One part of the radio hobby i enjoy is conversion of EXPMR radio's.
This all started many years ago when i first got licenced.
I do not do PMR Radio as a job only what i have read or info cleamed from PMR Engineers friends.
Thanks go to Phil G8MLA and Jake G1YFF .
Radio transceivers back in the 1980's were expensive to buy.
Back then there was a magazine available called Ham Radio Today or HRT.
Chris G4HCL Lorek was the editor. Luckly for me Chris lived in the next village to me so i regulary chatted to him.
Chris at that time worked for Pye of Cambridge.He started doing conversion details in HRT.
This inspired me to have a go at EXPMR conversion.
Chris Lorek, G4HCL, from Whitby, Enlgand, died suddenly on 28 April 2018 after being taken ill in Goa, India.
He was 61 years old.
He worked as Chief Engineer on radio communications systems and equipment, but will be known mostly to RSGB Members as a prolific author.
He wrote many equipment reviews in RadCom and Ham Radio Today magazine, for which he was Technical Editor for seven years. In addition to having hundreds of articles published, he wrote several books, including the PMR Conversion Handbook for the RSGB.
He also co-edited the 7th and 8th editions of the Radio Communication Handbook.
This how i cut my teeth so to speak, learning about how equipment worked.Beggering it up and fixing it . Most of the timeAnd i am still learning !
Rigs converted over the years were .
PYE PF2 70cm 3 channel PYE PF1 Pocket Phones
PYE Olympic for 70cm 12 channel. Storno CQM 700A 70cm.
Pye Europa 3 channel for 2m packet radio . PYE Westminster W15 for 4m 12 channels.
Philips FM914 for mobile 2m. Bosch KF453 70cm.
There were a few others !
Moving on to now i am still playing with EXPMR gear even though there are Chinese Radio's at low prices and do everything.
Gear i am playing with now :
KEY KM Series on 4m,2m,70cm KEY KME Series on 4m,2m,70cm Tait T500 Series 4m,2m,70cm
Tait t3010 9 channel Cleartone CM7200 thanks Ian G7GMN
Key KP80 4M Key KP150 2M
****** WANTED Key KP450, Microphone for Cleartone cm7000 *****
I have been playing with my Key series radio's.
In East Anglia i am lucky that i can access lots of repeaters .But they have different CTCSS tones.
On doing some reading i had a light bulb moment.
By using a double pole double throw switch and a single pole switch i could make the key radios work with 4 CTCSS tones. Namely 77hz , 94.8 hz , 71.9 hz & 110.9 hz.
Take a look at the tone Chart.
You will see that all the tones mentioned all use switch 1.
So i linked switch 1 on the tone board.
77hz uses switch 2 , 94.8hz uses switch 5, 110.9hz uses switch 4 , 71.9hz is switch 1.
So by soldering leads to the back of the DIL switch on the CTCSS board and wiring to switches.
Multi CTCSS tones can be had.
Other combinations of CTCSS tones can be had . It's all down to linking and switches.
Note make sure all DIL switches are switched off.
This mod has been carried out on a Key KM450 and a KEY KME150.
This idea can be used on other CTCSS boards.I have done the same trick on a SIGTEC C1012 board.
I have had a Tait t525 4m transceiver some time now and wanted to add extra channels.
I came across M1DYP Website showing me how to modify the Tait. So all credit goes to him.
The mod requires adding 2 DPDT switches to the front of the transceiver.This mod can be carried out on 2m &
70cm versions of the Tait T500 series transceivers.
The picture below shows the back of the switches.These are wired to the diode matrix.
The diode matrix has diode links one for receive and one for transmit.
By choosing the correct diode links extra channels can be had .
Values of the diode matrix:
On channel 1 is on 70.450 mhz. This was not altered
On channel 2 is on 70.425 mhz. All switches taken off this matrix.
Left switch clicked down and channel 2 gives me 70.325 mhz.
Right switch clicked down and channel 2 gives me 70.4375 mhz.
Both switches down and channel 2 gives me 70.3375 mhz.
So by adding 2 switches i have ended up with 5 channels.
By adding another switch would give me even more channels.
My thanks to Ken M1DYP for the idea.
Over the years i have gathered test gear so i can align my own equipment.
OK the gear is old but it works.
A Multimeter is useful, an analogue type is the best like an AVO.Digital types are no good as you need to see the swing on the meter while adjusting your radio.
Again i have an old bit of kit a AVO 8 and a PYE TM1 Meter ideal for the job.
AVO 8 Analogue Meter PYE TM1 Test Meter
Next you need a way to align your receiver.A signal generator is useful. I have had 2 or 3 over the years.
PYE SG3V, SG5U , Marconi 1064B. This is my latest Signal Generator a Racal 9081.
The signal generator needs to have a variable signal attenuation. I.E strong to weak signal so you can weaken the signal as you progress through the alignment.
A Power /SWR meter is a useful item in the shack. Go for the best you can i went for a Revex W570 1.8 MHZ TO 1300 MHZ .
A couple of dummy loads are useful.Make sure they are ok for VHF,UHF work. 60w power level is good for short tests.
Next a way of checking the Deviation or the transmitted audio.A rough way is to get a fellow amateur to listen while transmitting.Over deviation on a signal is like the signal chopping off on your peaks.Try shouting fours and six into your microphone as it will show up if you are overdeving .
A better way is to get a Deviation Modulation Meter.
I obtained a Marconi TF2303 some years ago.
I was given a Racal 9839 frequency counter by Phil G8MLA.This covers 10hz to 560mhz.
I have had the counter for many years.I also have a portable frequency N8 counter off Ebay that covers from 1mhz to 1000mhz.
One thing i have learn't about test gear never transmit straight into them as it is instant death.
To get over this i made up an RF T piece .Get yourself a TEE SO239,SO239 with a PL259 in the middle.
Mark the center pin where it goes into the nylon center.Unscrew the center pin.Cut it on the mark you made.
Cut a notch in the pin so you can screw it back in.Make sure it is flush to the nylon.I put a piece of insulating tape over the center pin .Next screw in an SO239 to S0239 joiner.I put a piece of RED tape around the SO239 joiner to indicate the sniffer section.OK next screw in a dummy load on one side of the tee and a PL259 patch lead to the other.Next screw another Patch lead to the Siffer end if the tee.This goes to you test kit.There will be just enough RF sniffed to be able to align your radio.