I don't think using your 8640B as a signal source to read on a wattmeter
is going to cut it. +20 dBm is only 100 mW. Unless you have a
wattmeter that has a 100 mW or so range, you aren't going to get much
needle deflection. The lowest range on my Telewave wattmeter is 5 Watts.

Scott
N0EDV

Mike Andrews wrote:

On Tue, 19 Dec 2006 09:58:41 -0500, Straydog wrote in m:



On Mon, 18 Dec 2006, Mike Andrews wrote:


Some friends and I have been looking into making antennas for 70 cm.
and higher frequencies, but we don't have an MFJ-269; my MFJ-259 tops
out at 175 MHz. I _do_, however, have an SWR meter that supposedly
works up to 500 MHz( and maybe higher), and an HP 8640B that is good
to about 1.2 GHz.

If the SWR meter is sensitive enough, could I get at least ballpark
SWR values using the 8640B as a source,


You did not say what an 8640B is. Signal generator? Transmitter? Power
out?


Lab-grade RF signal generator, official range from 500 KHz to 1.024
MHz. In practice it's good from 455 KHz up to about 1.2 GHz. Includes
FM, AM, and pulse modulation, with either internal modulation at variable
frequencies and amplitude (AM) or deviation (FM) or external modulation.
Has a very nice 6 1/2 digit counter good up to 1.2 GHz. Output range
is from -130 dBm (100 nanoVolts) to +20 dBm (3 Volts) into 50 Ohms.

It's a _very_ nice piece of gear indeed. You can see a picture of mine
(and other stuff on the workbench) at

http://mikea.ath.cx/testgear/index.html.


Main thing is to get the "forward" power to read something on the meter
(preferably full scale, but even if you get half or quarter scale, then
you are able to get a rough idea of usabiltiy of the meter). Then see what
it shows on the "reflected" scale. Figure ver roughly if the reflected
power is half the forward (regardless of the actual location on the meter
scale), then you have about 3:1 SWR. Turn the meter around to get an idea
if the diodes (and associated circuitry) are well matched for forward and
reflected.


I have used a number of el-cheapo CB SWR meters even up on two meters and
they work surprisingly well, even more sensitive than ham SWR meters for
VHF-UHF, and not that far off of what the ham SWR meters report, and so
are good for handie-talkie measurements. So, yes, you should get useful
ball park figures.


That's good to hear. I got to thinking about what an MFJ-259 or -269
does, and decided that I only needed a sensitive-enough SWR meter that
would give reasonably accurate readings from 100 MHz to 1.2 GHz, since
I already had the signal source. Of course, the HP 8640B weighs about
40 pounds, and is a good deal less portable than the MFJ products, but
if I can get this working, I'll be able to do things it won't.


running the signal through
the SWR meter to the antenna? Or am I way off in left field?


Looks like I'm well inside the ballpark and that I have some design
and construction to do. This should be fun.

Thanks!