CB SWR meter on 122Mhz?

Jim,

The RST-721 is a great little unit. In addition to tuning the antennas on
the local experimental sailplanes, I use it for my 2 meter equipment.

I didn't build one of your transceivers. I inherited the unit from a friend
who retired from soaring in his 80s.
(http://www.soaridaho.com/photogaller...k_is_Ready.jpg)

I wish aircraft tranceiver kits were still available. I enjoy building
electronics as much as working on my sailplane.
(http://www.soaridaho.com/Schreder/HP-14/N990/N990.html) I built all my
amateur radion HF equipment. (Heathkit SB-310, SB-200, SB-101 and SB640)
These old tube-based units are still running great.

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



"RST Engineering" wrote in message
...



{;-)

Jim


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

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

On Feb 13, 8:11*am, Jay Maynard
wrote:

Not worth a damn....

My experience runs the other way. I've tested and troubleshooted
several VHF radio antenna installations using a cheap SWR meter, and
system performance has seemed pretty uniformly inversely proportional
to the SWR reading. Of course, that's far from scientific, but it
suggests that inaccurate measurements are better than no measurements
at all.

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

That also runs counter to my experience. Yeah, where we're talking
about classic quarter-wave whips or commercially available blade
antennas, I certainly agree. But when it comes to custom antennas,
internal antennas, copper-tape dipoles, oddly-shaped dipoles, dipole
antennas in fins and rudders, dipoles near metal parts, and carbon
fiber ground planes (all of which are common in sailplanes), radio
problems are way too often caused by the antenna or its installation.

Thanks, Bob K.
http://www.hpaircraft.com

Bob,

I played around with this a couple years ago. I trimmed an antenna using a
CB SWR to as close to 1:1 as I could get. I then measured it with my
RST-721. The '721 read 3.5:1. That is quiet a difference.

I did the same test using my quality HF SWR unit and '721 with the same
results.

Wayne
HP-14 "6F"
http://www.soaridaho.com/


"Bob Kuykendall" wrote in message
...
On Feb 13, 8:11 am, Jay Maynard
wrote:

Not worth a damn....

My experience runs the other way. I've tested and troubleshooted
several VHF radio antenna installations using a cheap SWR meter, and
system performance has seemed pretty uniformly inversely proportional
to the SWR reading. Of course, that's far from scientific, but it
suggests that inaccurate measurements are better than no measurements
at all.

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

That also runs counter to my experience. Yeah, where we're talking
about classic quarter-wave whips or commercially available blade
antennas, I certainly agree. But when it comes to custom antennas,
internal antennas, copper-tape dipoles, oddly-shaped dipoles, dipole
antennas in fins and rudders, dipoles near metal parts, and carbon
fiber ground planes (all of which are common in sailplanes), radio
problems are way too often caused by the antenna or its installation.

Thanks, Bob K.
http://www.hpaircraft.com

On Feb 13, 9:45*am, "Wayne Paul" wrote:

I played around with this a couple years ago. *I trimmed an antenna using a
CB SWR to as close to 1:1 as I could get. *I then measured it with my
RST-721. *The '721 read 3.5:1. *That is quiet a difference.

I did the same test using my quality HF SWR unit and '721 with the same
results.

Thanks for that info. I guess its time for me to get a better SWR
meter.

Bob K.

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

"Bob Kuykendall" wrote in message
...
On Feb 13, 8:11 am, Jay Maynard
wrote:

Not worth a damn....

My experience runs the other way. I've tested and troubleshooted
several VHF radio antenna installations using a cheap SWR meter, and
system performance has seemed pretty uniformly inversely proportional
to the SWR reading. Of course, that's far from scientific, but it
suggests that inaccurate measurements are better than no measurements
at all.

There is a vast difference between a "cheap" SWR meter and one optimized and
sold specifically as a "CB SWR Meter". I've seen "cheap" SWR meters
designed for HF/VHF (and the one in the mentioned RST-721 is about as cheap
as you can get) give nearly identical results to the Bird and high end
meters. The difference is in the number of decimal places of accuracy. For
aircraft antennas that have to cover a 15% instantaneous bandwidth, you can
generally measure with a micrometer, mark it with chalk, and cut it with an
axe and come close enough.




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

That also runs counter to my experience. Yeah, where we're talking
about classic quarter-wave whips or commercially available blade
antennas, I certainly agree. But when it comes to custom antennas,
internal antennas, copper-tape dipoles, oddly-shaped dipoles, dipole
antennas in fins and rudders, dipoles near metal parts, and carbon
fiber ground planes (all of which are common in sailplanes), radio
problems are way too often caused by the antenna or its installation.

Yep, but this guy mentions a 22" length of wire (? brazing rod perhaps ?)
soldered into a coax connector and then that connector run into a "bulkhead"
connector with the coax soldered onto the back end. I think he meant "panel
mount" rather than "bulkhead" because a bulkhead connector by definition is
a coax connector with both ends terminated in an identical connector (like a
back-to-back female BNC with a mounting thread in the middle). Be that as
it may, I'd take a magnifying glass and a little wiggle action to see if the
"soldered" joints really are. Other than that, unless he's got that panel
mount connector on some sort of insulator other than a metal airframe skin,
the odds of it being the culprit are damned near zero.

Also, the comment about the ELT is well founded. Rather than just
disconnecting the antenna, I'd take the batteries out. THere is generally
enough leakage through the ELT plastic case to cause a bit of trouble also.
(Who'da ever thunk that the CB junction of the output transistor in the off
mode would be such a great varactor multiplier???)

Jim

I have a Radio Shack SWR bridge/wattmeter designed for CB radio. It uses
standard 1N914 diodes for the detectors, and it seems to work fine at air
band frequencies. I've never bothered to check it's calibration, but it's
plenty good for a rough check.

I have a used DAIWA CN-101L, 1.8-150MHZ SWR/PowerMeter for sale. $85
with BNC adapters.
Contact me at http://www.abri.net/sq2000/emailpers.html

On Feb 13, 10:04 am, noman wrote:
How well do you think a CB SWR meter will work for testing the antenna
installation in an airplane?

thanks,
tom