So its been a month since my last update here and I figured this is long over-due.
We’ve moved into the new house and have started tackling some of the myriad projects we bought with the house. I started by installing the house’s first sump pump since it was built – it was long over due and frankly, I am shocked there wasn’t one in the first place!
We’ve still got a lot of cleaning to do – most of which exists in our “out building” / cottage. I’d like to make the loft into a radio-room, and to do so will require a pretty thorough cleaning of the entire structure. I’ve got a contractor coming by tomorrow to offer a quote on trash removal – I’m looking at the $400 mark to get rid of all the previous owner’s trash. Oh the joys!
On the tower front, I may already have permission from my YL to erect it immediately behind the cottage – I think the only stipulation may be not to go the full 80′ I could theoretically manage. I’ll be looking at the 50′ mark or so I imagine. I would also like to find a spot for my mil. spec. high-precision azimuth / elevation control system that I picked up from the Fed. I can’t wait to start trying my hand at EME.
Perhaps I will string up my G5RV Jr. to make a few QSOs tomorrow – its been far too long since I last played radio!
On an electronics related note, I’ve spent some of my over-time money that I’ve been saving for quite some time .. I’ll give out some more details soon
Well, only nine days until we take possession of our new house and I couldn’t be more excited! My intentions were to sneak some radio-time into the past few weeks and I almost succeeded. Almost.
When I hooked everything up in my mobile station, I was getting a much lower than normal voltage value on the radio. Subsequent testing showed that the second battery system was putting out 12.8V (~14V while engine running) but the radio was reporting only 9.5V. I have the radio installed in the rear of the vehicle some 15′ (wire length) away from the battery. The immediate suspicion would be the length of the wire – voltage drop due to resistance. The wire is 0-gague (nearly 1/3″ thick) and its resistivity is ~0.3224 milli-Ω per meter, so voltage drop (even under high current) is negligible (compare it to 18-gague which displays ~20.95mΩ/m).
Once we are moved-in, I will take the time to further investigate this rather bizarre issue with the mobile installation.
On the radio / electronics side of life, I’ve been busy redesigning my sound-card interface board. The objective of this project is to provide a (nearly) one-board solution which is capable of providing galvanic (electrical) isolation between computer and radio while offering PTT / CAT (Yaesu) control of the radio, along with automatically controlling the ALC via the ALC-jack found on some Yaesu equipment.
As this project progresses, it is my intention to enhance the interface board with an on-board USB sound-card to both simplify the end-user’s experience and to hone my design skills.
At present, the board houses a number of prototyping features which will not be found on the “production” version(s). This is done to verify and compare boards between PCB fabrication houses, checking tolerances and part fitment. I am doing this because I create all of my own parts in Eagle CAD using the datasheets for the components I will be using. I know that this is reinventing the wheel and that I could use already-existing libraries, however, in some cases I’ve had to create parts for components not-yet present in distributed sources. I have found that creating my own library has greatly enhanced my working knowledge of Eagle CAD and electronics design in general.
So for the next few days, we will be doing a more comprehensive boxing-up of our belongings, leaving little time or ability to enjoy my many hobbies. I’ll try to post more in the near future, perhaps with something of actual interest to some who skim my blog site.
I’ve been away from the hobby for a bit as Julie and I recently purchased a new home! Yay! We are mostly done all of the running around, inspections, negotiations, etc. so I should have some more free time for the time being.
We will have to start packing and planning soon as our closing date is April 11th so any projects I take on / finish will be limited by the need to pack everything up (and more or less keep it that way).
I hope to have yet another look at the Raspberry Pi APRS all-in-one solution, and part of the problem I may have been having was the use of class-4 SD cards – I’ll pick up a couple of class-10 cards to experiment with. I think that the Pi could be a fantastic solution as a TNC for APRS operation, all depending on the software decoding of course.
Another project which came up in conversation with a few people online is the use of an Arduino (or simply ATMega micro) as a go-between CAT interface for controlling DDS based homebrew radios. I’ve already developed the library for the Wires (Arduino) platform, so writing a pass-thru style interface should be rather trivial (yes I am inviting ridicule when this statement comes back to haunt me).
Once we move in to the new house, I’ve got quite a few non-radio tasks to be tended to so I will very likely go radio-quiet again for a short time. With any luck, I can start the planning and consultation phase of my antenna tower project. With a little over 2.5 acres to play with, I am actually considering the use of the full 80′ however, this is still subject to the site-plan.
In any event, I am still alive – just a bit more busy than I was previously. I’ll try to make some time to put something of merit up here – so check back some time soon!
After we arrived home on Saturday (29th) and unpacked everything from the trip, I set out to determine the cause of my inability to operate digital while mobile. My first suspicion was an open in the cable, so I tested the continuity between the perf. board and the 6-DIN connector – no problems there! The reason I suspected an open was because of a bad kink in the cable where it appeared to have been pinched – in my usual line of work, this would be an instant cause for additional investigation.
My next task was to confirm that the sound card audio was in fact being received at the transformer. This was made challenging by a couple of factors: 1. I was too lazy to haul out my temperamental oscilloscope and 2. the connector pins are very close to each other which makes probing them while trying to multitask a real challenge.
The arrows in the picture indicate the pins which I was attempting to probe which are the data in and ground pins.
Notice that the pins are swapped on a horizontal axis – when compared to the pinout (PDF page 35) of the FT-857D manual. This can be a source of confusion when making a sound card interface, so I’ve added a numbered pinout of the manual drawing to assist with the understanding.
After finding that there was no audio making it to the 6-DIN connector, I had to confirm that the audio was being lost at the output transformer stage. Prior to testing the secondary side, I verified that I had the audio between the two “pins” of the primary winding. I then probed the secondary and it was at this stage that I found the fault in the circuit. There was no audio on the secondary side! There are only two causes which could explain this phenomenon, the first being an open circuit (ie. burnt out winding) which is easy to test – just look for infinite resistance between the two outer-most “pins”. The second cause would be a short-circuit between the pins!
In my sound card interface design (Sound-card interfaces .. home brew one!), I use a potentiometer to vary the output signal level (ie. peak-to-peak AC voltage seen by the radio). At some point, I must have adjusted the potentiometer to such a level as to present what was effectively a short-circuit to the secondary windings, preventing any useable amplitude in the audio signal.
The picture shows a blue box which is the potentiometer which caused all of the grief. After some fine-tuning while setting the computer’s audio output level to 50% and the digital gain (Menu #37) to 50% I adjusted the potentiometer so that only seven “rows” of ALC indication on the display were present.
The manual vaguely states (PDF page 66) to adjust your source audio level until a “few” dots of ALC are present but as high as “16 dots of ALC” on the meter.
Annoyingly, the manual displays a “full scale” display which happens to be “16 dots” tall! My take on this conundrum is to err on the side of caution which suggests operating so that only a total of “16 dots” are indicated which actually means a display which is only “7 rows” high.
My plan is to confirm my suspicion by monitoring the RF output of the radio using my oscilloscope, watching for the first signs of “flat topping” or “bottoming out” of the RF envelope. To do this, I will be making a resistive divider RF sampler – I just need to buy an aluminum housing for the project.
So in the interim, I’ve got my station back up and running which is fantastic! I just wish that I had remembered fiddling with the potentiometer – I could have saved a lot of grief and could have actually “played radio” while on vacation. Doh!
Well, despite my intentions, I am not able to operate /M using digital modes. On our way up to Webwood, ON. I tried to make a few PSK31 contacts while Julie drove but the radio indicated no ALC while in TX!
See, I should really have tested the whole setup prior to our road-trip but we’ve been exceedingly busy this holiday season. It is a poor excuse, I know, however it is a fact of life. So let this be a lesson to you! If you change your station setup in any way, it s a good idea to test it prior to intended (or emergency) use.
This afternoon, I tried some basic troubleshooting to see what was going on. I am able to receive just fine, and the PTT is working as it should, the problem is that in the “DIG” mode of the radio, there appears to be no audio being fed to the radio (as indicated by no ALC at even high audio levels w/ the digital gain set to 100/high).
So now it boils down to a couple of possibilities – neither of which I am presently equipped to test. The first being that the sound card interface cable I made is faulty – I saw a pinch in the cable and it is possible (though unlikely) that one of the conductors developed an open. The other leading likelihood is that the 6-DIN connector is not making good contact with the socket of the radio. In either event, more testing will be required to determine the cause.
Well, time to pack up the radio gear and make the long trek out to Webwood once again this year. Tomorrow morning, we are off to visit Julie’s mother & her family to spread some Christmas cheer and so this means I once again have the opportunity to operate /M (mobile).
With any luck, I will have a chance to operate some PSK31 and JT65A while Julie takes her turn at driving. Traditionally, I have had great results – I can only hope that the propagation is good for our trip. If you are tuning around the frequencies in the usual digital mode spots (ie: 14.070 & 14.076 for 20m PSK31 and JT65A respectively), you may very well hear me!
.. so I’ve been at it again. I purchased an 80′ mast kit from the Fed. for a cool $357.91 which as far as I’ve seen is substantially less than a similar kit could be found elsewhere.
In total, there were six auctions for 80′ tower kits which ranged in finishing prices of $318 through $503 which meant that my winning bid of $357.91 was just below the average price of $380.39 – a win in my books! While it is true that I might have won with a slightly lower bid, I feel that what I paid was well justified considering the timeline I was essentially forced to work with.
The antenna mast was located in Montreal, so this meant renting a 12′x6′ cargo trailer from a local moving company for $35 which meant the purchase of a 2″ drop ball-mount and 2″ ball which only cost another $25 and I wanted to have for the FJ anyways since it has a class III hitch & required wiring already. As it turned out, the choice of trailer was a very good one – the shipping crate just fit inside the walls (more on this later).
With the winning bid paid for and the “authority to release” documents printed and checked, my trusty ally and I headed out for our long journey to retrieve the tower. At approximately 13:00 we were on our way to Montreal – and the Crown Assets depot we were driving was expecting us for 15:00. Yikes!
After a long drive, spending some quality bumper-to-bumper time with the proletariat of Montreal, we arrived just in time to have our contact meet us at the loading dock. I backed the trailer up to a waiting forklift which was holding the crate aloft. After an initial inspection, it was determined that we were exceptionally lucky that the crate was just going to clear the rear gate / door of the trailer.
We weren’t sure that we’d be able to transport the whole kit in one piece – the backup plan was to demolish the crate and move the sections by hand onto the trailer for transport. We were both glad to not resort to this tactic.
So there we were at 15:45 ready for peak Montreal traffic, hauling a 12′ trailer with a ton of steel behind us. We stopped in at a fast-food joint as neither of us had eaten all day, and it was well deserved by this point. A few minutes later, we were back in traffic, headed west-bound back to Ottawa, albeit at a much more relaxed pace!
Being an apartment dweller, I had to arrange for temporary storage of my acquisition which meant asking my very loving parents if they would be so kind as to store my future antenna mast until Julie and I find a home of our own (which we are actively, and with great anticipation seeking). I feel a bit bad having the tower stored at my parent’s place – they put up with a lot of crap of mine, and so I am extremely grateful. Love you Ma&Pa!
Upon arrival at my parent’s house, it was originally planned for the tower sections to be hand-delivered to a predesignated storage area – that is until my sympathetic father saw the scope of the work ahead. In typical Buck fashion, a seat-of-the-pants plan was hatched which involved the following aspects:
tree-saver strap & tow chain
momentum & some leverage
Mercifully, we were able to unload the crate in excellent time with minimal headache (save for a few bald-ish patches of grass which I have to attend to in the spring).
For now, the great tower will lie in wait – eager to be thrust high into the sky (okay, maybe not 80′ high – maybe). More on this adventure later …
So I’ve been tinkering with my Raspberry Pi board, and one of the most recent additions is a pair of heat-sinks to offset the addition of additional thermal loading due to over-clocking. In an effort to get soundmodem working on the pi, I’ve increased the clock frequency by a moderate margin to see if I can alleviate some bottle-necking in the decoding of AX.25 packets.
I am using two different USB soundcards in an attempt to see if the sound devices themselves are part of the resource management issues the Pi seems to be having. In addition, I’ve added a powered USB hub to rule-out power issues for the USB back-plane on the Pi.
Despite my best efforts, the CPU load still seems to be pegged out while running soundmodem, which means that the packet capture rate will be extremely poor at best. This is very frustrating considering that the CPU on the Raspberry Pi should (on paper) be able to handle the task fairly easily.
Now I could take the easy road like many others and use a dedicated hardware TNC but that completely misses the point of this exercise. My objective is to create a $35 TNC/digipeater/igate/tracker module – all exploiting the Raspberry Pi’s hardware. In theory, this task should be relatively straightforward, I mean heck, a fricken’ Arduino is capable of encoding AX.25 packets! (I’ve made a transmit-only position reporter using an ATMega 328)
I haven’t given up on this project, but I am a little dismayed. I’m by no means a software expert and so my attempts at trimming the fat on the Pi have been fairly fruitless. I am hoping that someone a bit more talented has a look at the resource issues and make some headway on the soundmodem implementation on the Pi.
I’ll keep poking and prodding, perhaps I’ll uncover one of the root problems. I’m wondering how better to utilize the Pi in the meantime.
So last I wrote, the Tecom azimuth / elevation unit had position reporting issues when rotating the azimuth in the counterclockwise direction – it would falsely report +1.3° which prevented the “sector scan” and “raster” modes from operating as intended.
My first thought was that the synchro transmitter was faulty and therefore reporting an incorrect value when rotating counterclockwise, perhaps as a result in slop in the internal mechanics. Out of curiosity, I contacted a few firms that deal in surplus equipment to get a replacement price .. well, as predicted, the prices came back in the $650 range. Ouch. To replace a single synchro transmitter would mean spending 8 times the purchase price to repair the unit. It is pretty safe to say that replacing a synchro unit is not going to happen.
Instead of replacing what I thought was a faulty synchro transmitter, I decided to swap the units between azimuth and elevation (put A in B). After a bunch of effort to swap transmitters, the problem still persisted! Ah ha! It was in the signal path and NOT the synchro unit! … crap!
After a bunch of poking around and desperately searching for schematics, I managed to find a service manual for the motor controllers which the position control unit uses. I say busily tracing out all the wires and trying to visualize how the controller cards might integrate the data and work out how to control the motors. Once I drifted away from what turns out to be the brains of the position controller, I saw a couple COTS (commercial, of off the shelf) motor controllers.
I looked up the part number for the motor controllers, and after some intense searching, I found a complete circuit diagram which confirmed my initial suspicion. One of the four brown potentiometers on the control unit sets the position feedback gain for the buffer / amplifier, allowing me to increase the sensitivity as well as set the bias a tiny bit higher, allowing me to effectively “zero” the position.
All in all, it has been an extremely interesting tear-down / repair of the antenna rotor / elevation controller. I’ve learned a lot about the mechanical considerations in a high-precision, military spec. antenna positioning system. Show here is the drive mechanism which couples the DC motor to a 40:1 gear system which in turn drives a 8-10″ gear tied to the elevation mechanism. After opening the belt-access panel, it was clear that the mechanical tolerances used on this side were quite odd compared to the rest of the assembly. My suspicion is that this unit has been serviced in the past with parts which are not quite the same spec. – well the large drive gear anyways, since it appears to protrude out of the housing.
Aside from this little oversight which I fixed by using spacers and RTV compound to re-seal the panel, I have been extremely impressed with the build quality of the components.
There are some old-school techniques used in the circuitry which would never pass modern safety standards, but all the same, the unit appears to be well thought out and quite safe to operate. It is fun to see the engineering solutions of days past – in this case, some 20-30 years ago.
After a nice clean-up and resealing the unit, I believe it is almost ready to be pressed into service for my EME needs.
Next will be attempting to interface with the position controller unit via the built-in Serial port. This would in effect allow me to remotely control the antenna position from some distance, which is quite nice because the control cable (while long) is somewhat limited in its length. Oh, and at 40+ pins, it is unlikely that I will bother trying to lengthen it.
I’ve been browsing the PWGSC Crown Assets website for a few days looking for a spectrum analyzer or more modern oscilloscope to enhance my electronics tool-chest. Nothing terribly interesting had been coming up until very recently. I saw a listing for a: “Tecom controller” which caught my eye. I often look for inexpensive things to take apart to see what makes them tick, and this piece looked promising. When I looked into the auction a little bit more, I realized that the auction picture was for a azimuth / elevation controller. Further poking around showed what I thought was just a heavy-duty elevation rotor.
Initially, I posted a bid of $40 thinking “That would be cool to take apart”. After a bit more consideration, I thought, “aww heck, why not drop $80 and hope for the best?”. Well, the auction closed yesterday evening and the items were mine (after prompt payment of course)! I acquired this amazing piece of kit for roughly 20dB less than it is worth!!
While waiting for the auction to expire, I did some poking around to see what I could learn about the antenna controller / azimuth & elevation pedestal. Turns out that what I bought is a Tecom MIL-SPEC system most often used for tactical communications. There isn’t a whole lot of information available on the equipment, which is par for the course with equipment like this. When I picked the unit up, I was shocked / impressed with the mass and build quality of the pedestal. The darn thing weighs nearly 100lbs! I’m still trying to find the specs on the drive assembly but a cursory search suggests that the unit will accommodate at least 100lb of antenna.
After getting the units home, I had to connect everything and play! Testing the unit revealed that it is accurate to 0.1° in both the elevation and azimuth axes. Using the “PNT” button, I had the drive mechanism point to 90° & 90° which showed a systematic error of 1.3° when moving counter-clockwise.
I figured that the position reporting system was likely a potentiometer of some design, coupled to the motor output shaft to give a real-time indication of position for the controller. Often times, old, corroded connectors can play havoc with the resistance of a signal path, and this could have been the cause of the 1.3° error. I used some spec.-grade isopropyl alcohol to clean the myriad of pins in the connectors, resulting in plenty of gunge on q-tips.
After reconnecting the cables, I tested the temperamental azimuth mechanism and it still stalled out when going counter-clockwise. The same recurring 1.3° error was present when traversing counter-clockwise. The elevation control is flawless, always parking no more than 0.1° away from the instructed position. I had to crack the controller and the pedestal open in order to ascertain whether I can set the “zero point” or not. As it turns out, I did not see any potentiometer labeled for such a purpose.
On the right side, you can see a potentiometer on the bottom and a synchro control transmitter above it. As it turns out, it is the synchro control transmitter which reports the positional data back to the controller. I’ve tried making small adjustments in the mounting to correct for the 1.3° error which temporarily solved my problem. Once the pedestal was instructed to traverse from CW to CCW again, the 1.3° error was back! Drat!
I’ve requested quotes from various military supply houses to feel-out the replacement cost, and well, as you can expect with MIL-SPEC stuff, it looks VERY expensive. Put it this way, a brand-new Yaesu G-5500 would cost less. I’ve pulled the synchro out to see if I could reproduce the problem by checking for back-lash issues. No luck. I’ve tried increasing the tension in the anti-backlash gears to see if that would solve the problem. Still no luck. Sadly, it would seem that the synchro may be the root cause of the problem.
In either case, the unit is still accurate to ±1.3° which is actually fantastic! The controller can be programmed to scan a sector (elevation or azimuth), seeking out weak signals. Using a serial port, the controller can also be put into a remote mode, allowing for computer control (like most low-rent az/el controllers).
I’ve posted a video to YouTube to demonstrate the az / el pedestal drive mechanism.