?

Nice find Jon. I drew that schematic ?.

--
Mike G8GYW

On 15 Apr 2024, at 09:05, Jon Withers <jonathan.withers@...> wrote:

?

Hi Chris,

?

You may find the attached helpful – it shows the Tx RF circuitry of the pre-production B model (which was pretty close to the final from what I recall).? I worked on quite a bit of the RF of this unit, but it was a long time ago!? A couple of things that might be worth considering – the Tx ouput stage had two back-off mechanisms:

• A thermistor (P390 below TR21?) soldered to the heat clip on the PA output transistors – if that went open circuit you’d get no output
• There was a control loop to reduce the Tx power to maintain the battery voltage at 8 V in transmit so that you could maintain comms for as long as possible with an almost flat battery – again an issue there could cause no RF out.?

?

If the synthesizer were out of lock then there would be no output, but if the receive is OK then that is unlikely – one of the pins on ML4 will change state when it’s OOL.?

?

I’d be interested to hear how you go!

?

Jonathan

?

(PS in Sydney, so same timezone as yourself)

?

From: [email protected] <[email protected]> On Behalf Of Mike
Sent: Monday, April 15, 2024 4:45 PM
To: [email protected]
Subject: Re: [RacalRadio] PRM 4720

?

Hi Chris

I was one of the engineers who worked on the design of this radio but it was so long ago I cannot remember details of the schematic. You could try contacting Jon Withers who posted earlier in this thread. I'm pretty certain he still has a couple of the radios.

--
Mike G8GYW

<IMG_20180728_092852.jpg>

On 13/04/2024 21:15 BST julian1528 via groups.io <julian.barnard@...> wrote:

?

?

Hi Geoff - I think we have some of these new and boxed in our stores.

I’ll check on Monday and let you know.

Best regards,

Julian Barnard.

?

On 13 Apr 2024, at 16:09, Jeff via groups.io <jeff.akines@...> wrote:

HI Guys,
Still looking for the above item to buy or maybe swap
Jeff? G8XXI

?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????

?

Hi Chris

I was one of the engineers who worked on the design of this radio but it was so long ago I cannot remember details of the schematic. You could try contacting Jon Withers who posted earlier in this thread. I'm pretty certain he still has a couple of the radios.

--
Mike G8GYW

On 13 Apr 2024, at 16:09, Jeff via groups.io <jeff.akines@...> wrote:

?HI Guys,
Still looking for the above item to buy or maybe swap
Jeff? G8XXI

?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????