[Hammarlund] Why 2nd RF stage?

[Kenneth G. Gordon]

On 30 Nov 2014 at 10:14, Brian Burns wrote:

> Hello All,

Hello, Brian.

> May I bother you with an idle curiosity question? 

Of course: that is what we're here for.

> What's the idea behind having two stages of RF amplification in the front
> end of a receiver? Often, top of the line models have a second one. My SWAG
> (scientific wild-ass guess) is that it's for better adjacent signal
> handling. Surely it's not for additional gain, or is it?  

There are several reasons, but I think the primary one was improved image 
rejection.

For instance, in the HRO, the second RF amplifier is designed for a gain 
of 1. I think the older Hammarlunds were done that way also. I am most 
familiar with the BC-779 at this point, but that is they way it was set 
up.

The primary reason for this at the time (as far as I know) was to reduce 
image response, especially at the upper end of the frequency range, like 
10 meters. The added selectivity at the front end maximized this 
specification. This was when most receivers were single-conversion with 
an IF of 455 kHz or so and due to this, image rejection at the higher 
frequencies was marginal.

When I modified my first BC-779, back in the late 1960s, for a product 
detector to replace the original diode detector, I was amazed at both how 
quiet the receiver appeared, and how very sensitive it was with its two 
RF amplifier stages.

Carl KM1H, is most familiar with why the HRO had a second RF amp, biased 
for a gain of 1, and I hope he will respond to your question. He know far 
more about it than I do.

Ken W7EKB