Ham Radio - The Doublet antenna, QSOs and observations.

I "ass"ume you're one of the "experts" I mentioned. Funny!
I simply do business as usual. Real life, actual experience is what counts and I have thousands of feedback comments to back up the "anecdotes", unlike most on here.
Carry on.....................................
There's one in every crowd.
Brian
http://www.trueladderline.com

 

Well, yes. The thread was started by a ham trying to make us aware of the advantages of the doublet and somehow it ended up a discussion of whether a 4:1 or 1:1 balun was appropriate. I have a 4:1 Balun Designs as recommended by Brian from trueladderline and the antenna works very well. The doublet is a very effective, classic antenna and if you look at the FAQ on his website, you will some great analysis of why and how it works. As you point out, it’s great when you have trees and no towers.

 

I just tried to add another perspective and show how to get more versatility out of an open wire fed doublet, for cheap. Full output, full signal 160m operation can be achieved with an 80 meter doublet if you use a 1:1 balun on the input side of the antenna coupler and tune reactance out on the balanced portion of the feed line. This way has very little loss. Will work on a very low or very high impedance load. The 4:1 or 1:1 debate becomes irrelevant if these methods are used. Using a balun on input (1:1 is the only thing that makes sense in this application) and zeroing reactance on each portion of the balanced line is more effective than any other method discussed in my opinion. Everyone mentions using their balun on the OUTPUT of an unbalanced tuner, (4:1 , 1:1 , whatever) which is not what I am suggesting. So there you go, take it or leave it! Doublets can do amazing things.

 

I went back and looked at your drawing. If I understand this correctly, you have to bring the ladder line into the shack, or the tuner must be outside. Is that approach cheaper or more effective? It seems to me that using a 4:1 balun is simpler because the ladder line stays outside and the tuner stays inside. What say you?

 

Yes, I think so. It's not hard to do. I mentioned a few ways in a previous post. A 15$ piece of lexan in a window makes a nice pass through insulator for balanced line for instance. A garbage bag makes a very cheap and effective weatherproofing for a tuner, I know a guy who had his like that for 2 years. Works fine, another fellow is using it currently. Using a 4:1 to bandaid the output of an off the shelf tuner is much simpler. You're right. But it doesn't work as well at all.

My tuner is inside my shack on the wall. The line goes up through the shack ceiling through insulators, then out the attic roof through 1" OD 3/8" ID teflon sleeves (teflon rod 20$ at hamfest, cut in half and each piece drilled through) and weather boots. Pics on my qrz page. Some effort went into it, but the materials used were cheap and the end result was a doublet antenna that is far more effective in multiband operation.

 

I am getting back on the air after years of inactivity. HF and CW. I will use some of the variable caps I've kept for years and build an antenna tuner. Then build the ladder line, 16 AWG wire, plexi squares
and tie wraps. Then take advantage of the several acres available for long wire and dipole antennas. I'll try to get the wire up 30' or more, the trees surrounding the property go up higher. First licensed in 1959.

 

Α lightweight (<4Kg) 5+5m rotary dipole (aka doublet) fed with 450 Ohm open wire, balun and wide range tuner.
My all time favorite 20-10m antenna when conditions do not allow something bigger.

Even fixed oriented E/W never felt that I'm using a compromise antenna much weaker actually than my primary one, a > 25Kg Mosley beam.

 

I just looked at the performance of my doublet with the 4:1 balun. SWR 1.8:1 on 160, 80 & 40. On 30, 20, 17, 15, 12 & 10, 1:4.1 or lower. All full power (100W) CW.

 

Nice! I never thought of trying a variable inductor. Keep on spreading the good word. Some krazy kids like us might end up building something.

 

That's good. You should be able to enjoy the hobby with that. I can get 1:0:1 X=0 on any HF band.

Yes, sometimes it's what you need!

 

Bringing balanced line in to the house is just as easy as coax.

You use TWO pieces of coax. Shields tied together and each side of the open wire line tied to a respective lead of the open wire line. This is an electrostatic shielded open wire line.

A 4:1 balun is designed for 200:50 ohm conversion. It has been proven multiple times that using it to go from say 1k:250 ohms will result in lots of loss, cracked cores, etc.

I have a VNA at home (2 as a matter of fact) and have looked at this myself. Loss measured in multiple dBs because of Balun mismatch.

The amount of Baluns sold doesn't really matter. A lot of people think the G5RV is a great antenna as well.



Yes, using a 4:1 balun can help with mismatch as well as help a subpar tuner reach higher impedances than can be done without. But that doesn't mean you are doing it efficiently.

--Shane
KD6VXI

 

That should be a 4:1 balun that is designed for 200:50 ohm conversion HAS been proven blah blah blah.

Sorry for the typo / syntax. Typing on the phone.

--Shane
KD6VXI

 

My 4:1 balun has 600 Ohm line in and 50 Ohm Rg8X out. The SWRs are as noted above and the balun runs cool. I do not know what more to add.

 

It all depends on balun / core quality. My 4:1 balun (DX Engineering DXE-BAL200-H10-A) with 450 Ohm solid open wire line runs cool as cucumber on all bands even with max QRO.