Radiolab/Philips PRF1520

[VK4TIM]

Good evening,

The Philips PRF15 usually come set up for the 400-430, 450-470, 470-490 and 490-520 MHz bands.

I'm not aware of front panel programming on the PRF15s, but they should work OK on 430-450, but you will likely need to do some software trickery, or program the controller to tell it that it's a 425-450 version, similar to the mobile PRM80, then it should program where you want it.
The RF hardware will do it, the only possible mods might be small adjustments to the VCOs, but for small shifts, it will likely realign.
I have never had to rechannel a PRF15, so I can't comment on what software you would require to program the band and operating channel.

I'm sorry I can't be much more help at this stage, I do have documentation at work for these bases, if you had the next generation PRF28, I could tell you how to program and realign both the TX and RX without looking at one.

The Philips PRF15 has proven to be a reliable piece of equipment, and that's why I haven't had too much to do with them!.

[VK7DB]

Who wants a 490-520 one? I have one that I'll never use and want to get rid of it..

[VK2JDS]

some modification info on prf15's you fellows might be interested in :

i have a prf1520 here, its programmed by dip switches on the back panel, or can be set using jumpers on the receiver and tx pcb's themselves. the 1530 model is the front panel programmable one

this one is the 450-470MHz version and so far i have completed the receiver mods. these are :

figure out how to power the receiver outside the case - 12vdc connects to the end pin of the backplane plug closest to the voltage regulators.

next set the pll programming jumpers on the receiver pcb and retune/lock the vco. i chose to set the rx frequency to 434.025 as a test, and set the local oscillator to the high side to avoid major mods.
the vco is inside a shielded box about 3 inches by 2 inches. desolder the lid, apply 12v to receiver pcb and measure the loop voltage on the plug closest to the edge of the rx board. i got mine down to a bit over 12 volts which is good enough to reliably lock.

now we come to the work involved in the helical filters. to make them resonate on 434 they require about 1cm of extra wire added to each coil. i have included a few pictures to show how this is done.

dremel tool cut slot in helical resonator former

remove the filters and dismantle. cut a small slot in the plastic former with a dremel tool for the extra wire to fit snugly into and solder it to the end of the coil.

1cm of wire soldered on end of each coil

reassemble and refit to the front end pcb.
do both filters and align using spectrum analyser and tracking generator. there are small jumper pads provided to desolder the filters out of circuit to allow you to sweep them for tuning without damaging the receiver.

aligning filters

refit the jumpers and shield cans after alignment.
i measure mute opening at 0.3uV and nearly noisefree at 0.5uV to 0.6uV

so far so good, next job is the transmitter. i will keep you posted
73 from Dave vk2jds

[VK2JDS]

more progress on the repeater for the club . Amateur Radio Central West Group. (the group covers most of the central west of NSW rather than the old orange club which had problems....)

The receiver is working well , but requires the 'mute' button on the control panel to be pressed to actually hear the signal.
however the 'mute' LED on the receiver does illuminate indicating a signal once i raise the signal generator above 0.3uV..

next job today was the transmitter exciter which required a binary calculation to set the programming to the 439.025MHz test frequency. i was out by a megahertz, so fudged it by shifting jumpers to get it right

powering the exciter up outside the mainframe cabinet involves adding 12volts to the end pins on the mainframe plug in the same place as the receiver board

next was the pll and this was simply a matter of adding 5pf (3.3 to 5.6pf etc) capacitance across the trimmer cap in the VCO module and adjusting the loop volts to about 6 or so which seems to reliably lock. no further adjustments were made and a test of transmit was done with the PA connected by pressing the 'ptt' button on the control panel.
tomorrow i will hook up a better power supply , but the transmitter should sit at 50 watts and was pinning the meter on the the bird tonight off the small power supply.

whats next : its not working as a repeater! applying the sig-gen or keying up a handheld near it will not activate its transmitter, so its back to the manual to nut out whats stopping it from repeating.
i tried the spare mainframe unit as well and its the same. no repeat.... hmmmm

I will write down and post here the programming jumper settings required for various frequencies but the main thing is to keep the receiver LO injection frequency on the high side to avoid a lot of rx VCO mods.

73 from Dave

[VK7DB]

Maybe I can use my 1520 then.. What I need is a service manual though. Where might I find one of these?

Thanks,
Dion
VK7DB

[VK3KCX]

Maybe I can use my 1520 then.. What I need is a service manual though. Where might I find one of these?

Thanks,
Dion
VK7DB

You could try buying one from the manufacturer - Philips/Comgroup/Simoco http://www.simocogroup.com/australasia.

From memory it is a bit of a dog of a manual - circuits drawn by a draftsman, not an engineer and you are continually flicking back and forth trying to work out how all the different drawings connect up.
The product however is a good performer and quite reliable, apart from the very early units.

- David

[VK3KCX]

whats next : its not working as a repeater! applying the sig-gen or keying up a handheld near it will not activate its transmitter, so its back to the manual to nut out whats stopping it from repeating.
i tried the spare mainframe unit as well and its the same. no repeat.... hmmmm

Hi Dave, I had a bit to do with these devices when they were new - back in the early 90's. The no talk through on RX signal will have something to do with the configuration linking, many of these units were fitted with external CTCSS tone panels that handled all of the repeater functions, I guess you did not get this. They usually came fitted default with a single tone CTCSS module fitted internally, if this is the case, hook up the CTCSS decode + carrier detect with an AND function monostable, give a a few seconds of hang time,connect this to the PTT, connect the RX audio line out to the TX audio line in and you have yourself a repeater!

All the best. - David VK3KCX

[VK7DB]

Found a manual. This one is 500-520 I think, and narrow band, so would make a nice CB repeater if it will come down that far. Its no good for anything else, so I will have a go at the conversion. Ive had success with similar methods with the Unilab repeaters in similar band splits.

Dion.

[VK2JDS]

more progress, the unit is now keying up and there is a tail which is programmable on a dipswitch, info from the manual.
the next job is to port audio across. the secret is using the db25 connector on the back of the mainframe pcb, and jp6 on the mainframe for the audio.
you dont need to use a repeater controller, i will nut this out, its all there

i disabled the ctcss decoder (single module) with the dipswitches but thanks for the good suggestion David

i will post up the pin numbers when its daylight and i can get it to port through the audio.

i dont have the pinouts of the db25 on the mainframe board which makes things difficult!

these are a terrific repeater and i strongly suggest if you come across one to grab it straight away
73 from the bush, Dave

[VK2JDS]

today was very successful, I got the unit to forward the transmit audio and did a further tweak up on the cavities.

to fix the audio i powered up the transmit exciter pcb externally from the mainframe and applied ptt. next was poking about looking for audio to the vco and setting the jumpers on the audio processing pcb. everything appeared to be set ok so i traced out to the back plane pcb and followed that to the control pcb socket.
next was finding rx audio on the same socket. here is a picture of the correct placement of a electrolytic cap (10uf etc) to cross couple the audio

cap on back of control pcb socket on mainboard

here is the pic of the ptt control line jumper on the db25 socket, you want to link pin 18 to pin 21 on a db25 plug and push it on. note the audio didnt appear on these pins in a usable form on my unit.

tx link

next was tweaking the rx cavities. I had already swept them with the speccy and tracking generator and they were pretty close, but nothing beats a final tweak with the weak signal generator.
this photo shows the repeater is keyed up and a bit over 50 watts output is on the power meter on the left side of the shot, with the sig-gen outputting -119 dbm on the right side of the shot. audio was clear with slight hiss and this is measured with the cavities in line! got to be happy with that

next job is to take it up on the solar powered mountaintop site and connect it to antennas!

73 from Dave vk2jds

[VK2JDS]

The repeater has been running solar powered for a test run on my mountaintop. it all seems to be going ok , but i did change the link cable for the transmit keyup.

using the db25 on the back of the mainframe board results in keyup on carrier detect, but wont allow you to program the tail length with the dip switch S3 on the control pcb.
to fix this i ran a wire from the ptt button on the control pcb front cover board via a diode to the carrier detect line out of the receiver which appears on pin 21 of the db25. hence when carrier detect goes low it pulls down the ptt button line through a 1n4148 diode.
now the tail can be set up by s3 switch 7 and 8. turn both on and you get a 1 second tail, turn on only switch 8 and you get half a second.

what about if your repeater was missing its control module? how do we get around this and make it go.

firstly the carrier detect line from the receiver module appears on PLA c22 on the mainframe pcb behind the rx module, this needs to be linked directly to PLA a6 on the transmitter mainframe socket.
next to port audio across connect a jump wire via a 10uF capacitor from rx pcb connector on mainframe PLA a3 (rx ttr audio) to pin PLA a9 on the transmitter mainframe socket.
this will allow it to function as a repeater and the audio level is set by the VF pot on the receiver module front panel. it will have no tail, but will be a talk-through repeater.
to make a circuit in the ptt line to enable a tail and ident i suggest having a look on the net for someone who has already done this, or maybe someone could post up one here. the vk5dj repeater controller could be a good option

73 from Dave vk2jds

[VK2JDS]

test freq is 439.025 -5MHz offset, running on 2 diamond verticals at 950 metres on a mountaintop. qf46pu north-east of orange, nsw central table lands
signal reports welcome
73 from Dave

[VK2JDS]

the prf15 UHF repeater has had its final tune-up and test. The duplexer has been stripped and new silverplated cables and N connectors fitted, newish silver plated interconnecting N cables join up all the hardware. its all in rack mount cases ready to install and runs on a single diamond vertical using a retuned ex-commercial 6 notch combiner.

the business end of the repeater

next i have to connect up and link the audio and CD + PTT lines into the club vhf repeater and connect up the V/U combiner duplexer into the existing vhf repeater transmit antenna

the tuning of the transmit cavity can, the 6 notch filter duplexer and the dual receive cavity cans is critical.
no adjustment can be made to improve performance as it stands. half a turn will stuff it.
the output power is on the end-stop but we are achieving 22 watts up the heliax once its gone through so much hardware.

measured receiver sensitivity is good, mute opens at 0.3uV and clean audio through at 0.5uV and thats measured through the duplexer, the diplexer and the receiver cavities all inline
we are applying for 439.3 MHz as its operating frequency and its been running for a while on test there
73 from Dave vk2jds