Tuning the feedline for my G5RV

[Captain Kilowatt]

My only HF antenna at present is a 450 ohm ladder line fed doublet with 66 foot legs and hung as an inverted V. It works quite well for a simple wire antenna. I bring the ladder line into the basement directly under the shack and connect to a homebrew 4:1 balun (keep meaning to change that out to a 1:1) and then about 10 feet of Belden 8214 coax cable to the shack. Although it does not work as well as the tribander did it is in fact an all bander and I don't have to rotate it. After I finish with some major antenna work this summer I may leave it up as a 80m antenna or as a backup.

 

[HiDef]

OK. I read the article which is basically a proof that a G5RV can work almost as well as a dipole for each band as being argued on QRZ as we type.

Owen suggests trimming the balanced feedline for exactly an electrical half wave. That means that feedline is not performing ANY matching whatsoever on 20 meters.

On other bands the balanced line becomes part of the antenna electrically as far as resonant lengths go.

I see why he's saying that because the antenna is 3 half waves on 20 and is resonant by the old definition I mentioned.

 

[HiDef]

When a 300 ohm balanced line is connected to a 50 ohm load the balanced line acts as a transformer.


There will be a 50 ohm load presented whenever the 300 ohm line is an even number of electrical quarter waves. That's why it's curious that he didn't find a flat match somewhere.


If the frequency sweep results in no 1:1 reading anywhere I'd suspect the dummy load cannot behave as a balanced load. Many can't. You could try a 1:1 BalUn at the load to see if that changes things. A coil of coax ugly BalUn thrown together just for testing can be made from some scrap coax.

 

[HiDef]

(I don't 'like' baluns and don't use them if at all possible. This sort of thing is one of the few exception I'd make to that opinion.)

I love BalUns and use them every chance I get.

W8JI applied to extend the patent on what looks like the BalUn used at an old TV tuner. Interesting to say the least.

Baluns are great. I can see 3 of them from here and I'm not even home yet.

I'll bet this sentence I'm typing is coming to you through a whole bunch of BalUns.

Now there were some cheapie "voltage" 4:1 hammy hambone BalUns that gave BalUns a bad reputation back in the day. Those days are behind us.

Adopt a BalUn.

 

[AE5RD]

balun

I finally got my 1:1 match. I rolled up the extra coax and made a choke of sorts. My tuner is a LDG AT-1000 tuner made for coax connections not ladder line. It even says in my instructions use a balun for ladderline connections. Well everything seems ok now except I need a power supply. I am running on battery power now and I get very little power on ssb. How much power out can be developed using a battery? 20 watts?

 

[SR385]

That's a matter of the voltage drop and level and the radio using it....how it is designed.

So big batteries help keep the drop down as do heavy gauge and short power feed wires.

The design of the radio itself will depend on what power it outputs at 12V DC.

You can increase the size of the batteries supplying it.

You can use heavy gauge wire for feeds to reduce voltage drop.

You can use a 'battery booster' that will bring a 12V battery supply up to 13.8 and maintain it too if the radio doesn't work well at 12V.

 

[HiDef]

I finally got my 1:1 match. I rolled up the extra coax and made a choke of sorts. My tuner is a LDG AT-1000 tuner made for coax connections not ladder line. It even says in my instructions use a balun for ladderline connections. Well everything seems ok now except I need a power supply. I am running on battery power now and I get very little power on ssb. How much power out can be developed using a battery? 20 watts?

Another success thanks to the ugly Balun



BalUns are fun.

 

[bob85]

 

[hookedon6]

Another success thanks to the ugly Balun



BalUns are fun.

i'm kinda confused. he said "I rolled up the extra coax and made a choke of sorts" and you said "Another success thanks to the ugly Balun".

how is one single section of coax rolled into a coil a balun?.

it doesn't convert anything from BALanced to UNbalanced, or transform from (say) 300 ohms to 50 ohms.

all it does is to form a choke coil to help keep rf off the feed line.

 

[HiDef]

i'm kinda confused. he said "I rolled up the extra coax and made a choke of sorts" and you said "Another success thanks to the ugly Balun".

how is one single section of coax rolled into a coil a balun?.

it doesn't convert anything from BALanced to UNbalanced, or transform from (say) 300 ohms to 50 ohms.

all it does is to form a choke coil to help keep rf off the feed line.

A coaxial coil with sufficient reactance to choke common mode current from the outside of the coax shield is effectively a balanced to unbalanced transformer. It will not transform the impedance as you said.

In the example of this thread the 300 ohm feedline itself acts as an impedance transformer in every instance where it is not terminated with a 300 ohm load. That's where a lot of people get lost. The object isn't to match 50 ohms to 300 ohms. The object is to match the load impedance presented by the doublet and the feedline combination.

Just ask the guy who's stuff works NOW because he's using one. The proof is right here a few posts back