Doublet length

So I had decided to install the 40m (and higher) doublet to save on weight even though I had the space for the 80M doublet.  My original thinking was that some day it might be neat to compare the EFHW 80M antenna with the 80M doublet since my QRP Guys tuner that I plan to use with the doublet does not support 80M.  Then I read that a doublet will actually provide better performance on a given band if the antenna were resonant on odd harmonics for that band so I thought that since the doublet length is not critical I could play with the length to give a boost to a favourite band.  I knew there are websites out there that will calculate this for you so I went searching.

I looked at a couple and then found this page on Spookmate.com.  I was able to put in the frequency for 80M in the calculator and see what my options were.

As you can see where the harmonics are listed that 10.5 is the 3rd harmonic.  This is very close to 10.110 where I like to operate on 30M.  I then adjusted the frequency at the top until the 3rd harmonic was where I wanted it to be.  3.37 MHz does the job and the legs of the doublet would be 72.9' long.  The key with the doublet is that the antenna is not resonant on 80M if I want to use 80M.  It is not (although it may be too close) but I am not using the antenna on 80M so I'm not concerned about that.  Really I'm taking advantage of the 3rd harmonic which I would not have if I were to put up the 40M doublet.

The harmonic frequencies gave me no joy for the 17M band which I also enjoy so I will go with the 73' length.  This is what I plan to experiment with when I put this doublet up, hopefully this weekend, weather permitting.  I'm not sure how much luck nor do I have a way to get tangible results but my random wire is currently working well on 30M only so I can compare the two.

Now you may remember I was going to avoid the 80M doublet because of weight concerns but I have come up with a plan for a guyed wooden support pole.  It'll be a little "interesting" looking but I think it should do the trick.  I'm fine tuning my idea in my head daily and am almost there.

Cheers for now,

72/73 de Scott

QRP Guys Multi Z Tuner started

I got down to making the QRP Guys Multi Z Tuner 10-40 this evening.  The first thing I noticed was that my eyes really aren't what they used to be.  Even with glasses on I could have really done with a pair of these:

                                  or this    


My ageing eyes aside, I dove in and got started.  The project does not have a lot of components so the construction isn't too difficult however there are some challenging bits to keep you on the ball but the instructions are top notch.  The first step is joining some PCB pieces together with solder to create the "chassis".  Once complete I began installing parts per the checklist:

Aside from the standard components there is a small toroid to be wound with a center tap.  This went fine.  It's been a while but it all came back pretty quickly.

By the end of the evening I had everything together except for the most challenging part, the large transformer.  For that I will wait until my eyes aren't tired and there is some natural light.  Here is the finished product for this evening.

Back at it tomorrow.  Cheers es 72/73 de Scott