The QRPer Board

During a cross-country driving trip, we have been stopping to do Parks on the Air (POTA) activations at a number of state and national parks. At some locations it has seemed best to me to keep a very low profile, so that I do not distract others who are enjoying the area. For optimum stealth, I choose to use my Elecraft KX2 with its companion AX1 antenna. The setup shown in the next picture comes from an activation in a parking lot at the Mount Rushmore National Monument. I found I could clamp the AX1 to the base of the VHF/UHF mobile antenna on the fender of my truck, run the counterpoise wire over the hood and toss the remainder directly under the truck, and run the feedline in through the driver's side window. I was uncertain about the effectiveness of this setup for three reasons:

• The AX1 (a base-loaded 4 ft whip) starts as a compromised antenna system
• Having the whip parallel to and separated by only 2 inches from the mobile whip could have unpredictable effects
• Running the counterpoise wire mostly under the truck would also have uncertain effects

What would you expect from this antenna setup?

The next picture shows the QSO map from the activation. It took less than 30 minutes to log 11 contacts.
Based on this success, I decided to use the same setup during an activation in Yellowstone National Park. All went well for the first contact, then a large recreational vehicle (RV) pulled in to the next parking space. You can see it in the next picture. The RV was longer than my truck, and despite the perspective seen in the picture, it was actually higher than the top of the AX1 antenna.
What would you expect from this antenna setup?

The next picture shows the QSO map from the activation. It took 40 minutes after the first unobstructed contact to get 10 more contacts for a total of 11. This was not as quick, but persistence paid off.
I will say that I was surprised at my success with this configuration. A couple more pieces of might be useful. First, all contacts were made on the 20m band running CW mode at 5 watts. Second, solar conditions were good for both activations. I am definitely interested in your thoughts.

what's the length of the other antenna, and which band you made the contacts on ?

Hi Andrew,

Both antenna setups were identical, except for having the RV pull into the parking space beside my truck early in the second activation (a car towing a smaller travel trailer also pulled in on the other side, so i was truly boxed in). The mobile antenna is a dual band 2m/70cm whip. All operations at these activations were in the CW portion of the 20m band. Transceiver was Elecraft KX2, and its internal tuner was used for matching. The 13 ft counterpoise wire ran down over the front of the truck, with the remaining length being tossed under the truck onto an asphalt-paved surface.

Best 73 de Brian - K3ES

length of the V/U antenna ?

Whip length of the VHF/UHF antenna is 32-3/16 inches or 82 cm.

Thank you, on monday will put together a NEC model, I'm curious about the pattern

Brian,
With two successful activations under your belt, I'd have to say that yes, your antenna works!

73,
Mike, KL7MJ

Thanks Mike,

I was uncertain, but the AX1 continues to amaze me. A compromised antenna is, first and foremost an antenna.

Brian - K3ES

Brian

I've put together a "quick and dirty" model in 4NEC2, didn't include the car (which will have effects) but at a quick test, the antenna shows a multi-lobe radiation pattern with low takeoff angles and a preferred direction toward the shorter (VHF/UHF) whip, will try playing a bit more with the model, but in any case I hope that such preliminary infos may be useful

<GRRR>

I stand corrected, when putting together the model, I forgot a dot, so I was testing a frequency of 14000 instead of 14.000 MHz, go figure

Ok, this time I got it right, aside from the lack of "the car" (but I'm planning to add it !) here's what the antenna looks like when installed near the V/UHF whip

download/file.php?id=178
basically the shorter whip doesn't seem to affect the AX1 in a relevant way, gain isn't "stellar" and may probably be worse, but then and again, the model is still "very raw" so I'd need to improve/refine if willing to drill further down into "how it behaves"