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

--
Mike Andrews, W5EGO

Tired old sysadmin

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

What kind of "SWR meter" are you talking about? The '8640 may or may
not have enough power to be suitable.

On 18 Dec 2006 10:39:54 -0800, Wes wrote in .com:

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

What kind of "SWR meter" are you talking about? The '8640 may or may
not have enough power to be suitable.

A fairly el-cheapo no-name, but appearently good-enough on 2m and from
420 to 450 MHz. I haven't fiddled with it to see how much drive power
is required.

I suppose I can get a couple of RF amplitude measuring chips and make
the critter active instead of passive, if necessary. The 8640, IIRC,
is good for +20 dBm (3V) into 50 Ohms, or a lusty 180 mW flat-out, but
the finals on the 8640 are unobtainium and so I'm minded to stay well
below that -- and even lower outside the ham bands.

--
Mike Andrews, W5EGO

Tired old sysadmin

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

Mike-

You have to try it to find out.

One problem is that your SWR meter's diode output is non-linear for very
low voltages, resulting in SWR being higher than indicated for low
values of SWR. You may be able to get around this with a
hand-calibrated dial on the meter, or a calibration correction chart.

Fred
K4DII

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

--
Mike Andrews, W5EGO

Tired old sysadmin

In article ,
Fred McKenzie wrote:
In article ,
"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, running the signal through
the SWR meter to the antenna? Or am I way off in left field?

Mike-

You have to try it to find out.

One problem is that your SWR meter's diode output is non-linear for very
low voltages, resulting in SWR being higher than indicated for low
values of SWR. You may be able to get around this with a
hand-calibrated dial on the meter, or a calibration correction chart.

Fred
K4DII


Analog devices makes RF-log amp/detector chips which are good to microwave
frequencies (basically RF in, 10mv per dBm out, from -80dBm to 0dBm).
Replace the SWR meter's detector with one of these.

--
/* AB1GO */ /* Joseph H. Allen */
int a[1817];main(z,p,q,r){for(p=80;q+p-80;p-=2*a[p])for(z=9;z--q=3&(r=time(0)
+r*57)/7,q=q?q-1?q-2?1-p%79?-1:0%79-77?1:01659?79:0158?-79:0,q?!a[p+q*2
]?a[p+=a[p+=q]=q]=q:0:0;for(;q++-1817printf(q%79?"%c":"%c\n"," #"[!a[q-1]]);}

Joseph H Allen wrote:
Analog devices makes RF-log amp/detector chips which are good to microwave
frequencies (basically RF in, 10mv per dBm out, from -80dBm to 0dBm).
Replace the SWR meter's detector with one of these.

--
Andy writes:
I built one of those up -- the version that goes to 500 Mhz -- and
I use
it with a Mini-Ckts Fwd/Ref bridge and a Measurements 202, which only
puts out around 0 dbm. It works like a charm. I use the 202 to get
reference
measurements and use that system to tune antennae and transmission
lines.
It's a very very sensitive RF power meter and, while the absolute
accuracy may not be the best, it's very good for using low power signal

sources and taking relative measurement.

Andy W4OAH

On Mon, 18 Dec 2006 15:08:17 +0000 (UTC), "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, running the signal through
the SWR meter to the antenna? Or am I way off in left field?

You can achieve a lot on 70cm with an HT and a simple field strength
meter. Think matching stubs & shorting bars...
John Ferrell W8CCW

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?

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.


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

--
Mike Andrews, W5EGO

Tired old sysadmin

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!

--
Mike Andrews, W5EGO

Tired old sysadmin