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eHam Forums => Antennas and Towers and more => Topic started by: AF5FH on May 02, 2013, 12:38:06 PM



Title: Advice on fixing my AV-640 vertical
Post by: AF5FH on May 02, 2013, 12:38:06 PM
Would appreciate advice on fixing my Hy-Gain AV-640 vertical.

When I transmit on 20 meters, the SWR starts out as 1:1, and then jumps to over 5:1 after transmit for a few seconds. Output power drops (Icom IC-718 is probably protecting itself). Sometimes after transmit for a while, SWR jumps to 1:1 and stays there for a while, then jumps to over 5:1.

I don't have this problem on any other band. SWR stays low on all other bands, even after transmit for minutes.

I have tried disconnecting coax at the antenna and connecting the whole length of coax to a dummy load. SWR stays at 1:1 with dummy load even after several minutes, so I think Icom IC-718, entire length of coax, and all connectors are fine.

Since the antenna is on a roof tripod, I need to arrange for a helper, and it is a chore to take down and put back up. If possible I would like to take it down one time, fix it, put it back up, and be done. Any suggestions on fixing this antenna?

Thanks!

Jim, AF5FH


Title: RE: Advice on fixing my AV-640 vertical
Post by: KD2CJJ on May 02, 2013, 01:15:48 PM
It's the matching bing network base on the symphthom.  The black box.

It could be the torrid went bad or one of the caps (if it has)...



Would appreciate advice on fixing my Hy-Gain AV-640 vertical.

When I transmit on 20 meters, the SWR starts out as 1:1, and then jumps to over 5:1 after transmit for a few seconds. Output power drops (Icom IC-718 is probably protecting itself). Sometimes after transmit for a while, SWR jumps to 1:1 and stays there for a while, then jumps to over 5:1.

I don't have this problem on any other band. SWR stays low on all other bands, even after transmit for minutes.

I have tried disconnecting coax at the antenna and connecting the whole length of coax to a dummy load. SWR stays at 1:1 with dummy load even after several minutes, so I think Icom IC-718, entire length of coax, and all connectors are fine.

Since the antenna is on a roof tripod, I need to arrange for a helper, and it is a chore to take down and put back up. If possible I would like to take it down one time, fix it, put it back up, and be done. Any suggestions on fixing this antenna?

Thanks!

Jim, AF5FH


Title: RE: Advice on fixing my AV-640 vertical
Post by: WB2WIK on May 02, 2013, 02:20:54 PM
It's odd the problem would occur only on 20m, considering its design; but anyway, sounds like a bad connection at the 20m loading coil, or the "L20" tuning spokes (4 of them), or the coil strap at the 20m coil connection.

I'd take it down, carefully inspect, make sure all connections (hardware) is very tight, including the tubing clamps.  I hope you used an anti-oxide compound like NoAlOx or similar during assembly, otherwise intermittencies can occur where the tubing sections join and you can't visually see that.


Title: RE: Advice on fixing my AV-640 vertical
Post by: AF5FH on May 02, 2013, 02:52:44 PM
Thanks for the suggestions!

KD2CJJ, I took the cover off the black box. Can't see anything wrong with the toroid or the connections inside the box.

WB2WIK, I will take the soldering iron up to the roof with some solder. If it is a cold solder joint, that would be Hy-Gain fault, and I can fix that. If one of the tuning spokes is loose, then it would be my fault. I used Penetrox A, and tightened everything. Ended up with gray colored hands when I was done. But I still have lots of Penetrox left, so I can re-do the "L20" tuning spokes.

Thinking about spray painting the antenna flat black while I have it laying on roof. The bare aluminum is pretty noticeable on sunny days.


Title: RE: Advice on fixing my AV-640 vertical
Post by: W9GB on May 03, 2013, 03:58:38 AM
Quote from: AF5FH
WB2WIK, I will take the soldering iron up to the roof with some solder. If it is a cold solder joint, that would be Hy-Gain fault, and I can fix that. If one of the tuning spokes is loose, then it would be my fault.
Tin/Lead solder & a soldering iron will not resolve (fix) Aluminum connections.

Due to the weight/mass of the upper section on this antenna (and R7, R7000, R8), IF this antenna did not have small non-conductive guy wires -- the constant flexing in wind can loosen connections.

The new Cushcraft R9 states usage of guys, for the same reason.


Title: RE: Advice on fixing my AV-640 vertical
Post by: AF5FH on May 03, 2013, 05:56:39 AM
Tin/Lead solder & a soldering iron will not resolve (fix) Aluminum connections.

Due to the weight/mass of the upper section on this antenna (and R7, R7000, R8), IF this antenna did not have small non-conductive guy wires -- the constant flexing in wind can loosen connections.

The new Cushcraft R9 states usage of guys, for the same reason.

My AV-640 has three non-conductive guy ropes supporting it at 14 feet above the base per Hy-Gain instruction manual. See picture on my QRZ page.

About the connections to the 20m loading coil, I will have to wait until I get the antenna lowered. I recall from when I assembled it that the coil assembly for 40m, 30m, 20m came as one assembled part in the box.


Title: RE: Advice on fixing my AV-640 vertical
Post by: KQ6Q on May 04, 2013, 01:36:57 AM
when you have odd problems on one band on a multiband antenna, the problem can be that the feedline is an odd multiple of 1/4 wave on that band. Try adding a short piece of coax (1-2') to the feedline on the shack end of the cable,and see if the problem disappears.


Title: RE: Advice on fixing my AV-640 vertical
Post by: AF5FH on May 04, 2013, 09:09:53 AM
when you have odd problems on one band on a multiband antenna, the problem can be that the feedline is an odd multiple of 1/4 wave on that band. Try adding a short piece of coax (1-2') to the feedline on the shack end of the cable,and see if the problem disappears.


I will need to get a female to female coax connector so I can easily add a short coax jumper inline inside the house. When this SWR problem first happened about a week ago, I thought my coax from rig to antenna  might be the cause, so I swapped that coax out with a 50 foot coax jumper I have. Ended up wrapping the coax jumper extra length around the roof tripod, since it is longer than needed. Anyway that swap did not fix the problem. And then connected end of coax to dummy load on roof, while showed me that entire run of coax from rig to roof was fine.

Later today my son and I plan to lower the antenna to saw horses. I hope I can find the problem and fix it while the antenna is down.


Title: RE: Advice on fixing my AV-640 vertical
Post by: AF5FH on May 04, 2013, 10:29:24 AM
My son helped me lay the antenna down. I think I found the problem. See link to attached picture. http://i300.photobucket.com/albums/nn13/jimk0512/IMG_2757_zpse97019e4.jpg (http://i300.photobucket.com/albums/nn13/jimk0512/IMG_2757_zpse97019e4.jpg)
The screw holding the strap to the bottom of the 20m coil to the antenna is loose, and the nut is about to fall off. The entire coil assembly came per-assembled from the factory. Per their instructions, I took the coil assembly and connected it to the rest of the antenna. Never touched their connections. Clearly that was a bad plan. I am now re-doing all the Hy-Gain provided mechanical connections on the antenna. Grumble, grumble, grumble, "trust but verify", I should have known better ...

Hopefully this will fix the intermittent high SWR problem with 20m.


Title: RE: Advice on fixing my AV-640 vertical
Post by: AF5FH on May 04, 2013, 04:10:28 PM
OK, tightening the loose connection to the strap at the bottom of the 20m coil fixed the problem. Painted the antenna while it was laying down. Used cheap flat black spray paint from Home Depot. Here is a picture of the antenna after painting http://i300.photobucket.com/albums/nn13/jimk0512/IMG_2758_zps11ea559e.jpg (http://i300.photobucket.com/albums/nn13/jimk0512/IMG_2758_zps11ea559e.jpg)

I'm not sure flat black is a good color to make this antenna less obvious to the neighbors. Better than bare metal by a lot, but it still seems pretty obvious to me. Hopefully the black will fade over time with all the UV we get here, and the high winds in the spring and fall sandblasting it. I don't think I will be taking it back down and painting it a different color any time soon.  :)

Jim, AF5FH


Title: RE: Advice on fixing my AV-640 vertical
Post by: WN2C on May 04, 2013, 04:35:34 PM
Well, I would have used self tapping screws to put it together.  Had a 7000 and it came loose on a few of the joints.  Had to take it down to tighten, so I used self tappers in 2 spots (offset) so it wouldn't come loose.  Then the ground strap let go after a while.  Took it back down and took it apart.  Left the antenna outside and brought in the matching box inside to the garage.  Then had a fire in the garage and lost the box (melted goo) in the fire.  I wish I could find a matching box, but with all the trouble this antenna has given me I am not sure why.  HI HI.  I think Murphy came with it. 

Rick  wn2c