[Hammarlund] Why 2nd RF stage?

[Bob Camp]

Hi

The only really valid reason for a second RF stage is to make up for the loss inherent in more front end filtering. If you add more *gain* in front of a mixer, that’s a real bad idea. IMD goes up quite a bit when you do that.  You can get plenty enough gain from a single stage to get excellent sensitivity. The main tradeoff is the amount of front end filtering loss you can tolerate with a single stage. The next level tradeoff is the interaction of the front end filter stages with each other and with the antenna. More stages help you isolate things so they filter as they should. 

That all *assumes* you are talking about a well designed receiver made by somebody like Hammarlund / National / Collins. I’ve seen modern buyers pick out a radio simply by how loud the noise was when the volume was turned up (on > $2K radios no less). I’d ignore it if I’d only seen it a few dozen times. Buyers back 50 years ago were no different. People did design radios so that the “noise was loud” even back then … Not often a good thing for overload performance ...

Bob
 
> On Nov 30, 2014, at 1:14 PM, Brian Burns <brian at lessonsinlutherie.com> wrote:
> 
> Hello All,
> 
> 
> 
> May I bother you with an idle curiosity question? 
> 
> 
> 
> 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?  
> 
> 
> 
> Cheers,
> 
> 
> 
> Brian
> 
> 
> 
> 
> 
> 
> 
> ---
> This email has been checked for viruses by Avast antivirus software.
> http://www.avast.com
> ______________________________________________________________
> Hammarlund mailing list
> Home: http://mailman.qth.net/mailman/listinfo/hammarlund
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Hammarlund at mailman.qth.net
> 
> List Administrator: Duane Fischer, W8DBF
> ** For Assistance: dfischer at usol.com **
> 
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html