AVAIR AV-200 SWR & Power Meter - UK Vintage Radio Repair and Restoration Discussion Forum

Alf Fisher · 27th Mar 2021, 5:16 pm

Hi folks,

I have one of these units and was surprised to find zero ohms to ground on both of the SO-239 connectors.

I have a simple V/UHF one where there is no connection to ground between the SO-239 connectors but there is between the inner contacts which I would expect.

I'm questioning whether this is correct or whether it was a Friday afternoon model. I had a look inside and there are chokes wound on toroids from the centre contact of each SO-239 to ground.
This is supposed to work from 1.8 MHz to 200 MHz but it doesn't appear to work properly.

If someone who has a AV-200 could please check to see if there is zero ohms to ground on each SO-239, to confirm that this is correct.

Alf

Phil-G0SXY · 27th Mar 2021, 5:41 pm

I have the AV-1000 model and just checked it for you, when you say "ground" do you mean the negative of the power supply? If so, then no there isn't zero ohms, i read 6.5MΩ one way and open circuit the other.

The actual connectors (N type in my case) are all connected via the outer screw casing.

Alf Fisher · 27th Mar 2021, 7:33 pm

Hi Phil,
Thanks for checking yours.
I just measured between the inner and outer of the connectors.
I'd expect there to be a connection from inner to inner but I'm puzzled why there appears to be a short from inner to outer.

Alf

Phil-G0SXY · 27th Mar 2021, 8:36 pm

As luck would have it, i have dug out on old Diamond SX200 i don't have a circuit for this meter but it does have continuality between centre and outer, if it uses a transformer winding for the coupling then it will appear as a "short".

Alf Fisher · 27th Mar 2021, 10:07 pm

I took the box out to see what was in it and there is an inductor thats wound on a ferrite ring from each coax inner to ground.

The circuit looks quite complicated - certainly more so than a lot of the circuits on the web.

Radio Wrangler · 28th Mar 2021, 1:18 am

Look up "Tandem Match" which was published by the ARRL.

There is also a dual directional power meter I did for the G-QRP club. It was published in issue 61 of SPRAT... Googling "Stockton Power meter" will turn up different people's versions

Other VSWR meters make no connection to the through line but look at power flows induced off of it to side-mounted lines. Others have a single transformer and a capacitive tap (The Bruene circuit by Warren Bruene at Collins Radio).

On the whole, the two transformer ones give flatter performance and can save on adjustments.

Whether or not there is a DC path only becomes important if you want to go right down to DC

David

27th Mar 2021, 5:16 pm	#1
Alf Fisher Hexode Join Date: Sep 2005 Location: Potton, Bedfordshire, UK. Posts: 293	AVAIR AV-200 SWR & Power Meter Hi folks, I have one of these units and was surprised to find zero ohms to ground on both of the SO-239 connectors. I have a simple V/UHF one where there is no connection to ground between the SO-239 connectors but there is between the inner contacts which I would expect. I'm questioning whether this is correct or whether it was a Friday afternoon model. I had a look inside and there are chokes wound on toroids from the centre contact of each SO-239 to ground. This is supposed to work from 1.8 MHz to 200 MHz but it doesn't appear to work properly. If someone who has a AV-200 could please check to see if there is zero ohms to ground on each SO-239, to confirm that this is correct. Alf

27th Mar 2021, 5:41 pm	#2
Phil-G0SXY Triode Join Date: Feb 2021 Location: Olney, Buckinghamshire, UK Posts: 19	Re: AVAIR AV-200 SWR & Power Meter I have the AV-1000 model and just checked it for you, when you say "ground" do you mean the negative of the power supply? If so, then no there isn't zero ohms, i read 6.5MΩ one way and open circuit the other. The actual connectors (N type in my case) are all connected via the outer screw casing.

27th Mar 2021, 7:33 pm	#3
Alf Fisher Hexode Join Date: Sep 2005 Location: Potton, Bedfordshire, UK. Posts: 293	Re: AVAIR AV-200 SWR & Power Meter Hi Phil, Thanks for checking yours. I just measured between the inner and outer of the connectors. I'd expect there to be a connection from inner to inner but I'm puzzled why there appears to be a short from inner to outer. Alf

27th Mar 2021, 8:36 pm	#4
Phil-G0SXY Triode Join Date: Feb 2021 Location: Olney, Buckinghamshire, UK Posts: 19	Re: AVAIR AV-200 SWR & Power Meter As luck would have it, i have dug out on old Diamond SX200 i don't have a circuit for this meter but it does have continuality between centre and outer, if it uses a transformer winding for the coupling then it will appear as a "short".

27th Mar 2021, 10:07 pm	#5
Alf Fisher Hexode Join Date: Sep 2005 Location: Potton, Bedfordshire, UK. Posts: 293	Re: AVAIR AV-200 SWR & Power Meter I took the box out to see what was in it and there is an inductor thats wound on a ferrite ring from each coax inner to ground. The circuit looks quite complicated - certainly more so than a lot of the circuits on the web. Attached Thumbnails

28th Mar 2021, 1:18 am	#6
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,876	Re: AVAIR AV-200 SWR & Power Meter Look up "Tandem Match" which was published by the ARRL. There is also a dual directional power meter I did for the G-QRP club. It was published in issue 61 of SPRAT... Googling "Stockton Power meter" will turn up different people's versions Other VSWR meters make no connection to the through line but look at power flows induced off of it to side-mounted lines. Others have a single transformer and a capacitive tap (The Bruene circuit by Warren Bruene at Collins Radio). On the whole, the two transformer ones give flatter performance and can save on adjustments. Whether or not there is a DC path only becomes important if you want to go right down to DC David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done