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FDM DUO Attenuator behaviour

Bob G3PJT
 

When I set the attenuator all the signals disappear. Its as if the antenna is disconnected
Is there a setting somewhere to set the level of attenation. My DUO has only just started to do this
I have done a reset and no change
Any ideas?
73 Bob G3PJT

NEIL COLEY <neilcoley9@...>
 

Bob

I had a similar situation. 

Did all the on/off and resets but the problem remained 

I disconnect and reconnected the  antenna from the Duo and bingo...back to normal. 

No scientific approach or explanation. Maybe just coincidence 

Worth a try if you haven’t already 

Neil



On 6 Feb 2020, at 16:17, Bob G3PJT <bob@...> wrote:

When I set the attenuator all the signals disappear. Its as if the antenna is disconnected
Is there a setting somewhere to set the level of attenation. My DUO has only just started to do this
I have done a reset and no change
Any ideas?
73 Bob G3PJT

Neil Smith G4DBN
 

Attenuation is fixed at 20dB Bob, R67/68/69 switched in by RL2.

I guess you are hearing the faint click of RL2 when you enable attenuation? If you can measure the input impedance, you could check if the input impedance goes weird, with R69 gone open circuit or a relay contact fault or a short to ground.

Full input diagram is attached to message https://groups.io/g/EladSDR/message/14141

Neil G4DBN

On 06/02/2020 16:17, Bob G3PJT wrote:
When I set the attenuator all the signals disappear. Its as if the antenna is disconnected
Is there a setting somewhere to set the level of attenation. My DUO has only just started to do this
I have done a reset and no change
Any ideas?
73 Bob G3PJT
_._,_._,_

Tony_AD0VC
 

Assuming a 50 ohm load, that looks like a 12-13 db attenuator to me (?).

Tony


From: EladSDR@groups.io <EladSDR@groups.io> on behalf of Neil Smith G4DBN <neil@...>
Sent: Thursday, February 6, 2020 10:07 AM
To: EladSDR@groups.io <EladSDR@groups.io>
Subject: Re: [EladSDR] FDM DUO Attenuator behaviour
 

Attenuation is fixed at 20dB Bob, R67/68/69 switched in by RL2.

I guess you are hearing the faint click of RL2 when you enable attenuation? If you can measure the input impedance, you could check if the input impedance goes weird, with R69 gone open circuit or a relay contact fault or a short to ground.

Full input diagram is attached to message https://groups.io/g/EladSDR/message/14141

Neil G4DBN

On 06/02/2020 16:17, Bob G3PJT wrote:
When I set the attenuator all the signals disappear. Its as if the antenna is disconnected
Is there a setting somewhere to set the level of attenation. My DUO has only just started to do this
I have done a reset and no change
Any ideas?
73 Bob G3PJT

Neil Smith G4DBN
 

Indeed it does, about 11.8dB 
Odd...
Neil

-------- Original message --------
From: Tony_AD0VC <canthony15@...>
Date: 06/02/2020 19:17 (GMT+00:00)
To: EladSDR@groups.io
Subject: Re: [EladSDR] FDM DUO Attenuator behaviour

Assuming a 50 ohm load, that looks like a 12-13 db attenuator to me (?).

Tony


From: EladSDR@groups.io <EladSDR@groups.io> on behalf of Neil Smith G4DBN <neil@...>
Sent: Thursday, February 6, 2020 10:07 AM
To: EladSDR@groups.io <EladSDR@groups.io>
Subject: Re: [EladSDR] FDM DUO Attenuator behaviour
 

Attenuation is fixed at 20dB Bob, R67/68/69 switched in by RL2.

I guess you are hearing the faint click of RL2 when you enable attenuation? If you can measure the input impedance, you could check if the input impedance goes weird, with R69 gone open circuit or a relay contact fault or a short to ground.

Full input diagram is attached to message https://groups.io/g/EladSDR/message/14141

Neil G4DBN

On 06/02/2020 16:17, Bob G3PJT wrote:
When I set the attenuator all the signals disappear. Its as if the antenna is disconnected
Is there a setting somewhere to set the level of attenation. My DUO has only just started to do this
I have done a reset and no change
Any ideas?
73 Bob G3PJT

Tony_AD0VC
 

The S2 spec says 12db. I think the S1 was 20db. When using the Elad EXtio dll with my S2 and HDSDR or other SDR applications, the DLL always says 20db for the attenuation but I suspect that the dll was written in the S1 days and was never updated for the later radios. The actual attenuation is set by the hardware of course. Even SDR Console shows a "20 db" attenuation setting with my S2, probably for historical reasons. This has been a "wart" for a while.

Tony


From: EladSDR@groups.io <EladSDR@groups.io> on behalf of Neil Smith G4DBN <neil@...>
Sent: Thursday, February 6, 2020 12:26 PM
To: EladSDR@groups.io <EladSDR@groups.io>
Subject: Re: [EladSDR] FDM DUO Attenuator behaviour
 
Indeed it does, about 11.8dB 
Odd...
Neil

-------- Original message --------
From: Tony_AD0VC <canthony15@...>
Date: 06/02/2020 19:17 (GMT+00:00)
To: EladSDR@groups.io
Subject: Re: [EladSDR] FDM DUO Attenuator behaviour

Assuming a 50 ohm load, that looks like a 12-13 db attenuator to me (?).

Tony


From: EladSDR@groups.io <EladSDR@groups.io> on behalf of Neil Smith G4DBN <neil@...>
Sent: Thursday, February 6, 2020 10:07 AM
To: EladSDR@groups.io <EladSDR@groups.io>
Subject: Re: [EladSDR] FDM DUO Attenuator behaviour
 

Attenuation is fixed at 20dB Bob, R67/68/69 switched in by RL2.

I guess you are hearing the faint click of RL2 when you enable attenuation? If you can measure the input impedance, you could check if the input impedance goes weird, with R69 gone open circuit or a relay contact fault or a short to ground.

Full input diagram is attached to message https://groups.io/g/EladSDR/message/14141

Neil G4DBN

On 06/02/2020 16:17, Bob G3PJT wrote:
When I set the attenuator all the signals disappear. Its as if the antenna is disconnected
Is there a setting somewhere to set the level of attenation. My DUO has only just started to do this
I have done a reset and no change
Any ideas?
73 Bob G3PJT

Bob G3PJT
 

I checked things with the calibrated osc etc and the attenuation is 30+dB when the attenuator comes in. I checked on the RL bridge and the match degrades too.
Looks like the two upper boards need to be removed to get at the right layer.
This is a job for someone with a proper SMD set up. Maybe a return to Italy
Otherwise the DUO works fine.
Thanks for the info
73 Bob G3PJT