Panoramic Spectrum Display - HP/Agilent 8922 GSM Test Set


Amazing results obtained with the cheap tv-level meter increased my interest in this way of looking at the rf spectrum. Interestingly a piece of equipment I happened to mention in my first survey has dropped big time in price.

A lot of these GSM test sets have appeared on the market in the past year, probably in conjunction with the big push towards 3G sets. My unit seems to come from Alcatel. Back in January ('06) they were around 900, while now (Jul-06) can be had for 500/600 + 35 shipping. At this price I decided it was worth giving a try, as there's a lot of features inetersting to the hobbyst other than strictly mobile phone related. Specifications for a "M" model (8922M) with options 1 and 6 fitted feature:
  • 10 MHz to 1 GHz spectrum analyzer
  • 2 Hz to 50 kHz scope
  • 10 MHz to 1 GHz frequency counter
  • 10 MHz to 1 GHz RF generator
  • 10 MHz to 1 GHz RF analyzer
  • 90 MHz to 1 GHz RF power measurement
  • 20 Hz to 400 kHz AF analyzer
  • DC to 25 kHz AF generator
  • FM demodulator
  • RS232 for computer control
  • printer port for screen dump
  • programmable via internal Basic interpeter
This is a lot of functions for the money, as surplus separate instruments performing the same tasks fetch 100/200 apiece with a (20 year old) spectrum analyzer alone worth roughly the same money of the 8922M.

SIZE WARNING: mind you, this is a HUGE ***tard, weighting almost 35kgs!! On a side note cats seem to like it as a stand.

After lugging it at home the display was showing a problem, loosing sync after a few seconds of operation. The dealer offered to replace the entire unit, suggesting that something might have occurred during transport, as the device had been tested before shipping.
Luckily just under the hood 6 adjustment points are provided for the CRT module, for image position and size. Adjusting the trimmers with a hex key solved the problem. Smaller adjustments are possibile via software under the CONFIG > SERVICE menu, changing parameters of the crt_horiz_pos and crt_vert_pos variables.

I.F. FEEDING

The Spectrum Analyzer can span 10MHz maximum, which is ok for all receivers, however starting frequency is stated at 10.0MHz and this could mean that displaying only part of the IF out bandwidth. In fact the 10.0MHz indication refers to center frequency so there's no problem.
Frequency coverage is determined by the receiver. Aux RF-input connected to IF-out on your radio and center frequency typically set at 10.7MHz. Performance is absolutely fine and doesn't take much to understand most of the controls. A noticeable difference to the cheap tv-level meter is response time, as the HP displays an average of readings, resulting somewhat sluggish. A similar effect was noticed by Bob Grove in his review of the SR2000. The tv level meter shows instant readings, making the tuning of desired peaks much easier, as they move on the screen in sync with your VFO.
The big spike on the left is noise generated internally by my AOR8600 at -455kHz from the center frequency. As warned by AOR, a number of spurious signals gets out from the receiver when the all-mode if-out modification is performed. As visible in the picture, output doesn't seem to be linear.

STANDALONE MODE

Frequency coverage is restricted to the 10MHz-1GHz sported by the instrument, with an antenna connected to the AUX RF-in. I'm not sure at this stage if FM demodulation can obtained directly from the 8922 or that function is restricted to GSM signals demod. Obviously IF-out bandwidth and spurious signals are not an issue. On the other hand you need an antenna splitter if you want your radio to be operational at the same time. Another thing to check: is sensitivity the same?

Idea to develop: as the unit is fully programmable via IBASIC and designed to interact with other equipment, maybe an application can be written to control directly the wideband receiver (AOR, Icom...) from the 8922. With the two units connected by RS232 and the 8922 in spectrum analyzer mode, pushing one of the software buttons will tune the radio to the frequency where a marker is.

...work in progress...

Both modes work great and almost spoil the fun from finding active frequencies!


Last update: Jul06 Panoramic Spectrum Display - Cheap solutions survey
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