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Message |
    
Drzuo
Member
Username: Drzuo
Post Number: 77
Registered: 1-2006
| | Posted on Thursday, February 12, 2009 - 9:09 pm: | 
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A friend of mine bought an Imax. He lives very far away and I haven't been out there, been trying to troubleshoot over the phone. Setup: Imax mounted 20 feet above ground on 8' 2" foot mast. the mast is seated on a roof mount on his back porch roof and top mounted just left of the peak of the top floor. a ground wire (which made no difference) connects the mast to a ground rod below.The base of the Antenna is about 3 feet below the peak of the roof and about 5 feet away. His SWR's start at a 5 at 26mhz, drops to a 2.1 on ch1 climb to a 3 on 40 and has slight dips and peaks as you go up, bottoming at a 2.0 on 27.8mhz and then climbing to a 3 at 29mhz. He put a dummy load at the end of his coax and measured flat swrs, so the coax is good. He had a seven foot mast and had same results ( thinking mast was to close to resonant on 11 meter @ 8' 2") Read many reviews where antenna was initially tuned at ground level and achieved similar SWR's to elevated level.( thinking antenna was just too low) Roof reflection is all that's left to consider.(standard shingled roof) Am I missing something? Rings will shift the results slightly but still an swr below a 2 are impossible to obtain. Compared to stations in his area he transmits and receives as good if not better. we have tried 2 swr meters-same readings. All connectors and fittings tightened, sanded, cleaned etc...My setup is very similar except- 1) I have an A99, my porch is 2nd floor and roof peak is on 3rd floor, my antenna is 5 feet above the roof.(my antenna is up 31 feet above ground) My swrs are below a 1.5:1 from 26-28 mhz and very close throughout the entire 10m band. |
Tech565
Moderator
Username: Tech565
Post Number: 137
Registered: 7-2008
| | Posted on Thursday, February 12, 2009 - 10:37 pm: |
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maybe he got a bad antenna??? Can he try a different antenna? With what you are describing, it sounds like his antenna is bad. I had a antenna on a 10ft mast waaay below the roof which was a 2 story house and my swr was never above 1.3:1 from 26-28. Mine was one of those cheap rat shack blue archer antennas and it worked flawless.
Tech565
Net and Asst. Net controller
CVC#38
Ham#243
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Dale
Senior Member
Username: Dale
Post Number: 1410
Registered: 12-2002
| | Posted on Friday, February 13, 2009 - 3:19 pm: |
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one thing ya didnt mention is what type of
swr meter is he using.any other devices hooked inline while doing swr chweck.was he using the
swr meter in the radio?
dale/a.k.a.hotrod
cef426
cvc#64
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Drzuo
Member
Username: Drzuo
Post Number: 78
Registered: 1-2006
| | Posted on Friday, February 13, 2009 - 5:08 pm: |
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Dale, he tried the one in the radio and then a basic SWR meter from radio shack.They both were very close to the same read-out. I know rad shacks aren't so accurate for power readings, but I haven't ever had an issue with SWR. Another thing that caught my attention was the way the SWR curve was, with little bumps and dips all over- which I have seen while designing antennas and plotting well beyond their intended range. There is nothing else in line. |
Slim1
Intermediate Member
Username: Slim1
Post Number: 148
Registered: 4-2002
| | Posted on Saturday, February 14, 2009 - 6:28 am: |
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Metal roof on 2nd floor? Metal siding close to base of antenna? I'd try and borrow another SWR meter to be safe.Also,try a different run of coax;maybe it's bad? Keep us posted.
Slim |
Drzuo
Member
Username: Drzuo
Post Number: 81
Registered: 1-2006
| | Posted on Saturday, February 14, 2009 - 7:55 am: |
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there is aluminum siding. The antenna is mounted above the siding, and above the roof below it, but because its off set, the peak is a bit higher. The coax is new and like I stated he unplugged the antenna and put a dummy load at the end, went downstairs and check SWR's they were flat, so coax is good.Ill attach a pic. This pic is with the shorter mast. It is now about a foot higher. |
Tech808
Moderator
Username: Tech808
Post Number: 16581
Registered: 8-2002
| | Posted on Saturday, February 14, 2009 - 8:26 am: |
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Druzo pic reduced 75%
Lon
CEF#808~HAM#001/N9CEF
CVC#002
Tech808@copperelectronics.com
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Drzuo
Member
Username: Drzuo
Post Number: 81
Registered: 1-2006
| | Posted on Saturday, February 14, 2009 - 8:03 am: |
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more info...... When he calibrates and checks his SWR's, the SWR will rise the longer he is keyed resting about 2 points higher. he is testing with 8 watts. Also he has a variable voltage power supply. If he calibrates and tests under a lower voltage, like 11.5 volts, the swr's are lower than if he recalibrates and checks at 13.8v. Ive seen A99's do this at 1500 watts as the coil heats up, but 8 watts? |
Dale
Senior Member
Username: Dale
Post Number: 1412
Registered: 12-2002
| | Posted on Saturday, February 14, 2009 - 9:07 am: |
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i think when ya hook up a dummyload and read swr
your seeing the swr of the dummyload.its not
really telling ya if coax is good or not.
although being new it should be fine.only way
i know to check coax is with a dvm [digit volt meter]and check the continuety.i honestly
think the antenna needs to be higher.maybe a tri pod on the roof
dale/a.k.a.hotrod
cef426
cvc#64
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Drzuo
Member
Username: Drzuo
Post Number: 82
Registered: 1-2006
| | Posted on Saturday, February 14, 2009 - 9:53 am: |
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If the coax was open or shorted it would have showed high swrs even with the dummy load. The dummy load is used because you know its a near perfect match. Anything off would have been a sign of bad coax. |
Tech237
Moderator
Username: Tech237
Post Number: 1121
Registered: 4-2004
| | Posted on Saturday, February 14, 2009 - 10:54 am: |
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What the dummy load wont show you is if the antennas swr is "off" due to an improper length of coax. Because the dummy load is a near perfect match at a wide range of frequencies it is less effected by coax length than an antenna, which is really a tuned circuit, and thus effective at only a fairly narrow bandwidth.
BY the way Drzuo, I have known a dummy load test to miss a bad coax due the fluke that the coax itself presented a tuned circuit at the test frequency even though the other end was really an open circuit. You really need to test both with a dummy load and with a ohmmeter - testing both end to end continuity and shield to inner open with the far end not connected.
What is the SWR if measure right at the base of the antenna? how long is the length of coax. If you want more information on how coax can effect apparent swr check out the article on Coax Feed lines.
Simon
Tech237
N7AUS
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Skuggi
New member
Username: Skuggi
Post Number: 1
Registered: 2-2009
| | Posted on Saturday, February 14, 2009 - 11:23 am: |
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Hey, finally got setup on the forum here. Here's a new pic of the position when I put up the new mast to get it away from the roof.
I'm also startin to think it's the antenna, but I have yet to read about anyone getting a bad imax. |
Moderator136
Moderator
Username: Moderator136
Post Number: 1349
Registered: 4-2005
| | Posted on Saturday, February 14, 2009 - 12:13 pm: |
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Take the coax off the antenna and radio-- Check with ohm meter. Also check your jumper cables as well. Most of the time its coax going to the through radio - meter - amp - tuner. I solder all my connetions and check them. Allways check coax with a ohm meter before the install.. Saves alot of trouble 9 times out of 10 its a cold solder connection. And yes you could get a bad antenna from the factory and that most likely to be a bad solder joint. I use 60/40 flux core and never had trouble with it. That good old ohm and volt meter saves a bunch of headaces in a long long run. I allmost bet its a short with a jumper and swr meter check it out and let us know?
Hope i helped in some way?
Hal~Moderator136~KCØSVC
CEF#0136/CEF HAM#23 ~ CVC#0004
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Skuggi
New member
Username: Skuggi
Post Number: 1
Registered: 2-2009
| | Posted on Saturday, February 14, 2009 - 12:28 pm: |
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Ok, going to dig out my DMM and check the jumper. I got the cable and the antenna from here, so I think that the cable is good, looks good anyway. |
Drzuo
Member
Username: Drzuo
Post Number: 84
Registered: 1-2006
| | Posted on Saturday, February 14, 2009 - 2:12 pm: |
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You're right Simon, If its shorted at a resonant point in the coax, it could show a good swr. I was thinking well its long enough to be many times a resonant multiple, but that would only matter if the short was at the end, not thinking it could be somewhere in the middle. Skuggi unscrew the coax from the Imax and check with your multi-meter, pin to pin and ground to pin.
Thanks Simon |
Drzuo
Member
Username: Drzuo
Post Number: 85
Registered: 1-2006
| | Posted on Saturday, February 14, 2009 - 2:14 pm: |
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BTW welcome to the forum Skuggi. There is a lot of experience floating around here. We all have our niches, and generally can figure out whats going on. This is an amazing resource, you can spend days reading posts. |
Slim1
Intermediate Member
Username: Slim1
Post Number: 149
Registered: 4-2002
| | Posted on Saturday, February 14, 2009 - 10:07 pm: |
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"What is the SWR if measure right at the base of the antenna?"
Try what Simon is saying here.At least you can rule out the antenna itself this way!!!
Kind of a pain,but,priceless in another way!!!!
73.Slim |
Slim1
Intermediate Member
Username: Slim1
Post Number: 150
Registered: 4-2002
| | Posted on Saturday, February 14, 2009 - 10:12 pm: |
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Just some more ideas here. Whenever I buy a new antenna I always check each section for continuity
individually before I install it. I also always put
the new antenna on a 10'-15' mast/pipe with the exact piece of coax I'm gonna use and prop it up,then check the SWR. I know it's gonna be off a little so close to the ground,but it's a starting point as far as checking everything out first!!!
Good Luck.73.Slim |
Skuggi
New member
Username: Skuggi
Post Number: 2
Registered: 2-2009
| | Posted on Saturday, February 14, 2009 - 11:40 pm: |
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Ok, the jumper is giving me an odd reading. anywhere from .5 - 142 ohm resistance? continutity did check out though. Crack in the copper? Anyways hooked the antenna straight into the radio. Did an SWR check with the meter itself and nothing over 2. Now I guess the question of the day for the easy route is how well can a radio's meter be trusted. I probably won't be getting up to the antenna until tuesday at the earliest to do any testing up there. |
Drzuo
Member
Username: Drzuo
Post Number: 86
Registered: 1-2006
| | Posted on Sunday, February 15, 2009 - 7:43 am: |
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Fill this in Skuggi:
SWR
26.565-
26.765-
channel 1-
channel 20-
channel 40-
27.605 -
27.805 - |
Drzuo
Member
Username: Drzuo
Post Number: 87
Registered: 1-2006
| | Posted on Sunday, February 15, 2009 - 7:53 am: |
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Skuggi, if it is the jumper lemme know and I'll bring you a jumper to work when my mini Vaca is over on Monday. I remember you had this issue pre new swr meter and jumper, which is why you picked up the new meter for a second opinion. Maybe all the little things you were doing worked after all. If that's the case now you know why I wasn't excited about picking stuff up at the shack...lol. I'd return it and order a Dosy from Copper  |
Kf4gyp
Junior Member
Username: Kf4gyp
Post Number: 14
Registered: 11-2009
| | Posted on Friday, February 05, 2010 - 1:23 pm: |
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Helloo Mr. Skuggi
Glad to see you get on here with us and welcome.
The other thought would be to wind 10-15 turns of coax about 6" under the antenna to reduce radiation even further on the coax to smooth out even more on the swr curves. The reason this happens is because the feed line is not isolated well enough from the antenna and the coil of coax creates a choke so stray rf current cannot come back down the coax.These said currents DO NOT ALLOW THE OPERATOR TO STAY COOL WHILE STATION IS IN OPERATION!!!!(grin) Other than that every one that has posted before me has given you some great advice.
73 Ray/Hawk-Eye
DE KF4GYP
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Maxgain
Member
Username: Maxgain
Post Number: 57
Registered: 3-2007
| | Posted on Wednesday, February 17, 2010 - 11:15 pm: |
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My imax 2000 started to show sighns of higher swr for no apparent reason after 3 years of perfect performance.
No matter how the swr rings are ajusted the lowest point in the swr curve is a 1.7 and it used to be a 1.1
Possibly something internal. The constant swaying in the breeze may have stressed an internal connection of some kind or WATER intrusion may be a factor ( possible hairline cracks )
I am thinking about going back to an aluminum antenna of some kind possibly a maco V 58 , or a home-made .60 wave aluminum vertical. |
Charliebrown
Member
Username: Charliebrown
Post Number: 55
Registered: 10-2002
| | Posted on Thursday, February 18, 2010 - 6:45 am: |
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I had an a99 that has had no abuse. One day all my readings changed to the extreme and could not be used. I did as everyone here has done and the one thing that was bad was the antenna. The tech that lives here said there could have been an electrical discharge from lightning near by. Of course things that are man made are subject to go bad on there on just as radios cars and so on. I would check the antenna from top to bottom with the ohm meter as stated earler. There is very good advice here. This is avery good place to learn something new with the changes that are made in equipment from years ago to the equipment of today. Have a good day. Hope you find your problem. |
