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Author Topic: How to resonate 4btv traps  (Read 1556 times)
WT8E
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Posts: 55




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« on: September 09, 2010, 06:46:46 PM »

I have a Hustler 4BTV vertical antenna and a friend loaned me his MFJ analyzer.  I have the antenna apart for cleaning and some repairs. Is it possible to couple the individual traps to the MFJ unit to see the resonance of the trap? I would like to see what freq. they are set at. Or, does the antenna have to be assembled to get that information.

73
Walt
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K8KAS
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Posts: 569




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« Reply #1 on: September 10, 2010, 05:44:41 AM »

Walt---Put the antenna up per the book and install a radial system. I hope you do that is. Set the antenna lengths per the instructions in the book and you should be fine. the traps themselves are tuned from the factory so don't mess with them. I have used/owned 3 or 4 of these over the years and never had a problem. A antenna anzlr really helps getting the antenna tuned by sliding the sections up or down below the traps. This is a 1/4 wave antenna and is quite broad. Don't forget the radials without them it's just a dummy load. 73 Denny K8KAS
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W0FM
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« Reply #2 on: September 10, 2010, 12:09:06 PM »

Like Denny, I also have owned a number of 4, 5 andf 6BTV's.  Heed the warning about not messing with the traps.  That type of action is pretty much for extreme cases as the BTV's seldom need to have the (factory tuned) trap settings changed.  I accidentally did that to one 5BTV and fought with the traps for weeks trying to get them right again.

73,

Terry, WØFM

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K2QPN
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Posts: 70




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« Reply #3 on: September 11, 2010, 03:31:00 PM »

I would not adjust the traps unless you cannot adjust the antenna normally. I bought a brand new 6BTV and I could not reach resonance without adjusting the traps. I marked current trap position and moved the adjustment one quarter inch at a time. I got the antenna adjusted and all is well. DXEngineering.com has the trap adjustment procedure in their installation manual - http://www.dxengineering.com/pdf/BTV-INSTALL-GUIDE-Rev0.pdf

Good luck and 73, Bob K2QPN
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N8CMQ
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Posts: 379




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« Reply #4 on: September 11, 2010, 06:51:58 PM »

Walt, do you have the new style or old style of traps?
The old style has a cylinder capacitor with screws, the new style has a tapered bottom.
Anyways, if you use a GDO and receiver to track the frequency accurately, tune the trap by sliding the cap up and down till the frequency dips at a slightly lower frequency, like 26 or 27 MHz for ten meters.
Just lightly couple the GDO to the trap, no link, just capacitive coupling at the non shorted end.
Lightly tighten the screws on the old style till you get it set. The new style uses hose clamps.
Oh ya, if you use an antioxide coating, be sure it isn't covering the coil, it can detune the trap.
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N4CR
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Posts: 1672




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« Reply #5 on: September 11, 2010, 11:36:05 PM »

If you are going to dip the traps, you need to do it with all of the sections assembled. If you take a trap out and place it on a non-conductive surface it will dip a long ways from where it is resonant when it's all assembled. Been there, done that.

I got my 5BTV from someone who had moved the traps and it would not tuned up. I found that setting the traps to the published measurements worked well and I was able to get it to tune right up once that was done.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
WT8E
Member

Posts: 55




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« Reply #6 on: September 14, 2010, 02:13:44 PM »

Bob. K2PNQ tnx for the link.  That pretty well describes all the actions needed to reassemble the antenna. This antenna has the old style sleeve on the traps. I acquited it from an estate and it has been in use for 38 years as near as I can tell form the original paperwork and the statement from the widow. The bolt was broken on the 20 meter trap and let the sleeve slide down. I noticed some rust streaks on the aluminum tubing below the traps.  all the caps were cracked and let water run inside them.  On the 15 meter trap it played havoc with the rivits on the coil where it fastened to the tubing. Repairs had to be made to insure a good connection.

I figured I could get pretty close with the measurements and then do the final tuning, I was just curious if I could get a reading on the traps out of the antenna.  with the new caps on the sleeve on the trap will hardly move, so it looks like I will have to remove them and free up the sleeve. I bought a new set of caps for $10 (4) so when I get done it should be just about like new. I have cleaned all mating surfaces for a good connection.  I took a small wire wheel and modified it to go inside the tubing so that looks like new again.

I also got a Drake TR3 station in the estate along with a L4B, W4 wattmeter, a speaker , phone patch and various jumpers and wires.  I have had the TR3 on the air on 20 meters but the L4B is still just sitting there. Maybe I will get to it this winter.  It will be for sale or trade when I get it done.  Thanks again guys for all the help.

73 Walt
WT8E
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