[hpsdr] Hermes RX questions

[Sid Boyce]

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.

On 04/03/13 02:51, Joe Martin K5SO wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
>
>
> Hi Byron,
>
> Yes, when using OpenHPSDR receivers with high power transmitters you 
> do need to use a T/R switch to remove the receiver from its antenna 
> when the local transmitter(s) are operating, or at least you should 
> provide some type of antennuator switching when the local transmitters 
> are transmitting to ensure that the input level to the Hermes receiver 
> is not excessive.  Such T/R switching relays are provided on the Alex 
> Tx filter board and on the ANAN-series PA boards, as examples of 
> OpenHPSDR hardware.  Alternatively, you may certainly use your own 
> external T/R relay but whatever arrangement you use, the T/R relay 
> should be activated by the PTT lines of the local transmitters in 
> order to achieve the necessary protection.
>
> The ADC overload warning on Hermes (and Mercury and Angelia) comes on 
> when a signal is greater than about -10 dBm at the input of the 
> receiver.  The warning indicates that the input signal has exceeded 
> the amplitude conversion range of the ADC.  Levels greater than that 
> maximum level result in distortion in the output of the ADC, of course.
>
> Personally, I don't apply rf levels to my OpenHPSDR receivers greater 
> than the "alert" warning level even though the receiver inputs can 
> likely take ten times that amount or perhaps more before actually 
> destroying devices.
>
> For reference, typical test equipment inputs  (e.g., on high end 
> spectrum analyzers, etc) have max rf input limits around +7 dBm; that 
> fact might give you an idea of what is generally considered to be a 
> dangerous rf input level.
>
> 73,  Joe K5SO
>
> On Mar 3, 2013, at 6:05 PM, Byron Engler wrote:
>
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>> Hi all,
>> I am looking at using my Hermes in a contest station. There will be 2 
>> 1kw transmitters that can be transmitting at any moment. I plan on 
>> using Hermes to monitor which bands are opened and not for the actual 
>> QSO's and plan to use some form of random long wire antenna. Should I 
>> be concerned about 'burning out' the ADC?
>> Any precautions I should take to protect the Hermes board.
>> What is the maximum safe magnitude of Rf at the RX connector?
>>
>> 73
>> Byron, ZL3DXT
>>
>
>
>
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-- 
Sid Boyce ... Hamradio License G3VBV, Licensed Private Pilot
Emeritus IBM/Amdahl Mainframes and Sun/Fujitsu Servers Tech Support
Senior Staff Specialist, Cricket Coach
Microsoft Windows Free Zone - Linux used for all Computing Tasks

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