[NLRS] Spectrum analyzers

[Dr. Gerald N. Johnson]

I have more confidence in a conventional receiver, even the IC R7100 and 
similar "scanner" communications receivers. In my digging I have found 
the 7100 is NOT really a communications receiver. It has no hardware 
provisions for muting while transmitting. Studying its remote control 
command set it has capability of incrementing frequency or setting 
frequency and mode through the serial port and provisions for reading 
those plus signal strength. It has IF bandwidths from a couple kHz in 
SSB mode up to 150 or 200 kHz in wideband FM mode, and an IF output 
intended for a NTSC TV detector so probably a bit over 4.5 MHz.

It should not be difficult to gin up a control program that could set 
frequency, read level, move up (or down) an IF bandwidth and display the 
results on the computer screen. The graphics may be more bother in 
windoze or linux than the data collection.

It's also possible to mute and restore the receiver through that serial 
port. I'm working (very slowly) on a PIC chip program to make that work 
from TR switching.

A working R7100 can often be had for under $350 these days. And without 
the spectrum analyzer it can always be manually tuned by dial or by 
direct entry of frequency. Later receivers might be more effective or 
cover a wider band. I suspect it will respond to a preamp, like WA3IAC's 
using a PGA-103+. Have that kit too.

For finer resolution one might take the NTSC IF output to a SDR or 
simply take the audio while in SSB mode and run a computer sectrum 
analysis on that audio output, then move up one IF bandwidth, and 
repeat, putting the detailed spectra together.

73, Jerry, K0CQ

On 2/8/2013 7:50 PM, tosca005 at umn.edu wrote:
>
>
> I have been looking for an inexpensive but capable spectrum analyzer for
> RF work (testing, repair, design, etc.). I found a few nice ones on eBay
> from HP or Agilent, but they approached $1,000 with shipping. One that
> was "only" about $800 shipped was limited to a maximum of 4 GHz, whereas
> the more expensive units were rated to 22 GHz without the need for any
> external mixers. (Of course, the REALLY nice units that operate up to 50
> GHz were selling for around $30,000, which is extremely far out of my
> league.)
>
> I came across this unit which looks pretty interesting.
> http://micro.arocholl.com/
>
> It is called the RF-Explorer. It is a solid state, handheld unit (nice
> and portable) but can be connected via USB to a computer for better
> display than the native LCD screen, for extended data storage, plot
> captures, etc. There is one model, the WSUB3G, which covers the range
> from 15 - 2700 MHz, which is pretty nice. The designer is working on an
> adapter or plug-in module that would cover 5760 MHz (actually, the 5 GHz
> WiFi spectrum plus...), though there does not seem yet to be pressure on
> him to make a model for 3456 MHz. But the existing model obviously is
> good for the highest few HF bands, and the first seven VHF/UHF bands.
> This model is only $269 from seeedstudio.com:
> http://www.seeedstudio.com/depot/rf-explorer-3g-combo-p-1266.html?cPath=174
>
> One of the things that it lacks is a built-in sweep generator. He has
> some single-band units that include the sweep generator, but the
> wideband models omit them (for lack of space, I suspect, given the size
> of this little gem). That would not be an issue for me, since I own a
> WaveTek 2002 sweep generator that is good to 2500 MHz, so it is a good
> match for the capabilities of this little spectrum analyzer.
>
> Does anyone have any experience with this unit, or see any serious
> pitfalls that would likely make me regret investing the $269 in one of
> these?
>
> Thanks in advance for looking at this with me. (I'm also posting this in
> the hopes that if no one sees a "fatal flaw", that some others of you
> may find the item to be of interest.)
>
> 73 de W0JT/5
> John P. Toscano
>