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

Wed Oct 20 19:15:07 EDT 2004

Terry, I think the main purpose of the SM8512/8718 combo is for signal 
analysis rather than signal seeking.  With a decent panadapter or spectrum 
analyzer a good SIGINT op can estimate the characteristics of the signal and 
can more quickly set up the decoding equipment.  I can think of no other 
reason to have a signal monitor that covers 30 KHz max.

A panadapter that covers 4 MHz is another matter entirely, and I can see how 
this would be invaluable in seeking out new signals to listen to.  The pan 
on the PR-700 does this very well - you can display the whole band, a wide 
(10 MHz) chunk, or narrower (1 MHz, variable down to zero) chunk of 
spectrum.  Last, the PR-700 will display the spectrum of the *demodulated* 
signal to search for subcarriers.  The sweep speed on the PR-700 is fast 
(yet variable) and is absolutely the BEST for finding very short duration 
signals.

On the other hand, newer digital spectrum analyzers and panadapters have 
such a slow sweep speed that they're almost worthless for signal analysis or 
finding signals.  Also, they have an annoying "max hold" that holds the 
trace until the next sweep (the HP 8566 and 8568, while outstanding 
analyzers in ever other respect, have this annoyance).  This often goes hand 
in hand with blocky or low resolution displays that further hamper the 
utility of the device.  If you can find one of the older WJ add-on 
panadapters, they are quite good but usually limited to a hundred KHz or a 
MHz or so.  These use the little rectangular picture toob so there's no 
digitizing and resulting noisy crap coming from the unit, slow response, low 
res display, etc.

Another thing that you have to keep in mind is that, like spectrum 
analyzers, the narrower the filter (and therefore the resolution) the slower 
the sweep speed must be to avoid filter overshoot and ringing.   However, 
this is where the digital spectrum analyzers (and the HP 8566/68 series) 
shine - your display doesn't fade in between those slow sweeps.

A good pan is a true joy and adds a lot to a receiver.  Unfortunately, it 
seems that many of them are junk or pretty much worthless in one respect or 
another.

73 John

----- Original Message ----- 
From: "Terry O'Laughlin" <watkins-johnson at terryo.org>
To: <premium-rx at ml.skirrow.org>
Sent: Wednesday, October 20, 2004 12:33 AM
Subject: Re: [Premium-Rx] spectrum Analyzer to use as a signal monitor

>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.
>
>
>
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