EMRFD Message Archive 8557

Message Date From Subject
8557 2013-04-16 19:20:26 Jerry Haigwood The Measurement Receiver in the Power Meter Article
Hi Folks,

I have read the article, "Simple RF-Power Measurement" by Wes Hayward
and Bob Larkin from June 2001 QST several times. However, there is one part
that I am having a problem understanding. On page 43 (QST Page number),
figure 12 shows a measurement receiver. It is explained at the bottom of
the same page. I have read and re-read this section but fail to understand
this part completely. I am hoping someone on here can explain it to me in
terms that I can understand. As I understand, the description says the
filter is at 110MHz and a RF Generator is used as the LO and is tuned from
50 to 250MHz. What range of signals would we be looking at? The RF
Generator tunes below and above the 110MHz IF so we have low side injection
and also high side injection. That part really confuses me. A 3 resonator
tuned circuit is used at 110MHz so how narrow could this filter be? 5 or
10MHz wide? I have built helical filters at 432 MHz that were reasonably
narrow but it is a lot of work to get the aperture coupling just right.
What range of signals would be viewed/measured by this measuring receiver?
Has anyone built one of these? Can someone walk me through how this
receiver is suppose to work? Any enlightenment would really be appreciated.

Jerry W5JH

"building something without experimenting is just solder practice"

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8558 2013-04-17 03:50:43 Kerry Re: The Measurement Receiver in the Power Meter Article
A measurement receiver (probably the one described as "... the second measurement receiver ...") is described in EMRFD.

It's just a receiver really; it uses a signal generator as the LO instead of building a VFO. That allows any frequency up to the limits of the mixer.

One way of thinking of it is as a spectrum analyser that you tune manually.

I have been building my version of the EMRFD one for some years; I don't really need it but I'm intrigued by the concepts so it's not a high priority.

I have a mixer/post-amp module;


and a twin IF filter;


built and measured; this may, at first glance, not look like a narrow filter but it certainly is;


I am some way towards an IF amp and, finally, an AD8307 detector.

In preliminary tests I've been able to measure RF at -140 dBm or better with the narrow (208 Hz "normal" bandwidth, 280 Hz noise bandwidth) filter.

Its main use, if I ever finish it, will be for noise/noise figure measurements.

Kerry VK2TIL.