I took a quick look at these a while back, on paper, but have not actually played with one yet. And, quite likely, I will not bother unless I luck into one cheap. From the manuals description it is not really meant for monitoring, although it has the ability to demodulate multiple modes. It appears to be more meant as a low cost spectrum analyzer. The concept is interesting. Keep in mind I am grabbing this out of the operations manual and have not touched one myself.
In the detailed or narrow resolution bandwidth modes they are using a fairly narrow banded but high resolution DSP (240 kHz) as a detector. The Signal Hound has a mixer at the front end and a programmable signal generator as an LO (possibly two sets actually, double conversion, the manual is unclear but mentions two IFs, 2.9 MHz and 10.7 MHz), converting the desired 240 kHz chunk (or less) of RF down for the DSP to digitize. The Signal Hound people are calling it an “SDR” and the WinRadio G303/313/305/315 does a similar job, but with a narrower banded DSP (WinRadio also calls theirs an SDR but the DSP is only centered around 20’ish kHz). The SoftRock series and the USB66 do this also with about 200 kHz of bandwidth, but where the SoftRock or USB66 require the I/Q data to be transferred to the PC via audio cable this unit does a direct digital conversion.
What that means is that to scan a 1 MHz chunk of RF with high detail the unit actually steps through it, the size of the steps determined by multiple factors. But it appears that for the highest speed sweep it would have to take five 200 kHz steps to cover 1 MHz. Since these are done serially what you see at the begining of the 1 MHz width is not in sync with what you see at the end. If you have ever used a traditional spectrum analyzer you will understand what I mean. The Signal Hound does have a “wideband” mode that appears to be using the DSP to capture 5 MHz of bandwidth at a time. Naturally, when it does this the resolution goes down, the specifications are no longer guaranteed, and you cannot use any form of demodulation.
To demodulate SSB it recommends an IF setting of 30 kHz, and the manual specifically says that the span MUST be 200 kHz or less to demodulate audio (this is significantly less than several SDRs that can be found, and about on par with the SDR-IQ and the SoftRock/USB66 series). It also says that any changes (tuning, bandwidth, frequency, mode, etc) will cause the audio demodulation to stop, the new settings will be applied, and the demodulation can then begin again. If you have ever used a Hewlett Packard / Agilent 85XX series of spec an you will recognize the dance
This unit would probably be very good to augment a traditional superhet receiver or an honest SDR monitoring receiver. Use the Signal Hound to sweep wide bandwidths quickly to find potential “hits”. Use the more traditional receiver to monitor the hit and see what it is. Above 50 MHz I could see this being very useful if searching for new or unknown frequencies. However, if you want to do this at HF or VHF Lo something like the WinRadio Excalibur will do both task simultaneously, and DDC 2 MHz of instantaneous bandwidth and never drop audio while you are adjusting things.
So, this unit might be viewed as a scanner implementation of the SDR concept, getting above the 40/50/60 MHz top end of monitoring SDRs (below that freq area the other SDRs are probably significantly more usable than the Signal Hound). However, as a scanner it will not do trunking, it will not do digital modes like APCO-25, and it will not scan.
One last item...the specifications. They talk about the “display average noise level” and like terms. Be very careful with the terminology in the manual and on the web site. It would be easy to misunderstand it and believe the unit has an MDS of -161 dBm or something along those lines, and a Dynamic Range of 150+ dB. I do not believe anything on the web site or manual is incorrect, but several items are presented in interesting ways.
T!
