SDU5600 - Nice Piece of Gear...Just not for me!
As mentioned above I did purchase the AOR SDU5600 Spectrum Display Unit. My primary intent with it was to use it for finding signals during tropo and skip band openings.
The SDU5600 is a wonderful piece of gear. It is extremely well built with a very good manual that I read and re-read many times. Despite its sophistication it is a very easy device to operate. It is very fast and does a superb job of finding new signals, and an excellent job of tuning certain radios, such as my AR8600 (or an AR5000, IC-R8500) to the found signal by moving a marker to that signal and pressing a button. If you plan to use it for finding unknown local signals it is an expensive but likely welcome addition to your scan shack.
Perhaps it was my ignorance going in that made me believe I'd be able to do weak signal work with this device. The SDU5600, and any spectrum analyzer for that matter, shows the "noise floor", I guess akin to a radio's squelch being open. If the SDU5600 shows too much of the noise floor it's possible to "attenuate" the display so the noise floor drops below the visible screen. What happens when this is done pretty much eliminates the chance of seeing weak signals with this device. These signals are not discernable through the noise floor, because they are just above it, and are as a result virtually invisible. Attenuating the SDU5600 makes the noise floor disappear altogether. Medium to strong level signals remain visible, but any chance of seeing the weak ones goes bye-bye with this attenuation. It was suggested to me that a shortwave preamp be used inline from the 10.7 MHz IF output of the radio to the input on the SDU. I would imagine it would have to be one of very good quality, otherwise the noise floor would simply be amplified as well and the problem would remain. AOR only allows adjustments/attenuation to the SDU5600 in 10db increments. If that could be made adjustable down to 1db maybe (not sure if that would even be possible) it might make a considerable difference.
I worked with the SDU5600 for many nights, trying numerous different combinations of attenuation both with it and with my receiver, different antennas, and combinations of all three. Again, medium to strong signals were easy to snag, and the 5600 is marvelous in that aspect...superb actually. As far as I was concerned I had a near-total grasp of its operation but could not make it work for me the way I wanted it to. It was with mixed emotions that I returned it for a refund, but I concluded that for the price I paid for it I did not want something that I was not satisfied with sitting in the radio room. AES did whack me for a restocking fee of course, no surprise there, but the hit I took was a lot less expensive one than if it sat in the shack and collected dust.
This is by no means a knock on AOR. This is a wonderful device that will do an astounding job of finding signals in any chunk of the radio spectrum. It's great for discovering sources of interference. It has a wide variety of possibilities. Sadly, at least for me, weak signal work was not one of them.
Lindsay, I did try it briefly on HF also, but encountered the same problem for the most part as I did with weak signals in the VHF/UHF spectrum.
I hope that provides a basic description of what this device can, and apparently can't, do.
