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
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Tuesday, July 19, 2016

Carbon Fiber Pole Antenna QSO

Lunchtime QSO

I had an opportunity to set up my 39.7 foot carbon fiber pole at lunch today for a quick QSO. My outing yielded 3 QSOs into CA, PA, and TX on 14.060.

No Radials

I didn't run any ground radials just attached the black clip lead to the shank of the screwdriver and stuck in the ground. I cutoff about 18 inches of the aluminum section to match the length of the collapsed fishing pole. I stow the CF pole inside the aluminum pole section for protection when transporting it.

Tunes 40-6

When it is set up it basically slips over the bottom section of the CF pole to provide coupling to the bottom section. I don't really know how much capacitance is there but apparently it's enough to tune 40m. It won't tune 80m though but really wouldn't have expected it to.

Video of QSO

Here is a video of the latter part of my QSO with KD3CA, Don out near Pittsburgh running his KX3 at 5 Watts into a TriBander at 55 feet. (That helps).

Needless to say, it still works better than I thought. What a hoot! No wires. None.


RBN Hits

Here are the RBN spots.

I didn't work Germany...

Myron WV0H
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Thursday, July 14, 2016

Carbon Fiber Pole Antenna

Who Said That It Wouldn't Work?

This is the silliest thing. My telescopic pole I use for my Park Portable Doublet is just too handy not to consider its use for anything that needs to be put in the air.

Enter one vertical using only the pole

This shouldn't come as a surprise to you but this thing is conductive! I mean is it conductive enough to allow RF to be launched to and from it?

Really? I have heard of people using saltwater suspended in a PVC pipe and coupled through an antenna tuner or some sort of matching network but I had never considered it myself.

All I did was stick the screwdriver in the ground and slipped the pole over it like normal. Then I took a green aluminum Army camo pole and slipped that over the top of the pole to capacitively couple to it. Then I attached a short clip lead to the BNC to Banana jack adapter on an Elecraft T1 tuner. Hit tune and the 20m band jumped to life! Wow, this is encouraging. Now if they can only hear me. Sent out some CQs and low and behold, somebody answered me. WB2WIK in CA. He was running 500W to a LPDA up 55 feet but he turned his power down to 10W and continued the conversation with some QSB reported both ways. Then I called again and worked NS3C also in CA, then K4ISW in VA using a K3s at 100W. Some QSB out east but not as bad as west.

The pole stands 38 feet tall but can get to 39.7 feet if I want to stick in the tip-top section of the fishing pole. It is very thin and would only be able to support itself but may be worth trying.

The whole thing was amazing actually. I suspect much better than a salt water antenna I suppose.

I had to insulate the metal pipe with a PVC end cap to keep it up off the ground a bit. Also I started out using the T1 but could have easily used the BNC to Banana adapter directly on the KX3 and allowed the internal antenna tuner to take care of the match.

I laid out two 36 foot ground radials. I laid them on the grass and had to shoo the rabbits away in an effort to keep them from tangling themselves up in them.

Oh yeah, I worked K4FB fox as well.

Here are my RBN spots for tonight on this antenna.

73 all
Myron WV0H
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Sunday, June 19, 2016

2016 ARRL Field Day Dry Run

Murphy Repellant

So I wanted to get the new never used Spiderbeam 12m pole up with the new never used 88 foot doublet with the new never used ladderline before I try to use it at Field Day for the first time. That is a recipe for disaster. The weather forecast called for sunny and 98 degrees! Better get busy. So up at 6:00 am and I am out there pounding stakes. Using a rubber mallet doesn't make a lot of noise to wake neighbors...

I got the base of the pole set with guy lines and added the clamp set.

The next step was to get the rest of the clamps set on the pole and the Ladderline strung through the tip-top.

After that it was all up, guys and all. The guy was place at the bottom of section #8 as per the instructions. (About 26 feet up).

Predicted Data vs. Measured Data

After spending several weeks in EZNEC refining the model I couldn't be more happier with the measured results. Spot on. Gone are the days of cut and try.

SimSmith Predicted Response

SimSmith Measured Response

They are very close. I am pleased.

73 and see you on the air for FD 2016.

WV0H Myron
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