[Elecraft] start without ANY extra roofing filters....

Dave G4AON elecraft at astromag.co.uk
Mon May 7 13:27:05 EDT 2007


Adam (VA7OJ/AB4OJ) wrote:

"It is highly significant that professional receivers manufactured by the

likes of R&S, Rockwell-Collins, Racal and Harris have a single roofing
filter. This filter is typically 12 to 16 kHz wide, to pass multi-channel
ISB, VFT (multiplexed teletype) and high-speed crypto, all of which have
extremely stringent in-band IMD requirements. To quote a British engineer
who used to design shipboard HF receivers for the Royal Navy:"


Adam

I wouldn't get too hung up on commercial/military designs, while not 
wishing to start a thread running off at a tangent... a friend has a 
well maintained Racal RA1792 military receiver which is hopeless 
compared to even moderately good amateur gear such as his Kenwood 
TS-850, I appreciate the 1792 wasn't one of the better Racal receivers 
but they weren't cheap. A listening comparison - even under "non 
contest" conditions quickly leads to the Racal on/off switch. Add the 
generally poor sensitivity of those designs, weight and cost and there's 
no way they will ever compete with a K2 or K3. I don't come across many 
hams using ex military/commercial gear in preference to amateur gear... 
At least not those I work on QRP CW.

73 Dave
K1, K2 and soon K3/100 (on order)


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