Home > Uncategorized > G5RV (ZS6BKW) Antenna Working Well at Last

G5RV (ZS6BKW) Antenna Working Well at Last

Well I finally got around to pulling the ZS6BKW antenna down. Despite a good VSWR it was performing poorly and was very noisy on receive.

I checked it all over and found a bad joint at the braid connection to the feed-line socket. I fixed this, and while I was at it, I decided to finally properly terminate the feedline as best I could with the coax, using a 1:1 current balun wound onto a #43 ferite torroid, in a last ditch effort to beat the RX noise problem. I am surrounded on two sides by high tension power lines about 500 meters away, so I wasn’t confident of success, but the Bushcom antenna is quiet, so I hoped I could get something close to that. Obviously a terminated antenna is going to be quieter but I was sure the ZS6BKW could be a lot quieter than it was, and given its poor TX performance, I was sure I could fix it.

Feed-line (coax) loss on a G5RV is high at 3 MHz, and given the simple termination of my coax/ladder line, I hoped the 1:1 balun would help here too.

References-

Coaxial transmission line

An indeterminate length of coaxial line connects the parallel line /balun to the ATU near the transmitter. The coaxial transmission line is usually the single greatest contribution to poor efficiency. Fig 2 shows the contribution to loss of the three main loss components for a G5RV using nominal 450Ω ladder line and 15m of RG58C/U to the ATU.

Fig 2: Typical G5RV antenna system losses.

Optimising a G5RV is about adjustments to minimise feedline losses, and mostly the coaxial line loss.-

http://www.vk1od.net/G5RV/optimising.htm

After a few hours of balun making and antenna fixing, the antenna was up again and working brilliantly. I got greatly improved sig reports from local stations, so let’s hope it stays that way.

Sealed Balun

I wound enamelled copper wire onto a 1.5 inch ferite torroid of #43 material. I then wrapped it in self amalgamating tape (Isobond). The whole thing was then placed in an aluminium case which was fixed to the aluminium tower and earthed.

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