<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=ISO-8859-1">
</head>
<body text="#000000" bgcolor="#FFFFFF">
Hello,<br>
<br>
<u><b>HamWAN Lab Garage Sale Items</b></u><br>
<br>
<ol>
<li>I've managed to bring back to life an HP 8757A I've had for 6
months in a non-working state. Did it last night actually.
I'll be selling this on eBay since it's been obsoleted by
another item, so if anyone local is interested in it, let me
know.<br>
<br>
</li>
<li>Also managed to verify function of a 10MHz-26.5GHz detector
(HP 85025B) that I picked up 7 months ago. It actually works!
I'll be selling this too (works with the 8757A), so again if
you're local and interested, drop me a line.<br>
<br>
</li>
<li>Finally, I'll be doing a couple more tweaks to an HP 8566A
100Hz-22GHz spectrum analyzer and selling it. Right now it
still has a problem with one set of sweep speeds, which I
suspect is a constant-current ramp generator circuit failure.
An IF filter also seems misaligned by about 31Hz, so I'll be
touching that up and re-calibrating levels. Let me know if
there's any local interest in this unit, otherwise on eBay it
goes. They're beautiful machines, but I don't need 2 of them.</li>
</ol>
<p><br>
</p>
<u><b>HamWAN Lab Expansion</b></u><br>
<br>
<ol>
<li>Newly acquired HP 11720A Pulse Modulator. This thing can take
a 2-18GHz microwave signal and either pass it through or
dissipate it internally. Doesn't sound exciting, right? Until
you realize it can do the full on+off sequence in a span of less
than 50 nanoseconds! Rise and fall times are spec'd as less
than 10ns. On-off power ratio is spec'd as >80dB, but I just
verified it's actually >95dB on this particular unit @ 4GHz.<br>
<br>
So what is this good for? Let's assume the minimum pulse width
is actually 40ns. That corresponds to an RF signal in space
that's 12 meters long, traveling at the speed of light. Let's
call it an RF packet. An interesting object, but how is it
useful?<br>
<br>
We are doing high-performance (read: high dynamic range) antenna
radiation pattern measurements. When you shoot an RF beam at a
test antenna, that signal is not confined to the antenna
itself. It also goes into the surrounding environment and then
can bounce back at the antenna. These bounces add to the power
received by the antenna, and destroy the accuracy of power
readings you're trying to take. RF absorbers help the problem,
but do not eliminate it since they don't absorb 100% of the RF
energy scattering back and distorting measurements from weird
angles.<br>
<br>
Now imagine you take an RF-silent environment (go to the
mountains) and strike the same antenna now with an RF packet.
You then take a power reading 10ns after initial RF impact, and
for no more than 30ns after impact (avoid rise+fall times). As
long as there are no sources of reflection within a certain
radius, there will be ZERO power in the RX DUT antenna which
comes from reflections! Your dynamic range just increased
dramatically, and so did your measurement accuracy.<br>
<br>
What is this "certain radius" in this example? The RF packet
has a 10ns rise time, so that signal's already gone 3 meters
past your antenna before you start your readings. Your reading
window is 6 meters (20ns) long. The head of the rise envelope
would have to meet your readings no more than 30ns (9 meters)
from when it passed the DUT antenna to register and distort the
experiment. This means it would have to hit a reflector 4.5
meters away and then travel back. So there you have it, a
radius of 4.5 meters around the DUT clear of reflection sources
will guarantee no measurement distortion from reflections.<br>
<br>
One problem remains. Even though this instrument provides a
means to generate the necessary RF packets to perform such
testing, I don't yet understand how to receive a precisely timed
20ns window of RF and determine its power. If anyone has any
suggestions, I'm all ears. I suspect RF engineers familiar with
radar systems will have a lot of good input here.<br>
<br>
</li>
<li>Newly acquired 1W / 35dB gain microwave amplifier (CTT
APM/060-3032). It runs off 15V @ 1A, and is really small. So
small in fact that we can climb with it. What is this good
for? We often have a hard time aligning dishes. It can take an
hour in an awkward position on a tower tweaking with the noisy
measurements the modems give us, if we can find a modem signal
at all. The problem with the modem TX beacons is that while
they're 1W signals, they're spread out over at least a 5MHz
bandwidth. This reduces their power spectral density and makes
them harder to detect. They're also not continuous signals.
Sending a single frequency continuous 1W signal from a remote
dish would really help alignment.<br>
<br>
There is still the problem of how do you portably generate the
required precise 5.9GHz signal to feed the amp, and is this only
applicable when two sites are being worked on simultaneously.
But it's an interesting bit of equipment that can possibly solve
the alignment problems we face.<br>
<br>
</li>
<li>Corresponding to a single frequency transmission, you need a
single frequency receiver on the other end. The modems will not
pick this up. Actually, I have to verify if they'll pick it up
as noise floor fluctuation or not! That'd be an interesting
option if it works. Anyway, a portable receiver capable of 6GHz
work is really expensive. We're talking Agilent FieldFox or
Anritsu SiteMaster type of stuff. We already have spectrum
analyzers capable of 6GHz work, but they're too large to take on
a tower. So they have to live on the ground. Running LMR400
down a tower will eat a lot of the received signal (20dB for a
tall tower), and you may not hear the remote site. This calls
for a pre-amp of sorts! So I bought a JCA JCA48-4111B1 34dB
gain amplifier. It's also tiny and can be battery-powered, so
it can be installed @ an RX antenna to feed 200ft of LMR400
before it hits a proper receiver. I'm not sure if this will
work out or be worth it. A better LNA-type amplifier might be
needed, and the LMR400 may prove too bulky in field work, but
the amp was cheap, so might as well have it on hand. It might
also help with signal measures of circuits on the lab bench if
nothing else.<br>
<br>
</li>
<li>And then I bought a big amp. :) A 10W Traveling Wave Tube
amplifier made by Hughes, model 1177H13F000. It covers 3-8GHz
at this power level. It will be useful for such experiments as
"Hey Bob, go stand in front of that dish and tell me if you feel
warm." And, "Do I have a death ray yet?" :)<br>
<br>
But seriously, some of the experiments deal with RF leakage from
antennas, specifically near-field measurements from the rear of
antennas. Finding the sources of this leakage can be tricky
since tiny probes have to be used to maximize spatial
resolution, so this means low gain RX. The attenuation through
the back is already high, so there's very little there to be
heard in the first place. But if you blast the antenna with
lots of energy, you greatly increase your chances of picking up
the hot spots! +40dBm, here we go. :)<br>
<br>
While I'm not sure yet, this amplifier might be useful in pulsed
mode to possibly drive 100W (@ <10% duty cycle). Will have
to research this more and see how TWTs feel about pulsed RF.
Don't wanna cause internal arcing.<br>
<br>
The other useful application for this is as a reference
amplifier as we try to develop our own 10W cheap silicon amp.
When/if we do a 100W cheap silicon amp design, having 10W on
hand will be handy as a first stage. These amps would be useful
in more challenging links, like Cascades to Spokane. Amazingly,
the signal path doesn't hit the ground, but does have to travel
256km.<br>
<br>
Finally, if we end up doing filter design, and the filters end
up being good, we might need a lot of incident power to measure
their true attenuation. Having this bad boy on hand solves that
problem. Plus I like amps. And this is my first TWT amp. Joy!
:)<br>
<br>
</li>
<li>Oh, there is one more thing...<br>
<br>
HamWAN Lab will soon feature an HP 8573E Vector Network Analyzer
with options 006 (6GHz extension) and 011 (direct access to
S/R/A/B channels), along with an HP 87050A option H47
S-Parameter Test Set. This instrument features 110dB dynamic
range @ 6GHz and is useful down to 300kHz with the test set.
The special (rare!) test set that comes with this is extra nice
because it allows you to make measurements at higher than normal
power levels for this instrument by in-lining an amplifier.
Direct measurements at up to 1W can be made. It also allows the
switching in and out of up to 3 external stimulus/measurement
systems. The very broad frequency range of 300kHz-6GHz will
allow this instrument to characterize all sorts of devices,
including transistors from HF to HamWAN microwave. These
transistor characterizations are necessary when designing
amplifier input and output matching networks (for example), and
are not always provided by device manufacturers. Measurements
can also be made at power levels higher than 1W by using some
additional external components, so work @ 10W and 100W should be
possible, albeit with degraded accuracy compared to the native
1W TX / 0.4W RX system.</li>
</ol>
<p><br>
Just as a general note, HamWAN Lab is my own private collection of
stuff, not funded in any way by HamWAN. Although the work done in
this lab is a key to HamWAN's success. If you have any projects
which might benefit from some lab time, feel free to get in touch
with me. The (out of date) inventory is here:
<a class="moz-txt-link-freetext" href="https://www.hamwan.org/t/tiki-index.php?page=Labs&structure=HamWAN">https://www.hamwan.org/t/tiki-index.php?page=Labs&structure=HamWAN</a>
. Should really update that page. It's months out of date.<br>
</p>
<p><br>
--Bart<br>
<br>
</p>
</body>
</html>