COMPACtenna 2m/220/440: Theory & Design Video

prcguy

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I'm told there is the equivalent of a rolled up sheet of circuit board as a spiral conductor and the X-ray shows that's only a small part of the antenna and at the top. That would probably be operating partially as a capacity hat. I've seen drawings in patent applications that showed the entire length of the antenna might be a spiral circuit board but maybe that was only a prototype.

Looks like a capacity hat arrangement, like PRC mentioned.
 

W5lz

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Oops, forgot about this thread...
Odd, if those Compactennas are/were so good wonder why there aren't thousands more in use? Like it or not 'Jack', a shortened antenna just doesn't have the performance of a full sized one (1/4, 1/2, 5/8w whatever). So exactly how is that 'testing' done? And can you trust the testers?
 

prcguy

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If you read my earlier post I tested one and on 2m it was equal to or greater performance than a full size 1/4 wave whip on the same vehicle, same mount, same coax, same location receiving a variety of signals coming from different directions. That would be a roughly 7 1/2" tall antenna working as well or better than a 19" long antenna. On 220 and 440 I got varying results and I need to test again in a clear area away from anything to trust the results.

My testing was done with the antenna feeding an HP/Agilent 8594E spectrum analyzer with RF/EMI filter options and able to test to .1dB resolution. Is that good enough?

Oops, forgot about this thread...
Odd, if those Compactennas are/were so good wonder why there aren't thousands more in use? Like it or not 'Jack', a shortened antenna just doesn't have the performance of a full sized one (1/4, 1/2, 5/8w whatever). So exactly how is that 'testing' done? And can you trust the testers?
 

vagrant

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That is an interesting antenna. I'm thinking the tri-band may be a good fit with my tri-band Kenwood D74A and test mounting options with it (not actually mounted on the D74A). Basically, something portable but better than the Diamond 320A handheld antenna.

Dang, I really want Kenwood to make a mobile version of the D74A, this antenna looks like it would be a suitable pairing. While I would not use the Compactenna for contesting, it seems like it would TX/RX repeaters well enough and tone down my mobile porcupine.
 

DeepBlue

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I will say this, I am the guy that shot and edited several of the videos of Dr Jacks' antennas. I personally have the scanner type on my Jeeps rack and it does receive very well both on the 700-800 MHz spectrum as well as the Air and Mil-Air segments where I use it. It has reduced some of the well talked about multi-cast issues we deal with on the MARCs system in Columbus, Ohio ans picks up Mil-Air better than any antennas I own, and I too have a few. I can't speak to the way he wrote and presented in the videos but, given the lack of stats and testing I too was actually dubious. I can say that the particular antenna I have and use is working quite well. I have had it mounted on my Jeeps rack for over a year now. The only issue I have ever had was the rubber washer on the NMO mount deforming.

I have a great deal of respect for PRCGuy. He knows his stuff. It takes a long time for new ideas to percolate through a crowd that is staunchly set in their ways. Amateur Radio folks are like that for the most part. My only advice is either buy one and try it for yourselves as some of us have done or continue to grumble while some of us move on. If you look close in my Avatar pic you may see the antenna mounted in the back center of the rack on the Jeep.

When I first read Jacks patent info and saw the design, what I immediately thought was not that it was a capacity hat, but an actual capacitor, which it would be if it had a second plate. Inductors create a magnetic field when alternating current/voltage is run through them, just like a loop antenna and we all know a loop antenna is a fraction of the size of the wavelength in question, like using a hula-hoop for 40 meters. Why can't this design work?

Anyway, buy one and try it like we have. You might like it. I do.

Sean
KB8JNE
 

mancow

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It reminds me of how my TACO 225-400 is built. I have some pics of it disassembled somewhere.
 

bill4long

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There's also this video comparing the COMPACTenna to a very common dual band Diamond on receiving various ham repeaters in LA. On 2m, other than at one very specific point in a tunnel, the Diamond dual bander consistently beat it. UHF reception, though, actually seemed quite decent.
Been using 770 Diamond variants for many years.
My first recommendation to new hams (or anyone else.) Great performers and tilt-over to boot.
 

vagrant

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Agreed on the NR770 mobile. One is on a motorized lift on the roof rack. The other is low on the back rear handling APRS. I have an SUV.
Been using 770 Diamond variants for many years. My first recommendation to new hams (or anyone else.) Great performers and tilt-over to boot.
After DeepBlue's post about the scanner version, I'm wondering how it compares to the Larsen which is what I'm using now. It sits next to the AM/FM radio antenna near the passenger side windshield. My TX/RX stuff is on top and both sides of the back. The RX only stuff is front right to give it some separation. Anyone compare the Compactenna scanner version to the Larsen tri-band? If not, I may end up getting the scanner version first and test it.
 

prcguy

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I've been thinking about getting a scanner version myself for testing. I don't really need one but I'm curious. Maybe Dr. Jack can loan me one for testing? :)

Hey Jack, are you out there? Need my shipping address???

Agreed on the NR770 mobile. One is on a motorized lift on the roof rack. The other is low on the back rear handling APRS. I have an SUV.


After DeepBlue's post about the scanner version, I'm wondering how it compares to the Larsen which is what I'm using now. It sits next to the AM/FM radio antenna near the passenger side windshield. My TX/RX stuff is on top and both sides of the back. The RX only stuff is front right to give it some separation. Anyone compare the Compactenna scanner version to the Larsen tri-band? If not, I may end up getting the scanner version first and test it.
 

RadShackFan

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I tested the COMPACtenna against the Larsen tri-band last year. I had it on a permanent NMO mount at the time, and it was stolen. I have since changed to a Honda p/u which has a sunroof and a permanent NMO is out of the question because the sunroof pocket is so large. I have to use, the horror, a magnetic mount. In the new truck I haven't detected any change from the test results here:


Not trying to sell anyone on this antenna, just passing along the information.
 

TailGator911

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I tried both the tribander ham model and the scanner receive model on a recent adventure up to Alaska and the Canadian Rockies. They were nothing special (for awhile) compared to my ham/scanner antennas (Cushcraft AR-270b vertical, and my scanner antenna, the Diamond 220r) and the results were about dead even until we hit about 5k elevation. That's when I packed up my 2 Compactennas and went with my aforementioned radio antennas. The COMPACtennas did not fare well in the mountains. They were great at night sitting around the campfire in Canada and the US west coast, but when we started to climb I noticed too much static. At 5k elevation I changed them out once again at an RV park in Canada and suddenly I had radios again. They are just okay, but more suited to flat terrain I think. I installed them on our 4-wheelers here in Ohio and they serve us well locally.
 

AI7PM

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Oops, forgot about this thread...
Odd, if those Compactennas are/were so good wonder why there aren't thousands more in use? Like it or not 'Jack', a shortened antenna just doesn't have the performance of a full sized one (1/4, 1/2, 5/8w whatever). So exactly how is that 'testing' done? And can you trust the testers?
Ah the crumudgens.

Perhaps because it hasn't been available as long as those "thousands" you refer to.

"(1/4, 1/2, 5/8w whatever)" Are you suggesting "full size" includes 1/4, 1/2, 5/8, etc? I'll guess those were poo pooed back in the day same as the present offing is being. Last time I ran the numbers, full size on 2m was about 6 1/2 feet.
 

prcguy

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And how is the curmudgeon's comment relevant to this thread about a short antenna? Who said it outperforms a 1/2 or 5/8 wave? If someone needs a short antenna why would they look into a much longer 1/2 or 5/8 wave?

Ah the crumudgens.

Perhaps because it hasn't been available as long as those "thousands" you refer to.

"(1/4, 1/2, 5/8w whatever)" Are you suggesting "full size" includes 1/4, 1/2, 5/8, etc? I'll guess those were poo pooed back in the day same as the present offing is being. Last time I ran the numbers, full size on 2m was about 6 1/2 feet.
 

W5lz

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'Jack' here...
No one compared a compact antenna to a 1/2 or 5/8 wave. Read that post again. Any comparison was in reducing the 'size' of the antenna (yes, those are common sizes of antennas) to that of the Compactenna. And just for grins those "sizes" have been around for -quite- some time.
As for comparing this antenna to that antenna, it's all a personal observation unless you have a lab full of test equipment to give pertinent and reproducible results.
And get it right. It's a scurrilous curmudgeon...
 

cbehr91

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I've noticed the 2M/440 version is not rated for wideband receive (100-1000 mHz), but the tri-band version is.
 

prcguy

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I saw a side X-ray in the link but did not find a top down X-ray as mentioned. The internals of this antenna was described to me by Dr. Jack as a rolled up circuit board and the description of a top down X-ray as being "a form of small transmitting loop antenna with multiple loops" would sound about right.

Looks like a capacity hat arrangement, like PRC mentioned.
 
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