Tony's Spectrum Analysers - including 'home built'.

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SSA.Simple Spectrum Analyser (SSA). 13/5/07
VHF.VHF Comms based Analyser. -
HP 141.8552B, 8553B + TG & 8555. -

13/5/07 & 15/5/07
Simple Spectrum Analyser (SSA)

Designed by Roger Blackwell & Described in Radcom November 1989

This is a low cost design by Roger, based on an original idea by K2BLA in QST November 1985 with later modifications. The operating range was 1 - 90 MHz and uses an oscilloscope as the display. Components were conventional and readily available at the time.

I bought the 3 PCBs and assembled them according to my own requirements. For instance, I decided to use a first IF of 170MHz instead of 145MHz. I considered that running an IF on 2 metres might cause confusion if a 2m TX was being tested! The 3-section helical bandpass filter on 156MHz was harder to source and more expensive than the specified Toko one on 145MHz.

As can be seen in the photo the project is not really finished - I still have to apply front panel markings. I would also like to do more performance testing and circuit adjustments.

External view.
External view

Left to right (5x Control knobs):
Sweep Speed (Slow-Fast), Span (50KHz to 10MHz per div), Centre freq Coarse (10 turn) & Fine (LF to HF).

Bottom row(Coax Socket & Switches):
BNC i/p, Video Filter (In/Out), IF BW (15KHz/250KHz), Markers (1/10MHz), Mains on/off

Top left (2x switches):
10dB attenuator & 20dB attenuator

Top right LED:
Power ON

Internal view.

View inside

Top, left - RF Board
Clearly visible are the 3-section helical bandpass filter (long tin can), two blue relays (to switch IF filters) and 20 pin IC (VCO/1st mixer)

Top Right: - Mains transformer

Bottom Left: - Video/Sweep board
Lots of preset pots (sweep rate, X cal, sweep cal, coarse centre freq., fine centre freq., breakpoint adjust and Y cal)

Bottom Right: - Marker Generator & PSU
PSU area is at the top (+12v regulator bolted to chassis underneath)
Marker area at the bottom (10MHz xtal osc and divide by 10 IC)

Note the long shiny multi-turn pot on the front panel for Coarse Frequency Control.

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A Spectrum Analyser for The Radio Amateur

Designed & Described by DB1NV in VHF Communications 1989 onwards.

External view.
External view

This was rather an ambitious design by DB1NV published in VHF Communications. The series of articles started in about 1989 and with additions and updates, ran on for many years. Luckily, I was able to buy the main PCBs from the publishers; gradually I managed to obtain most of the required components or near equivalents. Some crucial parts were not available so I had to do some of my own design and evaluation to arrive at a usable system. I failed to finish building it before my retirement. However, later on, I did get the chance of completing and testing some of the important units using testgear, during visits back to work. I think the last time I worked on it was in 1994. This is why it looks so unfinished!

Most of the project seemed to be working in 1994 to some extent. However, at this stage of build, what is needed is a good spectrum analyser, a high frequency scope, a stable signal generator and external regulated power supplies. More important still is time and a good active brain!

Front panel controls

The miniature socket between the two BNC sockets supplies DC power for an active probe. I bought an old Tektronix probe that works well to at least 100MHz. The isolation it provides often makes it very useful for in-circuit testing.

Top, left to right:

Space for Marker & Input RF Filter boxes *
Input Mixer, IF (465MHz & 10.7MHz), Log Amp Variable Bandwidth Xtal Filter (10.7MHz)
Phase Locked Loop (0.465-1465MHz)


Space for Pre-Regulator box * (+20v, -20v, -9v, and +35v)
Space for Precision Regulators box * (+15v, -15v, and +30v)
Microstrip VCO (0.465-1465MHz)(1st LO)

* = Circuits designed but not built

Internal view - top.
View inside top

Internal view - bottom.
View inside bottom

Top, centre:
Tracking Generator (0dBm out)

Top Right:

Centre & Lower Left:
Framestore box (parallel printer port to rear panel)

Bottom Right:
Mains PSU (not built)

I originally drew this block diagram using 'GEMDRAW'. Unfortunately, in the conversion to '.jpg' the detail has considerably deteriorated but is just about readable.
Block diagram

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HP141 with Plug-ins & Tracking Generator.

Nothing but tales of woe!
(When I have time I ought to spend it fault finding instead of writing this section or cursing)

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