CB SWR meter on 122Mhz?

How well do you think a CB SWR meter will work for testing the antenna
installation in an airplane?

thanks,
tom

On 2008-02-13, noman wrote:
How well do you think a CB SWR meter will work for testing the antenna
installation in an airplane?

Not worth a damn. The sensing circuitry is almost certainly not going to work
properly at VHF. A meter designed for the 2-meter ham radio band would work,
though.

What are you trying to find out? Unless something is corroded or broken,
whatever problem you have is probably not your antenna.
--
Jay Maynard, K5ZC http://www.conmicro.com
http://jmaynard.livejournal.com http://www.tronguy.net
http://www.hercules-390.org (Yes, that's me!)
Buy Hercules stuff at http://www.cafepress.com/hercules-390

My radio seems to be overloaded by strong local commercial stations.
Otherwise, range and clarity are fine. I just got to wondering if my
homemade antenna or cable are a problem. To do the original install,
I used an rf field strength meter and simply adjusted the antenna
length for highest reading. It all seems to work fine, I can talk to
aircraft 40 miles away when we are both at 1000agl, but when I get
near some commercial antennas the station bleeds in and breaks the
squelch, even with it turned all the way up. I have seen this on
other rental planes, too.
tom

What are you trying to find out? Unless something is corroded or broken,
whatever problem you have is probably not your antenna.
--
Jay Maynard, K5ZC

As stated, the odds of a 27 MHz. SWR meter giving useable results on the VHF
aircraft band are slim to zero.

--
"If you think you can, or think you can't, you're right."
--Henry Ford

"noman" wrote in message
...

My radio seems to be overloaded by strong local commercial stations.

Not an unusual situation with inexpensive radios with poor front end
filtering, especially for high power FM stations at the top of the band and
at the image frequency of the radio (plus the various harmonic, crossmod,
and intermod combinations of the FM stations and your radio's
superheterodyne configuration).



Otherwise, range and clarity are fine. I just got to wondering if my
homemade antenna or cable are a problem. To do the original install,
I used an rf field strength meter and simply adjusted the antenna
length for highest reading.

That probably wasn't the cleverest way of doing it. Describe your
installation a little more, but I think I can guarantee you that it isn't
the antenna.


It all seems to work fine, I can talk to
aircraft 40 miles away when we are both at 1000agl, but when I get
near some commercial antennas the station bleeds in and breaks the
squelch, even with it turned all the way up. I have seen this on
other rental planes, too.

Then why in heaven's name would you suspect YOUR antenna if the same thing
happens to OTHER aircraft and their radios? Their antennas couldn't have
ALL failed in the same way.

On 2008-02-13, RST Engineering wrote:
"noman" wrote in message
...
Otherwise, range and clarity are fine. I just got to wondering if my
homemade antenna or cable are a problem. To do the original install,
I used an rf field strength meter and simply adjusted the antenna
length for highest reading.
That probably wasn't the cleverest way of doing it.

Maybe not the cleverest way, but it's probably good enough that it's working
fine.

Describe your installation a little more, but I think I can guarantee you
that it isn't the antenna.

I agree. This sounds like a front end overload problem. No antenna in the
world will fix that. (Well, at least not and still work for the intended
purpose.)
--
Jay Maynard, K5ZC http://www.conmicro.com
http://jmaynard.livejournal.com http://www.tronguy.net
http://www.hercules-390.org (Yes, that's me!)
Buy Hercules stuff at http://www.cafepress.com/hercules-390

Jay Maynard wrote:

On 2008-02-13, RST Engineering wrote:
"noman" wrote in message
...
Otherwise, range and clarity are fine. I just got to wondering if my
homemade antenna or cable are a problem. To do the original install,
I used an rf field strength meter and simply adjusted the antenna
length for highest reading.
That probably wasn't the cleverest way of doing it.

Maybe not the cleverest way, but it's probably good enough that it's working
fine.

I've had variable luck using that approach on other types of antennas.
It's probably a better approach than the typical SWAG.

Describe your installation a little more, but I think I can guarantee you
that it isn't the antenna.

I agree. This sounds like a front end overload problem. No antenna in the
world will fix that. (Well, at least not and still work for the intended
purpose.)

I agree - the only way his antenna is likely to fix it is by removing
it altogether (which, as you point out will not help the operation of
the radio much).

No doubt the problem is that (like Jim pointed out) the FM signal is
mixing with some other signal. The question is whether that's
happening inside the portable radio, or outside it.

If it's inside the radio, reducing the amount of broadcast FM signal
getting into the receiver's front end would help. Personally, I'd do
this by putting a T connector in line with the antenna, and plugg in a
shorted quarter-wavelength (at the offending FM frequency) chunk of
shorted coax on the extra connector. The length of the stub depends
on the coax you use, and the type of connector.

If this doesn't help it's likely that the mixing is occurring
somewhere else. If it's outside the aircraft, there's not a lot you
can do (though that would mean that almost everyone would have the
problem). If the mixing is happening in the aircraft, it'll be "more
fun" to find. Someone suggested unplugging your ELT (a possibility,
and easy enough to do - just don't schedule any crashes when doing
this). ;-) I've seen all kinds of metal structures become effective
RF mixers - so the problem could be almost anywhere in a typical
aircraft (note: I don't recommend removing metal in the process of
looking for the mixing source - you may really NEED that ELT if you do
that). ;-)

Mark Hickey

On Feb 13, 8:28 am, "RST Engineering"
Not an unusual situation with inexpensive radios with poor front end

The radio is an Icom A5. Definitely on the low end of the radio cost
spectrum.

That probably wasn't the cleverest way of doing it. Describe your
installation a little more, but I think I can guarantee you that it isn't
the antenna.

The A5 is connected to a DRE portable intercom and then to my
headphones. The
antenna is a simple wire about 22 inches long soldered to an rf
connector. The
connector is mated to a bulkhead rf fitting that has the cable
soldered to it. I forget the
cable designator, but it has fairly low attenuation at 100mhz, and is
the same impedance
as the output of the radio. I ran the power, headphone, and push to
talk wiring through
torroids near the radio, but that didn't do much improvement. The
only time this shows
up is near the more powerful transmitters. I suspected the front end
of the radio, but I
don't know how to prove or disprove that. I figured that if power was
clean and antenna was
clean, then I'm pretty much left with the radio. Oh yeah, taking the
intercom out of the
mix makes no difference.

Then why in heaven's name would you suspect YOUR antenna if the same thing
happens to OTHER aircraft and their radios? Their antennas couldn't have
ALL failed in the same way.

Agreed, and I misspoke. There was only one other plane that I know
has this problem.
But, again, I'm trying to eliminate what I can with the equipment I
have at my disposal. As
you can see from my choice of radio gear, I'm on a budget. 8^)

tom

noman wrote:
My radio seems to be overloaded by strong local commercial stations.
Otherwise, range and clarity are fine. I just got to wondering if my
homemade antenna or cable are a problem. To do the original install,
I used an rf field strength meter and simply adjusted the antenna
length for highest reading. It all seems to work fine, I can talk to
aircraft 40 miles away when we are both at 1000agl, but when I get
near some commercial antennas the station bleeds in and breaks the
squelch, even with it turned all the way up. I have seen this on
other rental planes, too.
tom

What are you trying to find out? Unless something is corroded or broken,
whatever problem you have is probably not your antenna.
--
Jay Maynard, K5ZC

I had similar symptoms in an earlier airplane, the problem turned out to be a problem with my ELT. I was led to that by info gained from this group. Try temporarily disconnecting the antenna from your ELT and see if your comm radio problems go away. Mine did. I bought and installed another ELT, no more problem. I have helped several other local people who were tearing their hair out trying to solve similar problems by giving them this information.

Jim Austin

Tom,

I concur with Jay. You need a unit designed for the frequency being tested.

MFJ Enterprises has as series of suitable VHF SWR/Watt Meters starting at
about $40.
http://www.mfjenterprises.com/Caterg...45fc51f462651f
or
http://tinyurl.com/yo26k6

I personally use the SWR in my old RST-721 test set.

Wayne
W7ADK
http://www.soaridaho.com/



"Jay Maynard" wrote in message
...
On 2008-02-13, noman wrote:
How well do you think a CB SWR meter will work for testing the antenna
installation in an airplane?

Not worth a damn. The sensing circuitry is almost certainly not going to
work
properly at VHF. A meter designed for the 2-meter ham radio band would
work,
though.

What are you trying to find out? Unless something is corroded or broken,
whatever problem you have is probably not your antenna.
--
Jay Maynard, K5ZC http://www.conmicro.com
http://jmaynard.livejournal.com http://www.tronguy.net
http://www.hercules-390.org (Yes, that's me!)
Buy Hercules stuff at http://www.cafepress.com/hercules-390

{;-)

Jim


I personally use the SWR in my old RST-721 test set.

Wayne
W7ADK
http://www.soaridaho.com/