A drunken challenge accepted means that I am in the process of developing a controller that will give the Clansman PRC344 radio a scan capability. This is pretty frivolous to say the least! - the radios 50kHz steps means many active frequencies will never be heard anyway! But, its a fun thing to try and make happen,
The idea is to develop a means of controlling the tuning of the radio in timed steps, with received signals halting the scan. Initially, the system will be 'blind', that is, entirely self contained within the radio with no functions other than to start and stop it, and to override the halt to continue scanning. But later, by sacrificing one of the radios audio connectors, and external controller could be attached for more sophisticated operation.
This is no easy task. For a start, I have to take control of the synthesiser, this means 14 control lines plus a means to break the ground connection to the frequency dials. But, I also need to override the radios RF front end tuning, which means taking control of another 18 lines, and switching over a further three! I also need to accept control inputs from 3 different parts of the radio! Plus, I need an RS232 port. All in all, that means arranging for a minimum of 38 control lines on my controller!
And all this has to not only run on 3V to be compatible with the synthesisers logic, but switch tuning voltages up to 70V! And, when not selected to scan - have zero current drain!
If all thats not bad enough, the entire thing must fit within the space left by the removal of the Tx control module!
Yet, I think I have the answer! And its all down to modern high performance microcontrollers and sophisticated logic chips. A string of resistors, a couple of 24v DPDT relays, two MOSFETs, a zener, a 3v regulator, three high voltage 8-port multiplexers, two 16-bit I2C port expanders, and a tiny little biddy PIC microcontroller! All built with SMT parts.
Just waiting on the prototyping samples to arrive. In the meantime, I have to do the daunting part that will form the heart of the system - Ive to learn to program in C...
Sunday, 27 January 2019
Saturday, 26 January 2019
QRPlabs Si5351A VFO kit
Once again today I have had the pleasure of building one of Hans Summers kits. Hans designs and sells, as QRPlabs, incredibly versatile and high quality radio kits, mostly based around a core Atmel processor control unit. Having previously built a six-band version of his Ultimate 3S QRP WSPR beacon transmitter (which can do so many more modes than that!) and the QLG1 GPS receiver to govern it, and having a need for an effective way to replace crystals in vintage military radios in order to test conversion to amateur bands, I decided to buy the QRPlabs Si5351A based VFO/Sig Gen kit.
The kit comprises a 2x16 backlit LCD module, the Si5351A DDS module, and the QCV control module. This is exactly the same as the U3S, the only difference being the firmware version of the processor chip, and some of the discrete components. The DDS module is capable of working up to at least 150MHz, and in this kit, produces two independent outputs. One output is fixed frequency, set up in presets in the firmware, the other the VFO output. The above photo shows the PCBs after populating.
This kit comes with a rotary encoder with a push button switch action. This was the only place I went astray during the build, as I managed to mix up one of the encoder lines with one of the switch contacts, resulting in some rather odd things happening when trying to test!
After a good rummage around, I came up with a metal enclosure for it. I had hoped to use a die-cast box, but all my stock were either too small or way too big! But I had this sheet aluminium box kicking about Its a slightly odd enclosure as it has the seams of one half on the outside of the other, rather than hidden inside.
What took most of the build time was the marking out, drilling and cutting of the box.
Unfortunately I havent been able to complete the build today, as I discovered that I dont have any panel mount push buttons in stock, nor any suitable stand offs to mount the unit into the case with! Ive now ordered these, but they may take several weeks to arrive!
A quick test showed all to be well. One thing I discovered though which I hadnt expected, was that the firmware includes backlight brightness control. I had already installed the link for full brightness as I didnt expect this feature, which is used in the U3S, to be in this firmware. So, that link was removed and the correct link for processor control of the brightness added.
Im so pleased with how well this has gone together that I decided I just had to build another of Hans' kits! So, since I needed to measure the QLG1 GPS units dimensions (as ive asked a work mate to 3D print me a box for it!) and this meant pulling out the U3S, I decided that what I really need is a touch more power for WSPR ... so now the QRPlabs 5W HF PA kit is on order, along with an upgraded firmware chip for my U3S, which will control the PA and also give me the ability to control an antenna changeover relay. The HF PA kit has the same PCB form factor as the rest of the kits PCBs, so effectively just 'bolts on'.
Tuesday, 22 January 2019
HT Chain issues
I have a requirement to replace the mechanical switch shown here, that selects one of 18 different HT levels 0-80v from a potential divider chain, with electronic switching controlled by a 3v logic port expander.
Im currently thinking p-channel MOSFETs for the HT switch, but these need biasing from the HT line they are on, which I think would kill the logic gates! So, I also need a driver device that will isolate the 3v logic control (MCP23017) from the HT and the switch.
Sunday, 20 January 2019
PRC-344 Alignment - Working Fully
The Clansman PRC344 is now probably as good, electrically, as it will get.
Having removed the Direct Current Amplifier module3, in order to disable the radios ability to transmit (since there is absolutely no legal way of using the transmitter, yet lots of ways to inadvertently send a signal that at best could get you prosecuted and at worse endanger an aircraft!), I could happily ignore all the alignment process relating to the transmitter.
So this evening I took the time to run through the alignment processes for the power supplies and the receiver. The only part of this that gave any problem was the AGC alignment. This required setting one control for 350mV peak waveform on the oscilloscope, and 0v on the voltmeter. However, although I could hear the receiver being affected by the adjustments, I couldnt get anything like the specified waveform levels!
*I have now realised that I was monitoring for the 0v on the wrong test point! It may be that I have to do this section again sometime!
But, the radio does now seem to be performing as specified. One downside to this being that with the mute setting as per the manual of -108dBm, the background level of QRM within my QTH is enough on many channels to open the mute!
The final test required, ive just completed. This is rather a frivolous aspect, but I wanted it to work, so ive tested the REMOTE and I/C settings using a Remote Handset and a few meters of DON10 telephone wire. But, with this working, it means that I could stick the radio up on the workshop roof and run telephone wire into my warm comfortable work position to monitor while I get on with something else.
Having removed the Direct Current Amplifier module3, in order to disable the radios ability to transmit (since there is absolutely no legal way of using the transmitter, yet lots of ways to inadvertently send a signal that at best could get you prosecuted and at worse endanger an aircraft!), I could happily ignore all the alignment process relating to the transmitter.
So this evening I took the time to run through the alignment processes for the power supplies and the receiver. The only part of this that gave any problem was the AGC alignment. This required setting one control for 350mV peak waveform on the oscilloscope, and 0v on the voltmeter. However, although I could hear the receiver being affected by the adjustments, I couldnt get anything like the specified waveform levels!
*I have now realised that I was monitoring for the 0v on the wrong test point! It may be that I have to do this section again sometime!
But, the radio does now seem to be performing as specified. One downside to this being that with the mute setting as per the manual of -108dBm, the background level of QRM within my QTH is enough on many channels to open the mute!
The final test required, ive just completed. This is rather a frivolous aspect, but I wanted it to work, so ive tested the REMOTE and I/C settings using a Remote Handset and a few meters of DON10 telephone wire. But, with this working, it means that I could stick the radio up on the workshop roof and run telephone wire into my warm comfortable work position to monitor while I get on with something else.
Pye PF8 - Stumped by the filters
With the band specific capacitors replaced, Ive managed to peak the transmit output of the PF8 up to about 170mW. This is still a far cry from the specified 500mW. Likewise, the receiver barely peaks higher than -85dBm.
In order to make certain this was a filter issue, I have bypassed the 3-pole input helical filter - and the receive sensitivity shot up!
But now I have a big problem. Not only are the correct filters simply not available, but the ones fitted cannot be modified to work better either. In fact, its near impossible to remove them anyway without destroying them (as I found when attempting to take one off my 'donor' unit!)
So, what to do? Well, pretty much all I can do is either find some 2- and 3-pole helical filters for 430MHz that will fit, probably impossible, or at least prohibitively expensive, or think up some way to replace the helical filters with small home brew band pass filters.
All this just so I can own a working, genuine Bodie and Doyle CI5 walkie-talkie!
In order to make certain this was a filter issue, I have bypassed the 3-pole input helical filter - and the receive sensitivity shot up!
But now I have a big problem. Not only are the correct filters simply not available, but the ones fitted cannot be modified to work better either. In fact, its near impossible to remove them anyway without destroying them (as I found when attempting to take one off my 'donor' unit!)
So, what to do? Well, pretty much all I can do is either find some 2- and 3-pole helical filters for 430MHz that will fit, probably impossible, or at least prohibitively expensive, or think up some way to replace the helical filters with small home brew band pass filters.
All this just so I can own a working, genuine Bodie and Doyle CI5 walkie-talkie!
Pye PF8 Conversion Progress
It has taken me a little longer than anticipated to get to this stage, as I replaced the crystals and did the initial tune up for 70cm way back in 2016! But today I finally embarked on the task of changing the band specific capacitors,
In order to replace these caps, the side of the radio needed to be removed, this involved also desoldering the 'call' switch, as well as removing the bolts through the PTT buttons. Whenever I work on something as delicate as this, I take copious photos - so I can see where everything goes back to!
The first two capacitors are along the very edge of the PCB, and up against one of the filters.
If fitting these was fiddly, then the next three were a nightmare! These three were in-board, and surrounded by other much taller, and very delicate parts. Replacing these took all the skill I could muster, and a lot of will power to ignore the pain of burning fingers!
A minor disaster awaited me - in desoldering C11, I inadvertently also desoldered C13 and R16! Both of which fell out. It took a lot of desoldering to clean up and open the PCB holes in order to be able to get them back in!
All this took over two hours! I then had to reposition and secure the wiring loom on the track side, refit the screening plate, and ensure that the tiny coax that goes to one leg of C47 was correctly resoldered.
So now im in a position to test again. All being well, the set will power up! If I get past that milestone, im hoping that at the very least I will now be able to bring the Tx power up closer to the designed 500mW. Whether I get any improvement on receive we'll have to wait and see.
In order to replace these caps, the side of the radio needed to be removed, this involved also desoldering the 'call' switch, as well as removing the bolts through the PTT buttons. Whenever I work on something as delicate as this, I take copious photos - so I can see where everything goes back to!
The first two capacitors are along the very edge of the PCB, and up against one of the filters.
 |
| C36, 2nd from left (brown) and C35, 4th from left (orange) fitted |
 |
| C45 black left of power transistor; C47 above transistor; C11 left of green cap |
 |
| PCB holes cleared to replace C13 and R16, and fit new C11 |
 |
| The wiring loom and shielding |
Saturday, 19 January 2019
PRC344 is alive
After repairing the 6v and 12v regulator modules, and proactively replacing the same capacitor in the 3v module, I now have a working PRC344 UHF AM transceiver.
Thanks to Alan G8LIT, I now have the EMERs for this radio, so further repair and alignment should be much easier. Ive already set up the various voltage rails correctly (most were a little low), but the receiver is still somewhat down. Further alignment will wait until I have printed out the instructions. There is also still an issue with the fit of the battle antenna, which refuses to rotate into the locked position.
One thing I have been able to do, now I have the information to work it out, is disable the transmitter! I had thought I would have to unsolder the supply rails etc to the transmit section modules in order to ensure none of the various ways that the radio can be put into transmit would operate, but it turns out that all the transmit controls are dealt with by module3, simply pulling this out totally disables the transmitter with no other detriment.
A few design flaws show themselves with this radio. The first is with its carrying method. It was intended to be fastened to a carrying harness using an adapter plate that used straps to hold the radio, and as such there are no bolt holes for the normal GS adapter plate as used with the PRC351. But, the radio is also very heavy and very square - which means just picking it up is awkward as theres nothing to easily get hold of! Second, internally there are several adjustable parts which have the same designation as each other! For instance, all the regulator modules are adjusted by an R7. This means that if you accidentally pick the wrong module you could cause quite some damage by adjusting the wrong supply rail!
Ive spent some time today clearing and tidying the RF bench, which really was cluttered up. This was mostly in order to find a place for my new variable bench power supply. In doing so, I decided to also rationalise and maximise the space used by the test equipment, so the test bench is much tidier now and more compact, less wasted space ('scope now on top of the Marconi, PSU on top of high power test load, frequency counter on top of the spectrum analyser). This created enough space that ive been able to put a couple of stackable bins next to the test kit to hold short coax leads and test leads/scope probes etc.
Ive already laid out the next job on the bench, which is the band change modifications to my Pye PF8. This task involves swapping five very small ceramic capacitors, to swap the radio from the U0 band to the T1 band, which covers 70cm. With these capacitors changed, I should hopefully be able to peak the radio up on 70cm without having to hit the bottom of the coils!
Thanks to Alan G8LIT, I now have the EMERs for this radio, so further repair and alignment should be much easier. Ive already set up the various voltage rails correctly (most were a little low), but the receiver is still somewhat down. Further alignment will wait until I have printed out the instructions. There is also still an issue with the fit of the battle antenna, which refuses to rotate into the locked position.
One thing I have been able to do, now I have the information to work it out, is disable the transmitter! I had thought I would have to unsolder the supply rails etc to the transmit section modules in order to ensure none of the various ways that the radio can be put into transmit would operate, but it turns out that all the transmit controls are dealt with by module3, simply pulling this out totally disables the transmitter with no other detriment.
A few design flaws show themselves with this radio. The first is with its carrying method. It was intended to be fastened to a carrying harness using an adapter plate that used straps to hold the radio, and as such there are no bolt holes for the normal GS adapter plate as used with the PRC351. But, the radio is also very heavy and very square - which means just picking it up is awkward as theres nothing to easily get hold of! Second, internally there are several adjustable parts which have the same designation as each other! For instance, all the regulator modules are adjusted by an R7. This means that if you accidentally pick the wrong module you could cause quite some damage by adjusting the wrong supply rail!
Ive spent some time today clearing and tidying the RF bench, which really was cluttered up. This was mostly in order to find a place for my new variable bench power supply. In doing so, I decided to also rationalise and maximise the space used by the test equipment, so the test bench is much tidier now and more compact, less wasted space ('scope now on top of the Marconi, PSU on top of high power test load, frequency counter on top of the spectrum analyser). This created enough space that ive been able to put a couple of stackable bins next to the test kit to hold short coax leads and test leads/scope probes etc.
Ive already laid out the next job on the bench, which is the band change modifications to my Pye PF8. This task involves swapping five very small ceramic capacitors, to swap the radio from the U0 band to the T1 band, which covers 70cm. With these capacitors changed, I should hopefully be able to peak the radio up on 70cm without having to hit the bottom of the coils!
Wednesday, 16 January 2019
New test kit
Ive been informed that my new bench PSU is awaiting me in the works postroom. My current bench supply is ok, but its an ancient 0-30V 500mA unit, that severely restricts what I can power!
So, ive taken a punt on a new unit from China, although supplied out of a UK based drop-shipper as its taken only 2 working days to arrive!
This is a 0-30V 0-5A unit, so should be far more versatile! Of course, the old one will stay on the bench, always good to have a choice.
Ive also, after reading lots of reviews and recommendations, ordered a new multimeter. Hopefully this will be more reliable than the cheapo little DVMs ive been using.
In light of the fault finding ive been doing recently I think these are probably a good investment! Now, if only I could find a 100MHz dual trace 'scope for under £50...
Also, ive ordered something in light of the work ive been doing on the Clansman PRC-349 conversion. The key to the conversion is the synthesiser mixer crystals. Ive scoured every supply I know of old units, and no one has anything suitable! Vince at IQD has some crystals that will do for testing initially, and I will talk to him about these in the next couple of days, but ultimately the correct frequencies will be needed, both for testing, and for final conversion. As custom crystals as one offs start at around £15 each, this is something I need to avoid until I can prove the conversion works. The, if theres enough interest, a bulk purchase at much lower unit cost could be arranged.
So, I need a way to simulate the crystals. This led me back to Hans Summers and QRPlabs.
QRPlabs do a Si5351A based VFO kit http://qrp-labs.com/vfo.html
This will work to a couple of hundred MHz, and has two outputs, one can be selected as a fixed frequency, and one variable as VFO. This would provide both conversion frequencies for the synthesiser. It will also be a very useful little stand alone unit on the bench for building receivers etc.
Theres little more I can do with the PRC-349s until I get either crystals or the VFO, but I can at least work on how best to open the modules to access the parts that require modification.
So, ive taken a punt on a new unit from China, although supplied out of a UK based drop-shipper as its taken only 2 working days to arrive!
This is a 0-30V 0-5A unit, so should be far more versatile! Of course, the old one will stay on the bench, always good to have a choice.
Ive also, after reading lots of reviews and recommendations, ordered a new multimeter. Hopefully this will be more reliable than the cheapo little DVMs ive been using.
Also, ive ordered something in light of the work ive been doing on the Clansman PRC-349 conversion. The key to the conversion is the synthesiser mixer crystals. Ive scoured every supply I know of old units, and no one has anything suitable! Vince at IQD has some crystals that will do for testing initially, and I will talk to him about these in the next couple of days, but ultimately the correct frequencies will be needed, both for testing, and for final conversion. As custom crystals as one offs start at around £15 each, this is something I need to avoid until I can prove the conversion works. The, if theres enough interest, a bulk purchase at much lower unit cost could be arranged.
So, I need a way to simulate the crystals. This led me back to Hans Summers and QRPlabs.
QRPlabs do a Si5351A based VFO kit http://qrp-labs.com/vfo.html
This will work to a couple of hundred MHz, and has two outputs, one can be selected as a fixed frequency, and one variable as VFO. This would provide both conversion frequencies for the synthesiser. It will also be a very useful little stand alone unit on the bench for building receivers etc.
Theres little more I can do with the PRC-349s until I get either crystals or the VFO, but I can at least work on how best to open the modules to access the parts that require modification.
Tuesday, 15 January 2019
Bugger!
Refitted module 6 and the (now identified) Schottky diode, attached a handset and battery. Checked 24v at cathode of the diode. All looking fine... turn on...
...sound and stench of another component somewhere in the radio expiring!
At least the dial light works now!
Pulling the modules, and performing a classic 'sniff' test indicated the 12v regulator module 4. A check of the voltages on its connections showed 25v, 1.2v, 0v. Compared with the other regulators these are correct, except that the 0v should be 12v! (that 1.2v is on the connection that goes to the regulators 'ref bypass' pin, whatever the heck that does!)
The actual electronics in the regulator modules, at least the 12, 6 and 3v units, is actually the same! Its a 1-40v adjustable regulator. Sadly, a quick metering doesnt show a short this time. So this one is going to take some testing!
Edit -
Well, it didnt take much testing! The ferrite bead inductor in the supply rail, before the 22uF capacitor, was open circuit! It had burnt out. Why? Because the bloody 22uF tantalum leaks like a sieve! So thats two of these caps dead! It didnt test short because A) it only shows short one way, and B) the leg had melted off!
...sound and stench of another component somewhere in the radio expiring!
At least the dial light works now!
Pulling the modules, and performing a classic 'sniff' test indicated the 12v regulator module 4. A check of the voltages on its connections showed 25v, 1.2v, 0v. Compared with the other regulators these are correct, except that the 0v should be 12v! (that 1.2v is on the connection that goes to the regulators 'ref bypass' pin, whatever the heck that does!)
The actual electronics in the regulator modules, at least the 12, 6 and 3v units, is actually the same! Its a 1-40v adjustable regulator. Sadly, a quick metering doesnt show a short this time. So this one is going to take some testing!
Edit -
Well, it didnt take much testing! The ferrite bead inductor in the supply rail, before the 22uF capacitor, was open circuit! It had burnt out. Why? Because the bloody 22uF tantalum leaks like a sieve! So thats two of these caps dead! It didnt test short because A) it only shows short one way, and B) the leg had melted off!
PRC-344 Module 6 repair
With module 6 removed from its shield, the next task was to track down the failed component(s). The large TO-5 can is the regulator IC, an LM100H. Very much obsolete and available only at extortionate prices!
Armed with the datasheet for the LM100H, so I knew which pins connected where, I first traced and drew out a rough circuit diagram. There are four connections to this module. Three make immediate sense - raw 24v, regulated 6v, and Ground. But the fourth im not sure of! But it does seem to rule out the plainly obvious repair of simply replacing the thing with a modern three-terminal device!
The first suspect, and the easiest to isolate and test, was the 22uF capacitor across the raw 24v input line. I lifted the +ve leg of this and metered it...
Bingo! Bloody thing was dead short! I lifted the other leg to take it totally out of circuit and confirmed this was the case.
Now, im not at all sure what type of capacitor this is! But its value, voltage rating, polarity, size and the fact it was across a supply rail leads me to suspect a tantalum. My next job was to physically remove it. Although these modules look normal, they are in fact washed over with a tropicalizing varnish, and the capacitor was stuck down solid. It required a careful application of a wood chisel to prize it off!
A modern standard electrolytic capacitor fits neatly in its place. I would have liked to have fitted an axial device, but the only 22uF 50v devices I have are radials, so I had to bend the legs around a little!
At this point, I havent yet put the module back in the radio and tested it. First, ive to check this beastie over -
This is mounted in fuse holder contacts in the supply line. My suspicion was that it was a varistor, but a bit of research online suggests it might actually be a Schottky diode!
Armed with the datasheet for the LM100H, so I knew which pins connected where, I first traced and drew out a rough circuit diagram. There are four connections to this module. Three make immediate sense - raw 24v, regulated 6v, and Ground. But the fourth im not sure of! But it does seem to rule out the plainly obvious repair of simply replacing the thing with a modern three-terminal device!
The first suspect, and the easiest to isolate and test, was the 22uF capacitor across the raw 24v input line. I lifted the +ve leg of this and metered it...
Bingo! Bloody thing was dead short! I lifted the other leg to take it totally out of circuit and confirmed this was the case.
Now, im not at all sure what type of capacitor this is! But its value, voltage rating, polarity, size and the fact it was across a supply rail leads me to suspect a tantalum. My next job was to physically remove it. Although these modules look normal, they are in fact washed over with a tropicalizing varnish, and the capacitor was stuck down solid. It required a careful application of a wood chisel to prize it off!
A modern standard electrolytic capacitor fits neatly in its place. I would have liked to have fitted an axial device, but the only 22uF 50v devices I have are radials, so I had to bend the legs around a little!
At this point, I havent yet put the module back in the radio and tested it. First, ive to check this beastie over -
This is mounted in fuse holder contacts in the supply line. My suspicion was that it was a varistor, but a bit of research online suggests it might actually be a Schottky diode!
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