recall that 26dB expresses a difference ratio of 400 times.

26dB can be broken down as: 10dB + 10dB + 3dB + 3dBrecall that for each 3dB you have a doubling (2x) and for 10dB it is an increase in magnitude (10x)
26dB can be therefore be thought of as: (10 * 10 * 2 * 2) = 400x
Transmitter output 100MHz FM "carrier"

Transmitter output of 100MHz FM “carrier”

A spectrogram of the FM carrier signal at 100MHz shows a series of sideband pairs (… Fc – Fa, Fc, Fc + Fa …)

The same carrier is seen at all harmonics and has precisely the same characteristics as the fundamental.

This means that if a radio were tuned to 200MHz and the FM transmitter was set to 100MHz (as in the test scenario), the signal could be interpreted.

Transmitter output 100MHz with 2.7kHz FM modulation

Transmitter output 100MHz with 2.7kHz FM modulation

When presented with a 2.7kHz tone, the FM signal character changes as seen as displayed in the spectrogram.

Using a function generator, it is possible to make a number of measurements of the transmitter’s performance.

I did not bother to measure the deviation of the signal at this point, though I may do so in the near future for interest’s sake. Agilent has a document with some details on how to measure deviation using a spectrum analyzer (p17).

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Changes …

Well, the end of an era has come. I just cancelled my 15+ year colocation contract in favour of hosting my domains in a more budget friendly sense. In a way, I regret cancelling the colocated server service as it has afforded me great autonomy with my hosting, etc. though I have failed to fully use the server in years.

With any luck, you did not even notice the transition! There may be a few hiccups still to come despite my best efforts to prevent any issues during the phase-out of the old system.

More to follow soon … with updates 🙂

73 for now

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