Saturday, October 1, 2016

A New PPD Length To Play With

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.

Swept Gain

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.

Myron WV0H
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Wednesday, September 21, 2016

Side KX Cover Mod for the KX2

Side KX and End Plates

I purchased the KX2 and have since installed the Gem Products Side KX cover and end plates for the rig, but...

Tight tolerances of the injection molded cover allow a perfect fit, trouble is removing it. I mean I had to really press down hard on one side of the cover to get that lid to pop off. Someone with fingers that has less strength may have great difficulty, not to mention the added stress on the end plates that place undo stress on the screws and screw holes.

Too Tight

Well, a quick phone call to Scott at Gem Products revealed possible fixes as we discussed possible solutions. More interested in finding a quick fix I thought of a way to relieve the stress in the cover and make removal easier. Make some relief slits to allow the side portion of the cover to flex inward a little.

Cutting Corners

To allow the side portion of the cover to bend in a little bit more, I relieved the stress in the corners of one side by cutting 45 degree angles at about 9/16" (15mm) deep. You can go deeper but I stopped at this depth because my saw was cutting at an angle towards the front. If you can cut precisely on the corner a deeper cut should allow for easier pushing of the cover tab.

Enter X-acto


A perfect solution with no impact to the functionality of the cover.

It's hard to see but there is just enough flex there to greatly relieve the stress on the cover and end plates.

You can install the cover in either direction, removal and replacement is unaffected by orientation of the cover..

Now, it's relatively easy to get that cover off.

Update October 9, 2016.

I had originally ordered my KX2 with the KXPD2 paddles but were backordered. I received them after publishing this blog post and wanted to tell you that the KXPD2 paddles do not fit on the KX2 when the cover is in place or vice versa. In order to remedy that, I took my cover to the 1 inch belt sander and ground a notch about 1/16 inch deep on the cover where the top of the KXPD2 meets the cover. Now I can install the cover and leave the KXPD2 paddles attached.

(I'll attach a photo tomorrow).

Myron WV0H
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Wednesday, September 7, 2016

A 80/40/10 Meter Doublet Fed With LadderLine

Ever since Field Day 2015 and the incorporation of the 88 foot doublet and tuned feeder giving a 50-ohm match for 40/20/17/12 meters I decided to see if I could make an additional doublet for 80 and 40 meters using the same concept, a tuned feeder with a correct length of deployed wire.

I modeled it set up at the same heights as the 88 footer, 39 feet in the middle and 31 feet at the ends yielding a 159 foot doublet.

Getting this much wire in the air always produces some decent gain on 80m and this example is no exception.

And the 40m gain is a real plus as well.

6 and 8dBi gain is nothing to sneeze at. You would be hard pressed to get as much gain with any vertical system.

You might be thinking you would have to "aim" the antenna for 40m. This is only true if the sun is down and 40m propagation goes from bouncing off the atmosphere in the immediate area to longer skip that exists in the midnight hours. I'm afraid I'm asleep by this time.

Like the 88 foot doublet with 41 feet of JSC #1318 Ladder Line, we can achieve 50-ohm matching  with 88 feet of the same Ladder Line. Just attach a 1:1 balun such as the Elecraft BL2 to the LaderLine feed point to get to coax or whatever.

Max SWR of 1.8 on 40m, good, good and you pick up a bonus band like 10m.

Okay, okay. The 10m pattern is going to be crazy, right? Well, yes but look for yourself.

And the gain plot for 10m.

There are some nice lobes there (pardon the Ferengi slang)...10dBi, okay that has to count for something!

Oh, BTW, I ordered a KX2 and a QRP Guys Mini Tuner Kit today.

Myron WV0H
Printed On Recycled Data

Sunday, August 7, 2016

Tuner At The Antenna Or In The Shack?

Antenna Tuners at the feedpoint or in the shack?

I had a question regarding the placement of an antenna tuner yesterday and was wondering what effect it would have placing the antenna tuner at the feed point of a GAP Titan vertical that is already somewhat tuned. He wanted to know if placing an automatic antenna tuner out at the feed point would lower the transmission line power dissipation. He didn't say what the exact SWR was at the feed point so I assumed two values of 2:1. So which will be more efficient? Instinctively I would say tuner at the antenna. But by how much?

SimSmith Approximations

Choosing two cases involved picking two 2:1 SWR impedances that could be realized at the feed point of any antenna. This installation also involves 140 feet of Davis RF Buryflex coax from shack to antenna as well as 500W input to the coax from an Elecraft KPA-500 amplifier. (20m was assumed for this discussion). Conservative tuner element values were assumed as well as an L network. Most automatic tuners utilize this topology. And we are ignoring the non-perfect characteristics of coax and the stray reactance that is present in real tuners, etc.

I might add, each SimSmith "building block" contain information regarding it parameters. The R and X values are those values looking into the right side looking left. Also, the ^W symbol indicates the amount of power "burnt up" in that block. When you left click on that W symbol it toggles through a bunch of parameters, ^dBW, <-dBw, <-W, ^W.

^dBW is the amount of power in dBW burned up in that block.
<-dBW is the amount of power in dBW entering into that block from the right.
<-W is the amount of power in Watts entering into that block from the right.
^W is the amount of power in Watts "burned up" in that block.

The G block is the generator block, the transmitter, your rig on the right. The xMtch(a) is the setting that allows the generator to produce a constant level of power regardless of the impedance seen downstream, unaffected by reflections from an imperfect load attached to it. The (a) part is telling the source to be the value in Watts in the "a" field just below it. That way we can set the transmit power out with just one field entry.

Baseline Case: Matched Loss to 50 ohm load (85W dissipated in coax, 500W input)

Case 1A: 2:1, High Z (80+j33ohms), Tuner in Shack

Case 1B: 2:1, High Z (80+j33ohms), Tuner at Antenna 

Case 2A: 2:1, Low Z (27-j13 ohms), Tuner in Shack

 Case 2B: 2:1, Low Z (27-j13 ohms), Tuner at Antenna


There is only a 15 Watt savings in power dissipation in the coax by locating the tuner out at the antenna, a 0.15dB difference. So as long as the antenna feed point SWR is somewhat low it's hardly worth the trouble.

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Saturday, August 6, 2016

CF Antenna SWR Response

The CFA input SWR response

The input SWR response was measured by the Sark-110 and imported to SimSmith.

The CF antenna is lossy and that helps with the match as it tends to shift the response to the left indicating a loss mechanism at play. Just how much loss, eh, about 2dB from what I can tell in EZNEC and the overlays.

The next blog post I will see if I can drum up the EZNEC response for comparison.

Myron WV0H
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LP QSOs on the Carbon Fiber Pole Antenna

Yesterday I had three low power 20m CW QSOs at lunchtime on my carbon fiber pole antenna. I extended only 34 feet of sections to get closer to 1/2 wavelength and reduce my dependency on ground. (If that's a valid point or not, I don't know). I was using my KX3 and internal tuner with my AnyVolt3 to allow 15W output from my station.

The first QSO was with Fred, KA4RUR running 5W in St. Louis, MO. Then off to Jerry, W7ANM in Oregon. He was running 12W to an inverted vee. Then back to Tennessee with WZ4L, Sam. He was running 10 W to a horizontal loop at 60 feet.

 The first two videos are with W7ANM out in Oregon. The third is with WZ4L in Tennessee. I didn't get KA4RUR on video.




So does the carbon fiber pole antenna work? Sure, how good? Good enough for quick 5-minute deployable situations. The SSN and SF were saying this shouldn't have happened...Oh, and carbon fiber poles shouldn't work either!

Myron WV0H
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Thursday, July 28, 2016

The Tip of the Iceberg

Using SimSmith v14.6 to Go Backwards!

Larry, W0QE, put together a video to show how one can use SimSmith to obtain efficiency of a tuner (or any other RF circuit) when connected to a load such as an antenna.

This post is going to be minimal but here is my crack at trying to set up a Pi Network tuner. This topology is what Elecraft uses in their switched L/C tuners except one element, either the input or output capacitor is switched to either the load or generator side. But for simulating, I have included both, to show the possible range.

I haven't figured out the plotting of colors yet. I'm not a programmer and will resort to freezing Larry's video and manually copy the code...

Please click on Larry's Video here:

Myron WV0H
Printed On Recycled Data