[hpsdr] ALEX - Call for Comments - II - Clarification

[pvharman at arach.net.au]

Hi Graham,

Thanks for taking the Project Leader role on for Alex.  Re your request 
below, based on my tests with the prototype Mercury setup the native 
performance should be very acceptable without any additional input filters. The 
Mercury board contains a switchable  1.5MHz HPF and 55MHz LPF to remove high 
level MW broadcast signals and prevent VHF signals from aliasing into the 
passband. 

I live in an area close to multiple MW broadcast stations and with the HPF in 
circuit have no problems on any HF band. If I want to listen on MW then I will 
bybass the HPF and if necessary turn off the preamps and use the 0-30dB 
attenuator. 

I used the Mercury prototype on 40m during the recent ARRL CW contest. As I 
test I mixed an S9+60 db signal in with the antenna and at 1kHz spacing could 
still copy a signal at the noise floor. The limit of the test was the sideband 
noise of my HB8640B not the receiver strong signal performance. 

Since we have little practical experience in using direct digital conversions 
receivers (and having a frontend fully open from 1.5 to 55MHz does not feel 
right to an analogue receiver designer!) Alex is there in case folks live in a 
high signal environment, require additional front end selectivity for contest 
or DXperdtion operations etc.  I suspect that in many cases with the natural 
selectivity offered by antennas, ATUs, HF beams etc then Alex may not be 
required. 

73's Phil...VK6APH








> 
> I assume the majority of the users want good ham band performance
> and casual SWL, WWV, and experimental capability.  The
> native performance of the underlying SDR should be good
> enough for the "casual" and incidental uses with the preselectors
> bypassed. [ Phil H, please comment. ]  Any serious or focused
> other uses can put a dedicated filter section in the user
> defined spaces, or rework the whole filter pack.  The PCB
> layout will accommodate third order (three inductor)
> bandpass or low-pass filters in each section.
> 


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