Well, no one said it would be straight forward! A set of this vintage is bound to have some issues. With the battery terminal fixed and the cells given a very gentle and cautions charge, ive been able to test the radio out 'on air'. Using a whip antenna on my Marconi 2955, I was pleased to discover that apart from being a little temperamental on the lower PTT control, she transmits quite nicely. Deviation is also acceptable at about 3.4kHz.
She also receives, the squelch, which seems very tight, breaking at -30dBm - but bear in mind thats over the air with the radio a few inch from the antenna! Volume is good and distortion is low. But - theres a problem!
According to the radios frequency plate, it should receive on 453.2MHz. According to the receive crystal, she should receive at 459.7MHz (same as Tx!), but she actually receives at 454.35MHz!
I suspect its an alignment issue. These are 3rd overtone crystals, so it might just need pulling in
Wednesday, 14 October 2015
Tuesday, 13 October 2015
Inside the PF8
The first task with the boxed Pye PF8 was to open it up and inspect it for completeness. Inside these radios, which are incredibly compact for their age, considering there are no modern 'surface mount' devices, everything is hidden away under a screening plate. In typical Pye form, this plate allows access to all the adjustment points, and labels them very clearly
Removing the plate reveals the electronics. Great use is made of hybrid and thick film modules in Pye's compact handheld transceivers. Whilst in this state, I attempted to apply battery power and measure the voltage at the radio's input. In doing so I discovered the first issue that required attention - the corroded battery terminal.
The 'donor' set had a nice clean terminal, so the whole unit - terminal, insulator, spring and wiring, was removed from each and swapped over.
This time, the test revealed 1.19v at the radios battery input. Good, DC is now getting to the circuits. Rebuilding the radio, and inserting both batteries into the case, I turned on and gave it a go!
And got a very brief flash of the Tx light on PTT before the batteries, which probably havent seen a charger for a couple of decades, went flat! But - It did show the radio working, even if just for a moment!
Next step then is to get the batteries recharged, and to test the radio against the test set. This I can do using the bench PSU. Testing it might be the trickiest part. These radios use an internal skeleton plate antenna designed by Roger G3XBM, with no external antenna connector. To start with at least, testing will be indicative only, but at this stage all I really want to see is if it will receive, and if it transmits!
Removing the plate reveals the electronics. Great use is made of hybrid and thick film modules in Pye's compact handheld transceivers. Whilst in this state, I attempted to apply battery power and measure the voltage at the radio's input. In doing so I discovered the first issue that required attention - the corroded battery terminal.
The 'donor' set had a nice clean terminal, so the whole unit - terminal, insulator, spring and wiring, was removed from each and swapped over.
This time, the test revealed 1.19v at the radios battery input. Good, DC is now getting to the circuits. Rebuilding the radio, and inserting both batteries into the case, I turned on and gave it a go!
And got a very brief flash of the Tx light on PTT before the batteries, which probably havent seen a charger for a couple of decades, went flat! But - It did show the radio working, even if just for a moment!
Next step then is to get the batteries recharged, and to test the radio against the test set. This I can do using the bench PSU. Testing it might be the trickiest part. These radios use an internal skeleton plate antenna designed by Roger G3XBM, with no external antenna connector. To start with at least, testing will be indicative only, but at this stage all I really want to see is if it will receive, and if it transmits!
37 to 45
After longing for one for a long time, I have today thanks to Alan C on the BVWS forum, acquired not just one Pye PF8 radio, in its original polystyrene packaging and including a pair of seemingly good NiCd's, but TWO! The second missing its baseplate and knob, and with one dicky PTT switch, but seemingly otherwise complete.
For those who dont recognise it, this is a Pye PF8 Pocketfone single channel UHF FM handheld transceiver, a revolutionary product in the early 1970s, and an iconic item, since its use by Mssrs Bodie and Doyle in the popular TV series The Professionals. Julie wouldnt let me acquire the other two iconic items from that series - namely the Ford Capri, or the L1A1 SLR service rifle!
The second radio will serve as a donor for spare parts. All I need now is a service manual! Since both radios still have their original channel crystals, and the ID plate is engraved with the Tx and Rx frequencies, and knowing they have a 10.7MHz IF (as confirmed by the IF oscillator crystal), it was little effort to deduce the oscillator multiplication factors needed to work out new crystal frequencies (x3 x3 for each)
A quick test has failed to get the set working, but a multimeter check seems to show that the battery isnt making contact. This is probably just due to the tarnishing of the positive contact, but might be down to physical positioning or size of the contacts. I'll power the radio directly with 2.4v clipped to the terminals to see. Hopefully the inverter circuits are sound.
For those who dont recognise it, this is a Pye PF8 Pocketfone single channel UHF FM handheld transceiver, a revolutionary product in the early 1970s, and an iconic item, since its use by Mssrs Bodie and Doyle in the popular TV series The Professionals. Julie wouldnt let me acquire the other two iconic items from that series - namely the Ford Capri, or the L1A1 SLR service rifle!
The second radio will serve as a donor for spare parts. All I need now is a service manual! Since both radios still have their original channel crystals, and the ID plate is engraved with the Tx and Rx frequencies, and knowing they have a 10.7MHz IF (as confirmed by the IF oscillator crystal), it was little effort to deduce the oscillator multiplication factors needed to work out new crystal frequencies (x3 x3 for each)
A quick test has failed to get the set working, but a multimeter check seems to show that the battery isnt making contact. This is probably just due to the tarnishing of the positive contact, but might be down to physical positioning or size of the contacts. I'll power the radio directly with 2.4v clipped to the terminals to see. Hopefully the inverter circuits are sound.
Sunday, 4 October 2015
Tropo, and another fault
Over the past week, there has been a high pressure system over Scotland. This, combined with conditions for strong radiative ground cooling over night, led to widespread morning fog - and strong tropo!
For me, this was mostly a nightmare. I was working nights, and the enhanced tropospheric propagation of VHF and UHF signals meant massive amounts of co-channel interference to the DTV network! The one saving grace was that, as I left for home on friday morning, 2m FM was buzzing! By the time i'd reached the M62, i'd worked SM7YES in Sweden! Now, Per has a very, very good VHF set-up, but even so, it takes some seriously good conditions to work Sweden on 2m FM from the middle of Yorkshire! Bob, M1BBV, over in Doncaster, even worked him on a 5W handheld!
On reaching home, I quickly rigged up my FT-290Rmk1, 30w Linear amp and assorted ancillaries, to see what could be had on SSB. A couple of Germans worked and I began to notice something was amiss. It seems the 290 has a fault on USB only, a strange tone/carrier that jumps up in level when the rig is keyed, then slowly decays, before sometimes coming back up again! Im totally stumped as to whats causing this.
I visited Hornsea rally today. Sadly I didnt find much I wanted, but I did acquire the battery extension cable for the Clansman radios. I can now power them even when open for repair or alignment. More pressing now though is the need for a charger!
For me, this was mostly a nightmare. I was working nights, and the enhanced tropospheric propagation of VHF and UHF signals meant massive amounts of co-channel interference to the DTV network! The one saving grace was that, as I left for home on friday morning, 2m FM was buzzing! By the time i'd reached the M62, i'd worked SM7YES in Sweden! Now, Per has a very, very good VHF set-up, but even so, it takes some seriously good conditions to work Sweden on 2m FM from the middle of Yorkshire! Bob, M1BBV, over in Doncaster, even worked him on a 5W handheld!
On reaching home, I quickly rigged up my FT-290Rmk1, 30w Linear amp and assorted ancillaries, to see what could be had on SSB. A couple of Germans worked and I began to notice something was amiss. It seems the 290 has a fault on USB only, a strange tone/carrier that jumps up in level when the rig is keyed, then slowly decays, before sometimes coming back up again! Im totally stumped as to whats causing this.
I visited Hornsea rally today. Sadly I didnt find much I wanted, but I did acquire the battery extension cable for the Clansman radios. I can now power them even when open for repair or alignment. More pressing now though is the need for a charger!
Saturday, 26 September 2015
Chinese Airband Receiver Kit - Now with Digital readout!
Ok, so, its NOT a synthesiser, its not even a PLL, its still a free running LC VHF oscillator under varicap DC control. But, it is now much easier to put on frequency, or at least, close enough that the wide IF bandwidth means i'll hear the signal im listening for!
A couple of points here. First, the connections are only tag soldered onto the underside of the PCB at present, and the LCD is powered from the 8v regulator. I need to check that the additional current load isnt too much, although I doubt that the whole shebang takes the 100mA limit of the regulator. Second, the signal input to the counter is at present a single wire, eventually that will be replaced with a length of thin coax. Incidentally, the plugs and wires as supplied with the counter are such that the signal input is a black wire and its ground is a red one! Something to be wary of! I might modify the LCD module to allow the backlight brightness and the contrast to be adjusted.
On the back of the counter module are two push buttons. These allow the display to be changed between 1kHz or 100Hz resolution. Ive set it to 1kHz here, as the oscillators stability isnt up to 100Hz! The buttons also allow setting of an IF offset frequency and direction. By setting it to -10.7MHz, I have a readout of actual receive frequency, or as close as makes no odds.
If its of any interest, here its tuned to Leeds East Airport.
 | ||
| Chinese Airband Receiver with LCD Frequency Counter module |
A couple of points here. First, the connections are only tag soldered onto the underside of the PCB at present, and the LCD is powered from the 8v regulator. I need to check that the additional current load isnt too much, although I doubt that the whole shebang takes the 100mA limit of the regulator. Second, the signal input to the counter is at present a single wire, eventually that will be replaced with a length of thin coax. Incidentally, the plugs and wires as supplied with the counter are such that the signal input is a black wire and its ground is a red one! Something to be wary of! I might modify the LCD module to allow the backlight brightness and the contrast to be adjusted.
On the back of the counter module are two push buttons. These allow the display to be changed between 1kHz or 100Hz resolution. Ive set it to 1kHz here, as the oscillators stability isnt up to 100Hz! The buttons also allow setting of an IF offset frequency and direction. By setting it to -10.7MHz, I have a readout of actual receive frequency, or as close as makes no odds.
If its of any interest, here its tuned to Leeds East Airport.
More musings on the Chinese Airband Receiver kit
After a fair bit of testing, several negatives have come to the fore with this kit. None is a really major problem, and for most builders just wanting to have a pootle about the air band they wont be of any consequence. These are as follows -
1. Sharp crackles from the loudspeaker if the antenna touches anything, or nearby switches are operated
2. IF bandwidth is about 800kHz!
3. A bit low on sensitivity
4. Squelch isnt very good
5. Tricky to tune - whole 118 - 136MHz in just a 270degree turn!
Addressing these in turn, no. 1 is of no real worry, and such noise susceptibility is to be expected working on AM. I expect a bit of extra front end protection is needed, maybe a high value resistor to ground or an RF choke. No. 2, well, ok, it means I receive several channels at once, but lets face it where I live the band isnt exactly crowded, I might have the ceramic filter in the wrong way around, although I thought they were bidirectional! No. 3, only really an issue picking up the ground station, and I can hear both my local airfields towers on it. No. 4 is a bit annoying, but really, see no.3!
So, no. 5 is the issue that is most problematic. With the supplied 10k pot the whole coverage is in a single turn, which means its very easy to miss a signal by tuning right over it. I considered replacing the oscillator with a DDS unit, but mine is only good to about 40MHz, far too low. A simple fix, which ive done, is to replace the 10k pot with a 10k 10-turn precision potentiometer.
Tuning is now much cleaner, but more time consuming! And, since the knob goes around ten times, impossible to know what channel your on except from ID'ing the traffic! I could add a turns counter. But, instead, my thought is to add the el-cheapo LCD frequency meter module I have! I have yet to see if connecting it to the oscillator will cause unacceptable pulling, but will try it out. It might need a little FET buffer circuit.
With the addition of a multipole switch, and a bank of 10-turn presets, I can tune in several local frequencies to switch between. And from there, its not much more effort to add a simple timer and stepping system to allow scanning.
1. Sharp crackles from the loudspeaker if the antenna touches anything, or nearby switches are operated
2. IF bandwidth is about 800kHz!
3. A bit low on sensitivity
4. Squelch isnt very good
5. Tricky to tune - whole 118 - 136MHz in just a 270degree turn!
Addressing these in turn, no. 1 is of no real worry, and such noise susceptibility is to be expected working on AM. I expect a bit of extra front end protection is needed, maybe a high value resistor to ground or an RF choke. No. 2, well, ok, it means I receive several channels at once, but lets face it where I live the band isnt exactly crowded, I might have the ceramic filter in the wrong way around, although I thought they were bidirectional! No. 3, only really an issue picking up the ground station, and I can hear both my local airfields towers on it. No. 4 is a bit annoying, but really, see no.3!
So, no. 5 is the issue that is most problematic. With the supplied 10k pot the whole coverage is in a single turn, which means its very easy to miss a signal by tuning right over it. I considered replacing the oscillator with a DDS unit, but mine is only good to about 40MHz, far too low. A simple fix, which ive done, is to replace the 10k pot with a 10k 10-turn precision potentiometer.
Tuning is now much cleaner, but more time consuming! And, since the knob goes around ten times, impossible to know what channel your on except from ID'ing the traffic! I could add a turns counter. But, instead, my thought is to add the el-cheapo LCD frequency meter module I have! I have yet to see if connecting it to the oscillator will cause unacceptable pulling, but will try it out. It might need a little FET buffer circuit.
With the addition of a multipole switch, and a bank of 10-turn presets, I can tune in several local frequencies to switch between. And from there, its not much more effort to add a simple timer and stepping system to allow scanning.
Friday, 25 September 2015
Shack Teardown
Starting this evening, everything on the shelves in my 'shack' will be packed into boxes. The rigs will be disconnected and boxed, the cables coiled, and the desk itself dismantled.
No, im not closing down! But im finally getting a carpet (rather than random offcuts) in the shack, and the desk, which is attached to the wall at one side, has to come out. When its rebuilt, it will have two sides, and be movable, so I can access the cables at the back.
The only thing that will be left connected will be the MVT-7100 scanner and the coax to the discone, so I still have airband monitoring for tomorrow. Other than that, its handhelds, manpacks, or mobile for a while!
No, im not closing down! But im finally getting a carpet (rather than random offcuts) in the shack, and the desk, which is attached to the wall at one side, has to come out. When its rebuilt, it will have two sides, and be movable, so I can access the cables at the back.
The only thing that will be left connected will be the MVT-7100 scanner and the coax to the discone, so I still have airband monitoring for tomorrow. Other than that, its handhelds, manpacks, or mobile for a while!
Thursday, 24 September 2015
Airband receiver kit complete - first thoughts
So, on arriving home I got out to the workshop and cracked on with the Chinese Airband radio. I had only intended doing the electrolytics and the connectors, but it took no time at all to solder those in, so I got on with the diodes, then the transistors and the 78L08 regulator. This done I tested it with 12v but without installing the ICs, and checked I had an 8v DC rail.
All was well, so I depowered and installed the ICs. The kit as supplied has a3.5mm jack socket audio output, so I tag soldered a loudspeaker across it for testing. Power applied, I was relieved to find that I had noise from the speaker, and that it stopped when I adjusted the squelch control.
With it connected to my Marconi 2955B and being fed a -100dBm 125MHz AM signal (1kHz at 70%), a bit of tweaking and I located the signal. This was quite poor, but much improved after adjusting the IF transformer. Ive pretty much left the band pass filter alone for now, as my to hand trimming tools dont fit.
It isnt quite as sensitive as i'd hoped, 12dB SINAD being around -105dBm, but its not too bad. After a lot of fiddling I managed to adjust the VFO coil to put 118MHz at the extreme of the tuning control, although I couldnt go any lower as the coils slug was all the way out. The tuning is varicap controlled by a 10k pot, and the range is so wide (top end at least 136MHz) that in its current form finding a signal is very tricky. Several ways might solve this, I could modify the circuit for a smaller bandspread, or swap the control for a 10 turn precision pot and a turns counter dial. Or, I could replace the VFO with a DDS synthesiser!
Even as is, mooching about with the control and with a 1m telescopic antenna, it pulled in several aircraft comms signals, ranging from late evening long haul ATC traffic, to my local field with a request that 'as were the last landing you can turn off the lights'!
Next step is to get the frequency counter on the VFO and see exactly what the bandspread is. If need be i'll modify the circuit to reduce this. Ideally, I want to modify the VFO anyway to get coverage down to 108MHz.
But, all in all, for about £12 its a fun little project.
All was well, so I depowered and installed the ICs. The kit as supplied has a3.5mm jack socket audio output, so I tag soldered a loudspeaker across it for testing. Power applied, I was relieved to find that I had noise from the speaker, and that it stopped when I adjusted the squelch control.
With it connected to my Marconi 2955B and being fed a -100dBm 125MHz AM signal (1kHz at 70%), a bit of tweaking and I located the signal. This was quite poor, but much improved after adjusting the IF transformer. Ive pretty much left the band pass filter alone for now, as my to hand trimming tools dont fit.
It isnt quite as sensitive as i'd hoped, 12dB SINAD being around -105dBm, but its not too bad. After a lot of fiddling I managed to adjust the VFO coil to put 118MHz at the extreme of the tuning control, although I couldnt go any lower as the coils slug was all the way out. The tuning is varicap controlled by a 10k pot, and the range is so wide (top end at least 136MHz) that in its current form finding a signal is very tricky. Several ways might solve this, I could modify the circuit for a smaller bandspread, or swap the control for a 10 turn precision pot and a turns counter dial. Or, I could replace the VFO with a DDS synthesiser!
Even as is, mooching about with the control and with a 1m telescopic antenna, it pulled in several aircraft comms signals, ranging from late evening long haul ATC traffic, to my local field with a request that 'as were the last landing you can turn off the lights'!
Next step is to get the frequency counter on the VFO and see exactly what the bandspread is. If need be i'll modify the circuit to reduce this. Ideally, I want to modify the VFO anyway to get coverage down to 108MHz.
But, all in all, for about £12 its a fun little project.
A bit more done on the Airband kit
I had a few moments spare last night to progress building the Chinese airband receiver. The ceramic capacitors, ceramic filter, and inductors are now fitted.
(just realised that photo is before I fitted the IF can!)
I'll add the electrolytics, connectors and controls tonight, and if ive time might get onto the semiconductors. At this rate, I might have it operational for saturday morning, which is the day of the inaugural East Leeds Airshow. Despite being only a few miles up the road at RAF Church Fenton, I shant be attending this time, the number of ground exhibits, aerial displays and stalls doesnt to me justify the £50 family ticket price tag!
The only aircraft I really want to see that will be displaying is Vulcan XH558 - and I should be able to easily see her from my own garden!
(just realised that photo is before I fitted the IF can!)
I'll add the electrolytics, connectors and controls tonight, and if ive time might get onto the semiconductors. At this rate, I might have it operational for saturday morning, which is the day of the inaugural East Leeds Airshow. Despite being only a few miles up the road at RAF Church Fenton, I shant be attending this time, the number of ground exhibits, aerial displays and stalls doesnt to me justify the £50 family ticket price tag!
The only aircraft I really want to see that will be displaying is Vulcan XH558 - and I should be able to easily see her from my own garden!
Wednesday, 23 September 2015
4m FM - where's the activity?
After trying each lunchtime from work to make a contact on 70.450MHz FM using the PRC-351, I decided today to try the same using my FM-1100. This uses the same magmount antenna as i'd been using with the '351, but at 15W rather than 4W, and is capable of 12.5kHz steps, giving me the whole of the 4m FM allocation.
But not a sausage! Where has all the 4m FM activity midday gone? There used to be at least a couple of stations monitoring that i could reach from Emley!
But not a sausage! Where has all the 4m FM activity midday gone? There used to be at least a couple of stations monitoring that i could reach from Emley!
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