AR88 Muting - UK Vintage Radio Repair and Restoration Discussion Forum

gw3xjc · 23rd Oct 2007, 7:34 pm

Hi Gang. I am just about to get back on to 80m Am mode with an old Codar AT5 and an AR88d receiver. I used a similar combination back in the late 60's albeit with a DX100 as a transmitter. I recall I used to mute the AR88 with a pot which I brought out of the back of the AR88. I could vary the degree of mute by adjusting this pot. However years have gone by and I be dammed if i can remember how I did it. I do know it was a common modification as we all seemed to be using that rx at the time. I have a feeling a lifted the earthly end of the series resistor with the RF control and put a pot in series with it. The transmit relay would short the pot out on normal receiver and bring it back into being on transmit,

Or did I feed some negitive back up the AGC line on transmit.
Any of you guys remember doing this or something similar.
73's Rog

Gw3XJC

RobinBirch · 23rd Oct 2007, 8:40 pm

Curious,
Looking through my 88 manual, the "official" method was to control the transmitter from the receiver with a transmitter relay attached to the back.

The down side to this I guess was that the rotary switch would be continually making and breaking the HT and so might start arcing and so on. Some form of relay that gave the same effect from a transmit/receive switch would give the same effect.

As to a pot, maybe you drove the gain down but I'm not sure that this would be enough and tying the transmitter relay, the antenna relay and the receiver HT might be better if a more reliable method than the rotary switch could be found.

Robin

Station X · 23rd Oct 2007, 8:47 pm

The RAF version of the AR88 (R1156A) had an "official" modification to mute the receiver.

A two pin socket was wired in series with the earthy end of R55. Normally this socket had a shorting plug in it. The shorting plug could be removed and a plug forming part of "Control Unit Type 88" inserted in to the socket.

I've never managed to find a circuit for the Control Unit Type 88, but I suspect that on receive it shorted the plug and on transmit left it open circuit. That's certainly how I mute my AR88.

gw3xjc · 23rd Oct 2007, 9:18 pm

Yes thanks both. Yes I remember that the tx/rx switch was on the receiver but I think you will find not many amateurs used that as (again from memory 40 yrs now) that switch removed the HT off the receiver rendering dead.
On CW morse we used to monitor our outgoing signal we could then monitor any chirp or drift. Graham I think you are correct with the earthy end of r55. By switching a pot or being more precise a variable resistor in series with it it is going to reduce the gain. I used to use an old PO 3000 relay to switch the mute into circuit, change the aerial from tx to rx and also switch the ht on and off the old DX100u. They would good old days for sure, learnt many, many things in those days, I was in my mid teens. At the age of 55 the AR88 seems to be heavier??

73 Rog GW3XJC

jim_beacon · 23rd Oct 2007, 10:15 pm

A good method would be to ground the screen of the RF stage - this would effectivly mute the RX, but you may have to change the screen resistor, so that it will handle the extra current. This has the advantage of fast operation, and it leaves the RX on, so there is no frequency drift. It also prvents overload of the RF and mixer stage during transmit, which may lead to blocking.

I believe some other manufacturers (Hallicrafters?) use this method of TX/RX switching.

Jim.

gw3xjc · 24th Oct 2007, 6:27 am

Yes good idea Jim, i will still need to make the mute "variable".
I went to take the AR88 out of it's case last night. i had forgotten how heavy it was. I used to carry one of them upstairs on my own in my younger days, are well i decided to pour myself a large Scotch instead.

73's rog
GW3XJC

Herald1360 · 24th Oct 2007, 12:56 pm

Quote:

Originally Posted by gw3xjc

I used to carry one of them upstairs on my own in my younger days, are well i decided to pour myself a large Scotch instead.

Slightly off topic.... I once single handedly got a B40 up into the loft at my digs where the landlord let a couple of us set up a shack. Wouldn't care to repeat the experience (same age as GW3XJC).

Chris

Skywave · 24th Oct 2007, 6:20 pm

Have a look the circuit of some of the classic Eddystone receivers - 888A, EA12 for example. In these sets the required result is achieved by putting a large +ve bias on the cathode of the RF and / or IF amp. when the set is switched to 'Stand-by'. A pre-set pot. is fitted to enable the 'Mute Threshold' to be adjusted when in 'Stand-by'. (This pre-set is commonly labelled 'Stand-by Sensitivity')

In my experience, this scheme works well, especially for monitoring one's own transmissions.

Al / Skywave.

RobinBirch · 25th Oct 2007, 9:30 pm

That sounds good as I have an AR88 in store that I have had for ages and I dearly love. I intend setting up a rig at my new address and I have always wanted a QRP transmitter and either an 88 or an RA17 as the receiver.

I'll look at adding what you suggest to the AR88.

Cheers

Robin

gw3xjc · 1st Nov 2007, 8:43 pm

Hi Guys been away for a while, back now though. Thanks for all your suggestions. mY next project over the winter is to restore an old KW Vanguard, anyone remember them??

73 Roger Gw3xjc

Station X · 1st Nov 2007, 8:54 pm

If you want to discuss KW Vanguards please start another thread.

23rd Oct 2007, 7:34 pm	#1
gw3xjc Retired Dormant Member Join Date: Jun 2005 Location: Maesteg, Bridgend County Borough, Wales. Posts: 26	AR88 Muting Hi Gang. I am just about to get back on to 80m Am mode with an old Codar AT5 and an AR88d receiver. I used a similar combination back in the late 60's albeit with a DX100 as a transmitter. I recall I used to mute the AR88 with a pot which I brought out of the back of the AR88. I could vary the degree of mute by adjusting this pot. However years have gone by and I be dammed if i can remember how I did it. I do know it was a common modification as we all seemed to be using that rx at the time. I have a feeling a lifted the earthly end of the series resistor with the RF control and put a pot in series with it. The transmit relay would short the pot out on normal receiver and bring it back into being on transmit, Or did I feed some negitive back up the AGC line on transmit. Any of you guys remember doing this or something similar. 73's Rog Gw3XJC

23rd Oct 2007, 8:40 pm	#2
RobinBirch Hexode Join Date: Apr 2003 Location: Cotswolds, UK. Posts: 465	Re: AR88 Muting Curious, Looking through my 88 manual, the "official" method was to control the transmitter from the receiver with a transmitter relay attached to the back. The down side to this I guess was that the rotary switch would be continually making and breaking the HT and so might start arcing and so on. Some form of relay that gave the same effect from a transmit/receive switch would give the same effect. As to a pot, maybe you drove the gain down but I'm not sure that this would be enough and tying the transmitter relay, the antenna relay and the receiver HT might be better if a more reliable method than the rotary switch could be found. Robin

23rd Oct 2007, 8:47 pm	#3
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: AR88 Muting The RAF version of the AR88 (R1156A) had an "official" modification to mute the receiver. A two pin socket was wired in series with the earthy end of R55. Normally this socket had a shorting plug in it. The shorting plug could be removed and a plug forming part of "Control Unit Type 88" inserted in to the socket. I've never managed to find a circuit for the Control Unit Type 88, but I suspect that on receive it shorted the plug and on transmit left it open circuit. That's certainly how I mute my AR88. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

23rd Oct 2007, 9:18 pm	#4
gw3xjc Retired Dormant Member Join Date: Jun 2005 Location: Maesteg, Bridgend County Borough, Wales. Posts: 26	Re: AR88 Muting Yes thanks both. Yes I remember that the tx/rx switch was on the receiver but I think you will find not many amateurs used that as (again from memory 40 yrs now) that switch removed the HT off the receiver rendering dead. On CW morse we used to monitor our outgoing signal we could then monitor any chirp or drift. Graham I think you are correct with the earthy end of r55. By switching a pot or being more precise a variable resistor in series with it it is going to reduce the gain. I used to use an old PO 3000 relay to switch the mute into circuit, change the aerial from tx to rx and also switch the ht on and off the old DX100u. They would good old days for sure, learnt many, many things in those days, I was in my mid teens. At the age of 55 the AR88 seems to be heavier?? 73 Rog GW3XJC

23rd Oct 2007, 10:15 pm	#5
jim_beacon Retired Dormant Member Join Date: Mar 2003 Location: Bishop's Waltham, Hants, UK. Posts: 939	Re: AR88 Muting A good method would be to ground the screen of the RF stage - this would effectivly mute the RX, but you may have to change the screen resistor, so that it will handle the extra current. This has the advantage of fast operation, and it leaves the RX on, so there is no frequency drift. It also prvents overload of the RF and mixer stage during transmit, which may lead to blocking. I believe some other manufacturers (Hallicrafters?) use this method of TX/RX switching. Jim.

24th Oct 2007, 6:27 am	#6
gw3xjc Retired Dormant Member Join Date: Jun 2005 Location: Maesteg, Bridgend County Borough, Wales. Posts: 26	Re: AR88 Muting Yes good idea Jim, i will still need to make the mute "variable". I went to take the AR88 out of it's case last night. i had forgotten how heavy it was. I used to carry one of them upstairs on my own in my younger days, are well i decided to pour myself a large Scotch instead. 73's rog GW3XJC

24th Oct 2007, 6:20 pm	#8
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Re: AR88 Muting Have a look the circuit of some of the classic Eddystone receivers - 888A, EA12 for example. In these sets the required result is achieved by putting a large +ve bias on the cathode of the RF and / or IF amp. when the set is switched to 'Stand-by'. A pre-set pot. is fitted to enable the 'Mute Threshold' to be adjusted when in 'Stand-by'. (This pre-set is commonly labelled 'Stand-by Sensitivity') In my experience, this scheme works well, especially for monitoring one's own transmissions. Al / Skywave.

25th Oct 2007, 9:30 pm	#9
RobinBirch Hexode Join Date: Apr 2003 Location: Cotswolds, UK. Posts: 465	Re: AR88 Muting That sounds good as I have an AR88 in store that I have had for ages and I dearly love. I intend setting up a rig at my new address and I have always wanted a QRP transmitter and either an 88 or an RA17 as the receiver. I'll look at adding what you suggest to the AR88. Cheers Robin

1st Nov 2007, 8:43 pm	#10
gw3xjc Retired Dormant Member Join Date: Jun 2005 Location: Maesteg, Bridgend County Borough, Wales. Posts: 26	Re: AR88 Muting Hi Guys been away for a while, back now though. Thanks for all your suggestions. mY next project over the winter is to restore an old KW Vanguard, anyone remember them?? 73 Roger Gw3xjc

1st Nov 2007, 8:54 pm	#11
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: AR88 Muting If you want to discuss KW Vanguards please start another thread. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.