Ham Radio - The Doublet antenna, QSOs and observations.

Ham Radio - The Doublet antenna, QSOs and observations.

 

I am very jealous! I've never heard a ZS on SSB, but every once in awhile I see a station on FT-8, but they never seem to hear me... It looks like your doublet is a pretty good setup! how high was it?

 

Outstanding!

 

I run 2 160m doublets, one broadside NW/SE and the other NE/SW. Unfortunately one of the legs of the NE/SW broke off and I have to reattach it but the surviving leg acts like a long wire. I've had excellent reports off of both with very little line loss on transmit. I just wish I had trees that were more than 40-45 feet tall to act as supports.

 

I run a 102' doublet fed with 450 ohm window line. It's an inverted vee and even though the center is only about 20' in the air it works really well for me.

 

I use a 66ft doublet at about 25ft high,Its quite good but would be better if higher.

 

Merry Christmas and HNY to all.
I think doublet is one of the better multiband antennas, I am using one (10-40m) with decent results from qrp to 100W maximum 73

 

135' with 4" spaced ladder line at 50' here. I made it from 4" electric fence insulators and tyraps.

 

My Doublet antenna system controlled via remote..

 

I was ready to build a doublet, but trueladderline had them at good prices and I bought a 125’ 80-10 version. I had a tough time getting it to work properly due to ignorance, but when I squared away the RF and SWR problems it works very well. I hardly ever use my OCF dipole antenna.

BTW, under FAQs on trueladderline, they have Dick Cebik’s article “The All-Band Doublet”, which I recommend to all those interested. He is a SK now, but he was a great technical writer. I learned a lot from that article.

 

On the topic of doublets, has anyone figured out what's the best balun for a 600-ohm ladder line? I'm using a 4:1 but I'm thinking that that may not be enough. I know the SWR is still very high but I think my MFJ autotuner is handling it. I was thinking of a 12:1 but not sure....

 

I’m using a 4:1 from Balun Designs and a MFJ 939 tuner. Highest SWR is about 1.8:1 on 40M. Other bands 1.3 and very close to 1:1 20 and up. These SWRs are after the tuner has done its magic - untuned SWRs can be very high with ladder line. Is your ladder line clear of other structures? Does it twist or does it go smoothly to the balun? I had a devil of a time with high SWR and RF in the shack until I figured this out. Finally, how long is your ladder line? There are lengths that will give problems. Check out this article http://kv5r.com/ham-radio/ladder-line/ for interesting points on lengths. My line is 46’ and that works.

Hope that helps.

 

The impedance of your ladder line is really not relevant when selecting a balun. Here is a tech article that will help explain our approach and here is another article that will help with trouble shooting a matching problem courtesy of Hamuniverse. Just FYI, bringing ladder line into your shack to a balanced tuner can be a possible source of RFI. Some ops never have a problem, but we always recommend terminating your ladder line outside into a balun and then running coax to an unbalanced tuner. This will minimize RFI created by radiated RF from balanced feedline which is always unbalanced to some extent by type of installation, run of feedline and surroundings.

Also, remember that tuners are more efficient when creating a match to high impedance loads and many tuners (although they claim otherwise) struggle to match a low impedance load. Although counter intuitive, shortening your overall antenna length can help with matching problems. Even though the pure resistive component of the antenna goes down for the base band of the antenna, the reactance goes up which allows for an easier match. An example would be a dipole covering 80-10m. Rather than cutting your antenna to the traditional 135 feet, you might find 110 feet overall is easier for your tuner to match.

Bob
Balun Designs

 

I agree with Bob, 100%! Every person that's purchased a doublet from me, to replace a Cobra, End-Fed, MyAntenna, G5RV etc., has been 100% satisfied once they put the time into getting it to work properly. Sometimes it's super simple and other times it takes a bit of tweaking. There's just no comparison to a simple doublet made from two, continuous pieces of wire. The way it used to be before we were blessed with coax.
Most of my customers find the best results with a 4:1 although, depending upon the tuner, a 1:1 may work best.


Brian

http://www.trueladderline.com

 

If the feed impedance of an all-band doublet is high on every band, then using a 4:1 choke balun might help your ATU cope with high impedances, but if one or more of the bands has a low feed impedance then reducing it further with a 4:1 balun could push your ATU into a high-loss region of operation.

It always seemed to me that having a doublet that is self resonant on any band (low impedance) will have very high impedance on harmonically related bands, and give your ATU a hard time. Deliberately choosing a length that is not resonant on any band will mean that the feed impedance is never low on any band, but also it will never be insanely high. Meaning that your ATU will cope more easily.

I use an 84ft doublet on all bands from 80-10m and my old KW Ezee match ATU copes just fine. I found that having it much longer deteriorated performance on 10m and 15m. Mine is in an inverted-vee configuration. With higher bands being predominantly end-fire, if the ends are pointed at the ground then.....