[Premium-Rx] Noise Power Ratio Testing of Radio Receivers

[Peter Rovardi]

Hello,


This dicussion about NPR and IMD brings back  memories of attempts (albeit 
more a learning curve, circa 1987) for improvment of  IMD on my Drake TR7 
PA  along with general "front end" receiver improvements / experiments.

As I recall, I fitted an  extra pair of 48.05Mhz Drake roofing filters (8 
poles total), in series with the original filters on the up-convertor board. 
The board is common for both TX and RX sigs.     I found by using  wideband 
audio "pink noise" feed at the mic. input  gave by far the best results  for 
observation  of  the "actual" TX filter bandwidth on the spectrum analyser, 
and was also a very usefull tool for observing exactly what happens on PA 
overdrive ect, as this signal "fills in" so to speak, the full filter 
passband, mixer spuri  warts and all!  A sort of  NPR in reverse, I suppose?



73,s
Peter G4HSB.





----- Original Message ----- 
From: "Michael O'Beirne" <michaelob666 at ntlworld.com>
To: "PREMIUM-RX" <premium-rx at mailman.qth.net>
Sent: Wednesday, December 05, 2012 9:23 PM
Subject: Re: [Premium-Rx] Noise Power Ratio Testing of Radio Receivers


>
> Gents
>
> The comment attributed to Ulrich Rohde was in voiced some years before in
> one of Pat Hawker's Technical Topics pieces. I can't place in which issue.
>
> I well recall at the time thinking along parallel lines in relation to the
> then eagerness  to achieve the maximum carrier suppression for SSB but
> ignoring (or forgetting) that the transmitter's IP3  products were at 
> vastly
> higher levels and would completely mask any residual carrier.
>
> As for PAs, I still stand by traditional valved ones.  Angus McKenzie's
> spectrum shots in his review of the Trio TS83S in the old "Amateur Radio"
> are absolutely stunning, the level falling by 75dB within about +/- 3.5 
> kHz.
> It used a pair of 6146 valves.
>
> 73s
> Michael
> G8MOB
>
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