[Hammarlund] Why 2nd RF stage?

[Richard Knoppow]

----- Original Message ----- 
From: "billriches" <bill.riches at verizon.net>
To: <hammarlund at mailman.qth.net>
Sent: Sunday, November 30, 2014 2:52 PM
Subject: Re: [Hammarlund] Why 2nd RF stage?


>I had heard somewhere that one reason was to prevent hf 
>oscillator signal
> from being transmitted on the rx antenna.  The enemy could 
> pick it up and
> home in on the ship.
>
> 73,
>
> Bill, WA2DVU
> Cape May


     Local oscillator radiation is an important factor. Its 
not just to prevent homing on a receiver using the LO its 
also to prevent interference between receivers in multiple 
receiver set ups. This is probably a more important reason 
because many receivers were not used on board ships.  It 
takes more than just a couple of RF stages to reduce LO 
radiation, the oscillator and mixer stages must be well 
shielded and the power supply must isolate them. Probably 
the reduction of image response was the most important 
reason for the use of multiple RF stages. However, they are 
not all equal in that reduction. For instance, one of the 
military handbooks for WW-2 receivers shows the spurious 
responses of several receivers, the Super Pro (I think a 
BC-1004C is shown) has only one spur, the image, while the 
SX-28 looks like a cornfield.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com