[hpsdr] Hermes RX questions

[Joe Martin K5SO]

Hi Sid, 

From your description I think the situation you have is that Hermes is connected to your Quad antenna (without an Alex or equivalent filter) and your HiQSDR transmitter is connected to the 40m sloper.  If I mis-interpreted your statements I apologize.   If not, let’s look at the signal levels involved: 

1)  10 W transmit from HiQSDR is a +40 dBm signal.

2) The Hermes overload warning comes on around -10 dBm.  

3) In order to keep the Hermes from overloading the attenuation/isolation between the two rigs must then be about 50 dB without the 20 dB attenuator setting on Hermes, or 30 dB with the the attenuator setting in place.  

My guess is that the direct radiation path loss from your sloper antenna to your Quad antenna is less than 30 dB, and that is the reason your Hermes is overloading.  

In any case, keep in mind that Hermes has a 31-dB step attenuator on board, not simply the 0 dB and 20 dB settings.  Earlier software programs only used 0 dB and 20 dB settings for that attenuator.  Recent versions of PowerSDR allow you to select any setting of the attenuator from 0dB to 31 dB in 1 dB steps.  I don’t recall if Hermann has implemented the full 31 dB step attenuator range for Hermes in his latest versions of cuSDR or not but you could, as a test, try PowerSDR with 31 dB attenuation selected to see if that amount of attenuation will prevent the Hermes overload signal from coming on when you key the HiQSDR rig.  If it doesn’t, then you will need more attenuation than the 31 dB attenuator on Hermes can provide.  

One way to obtain more attenuation options with Hermes (in addition to using a software program that implements the full range of the Hermes attenuator) is to use an Alex filer set with your Hermes board.  By doing that you have additional attenuator selections that include the Hermes 0-31 dB step attenuator and the additional “fixed” attenuator selection options of Alex.  

A second way to obtain more isolation is to use an external T/R relay for Hermes that is activated by the PTT on the HiQSDR, which removes the antenna from Hermes when the HiQSDR is transmitting. 

Hope these comments give you some ideas about how to configure your setup to prevent overloading your Hermes.  

73,  Joe K5SO

On Mar 5, 2013, at 6:48 AM, Sid Boyce wrote:

> ***** High Performance Software Defined Radio Discussion List *****
> 
> I had a problem on the HiQSDR Preselector that prevented it going into TX and now it's fixed I decided to test with the integral 10W PA that uses the BPF's for both RX and TX.
> 
> Hermes was set up with 2 RX, one on 20m and one on 40m and connected to the Lightning Bolt Quad.
> 
> HiQSDR was connected to the 40m 1/4 wave sloper fed against the tower.
> 
> When I activated PTT on the HiQSDR I got ADC overload flashing on Hermes using cuSDR64 and 20dB attenuation.
> 
> Any thoughts or suggestions?
> 73 ... Sid.



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