Buxcomm antenna construction

[KD0BVQ]

Trying out a free Buxcomm antenna. There is a startling lack of technical info on this antenna's website.

I would like to attach ladder line - but it is "hard-wired" for coax so I presume I will have to cut the antenna wires and discard the balun. It's a folded dipole so here's my question: is the non-feed line component continuous thru-and-thru the balun, or does it terminate in there? Because after I cut it I'll need to put it back the way it was.

Or is this just a stupid idea? Any and all suggestions, hints and even criticisms will be very welcome. And thanks

Hank KD0BVQ

[WB2WIK]

What's the model number of the antenna? I have lots of information on Buxcomm antennas, but they're all different.

[KD0BVQ]

WB2WIK, thanks for your reply.

It seems a little weird to me that this antenna has no identifying marks of any kind - not even a brand name. I know it to be a Buxcomm because they guy who gave it to me bought it directly from them over the Internet. If a description will help, I'll give that a shot.

It has two doubled wires about the size of old TV antenna wire, each side nearly equal (to with 2 inches) at about 10.5 meters - that is, about 21 meters full length including the balun in the middle. Being a folded dipole, I guess that makes it nominally 40 meters. The balun is thick, heavy, solidly glued PVC pipe, not openable without breaking it or sawing it. All wires disappear into the plastic housing and have a weather seal, not designed for removal, alteration or maintenance. No external feedlines. The bottom of the balun has a steel coax connector as the only way to connect it to anything.

Hope this helps. And thanks.

Hank KD0BVQ

[WB2WIK]

Does it look like this?

http://www.packetradio.com/catalog/i...4c4gu032fssl34

[KD0BVQ]

Yup, it looks exactly like the 8010 model (total length 69 feet), except it doesn't have "Buxcomm" printed on it anywhere.

Thanks,

Hank KD0BVQ

[WB2WIK]

I'd use coax and see how it works with that.

I'd also attach a reasonably short length of coax to the suspended (installed) antenna, and standing out in the yard under the antenna, attach that to an antenna analyzer, sweep the spectrum, and take some data. That will reveal where the "sweet spots" are (frequencies with lowest SWR), and also reveal what frequencies the mismatch is terrible, so I could make some calculations about line loss when the line is full length to the station.

[KD0BVQ]

Thanks for the suggestions. Here are the "sweet spots".

Mhz SWR

2.665 3.6
4.815 1.6
17.08 2.5
21.06 2.6
29.38 4.6
34.56 3.1
48.16 3.2
61.32 2.6

I am running a Kenwood 570D and LDG autotuner (the AT-200pro) and it tunes and transmits most anywhere in 40 meters but won't tune anywhere in 80 meters. I also have an 80M dipole of my own construction cut to 3.85 MHz, with ladder line. The autotuner will tune it to anything I have asked it to (so far) and I got in QSO on some frequencies where both antennas would tune and got signal comparisons. The Buxcomm is very noticeably weaker.

My experience with the home-brew 80M was that all my signal reports on all frequencies got a lot louder after I swapped out the original coax for ladder line (using the autotuner on both the coax and the ladder line so as to have a valid comparison).

So, I was hoping to try this on the Buxcomm, but I am stymied by the design, which is apparently never intended for ladder line. If I can coax halfway reasonable signals out of it on 80M, I'll be able to use it for mobile emcomm. Otherwise, it's worthless to me.

If that's how it turns out, you're welcome top have it for the cost of shipping it to you.

Thanks,

Hank KD0BVQ

[WB2WIK]

Thanks for the suggestions. Here are the "sweet spots".

Mhz SWR

2.665 3.6
4.815 1.6
17.08 2.5
21.06 2.6
29.38 4.6
34.56 3.1
48.16 3.2
61.32 2.6

Interesting. What are you measuring this with and how long is the coax from the antenna to the SWR instrument? Also, how high above ground is the antenna when you made these measurements?

[KD0BVQ]

Measured with a (borrowed) MFJ-269 antenna analyzer. The antenna is horizontal at 20 feet (intended to be at NVIS for 40M). The coax is about 20 feet.

[WB2WIK]

Did you record more data, such as the R and X numbers, and also sweep each of the amateur bands edge to edge to see where it goes?

Since the antenna obviously isn't matched at all anywhere useful (or so it seems thus far) the coax has become a transformer; there may be a more optimum length for the cable what will present a much better match to the rig.