View Single Post
Old 23rd Mar 2022, 12:01 am   #9
regenfreak
Heptode
 
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 655
Default Re: 6-gang FM stereo tuner heads

Thanks Steve. Now I get the idea of quieting curves. Quieting is a kind of like a squelch function in HF transceivers; a circuit detects the condition when there is no signal and it filters out the hiss. Attached is the SNR versus Rf input for different receivers from the Ofcom report on page 28 . It is essentially the same graph:

https://www.ofcom.org.uk/__data/asse...10/annex-f.pdf

This is the first time I heard of WBRD. You are right that Radford FMT1. It has a WBRD as there is a 8.2K resistor across the primary tuned circuit of the ratio detector (see attachment 2). I built a few cheap DIY FM radio kits with IC chips using quadrature detectors or PLL (e.g. sc3610d, cxa1691, SC1088 ).

I didn't know that 6CS6 heptode ended up in FM demodulation application. In fact, I built my first MW superhet using a 6CS6 as a frequency convertor.


PS: BTW it is possible to measure the gain, one db compression point, 3rd order intermodulation intercept point, noise figure of an amplitude using a TinySA:

https://youtu.be/HJKjrEZRAKg

Even it is nothing like the real deal, this is something I will try next.
Attached Thumbnails
Click image for larger version

Name:	Ofcom SNE.jpg
Views:	59
Size:	50.1 KB
ID:	253980   Click image for larger version

Name:	WBRD.jpg
Views:	114
Size:	60.9 KB
ID:	253981  
regenfreak is offline