A Day in the Backyard
New Doublet Lengths
I found some Teflon insulated #26 with 19/38 stranding on an internet shopping site and decided to get some. It was advertised as only being 150 feet for under $20 and I jumped because 100 feet of new stuff will set you back some cash. I wanted to test out a new doublet length that would keep the radiation from 15m broadside to the wire and keep 40m gain respectable.
The 66 foot PPD I had made a 15m pattern that was a cloverleaf due to it's longer than 1.25 wavelength radiator. I settled on two wires 60 feet long each. The length that gets "consumed" as transmission line is dependent upon how tall the mast is and I decided that 31 feet was the shortest I wanted to go. This created a 58 foot doublet. Shortening it caused the doublet to undergo some pattern shifting on 15 and that is what I wanted. Let's see how it did on 40.
Will the MiniBalun BLT and BL2 BLT Still Tune It?
Pretty much any decent length doublet fed with high impedance line such as the PPD will pretty much have an input impedance landing on the right side of the Smith chart. I didn't bother modeling it as I had a pretty good idea that it should work. But I couldn't help it, I modeled it.
In reducing any doublet or dipole length you will sacrifice some gain when you go shorter than a half-wavelength. There is a point where the gain on the low end will taper off. How much you want to sacrifice is totally up to you. I chose to keep the loss around 0.7dB. But there is very little loss at 30m. This is a function of overall length and I wanted to go as short a possible to keep the pattern decent on 15m but not sacrificing too much gain on 40m.
This puts our doublet at about 58 feet long and a good compromise.
Here is the 15m broadside response when the apex is at 33 feet, ends at 20 feet.
And the 15m gain not counting feed line loss.
Here is the 20m pattern at the same heights.
Right Side Response
This is the response seen at the tuner feed point using SimSmith and the known k1 k2 k3 constants and measured TL parameters from yesteryear.
The antenna looks good so far, now let's set it up and test it out. Here is my backyard experiment.
I attached my KX2 and the MiniBalun BLT co-located at the feed point. I went through the bands and wrote down the tuner settings so could quickly return to any band.
Just a Toy
I acquired a FLIR TG165 the other day and just had to play. It really does well with subtle temperature gradients and changes but lacks a little accuracy is probably wholly dependent on emissivity so I wouldn't place any confidence in the temperature readings.
This is a screen grab of the Elecraft BL2 BLT. Looks weird in infrared.
This is a shot of the telescopic pole and the TL/wire.
One hot radio?
So there you have it, a visual look at what's cooking...not the inductor or balun, quite the opposite.
Printed On Recycled Data