(LONG) Re: [NLRS] Homebrew gear to test at 10 GHz?

[Donn Baker]

Hi Scott,
Glad Chris pointed out Peter's web page... unfortuantely, thats about all I
know about.  There MUST be others, but I don't know where.

As Gerald also pointes out, homebrew test equipment for 10GHz is not easy,
but it can be done.  There are, however, a few things that you need that
you really can't build.  My list is:

1) HP 415E SWR meter.  This is THE basic tool.  Its actually a 1000 Hz
amplifier and a precision 60 dB attenuator.  Its use to measure SWR,
attenuation, and other stuff.  E-bay will usually have one or two; expect
to pay $50-$75 of one promised to work.  There are three out there today:
one for $49 claimed to be fully functional; one for $65 from England ; and
(the joke of the day!) one for $1,499 with eight pieces of waveguide and
slotted line parts.  Yeah, useful, but not for $1,500 !!!

You CAN use a standard voltmeter for some measurements, but the 415E really
needs to be on your bench.  A digital voltmeter works, but an analog meter
is better.  Not only is it easier to small changes, but usually, at least
one scale will be calibrated in dB so you don't have to do all the
arithmetic to convert voltages to dBs.

2) Detector(s)  A 1N34 diode won't work at 10GHz.  You need to spend some
mony to get at least one or two that are good.  It is possible to buy
diodes and make your own for most things.  You still need at least one for
the "lab standard."  HP 423A is top of the line, HP 420s only a little
below that.  Wiltron/Anritsu make similar ones.  You need ones that match
the connector series you use (i.e., N, SMA, etc.).  The outputs are almost
always BNC.

3) Attenuator(s)  At least one each 3dB, 10dB, 20dB high quality
attenuators.  Make sure they're rated to at least 10GHz; 18 GHz (if using
N-connectors) is better.  Use these only for calibration of other, cheaper
attenuators.  Don't use'em for run of the mill stuff.

4) Dummy load.  At least one high quality 50 ohm load.  Again, use ONLY for
calibrating other, cheaper loads.

5) Signal generator w/1000 Hz modulation.  Obviously, you can use your
transverter with a 1000 Hz tone being transmitted (AM or SSB.  Not FM)

Once you have these, you're on the way.  To measure SWR (or Return Loss),
you also need a slotted line (lab-quality measurements), or Directional
couplers (usual measurements).  Directional couples can be home-built...
the Radio Society of Great Britian (RSGB) Microwave Handbood, or their VHF
Handbook have details for making "cross couplers" for 10GHz with scraps of
WR90 waveguide.  You can also buy directional couplers for 10GHz at
reasonable prices... $10 to $30 depending on the exact type, etc.  20 to
30dB coupling are the most common.  You probably don't want anything below
10dB, and I'd even stay away from 10dB ones, too.  You don't want anything
over 40dB, either, without a 415E to use with it.  You have to be careful
about what connectors are being used.  Waveguide couplers are cheapest, but
you'll need transitions to get to/from the waveguide.  N-connectors are
common on older stuff that's not waveguide and SMAs are used on newer
equipment.  (Transitions can be homebrew, by the way.)

Hook up the generator (with 1000Hz tone on) to the directional coupler to
the unit (antenna) you're testing so that it measures in the forward
direction.  Connect the detector to the coupled port.  Note the voltage,
etc. on the 415E or voltmeter.  Reverse the directional coupler so that it
measures the energy being relected from tha antenna.  Note the dBs or
voltage.  Convert the voltages (both of'em) to dBs.  The difference in dBs
is the Return Loss (RL) of the antenna.  You'd like to see a >20 or 25 dB
difference.  If you "diddle" with the antenna, you need to verify the
forward measurement to get an accurate RL, as changing the RL can affect
how much power is put out by the generator.

73 Donn
WA2VOI/0

At 02:47 05-05-05 +0000, Scott wrote:
>
>
>Does anyone know of a good website(s) that has some homebrew test 
>equipment for 10 GHz use?  I would like to be able to measure SWR up 
>there as I play with different feed systems, etc.  Thanks!
>
>-- 
>Scott N0EDV
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