23cm interference


Dave - G4RQI
 

Hello...

 

Can anyone identify the signal/interference in the movie clip I have uploaded to OneDrive?

https://1drv.ms/v/s!Ajxtoe7Wo30041ruyQwZ09EwG5an?e=u8BVKr

 

The signal appears to be centred on 1297.750 and produces additional carriers in multiples of 66Khz either side and is detectable below 1296.200 Mhz.

 

From my QTH in West Yorkshire the bearing is 200 degrees so I am looking for stations locally with 23cm to take a listen.

 

73 David – G4RQI

Sent from Mail for Windows 10

 


Graham Shirville
 

Hi David,

Anything that repeats every 60kHz or so says to me a SMPSU powering a ethernet and/or wifi router.

You can see a similar effect at 145 MHz  here https://vhf-goonhilly.batc.org.uk/  although I have never heard them on 23cms!

good luck

73

Graham G3VZV

On 11/11/2020 10:00, Dave - G4RQI wrote:

Hello...

 

Can anyone identify the signal/interference in the movie clip I have uploaded to OneDrive?

https://1drv.ms/v/s!Ajxtoe7Wo30041ruyQwZ09EwG5an?e=u8BVKr

 

The signal appears to be centred on 1297.750 and produces additional carriers in multiples of 66Khz either side and is detectable below 1296.200 Mhz.

 

From my QTH in West Yorkshire the bearing is 200 degrees so I am looking for stations locally with 23cm to take a listen.

 

73 David – G4RQI

Sent from Mail for Windows 10

 


David Redman
 

Hi David
No sign of the signal here on any 55el beam heading
Must be fairly local to you
No idea what it is , can you drive around / M 

( Any yes the RX is working GB3MHZ is its usual strength )
 
Dave
G4IDR
IO93BP


Dave - G4RQI
 

Hello... sorry for the delay in replying. I will go out and look for it probably in the new year. For now it’s just an annoyance, maybe if I’m lucky it’ll go faulty

Thanks for looking

David - G4RQI


From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of David Redman <davidredmang4idr@...>
Sent: Wednesday, November 11, 2020 11:40:55 AM
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference
 
Hi David
No sign of the signal here on any 55el beam heading
Must be fairly local to you
No idea what it is , can you drive around / M 

( Any yes the RX is working GB3MHZ is its usual strength )
 
Dave
G4IDR
IO93BP


Robin Szemeti - G1YFG
 

A good tip is have a listen in AM .. the 50Hz buzz of an SMPS is often readily apparent.


On Mon, 30 Nov 2020 at 21:17, Dave - G4RQI <io93ir@...> wrote:
Hello... sorry for the delay in replying. I will go out and look for it probably in the new year. For now it’s just an annoyance, maybe if I’m lucky it’ll go faulty

Thanks for looking

David - G4RQI


From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of David Redman <davidredmang4idr@...>
Sent: Wednesday, November 11, 2020 11:40:55 AM
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference
 
Hi David
No sign of the signal here on any 55el beam heading
Must be fairly local to you
No idea what it is , can you drive around / M 

( Any yes the RX is working GB3MHZ is its usual strength )
 
Dave
G4IDR
IO93BP


--
Robin Szemeti - G1YFG


g4bao
 

Have you looked for it on 432.58?

I have something similar here.
3rd harmonic of some sort of crappy licence free thingy.

73
John


Dave - G4RQI
 

No but I will once the 70cm yagi goes up ready for Tuesday night... ta

David


From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of g4bao <john@...>
Sent: Saturday, December 5, 2020 12:52:08 PM
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference
 
Have you looked for it on 432.58?

I have something similar here.
3rd harmonic of some sort of crappy licence free thingy.

73
John


Dave - G4RQI
 

Hello John

I looked for the device either side of 432.580 and there’s nothing there. Tonight it’s particularly strong and noisy and is present as low as 1296.200. I’ve noticed that it drops in level sometimes but it’s always on the same heading. I could do with a portable analyser/SDR.

Anyone successfully connected an SDRplay to a tablet?

73 David


From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of Dave - G4RQI <io93ir@...>
Sent: Saturday, December 5, 2020 9:44:09 PM
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference
 
No but I will once the 70cm yagi goes up ready for Tuesday night... ta

David


From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of g4bao <john@...>
Sent: Saturday, December 5, 2020 12:52:08 PM
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference
 
Have you looked for it on 432.58?

I have something similar here.
3rd harmonic of some sort of crappy licence free thingy.

73
John


Ed G3VPF
 

Dave

SDRPlay works fine with one of the cheap Windows-based tablets.

Ed G3VPF IO80RQ


From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of Dave - G4RQI <io93ir@...>
Sent: 08 December 2020 18:56
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference
 
Hello John

I looked for the device either side of 432.580 and there’s nothing there. Tonight it’s particularly strong and noisy and is present as low as 1296.200. I’ve noticed that it drops in level sometimes but it’s always on the same heading. I could do with a portable analyser/SDR.

Anyone successfully connected an SDRplay to a tablet?

73 David


From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of Dave - G4RQI <io93ir@...>
Sent: Saturday, December 5, 2020 9:44:09 PM
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference
 
No but I will once the 70cm yagi goes up ready for Tuesday night... ta

David


From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of g4bao <john@...>
Sent: Saturday, December 5, 2020 12:52:08 PM
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference
 
Have you looked for it on 432.58?

I have something similar here.
3rd harmonic of some sort of crappy licence free thingy.

73
John


G0FVI
 

Morning John, I've connected an rsp1a to a lynx windows tablet also an android phone (this was a wee bit more tricky but there are some good videos on YouTube).


From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of Ed G3VPF <g3vpf@...>
Sent: Tuesday, December 8, 2020 7:34:44 PM
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference
 
Dave

SDRPlay works fine with one of the cheap Windows-based tablets.

Ed G3VPF IO80RQ

From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of Dave - G4RQI <io93ir@...>
Sent: 08 December 2020 18:56
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference
 
Hello John

I looked for the device either side of 432.580 and there’s nothing there. Tonight it’s particularly strong and noisy and is present as low as 1296.200. I’ve noticed that it drops in level sometimes but it’s always on the same heading. I could do with a portable analyser/SDR.

Anyone successfully connected an SDRplay to a tablet?

73 David


From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of Dave - G4RQI <io93ir@...>
Sent: Saturday, December 5, 2020 9:44:09 PM
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference
 
No but I will once the 70cm yagi goes up ready for Tuesday night... ta

David


From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of g4bao <john@...>
Sent: Saturday, December 5, 2020 12:52:08 PM
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference
 
Have you looked for it on 432.58?

I have something similar here.
3rd harmonic of some sort of crappy licence free thingy.

73
John


Dave - G4RQI
 

Found it ! - a neighbour has his computer connected up to a KVM switch and when he connects his surface pro doc I get a S9+10 on 1297.750 with sidebands spaced in multiples of 66Khz across 23cm. He also has a power line adapter.

So far we’ve had 30 min on the phone trying to resolve it but with little success. I can’t be sure what is producing the strong carrier on 1297.750

The question is how to resolve it. Plug everything in to a SEK mains filter apart from the power line adapter? I don’t care about the 1297.750 carrier it’s the sidebands that are the issue. Anything else?

Unfortunately the same neighbour wiped me out on 4m when he bought some new (cheap) led lights. Fixed that with ferrite. I was so hoping it wasn’t going to be him...

David - G4RQI


From: David Warr <io93ir@...>
Sent: Saturday, December 12, 2020 6:28:12 PM
To: g3vpf@... <g3vpf@...>
Subject: Re: [UKMicrowaves] 23cm interference
 
Found it ! - a neighbour has his computer connected up to a KVM switch and when he connects his surface pro doc I get a S9+10 on 1297.750 with sidebands spaced in multiples of 66Khz across 23cm. He also has a power line adapter.

So far we’ve had 30 min on the phone trying to resolve it but with little success. I can’t be sure what is producing the strong carrier on 1297.750

The question is how to resolve it. Plug everything in to a SEK mains filter apart from the power line adapter? I don’t care about the 1297.750 carrier it’s the sidebands that are the issue. Anything else?

Unfortunately the same neighbour wiped me out on 4m when he bought some new (cheap) led lights. Fixed that with ferrite. I was so hoping it wasn’t going to be him...

David... G4RQI


From: David Warr <io93ir@...>
Sent: Wednesday, December 9, 2020 8:31:51 PM
To: g3vpf@... <g3vpf@...>
Subject: FW: [UKMicrowaves] 23cm interference
 

Hello Ed,

 

I was thinking of a second hand Panasonic Toughpad with an Intel Celeron. There’s quite a few for sale on ebay but I don’t know if the Celeron is up to it or not. I have a laptop but it doesn’t lend itself to wandering around with hence I was thinking of using a tablet.

 

I have looked to see what others are using but I was hoping the interference might just disappear. I considered reporting it to Ofcom as they sorted out a problem for Mel on 70cm a couple of years ago but we weren’t in the middle of a Pandemic back then.

 

David

Sent from Mail for Windows 10

 

From: Ed G3VPF
Sent: 08 December 2020 19:34
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] 23cm interference

 

Dave

 

SDRPlay works fine with one of the cheap Windows-based tablets.

 

Ed G3VPF IO80RQ

From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of Dave - G4RQI <io93ir@...>
Sent: 08 December 2020 18:56
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference

 

Hello John

 

I looked for the device either side of 432.580 and there’s nothing there. Tonight it’s particularly strong and noisy and is present as low as 1296.200. I’ve noticed that it drops in level sometimes but it’s always on the same heading. I could do with a portable analyser/SDR.

 

Anyone successfully connected an SDRplay to a tablet?

 

73 David

 

From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of Dave - G4RQI <io93ir@...>
Sent: Saturday, December 5, 2020 9:44:09 PM
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference

 

No but I will once the 70cm yagi goes up ready for Tuesday night... ta

 

David

 

From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of g4bao <john@...>
Sent: Saturday, December 5, 2020 12:52:08 PM
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference

 

Have you looked for it on 432.58?

I have something similar here.
3rd harmonic of some sort of crappy licence free thingy.

73
John

 


Glyn M0XGT
 

Given that it’s related to a laptop and dock it's worth checking whether it related to known issues with (older) USB3.0 kit. See Intel’s white paper on USB3.0 generated RF interference and mitigation (focus is 2.4 GHz WiFi, but clearly can also wipe out L1/L2/L5 GPS and 1.3 GHz amateur, etc.).     
Glyn M0XGT
 


David Redman
 

Well done Dave
At least you have found it
Good luck resolving the issue

Dave
G4IDR

On Sat, 12 Dec 2020, 19:22 Dave - G4RQI, <io93ir@...> wrote:
Found it ! - a neighbour has his computer connected up to a KVM switch and when he connects his surface pro doc I get a S9+10 on 1297.750 with sidebands spaced in multiples of 66Khz across 23cm. He also has a power line adapter.

So far we’ve had 30 min on the phone trying to resolve it but with little success. I can’t be sure what is producing the strong carrier on 1297.750

The question is how to resolve it. Plug everything in to a SEK mains filter apart from the power line adapter? I don’t care about the 1297.750 carrier it’s the sidebands that are the issue. Anything else?

Unfortunately the same neighbour wiped me out on 4m when he bought some new (cheap) led lights. Fixed that with ferrite. I was so hoping it wasn’t going to be him...

David - G4RQI

From: David Warr <io93ir@...>
Sent: Saturday, December 12, 2020 6:28:12 PM
To: g3vpf@... <g3vpf@...>
Subject: Re: [UKMicrowaves] 23cm interference
 
Found it ! - a neighbour has his computer connected up to a KVM switch and when he connects his surface pro doc I get a S9+10 on 1297.750 with sidebands spaced in multiples of 66Khz across 23cm. He also has a power line adapter.

So far we’ve had 30 min on the phone trying to resolve it but with little success. I can’t be sure what is producing the strong carrier on 1297.750

The question is how to resolve it. Plug everything in to a SEK mains filter apart from the power line adapter? I don’t care about the 1297.750 carrier it’s the sidebands that are the issue. Anything else?

Unfortunately the same neighbour wiped me out on 4m when he bought some new (cheap) led lights. Fixed that with ferrite. I was so hoping it wasn’t going to be him...

David... G4RQI


From: David Warr <io93ir@...>
Sent: Wednesday, December 9, 2020 8:31:51 PM
To: g3vpf@... <g3vpf@...>
Subject: FW: [UKMicrowaves] 23cm interference
 

Hello Ed,

 

I was thinking of a second hand Panasonic Toughpad with an Intel Celeron. There’s quite a few for sale on ebay but I don’t know if the Celeron is up to it or not. I have a laptop but it doesn’t lend itself to wandering around with hence I was thinking of using a tablet.

 

I have looked to see what others are using but I was hoping the interference might just disappear. I considered reporting it to Ofcom as they sorted out a problem for Mel on 70cm a couple of years ago but we weren’t in the middle of a Pandemic back then.

 

David

Sent from Mail for Windows 10

 

From: Ed G3VPF
Sent: 08 December 2020 19:34
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] 23cm interference

 

Dave

 

SDRPlay works fine with one of the cheap Windows-based tablets.

 

Ed G3VPF IO80RQ

From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of Dave - G4RQI <io93ir@...>
Sent: 08 December 2020 18:56
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference

 

Hello John

 

I looked for the device either side of 432.580 and there’s nothing there. Tonight it’s particularly strong and noisy and is present as low as 1296.200. I’ve noticed that it drops in level sometimes but it’s always on the same heading. I could do with a portable analyser/SDR.

 

Anyone successfully connected an SDRplay to a tablet?

 

73 David

 

From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of Dave - G4RQI <io93ir@...>
Sent: Saturday, December 5, 2020 9:44:09 PM
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference

 

No but I will once the 70cm yagi goes up ready for Tuesday night... ta

 

David

 

From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of g4bao <john@...>
Sent: Saturday, December 5, 2020 12:52:08 PM
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference

 

Have you looked for it on 432.58?

I have something similar here.
3rd harmonic of some sort of crappy licence free thingy.

73
John

 


Dave - G4RQI
 

I post this in case you find yourself with the same issue. This morning I think we identified the Mini DisplayPort to HDMI cable as the culprit. Placing a hand over the device reduced the noise and unplugging it eliminated the noise altogether. The device appears to produce a carrier on 1297.750 with sidebands spaced in multiples of 66Khz.


Is anyone using a DisplayPort to hdmi device without any issues. If so what make and model is it?

We have managed to reduce the signal strength by bypassing a KVM. Wurth clip on ferrite good to Ghz made no difference. COVID restrictions meant this was all done over the phone so not ideal.

David


From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of David Redman <davidredmang4idr@...>
Sent: Saturday, December 12, 2020 9:15:55 PM
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference
 
Well done Dave
At least you have found it
Good luck resolving the issue

Dave
G4IDR

On Sat, 12 Dec 2020, 19:22 Dave - G4RQI, <io93ir@...> wrote:
Found it ! - a neighbour has his computer connected up to a KVM switch and when he connects his surface pro doc I get a S9+10 on 1297.750 with sidebands spaced in multiples of 66Khz across 23cm. He also has a power line adapter.

So far we’ve had 30 min on the phone trying to resolve it but with little success. I can’t be sure what is producing the strong carrier on 1297.750

The question is how to resolve it. Plug everything in to a SEK mains filter apart from the power line adapter? I don’t care about the 1297.750 carrier it’s the sidebands that are the issue. Anything else?

Unfortunately the same neighbour wiped me out on 4m when he bought some new (cheap) led lights. Fixed that with ferrite. I was so hoping it wasn’t going to be him...

David - G4RQI

From: David Warr <io93ir@...>
Sent: Saturday, December 12, 2020 6:28:12 PM
To: g3vpf@... <g3vpf@...>
Subject: Re: [UKMicrowaves] 23cm interference
 
Found it ! - a neighbour has his computer connected up to a KVM switch and when he connects his surface pro doc I get a S9+10 on 1297.750 with sidebands spaced in multiples of 66Khz across 23cm. He also has a power line adapter.

So far we’ve had 30 min on the phone trying to resolve it but with little success. I can’t be sure what is producing the strong carrier on 1297.750

The question is how to resolve it. Plug everything in to a SEK mains filter apart from the power line adapter? I don’t care about the 1297.750 carrier it’s the sidebands that are the issue. Anything else?

Unfortunately the same neighbour wiped me out on 4m when he bought some new (cheap) led lights. Fixed that with ferrite. I was so hoping it wasn’t going to be him...

David... G4RQI


From: David Warr <io93ir@...>
Sent: Wednesday, December 9, 2020 8:31:51 PM
To: g3vpf@... <g3vpf@...>
Subject: FW: [UKMicrowaves] 23cm interference
 

Hello Ed,

 

I was thinking of a second hand Panasonic Toughpad with an Intel Celeron. There’s quite a few for sale on ebay but I don’t know if the Celeron is up to it or not. I have a laptop but it doesn’t lend itself to wandering around with hence I was thinking of using a tablet.

 

I have looked to see what others are using but I was hoping the interference might just disappear. I considered reporting it to Ofcom as they sorted out a problem for Mel on 70cm a couple of years ago but we weren’t in the middle of a Pandemic back then.

 

David

Sent from Mail for Windows 10

 

From: Ed G3VPF
Sent: 08 December 2020 19:34
To: UKMicrowaves@groups.io
Subject: Re: [UKMicrowaves] 23cm interference

 

Dave

 

SDRPlay works fine with one of the cheap Windows-based tablets.

 

Ed G3VPF IO80RQ

From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of Dave - G4RQI <io93ir@...>
Sent: 08 December 2020 18:56
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference

 

Hello John

 

I looked for the device either side of 432.580 and there’s nothing there. Tonight it’s particularly strong and noisy and is present as low as 1296.200. I’ve noticed that it drops in level sometimes but it’s always on the same heading. I could do with a portable analyser/SDR.

 

Anyone successfully connected an SDRplay to a tablet?

 

73 David

 

From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of Dave - G4RQI <io93ir@...>
Sent: Saturday, December 5, 2020 9:44:09 PM
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference

 

No but I will once the 70cm yagi goes up ready for Tuesday night... ta

 

David

 

From: UKMicrowaves@groups.io <UKMicrowaves@groups.io> on behalf of g4bao <john@...>
Sent: Saturday, December 5, 2020 12:52:08 PM
To: UKMicrowaves@groups.io <UKMicrowaves@groups.io>
Subject: Re: [UKMicrowaves] 23cm interference

 

Have you looked for it on 432.58?

I have something similar here.
3rd harmonic of some sort of crappy licence free thingy.

73
John

 


alwyn.seeds1
 

Dear Dave,

Rankie have a UK subsidiary, so you could write to Mr Huang about it.

Regards,

Alwyn

_____________________________________________________

Alwyn Seeds, Director
SynOptika Ltd.,
114 Beaufort Street,
London,
SW3 6BU,
England.


SynOptika Ltd., Registered in England and Wales: No. 04606737
Registered Office: 114 Beaufort Street, London, SW3 6BU, United Kingdom.
_____________________________________________________


g4bao
 

Hi Dave
I found around 10 years ago that a very early version of the "Display Link" (The inventors of USB to VGA) adaptor,  wiped out 23cm here.
One of their tech guys gave me it to play with. No interest whatsoever from the company in my observations  ... (their reaction was rather like the famous Python Sketch with John Cleese as a banker totally failing to grasp the concept of a Charity collector asking him for a donation. :-)

I gave it him back!

Probably the same effect.

73
John   


alwyn.seeds1
 

Dear John,

I must buy myself the Monty Python series to refresh my memories.

However, my attempts to interest a moderately eminent employee of BT in the difficulties that their power line adapters were causing met a similar lack of comprehension.

Regards,

Alwyn

_____________________________________________________

Alwyn Seeds, Director
SynOptika Ltd.,
114 Beaufort Street,
London,
SW3 6BU,
England.


SynOptika Ltd., Registered in England and Wales: No. 04606737
Registered Office: 114 Beaufort Street, London, SW3 6BU, United Kingdom.
_____________________________________________________


militaryoperator
 

.. (their reaction was rather like the famous Python Sketch with John Cleese as a banker totally failing to grasp the concept of a Charity collector asking him for a donation. :-) 


I have the same trouble John. Are there no workhouses anymore? are there no chimneys that need sweeping?

Its give give give all the time.

bah humbug, I say. 

Ben.


Brian Howie GM4DIJ
 

In message <19871.1607902730460929908@groups.io>, g4bao <john@g4bao.com> writes
Hi Dave
I found around 10 years ago that a very early version of the "Display
Link" (The inventors of USB to VGA) adaptor,  wiped out 23cm here.
One of their tech guys gave me it to play with. No interest whatsoever
from the company in my observations  ... (their reaction was rather
like the famous Python Sketch with John Cleese as a banker totally
failing to grasp the concept of a Charity collector asking him for a
donation. :-)

I gave it him back!
Probably the same effect.
73
John   
I've a HDMI to VGA adaptor that produces sprogs on 70cm. I think it might do it on 23cm as well. I can alter the levels by changing the cable routing. Time to dig out the clip-on ferrites.

Brian GM4DIJ
--
Brian Howie