What is happening to my SWR?

[montana]

Hello. I am having a problem that started out of the blue. I am using a simple antenna, a G5RV, and now for some reason, it will not load up as it use to. 35 or 40 watts on17, 40, 80, and a very high swr, all but 20. In the past, those bands worked very well, and yes, I have taken the time to check the cables making sure ther are no faults with those that hook up to antenna. Is it possible for the matching transformer on the antenna to have gone bad. Just surprised that after all of this time for it to give up the ghost. Using tube rigs at 100 watts. Tnx for your time & God Bless.
73's
Dennis.

[K4ICL]

One of the reasons I finally took my G5RV down was the difficulty of keeping water out of the balan. I gooped with with silicon rubber, etc. but no matter what, it would get water in it. I suspect water was gaining entrance by travelling down the inside of the wire of the ladder line.

Just a thought. May be worth checking out.

K4ICL

[W4FJF]

Who uses a BALUN on a G5RV? At high swr the balun saturates and will self-destruct. The specified length of ladder line is your transformer, no balun is needed . Browse for the original designs of the G5RV, and you will see that there is NO balun incorporated in the design. A lot of transmitter power is lost in a balun due to "copper loss" and the heating caused by high swr and high power will destroy a saturated balun. I found this out the hard way. My 1:1 balun destroyed itself quite easily one day shortly after I built a G5RV to the specs. Not to mention the line loss caused by a saturated balun, best to use a B&W dipole center insulator to change from the ladder line to coax to bring the transmission line into the shack. The G5RV is an excellent antenna if you construct it right.

[K4ICL]

Who uses a BALUN on a G5RV?

Users who know that the G5RV is a non-resonent antenna capable creating all kinds of radiation problems, upseting neighbors.

Read on...

An eighty foot length of RG/8 unbalanced 50 ohm coax is matched to the approximately 37 foot length of 400 ohm balanced feedline using a 2 kW rated 1:8 balan.

Why?

To match the coax to the ladder line and keep the coax from radiating.

Why?

Keeps the neighbors happier. Not happy, just happier.

K4ICL

[W0LPQ]

Never used one but I gotta get some of that latter line..! May be later than you think..!

73

Bill, W0LPQ

[W4FJF]

my neighbors have yet to complain about TVI, and I use no baluns now. A good E.F. Johnson low pass filter and an excellent ground system does more to eliminate TVI than a "BALAN" (as you call it).

[K4ICL]

W0LPQ: Hmmm. So much for spell checking. Thanks...

W4FJF: You are lucky. BTW, the G5RV I am using is not my design. I used it in Africa for TTY DX. Cheers...

[w2ass]

One of the reasons I finally took my G5RV down was the difficulty of keeping water out of the balan. I gooped with with silicon rubber, etc. but no matter what, it would get water in it. I suspect water was gaining entrance by travelling down the inside of the wire of the ladder line.

Just a thought. May be worth checking out.

K4ICL

i have a van gordan all band dipole, no balan just 450 ladder line to a w9inn 9 to 1 balan thats attches to the house under the gutter, this is brand new never put up. i want to use it. but am i wasten my time then, i use a titan dx vertical for 10 -80 mtrs and i want to use the dipole for 160. what do you think?

i rent a house in wisnton salem till we find something i can put up my towers
we just moved here in june 2005
73

[K4ICL]

First, welcome to the Carolinas. A great place to live and play.

I am not familiar with van Gordon All band dipole and have never used one. Sounds like the under-the-gutter trick ought to work. Worth a try.

Verticals are nice as far as space is concerned and will do a good job for DX when the propogation is good but dipoles are better. Of course, it depends on how you install them.

Good luck on getting on the air at your new locations, when you find it.

Cheers,

K4ICL

[k8ag]

Hi Dennis,

I have been using a ZS6BKW for several years now. Its based on the G5RV but has different lengths and better swr and band coverage.

The transformer section also radiates and so you might check to see if it is near metal objects or the ground. If something is nearer than it was when the swr was OK you may need to move it round.

A "current" balun (I use 12 or so turns of coax) does help keep RF from the shield of the coax. If you have a balun that is what I would suspect first. The antenna should work without the balun, but RFI sensitive equipment may be effected by the RF on the coax shield. You could connect directly to the transformer section and see if it cures the SWR problem. If so I would simply replace the balun with 10 or 12 turns of coax around a 2-liter bottle.

Hope this helps.