Possible SWR problems with 70cm antenna
I'm having some problems with a homebrew lineasrly polarized "cheap yagi" for 70cm. I don't have any success hearing myself on VO-52 or AO-7. This antenna used to work reasonably well for both. The way the power out meter on my radio acts, it leads me to believe I may have an SWR issue. Unfortunately I don't own or have access to an SWR meter or anylyzer capable of working at 70Cm. I'm going to take a wild shot in the dark here and ask the bb because I sure don't know. Would it be possible to put my 2 meter SWR meter in the 70cm line and at least get a ballpark figure of SWR? Or would the reading be so far off, it would be useless? I'm not intending to try and tune the antenna in this manner, I just want to get some indication as to if SWR is indeed the problem. I must confess I don't know what the frequency range determining elements of an SWR bridge are. I must have missed that at some point or the other. Any other ways to determine if I have an SWR problem without a meter? It's just not in the budget to buy one right now. Any suggestions are appreciated. Tnx and 73, Michael, W4HIJ
Michael, I doubt a 2 meter SWR meter will give you any type of useful information for 440. Many are rated for 1.8 Mhz - 148 Mhz or similar.
Before you blame the antenna, take a look at your coax, primarily the connectors. Make sure the connectors and the coax don't twist if you attempt to move them.
You didn't mention what type of rig you are using. Or how difficult it would be for you to get a close look at the antenna. Since it's homebrew, whatever system you used to match it, might have moved. Consider testing it on the FM part of the band, and see if your rig complains.
If it doesn't, then that's your answer. Your tuning method isn't working. Or, try using a local 440 repeater and see if a local ham will loan you an SWR meter that will work on 440.
73 de W4AS Sebastian
On Jun 3, 2008, at 8:33 PM, Michael Tondee wrote:
I'm having some problems with a homebrew lineasrly polarized "cheap yagi" for 70cm. I don't have any success hearing myself on VO-52 or AO-7. This antenna used to work reasonably well for both. The way the power out meter on my radio acts, it leads me to believe I may have an SWR issue. Unfortunately I don't own or have access to an SWR meter or anylyzer capable of working at 70Cm. I'm going to take a wild shot in the dark here and ask the bb because I sure don't know. Would it be possible to put my 2 meter SWR meter in the 70cm line and at least get a ballpark figure of SWR? Or would the reading be so far off, it would be useless? I'm not intending to try and tune the antenna in this manner, I just want to get some indication as to if SWR is indeed the problem. I must confess I don't know what the frequency range determining elements of an SWR bridge are. I must have missed that at some point or the other. Any other ways to determine if I have an SWR problem without a meter? It's just not in the budget to buy one right now. Any suggestions are appreciated. Tnx and 73, Michael, W4HIJ _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
"... The way
the power out meter on my radio acts, it leads me to believe I may have an SWR issue. Unfortunately I don't own or have access to an SWR meter or anylyzer capable of working at 70Cm..."
You don't mention what rig you have but many of the modern transceivers have High SWR protection circuits and will cut back on the power as evidenced by the meter already in the rig in the presence of return power.
If you have a good dummyload, note the power meter reading directly into it. It ahould be high on the scale. Then compare it to your antenna meter reading. If it drops down it's time to start isolating parts of the antenna system using the same method.
Watch your coaxial jumpers. Your connecters as previously noted, and one stab in the dark...check your power supply voltage to make sure you are maintaining your 13.6 os so on transmit. RF into some power supplies drives them funky.
Maybe you can borrow a meter from a club member or just rebuild the whole shooting match. You already have all the parts. There is not much to those antennas so I would assume, if you have a problem it is coax or matching connections related.
Roger WA1KAT
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From: [email protected] To: [email protected] Date: Wed, 4 Jun 2008 08:01:27 -0400 Subject: [amsat-bb] Re: Possible SWR problems with 70cm antenna
"... The way
the power out meter on my radio acts, it leads me to believe I may have an SWR issue. Unfortunately I don't own or have access to an SWR meter or anylyzer capable of working at 70Cm..."
You don't mention what rig you have but many of the modern transceivers have High SWR protection circuits and will cut back on the power as evidenced by the meter already in the rig in the presence of return power.
Actually, I've seen the reverse - the meter on my Yaesu 767GX seems to read higher when the match is going bad. Seems like it's reading both the forward and reverse power and adding them together. So, you get a higher number when in fact the transmitter is putting out less. Counting some of the the watts twice.
But, back to the original problem, you might consider making something simple as a 1/4 wave ground plane antenna, or using the rubber duckie from your HT, and putting it in place of the suspect one. Think of it as a slightly radiating dummy load, which it is. Just watch the power rating if you use your HT antenna.
Greg KO6TH
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My thanks to Sebastian and all the other kind folks who have reponded to my query. A little more information seems to be in order. My rigs here are an Icom 820H and a 706 MKIIG. I can test with either. The antenna used to work when I had a TS-2000X and An ARR preamp. I had to get out of the radio game awhile and sold both those. In addition to the rigs mentioned above my mast mount preamp is now an Icom AG-35. I did do some swapping around of cables between when it worked and now but I've checked all of that I know to check. The cable between the shack and preamp reads good with continuity in the center conductor and the shield and no shorts in between. If you are familiar with the driven element design on Kent Britains's "cheap yagi" antennas you will understand that the coax between it and the receive preamp will read a dead DC short. However, I have disconnected the coax from the element and I have continuity in the center conductor and continuity in the shield with no shorts between them.. The behavior of my 820's meter is such that if I key the rig on 70cm on high power, the needle of the meter pins to the max. It's always been my experience that this can sometimes be an indication of some type of problem in the antenna circuit. I don't really wish to leave either rig keyed until the SWR protection kicks in. It's not hard to get to the antenna so I guess I'll go over everything again. Unfortunately there is not a 70cm. repeater within range of my QTH for me to test with. At least not one with published frequencies that I can find. BTW I don't even own a dummy load, HF or otherwise, I know I need one but my budget is very tight right now and I'm lucky to have the gear I've got. I'm also kind of a lone wolf, I don't belong to any clubs where I can borrow equipment. Years ago when I used to work at HRO and needed a meter, I'd just borrow the store display model overnight! I miss those days...hi hi Tnx and 73, Michael, W4HIJ ----- Original Message ----- From: "Sebastian" [email protected] To: "AMSAT-BB BBs" [email protected] Sent: Tuesday, June 03, 2008 10:20 PM Subject: [amsat-bb] Re: Possible SWR problems with 70cm antenna
Michael, I doubt a 2 meter SWR meter will give you any type of useful information for 440. Many are rated for 1.8 Mhz - 148 Mhz or similar.
Before you blame the antenna, take a look at your coax, primarily the connectors. Make sure the connectors and the coax don't twist if you attempt to move them.
You didn't mention what type of rig you are using. Or how difficult it would be for you to get a close look at the antenna. Since it's homebrew, whatever system you used to match it, might have moved. Consider testing it on the FM part of the band, and see if your rig complains.
If it doesn't, then that's your answer. Your tuning method isn't working. Or, try using a local 440 repeater and see if a local ham will loan you an SWR meter that will work on 440.
73 de W4AS Sebastian
On Jun 3, 2008, at 8:33 PM, Michael Tondee wrote:
I'm having some problems with a homebrew lineasrly polarized "cheap yagi" for 70cm. I don't have any success hearing myself on VO-52 or AO-7. This antenna used to work reasonably well for both. The way the power out meter on my radio acts, it leads me to believe I may have an SWR issue. Unfortunately I don't own or have access to an SWR meter or anylyzer capable of working at 70Cm. I'm going to take a wild shot in the dark here and ask the bb because I sure don't know. Would it be possible to put my 2 meter SWR meter in the 70cm line and at least get a ballpark figure of SWR? Or would the reading be so far off, it would be useless? I'm not intending to try and tune the antenna in this manner, I just want to get some indication as to if SWR is indeed the problem. I must confess I don't know what the frequency range determining elements of an SWR bridge are. I must have missed that at some point or the other. Any other ways to determine if I have an SWR problem without a meter? It's just not in the budget to buy one right now. Any suggestions are appreciated. Tnx and 73, Michael, W4HIJ
On Tue, Jun 03, 2008 at 08:33:11PM -0400, Michael Tondee wrote: ...
I'm going to take a wild shot in the dark here and ask the bb because I sure don't know. Would it be possible to put my 2 meter SWR meter in the 70cm line and at least get a ballpark figure of SWR? Or would the reading be so far off, it would be useless?
My advice is to stick your swr bridge on a 70cm line with a 50 ohm dummy load and see how close it reads to 1:1. It's possible it might work.
- 73 Diane VA3DB -- - [email protected] [email protected] http://www.db.net/~db
----- Original Message ----- From: "Michael Tondee" [email protected] To: "amsat-bb" [email protected] Sent: Wednesday, June 04, 2008 2:33 AM Subject: [amsat-bb] Possible SWR problems with 70cm antenna
I'm having some problems with a homebrew lineasrly polarized "cheap yagi"
for 70cm. I don't have any success hearing myself on VO-52 or AO-7. This antenna used to work reasonably well for both. The way the power out meter on my radio acts, it leads me to believe I may have an SWR issue. Unfortunately I don't own or have access to an SWR meter or anylyzer capable of working at 70Cm.
I'm going to take a wild shot in the dark here and ask the bb because I
sure don't know. Would it be possible to put my 2 meter SWR meter in the 70cm line and at least get a ballpark figure of SWR? Or would the reading be so far off, it would be useless?
I'm not intending to try and tune the antenna in this manner, I just want
to get some indication as to if SWR is indeed the problem.
I must confess I don't know what the frequency range determining elements
of an SWR bridge are. I must have missed that at some point or the other.
Any other ways to determine if I have an SWR problem without a meter? It's
just not in the budget to buy one right now.
Any suggestions are appreciated. Tnx and 73, Michael, W4HIJ
Hi Michael, W4HIJ
To measure the VSWR with accuracy you can build by your self a set of inexpensive directional couplers ranging from 100 MHz to 10 GHz using semirigid coax cables as described into the RSGB Microwave Handbook Volume 2 pages 10.13 to 10.18
73" de
i8CVS Domenico
participants (6)
-
Diane Bruce -
Greg D. -
i8cvs -
Michael Tondee -
Roger Kolakowski -
Sebastian