[Premium-Rx] spectrum Analyzer to use as a signal monitor

[Terry O'Laughlin]

I agree with some of what John says.  I have a Watkins Johnson WJ-8617B-26 
which covers HF and can display up to 4 MHz of spectrum and a WJ-8718/MFP 
with an SM-8512 panadapter that can display 5, 15 or 30 kHz of spectrum.

The 30 kHz display is a bit narrow.  A span of 100-150 kHz is about ideal 
for HF.  It allows you to see enough adjacent spectrum to be useful, but 
not so much that the signals blend together and look like an elevated noise 
floor.

The AGC does exactly as he says, it pushes a weak signal into the noise 
floor when a strong signal is in the receiver passband.  A panadapter with 
a lot of vertical range (logarithmic, of course) can help.  The WJ-9188-18 
and WJ-9205 panadapters and true spectrum analyzers cope better with AGC 
action.

Unlike John, I find panadapters on HF useful.  I like to listen to utility 
stations.  Finding commercial and military air traffic or other short 
bursts of communication is much easier on HF with a panadapter set to about 
100-150 kHz wide.  I've grown quite used to them.  When I use a receiver 
without a panadapter, I feel blind.

I think the ultimate HF signal monitor is a WJ receiver with a pan/sector 
display option like the 205/215 series with an HH-1 tuner or a 
WJ-8617B/8618B (but pan/sec is a rare option on these radios).  For the 
205/215, the pan with an HH-1 shows all of 2-30 MHz and you can set the 
sector to any portion of the HF spectrum.  Both spectrums appear on the 
display at the same time.  This is nice for simultaneously watching band 
openings in detail and the MUF in general.  With a second receiver and a 
VM-101 marker generator, you get a pip on the spectrum display allowing you 
to quickly zero in on signals with the second receiver.  I don't have 
pictures of this system on my website yet, but parts of it can be found in 
the RS-160 system, which is a larger version of a spectral SIGINT system 
based on the 205 receiver.

Terry O'
http://watkins-johnson.terryo.org





At 08:40 PM 10/19/2004, you wrote:
>I've been viewing the current interest in panadapters with some interest.
>I've found that panadapters aren't really as useful as you might imagine. 
>The spectrum width you see is limited by the bandwidth of the roofing 
>filter, which is often <20 KHz.  More useful would be a 100 KHz range. 
>Also, in many receivers, AVC action will prevent you from seeing a small 
>signal next to the big signal that's centered in the passband of the final 
>filter and detector.