[HBR] Receiver debug/improvement

[windy10605 at juno.com]

To many of you, this is probably old news, but sometimes you/I can hear
things discussed, even participate in the discussions, but it just does
not sink in or you don't realize the application until you see it
demonstrated and focus a little. Many times we are in conversations, hear
a few key words, and the brain either clicks "in" or "out". That just
happened to me, except this time I clicked "in". I know Spectrum
Analyzers are expensive and the computer software/ hardware most people
have is not sufficient for a Mhz/Ghz SA. However, here is one that does
work, is easy to use, provides great results, and is free. All you need
is a computer with the typical sound card. I'm a great advocate for
tools, especially cost effective tools.

It's very useful to be able to analyze signal bandwidths for each
section/element of a receiver and that will require a Spectrum Analyzer
(or a lot of time on a scope), but what if we look at the total receiver
as ONE section/element ? What you really want to analyze on a given
receiver is the end result, the audio you hear. That audio is simple for
a sound card to digitize and for other software to massage into a visual
display. What you will "see" is the audio from 0 to xxKhz coming through
the receiver passband.....1) the signal you are receiving  2) the noise,
3) adjacent signals, 4) the effect of filters, 5) DSP effect, 6) notch
filter effect, 7) Q-Multiplier results, 8) audio stage design, 9) etc,
etc. The particular program I'm using is called Spectrogram (freeware)
and you connect the receiver "audio out" to the computer "microphone in".
The resolution is adequate to see the shape of the filters (peak or
notch) as you tune across the signals and any design changes you make.
You don't have to be attached at the filter, running at the RF/IF
frequency, etc. You are monitoring the RESULTS of whatever
selectivity/sensitivity components are installed (tuned RFs, IFs,
filters, DSPs, etc) in the total receiver passband at the audio out end,
the human interface end.

Cool !

73 Kees K5BCQ