High SWR on Hy-Gain TH3MK3

[VE3FMC]

If I had those swr readings on my two element TA-33 I would be as happy as a pig in mud.

Who says you can not use a tuner on a trap antenna?

[VA3GUY]

TOM:  If you download the assembly manual for the TH3MK4, it states in the manual that the BN-86 is a voltage-balun.  That's where I found that information.  In the TH3MK3 manual, they do not say that about the BN-86 though.

In the TH3MK3 manual, they recommend the BN-86 but are not clear on lengths of wire from it to the DE or from the DE to the beta match.  I based my 6" wire leads on the distance from each when assembled.  In other words, when the beta match is assembled and mounted, there is approx a 4"-5" space from the match to the DE so I chose 6" for the wires.

ALL:  As I stated, when I assembled the antenna, I was very careful to use the specs recommended.  The antenna was assembled for the CW portion.  I know about lengthening and shortening the elements to adjust (tune) the antenna.  The numbers I posted originally are the best I can get.  There isn't too much more adjusting I can do as the tubes are lengthened almost at their ends.

I will try a few of the suggestions here and hopefully have some good results.

Thank you all...

[K8AXW]

GUY:  I haven't gone to my filing cabinet to locate the assembly manual for my TH6DXX (Now TH7DX with the additional elements) to see exactly where the adjustment information is.

It is QUITE POSSIBLE that the information came directly from Hy-Gain (before MFJ bought them out) because I had major problems getting the resonant points right for the 3 bands.  I ran SWR graphs on each band.  They were all messed up and I called Hy-Gain a couple times for help.  I finally got the element lengths adjusted quite well. 

I use the BN-86 balun, which was sold and recommended by Hy-Gain.  I also used their wire jumpers to connect the balun to the antenna.  This meant the balun was located where Hy-Gain suggested it be mounted.

I suggest a phone call to MFJ (or the Hy-Gain contact number) and discuss this problem with them.  Plan B would be to research the procedure for tuning a trap dipole which will be the same procedure for the beam. 

I would avoid using an antenna tuner to "correct" the unacceptable SWR on the one band. 

I mentioned tuning this antenna will be a PITA but it's the only way.  If you can get someone to help you the process will go much faster.

[W8JI]

TOM:  If you download the assembly manual for the TH3MK4, it states in the manual that the BN-86 is a voltage-balun.  That's where I found that information.  In the TH3MK3 manual, they do not say that about the BN-86 though.

I was involved in modernizing the BN-86 about 15 years ago. It is a current balun.

In the TH3MK3 manual, they recommend the BN-86 but are not clear on lengths of wire from it to the DE or from the DE to the beta match.  I based my 6" wire leads on the distance from each when assembled.  In other words, when the beta match is assembled and mounted, there is approx a 4"-5" space from the match to the DE so I chose 6" for the wires.

I'm a little confused by that. Do an SWR sweep if you can and post the lowest SWR frequency.

Maybe your antenna elements are too long.

[G3OAG]

My TH3 has been up for around 15 years and tuned to the CW end of each band where the SWR is at it's lowest. I use an simple L-match if I venture up to the phone part of the band, which easily brings the SWR down. No problems experienced with this setup. The need for a tuner is mostly needed on 14Mhz, where the SWR would be around 2.5:1 at 14260khz without it. 15 & 10m are much flatter in their response.

Steve, G3OAG