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#1
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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 |
#2
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CB SWR meter on 122Mhz?
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 |
#3
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CB SWR meter on 122Mhz?
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 |
#4
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CB SWR meter on 122Mhz?
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. |
#5
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CB SWR meter on 122Mhz?
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 |
#6
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CB SWR meter on 122Mhz?
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 |
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CB SWR meter on 122Mhz?
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#8
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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/ |
#9
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CB SWR meter on 122Mhz?
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 |
#10
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CB SWR meter on 122Mhz?
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 |
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