[hpsdr] ADC Overload

[Helmut, DC6NY]

Hi guys,

ADC overload with by-passed pad in front of the preamp happens at -12 dBm.
When using a 1.5 kW PA the total crosstalk isolation has to be at least 74
dB. This can be achieved with 2 relays in the TX path: one at the input of
the PA, one at the output, so they are in series relative to the RX path. If
that's not enough, use an antenna relay, that grounds the unused port.

73, Helmut, DC6NY
-----Ursprüngliche Nachricht-----
Von: hpsdr-bounces at lists.openhpsdr.org
[mailto:hpsdr-bounces at lists.openhpsdr.org] Im Auftrag von wully
Gesendet: Montag, 17. September 2012 13:34
An: hpsdr at lists.openhpsdr.org; jeffrie at talktalk.net
Betreff: [hpsdr] ADC Overload

***** High Performance Software Defined Radio Discussion List *****

Hi Jeff, All

I agree completely with you. In my own software TRX for HPSDR, I am also 
switching the mercury
to -20db Attenuation, when starting TX on pennylane, because I do also 
get sometimes Overload signals
when not doing the attenuation. Since this is a very simple software 
measure, why not do it that way?

73, Alfred, hb9epu
> Date: Sun, 16 Sep 2012 21:31:01 +0100
> From: Jeff Cook<jeffrie at talktalk.net>
> To:hpsdr at lists.openhpsdr.org
> Subject: [hpsdr] ADC Overload.
> Message-ID:<50563705.3080809 at talktalk.net>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Dear All,
>
> Lately, and for reasons I know not what of, I've  been plagued with RF
> getting back into Mercury via its antenna input, causing the ADC warning
> to show.  I've noticed that when I run in tx mode with Mercury's
> attenuator switch set at -20 dB the problem ceases to exist.  Would it
> be possible to write into the software the instruction to hold Mercury's
> attenuator switch at -20dB whenever Penelope is tx-ing, and to release
> that instruction when back in receive mode?
>
> Now I know what you will say, and that is, why don't you sort out the
> problem you've got yourself rather than ask a software engineer to find
> a way around it for you?  Believe me I've tried, and to no avail, cable
> layout, station element positions etc.  I'm no engineer of any sort, but
> it seems to me that to turn off Mercury's preamp when transmitting would
> probably be good practice in any event, or am I talking rubbish?
>
>
> Jeff Cook, G0AFQ.
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