[Amps] Cheap network analyser on eBay

Sat Jun 25 12:23:21 EDT 2005

Karl-Arne Markstro"m wrote:
> This early 1970's "network analyser" is only a small part of a measuring system.
> The unit offered is the transmission test part, and was intended for measuring the transmission properties
> of components in baseband and FDM telephony multiplex systems (which explains its frequency range 50 Hz - 13 MHz).
> 
> To make up a full network analysis system this piece of equipment needs to be complemented with:
> 
> - Signal source, preferably synthesized with GPIB interface
>   (i.a. HP3330 or HP3325, the HP3320 can be pressed into service)
> - Reflection test set (return loss bridge)
> - Power splitter and switching arrangement to alternately read transmission and reflection
> - Software to read the instrument output data and present it in a rectangular or polar (preferred) display system
> 
> In my humble opinion this would be a very considerable amount of equipment and work to make up a network
> analyser that stops just "south of" twenty meters.
> 
> 73/
> 
> Karl-Arne
> SM0AOM

It's clearly going to be some work to do a full S-parameter 
characterisation, but for simple things like analysing antennas, I think 
all you would need is a couple of directional couplers and of course 
some form of sig gen - or even your amateur transmitter, with a lot of 
attenuation!

But whether you write down the numbers, or have the lot under full 
computer control, is up to you of course.

GPIB programming is normally trivial if all you want to do is collect 
the data into a file. You could probably set the amplitude and frequency 
of a sig gen in under 25 lines of C code. Assuming that network analyser 
gives out ASCII, and is not limited to a binary mode that takes more 
work to decipher, reading data from that would add another 20 lines I 
expect. There would be no point in writing software to plot them - just 
do it using your favorite package.

Here's some data I collected the other day from two bits of test kit - a 
time interval counter and a DVM.

http://www.g8wrb.org.uk/useful-stuff/time/data/abrupt-changes-in-TI/foo.jpg

A very small thermistor was connected to the DVM to measure resistance, 
which gives temperature. The data looks a bit noisy, since there is no 
averaging and since the thermistor is mounted at the air input of one of 
the instruments, the time-constant is very short indeed.

The actual code for reading the instruments (I wrote in C using the free 
gcc compiler), putting them on a disk file, converting the text file to 
a jpeg graph (using the free gnuplot program), copying them to a web 
server (using the free openssh scp program to give security without the 
need for passwords), was no more than 4 hours. The hardest part was 
sorting out the relationship between resistance and temperature of the 
thermistor - not made easy as I mis-read the data sheet, and typed in a 
list of the wrong numbers!!

The N2PK VNA
http://users.adelphia.net/~n2pk/VNA/VNAarch.html
might well be better, but I gather is not simple to build.

Anyway, I thought someone might be interested, so I put it here, 
although the fact I did not bid myself I guess indicants I was not.

Had the frequency range been a lot higher, I would have done, but then I 
doubt it would be under $75.

David Kirkby,
G8WRB

> ----- Original Message ----- 
> From: "David Kirkby" <david.kirkby at onetel.net>
> To: <amps at contesting.com>
> Sent: Saturday, June 25, 2005 1:44 AM
> Subject: [Amps] Cheap network analyser on eBay
> 
> 
> 
>>There is on eBay at the minute what appears to be a very cheap HP 
>>network analyser, which I guess would double as a cheap power meter too.
>>
>>The "buy it now" is under $75. Cheaper than the amateurish instruments 
>>that give "some idea about the magnitude of the impedance".
>>
>>It's an HP 3570A, which the tucker web site give a bit of info
>>
>>http://www.tucker.com/java/jsp/doorway_partnoH-P3570A_invid2370.htm
>>
>>although I think the max frequency is 13MHz, not 500 as stated there. 
>>Hence the frequency range is a bit limited.
>>
>>Here's a bit more info.
>>
>>http://www.tucker.com/images/images_spec/00004350.pdf
>>
>>The unit on eBay has option 004, which is the GPIB interface, so you can 
>>read (and often set) the instrument via a computer.
>>
>>The seller is definitely in what I would call the "doggy" category. 
>>Although he has over 1000 feedbacks, there are a lot of negatives (94.8% 
>>positive).
>>
>>A friend tells me the model number indicates it is likely to be very old.
>>
>>Anyway, here's the link to the eBay site.
>>
>>http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=97192&item=7525812615&rd=1
>>
>>It's clearly not without its risks, and I don't know much about it, but 
>>on the face of it, the unit would seem quite cheap and useful. But 
>>perhaps someone knows otherwise.
>>
>>You could extend the frequency range with mixers and a couple of sig 
>>gens, but then calibration would be much more difficult.
>>
>>PS
>>If you do buy it, do your homework. Don't blame me if it needs an XYZ 
>>that is impossible to obtain, or if its dead and the seller will do 
>>nothing about it.
>>
>>-- 
>>David Kirkby,
>>G8WRB
>>
>>Please check out http://www.g8wrb.org/
>>of if you live in Essex http://www.southminster-branch-line.org.uk/
>>
>>
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>>
>>
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>>
> 
> 
> 

-- 
David Kirkby,
G8WRB

Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/