At 07:15 AM 7/26/2007, jeremy-ca wrote:
>>Jim Brown's paper has very high quality measurements done with
>>traceably calibrated lab gear (a VNA) on a wide variety of
>>configurations. Not that measurements done 20-30 years ago are not
>>valid, but measurement technology has improved a lot, particularly
>>for high insertion losses. The ability to make the measurements
>>more rapidly means you can make 30 measurements intead of one, and
>>that lets you spend more time on doing good fixturing for the
>>tests. The other thing is that modern test equipment does fixture
>>calibration for you.
>>
>>(I want a Agilent 4 port PNA-X with the two sources and an E-cal for
>>my garage, although I wish it went down to 300kHz like the N5230A! I
>>wouldn't turn down a more elderly 8753..)
>>
>>Jim, W6RMK
>
>My shop currently has a 8757A, 8753B and an assortment of SA's, sig
>gens, sweeper, NF meter, cal sets, etc. Older technology but more
>than adequate for my needs. Plus they show up at rather distressed
>prices in this area. A friend who was the cal lab manager at a
>previous job now has his own shop out of his home and thinks he can
>land me a 8510B with a load of accesories at a bargain price.
Until the 8510 breaks, since Agilent doesn't support them anymore,
even for repairs. (I have an 8510C in the lab here at work, and it
has a strange lockup problem...)
>The advent of the E series and later has taken its toll on the
>resale market. Cal shops are closing as qualified techs are retiring
>or changing professions. Pretty soon the venenerable 141T package
>and others of the era are going to be a collectors item on Ebay
>bringing huge prices!
More power to them. They can put it next to their spark gap
transmitter and tell people how wonderful it was when the CRT
actually worked.<grin>
This relates to towers and antenna stuff.. Now, with all the
relatively low priced ham oriented VNAs and analyzers out there (all
in the <$1000 range), you'd really have to think twice about trying
to adopt an aging piece of HP gear with all their foibles and parts
that have no direct replacement, no matter how good the measurements
you can make when they are working. (Except as a museum curiosity,
antique restoration kind of thing.. like that guy down south with a
barn full of just about every oscillator HP ever made)
If you're interesting in restoring old gear, that's one thing, but if
your goal is to make antennas and just get the measurement done, even
if you save some money by buying the used gear, there's a cost in
time for finding it, repairing it, calibrating, etc.
I would expect that within a year or two, you'd be able to buy a
small box that duplicates the performance of an 8753 for less than
$1000 (plus the PC you already have), and which can dump the data
into an file for easy manipulation later without needing to have a
GPIB adapter and driver software. It's almost there now. I have a
TenTec/TAPR VNA, and while the software has some hiccups, and it's
really half a 2 port analyzer (you can make S11 and S21, but you have
to recable to do S22 and S12), and it's a wideopen detector, it's
still a nifty piece of gear, and things like this will push that sort
of measurement to a much wider area. No more would you need to lug
that Impedance bridge out to the array, and do the whole open, short,
lay the other antenna down, sort of thing for dialing in a phased array.
Yes, products like the TAPR VNA have their shortcomings (frequency
range, ultimate isolation, etc.), but generically, the expected
standard of performance is getting better, too.
>Carl
>KM1H
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