K2MK: I had about the same bandwidth as you and didn't need any matching network.

WD4ELG: All my topband QSOs to the west including Pacific/Oceania have been at my sunrise or just prior to sunrise.  When I worked the long-haul stuff it was most often at their sunset = double grayline.  I found it easier to work the Pacific than to work into central or eastern EU.

73, K3VAT


 

We're building a two-element yagi for 20M.

We have dozens of 6', 8', and 12' aluminum square tubing pieces - most are 0.065 or 0.125 wall thickness and most are between 1" and 2" on a side; Al grade looks to be 6061 extruded.  There are no round sections in this collection.

QUESTION: for HF operation such as 20M and disregarding windload, is there any disadvantage (RF wise) to using this square tubing in place of round tubing for the elements?

thanks, 73, Rich, K3VAT

Tree-mounted verticals do work.  If you really want to go stealth and multiband, then I recommend you build it with black insulated wire and use Unadilla traps for your favorite bands.  You'll need at least some kind of radial field for this antenna to operate with decent results, say a dozen or so radials spread in a circle if you can get it.

Pick a fairly heavy gauge insulated wire like # 12 or # 10; you don't need to staple the wire to the tree, in fact, you want a bit of distance between the tree and the wire to reduce any possible loss, especially when it rains.  Aluminum could work if it is thoroughly camouflaged but often tree branches get in the way of a straight run like telescoping aluminum sections.

W3HKK: Bob, he lives in an HOA antenna restricted community and needs to have a completely stealth operation so I don't think that the loop would work.  Everything must be close to invisible including any supports, insulators, coax, etc.

Terry: if you'd like to see a couple of photos of my stealth 40M/80M vertical drop me an email.  GL, 73, Rich, K3VAT
(k3vat at arrl dot net)

No, very low to ground 160M dipoles sometimes surprise you like they did me when I heard and worked VK6!  Low band propagation is not well understood.  Besides low dipoles there are several forms of askew ducting: the DX is geographically to the NE (like EU from here), but the 160M DX signals are coming in loudest on a bearing of SE !!

Go ahead and install the antenna and let us know how it goes.  You may have to tweak the feedline to match on the bands of interest.

GL, 73, Rich, K3VAT

Wow, that's substantial powerline noise!  Ever try and track it down - possibly you could get some assistance from the local power company and, if all goes well, they can often isolate the source (arcing transformer, broken insulator, etc.) and fix it for you.  Otherwise, you might be better off with a receive antenna that can null the noise rather than enhance signal-to-noise.  I'm speaking of something like the new Pixel Technology receive mag loop.  Google it and check it out.  GL, 73, Rich, K3VAT

That's a nice project.  When you say, "the apex at the bottom" do you mean that this antenna will be in the form of a delta loop (3 sided with the upper part being horizontal between those 70' trees?)  Before we can model we need to know the length of the wire ... is this a fullwave version (~ 534') or something different?  How far above ground is the "apex"?   GL, Rich, K3VAT

Yes, phased arrays are indeed sensitive to radial field irregularities.  Each vertical antenna's radial field should be the same, or nearly the same topologically.  That is, if possible, the same number of radials, the same length of those radials, and the installation of a common buss or tie wire mid-way between the two antennas that mutually connects together those radials that would otherwise intersect.  The recommended number of radials per antenna is between 2 and 3 dozen, but some stations have considerably more (50 or 60 or +).  Finally, the wire should be of the same type but this is not as critical as the above 4 points.  This is more or less an ideal situation; compromises can and do occur which may have a minimum impact on performance.


I suspect that it is due to violations to the above points.  I didn't see what type of feed mechanism you used for your phased array (coax delay, power splitter, hybrid coupler, etc.) so this key component could also be a source of difficulties.  This is confirmed by the fact that a single antenna is outperforming the array (for long haul DX it should be the reverse: the array should win nearly every time).

73, Rich, K3VAT

Fred is essentially correct: one would not expect to see any substantial interaction between the two sets of radials as long as they were not mechanically connected.  In fact, the addition of ground buried radials directly underneath elevated radials should enhance the efficiency of the antenna system that uses elevated Tuned radials.

Vertical dipoles usually do not require radial fields (see N6BT dot COM) and certainly not elevated radials.  The bottom half of the vertical dipole serves as the radial field.  As above, installing buried radials underneath a vertical dipole might enhance your signal in some particular direction and at some particular elevation.

Some of the theory for the above is covered in ON4UN's text, Low-Band DXing and as mentioned by W5WSS Tom's website http://www.w8ji.com/antennas.htm.  The text is worth buying if you're serious about learning antenna theory with LOTS of practical antennas and ideas for the experimenter like yourself.

GL, 73, Rich, K3VAT

Beverage antennas are extensively covered in ON4UN's text, LowBand DX'ing.  Another excellent source of info is http://www.w8ji.com/antennas.htm.  Have you checked these out?  One person's Beverage design may or may not work at your qth.  For example, soil condx play a big part in Beverage performance; likewise, height of Beverage (six feet may or may not be an optimum [plus for us tall guys, it gets in the way - hi]).  The sources should provide you with all the 'good engineering practice' techniques that will make your Beverage perform adequately.


Why not run a bi-directional - you can have both directions and the above references show you how.  Or a 2nd Beverage system to the NW for Japan and some of the Asian rim DX.  Lately we've have had some good 160 JA openings on 160 right at sunrise.

My old QTH used 160M Beverage where L=1100 feet and H=8 feet.

GL, 73, Rich, K3VAT

Thanks John,
Don K has been hard at work on a significant upgrade called, of course, the [Kessler] AT-AUTO II.  I (and apparently many others) was hoping that this unit would be in delivery status by last summer, but I guess that there are lots of stuff to refine.  Once done, this unit should be one of the top tuners in the world (IMHO).  GL, Rich, K3VAT

In addition to the above posts, there are dozens if not hundreds of others available on this popular topic by searching:
http://www.eham.net/ehamforum/smf/index.php?action=search

You may have to spend a bit of time; some of the postings reference empirical data, but most anecdotal.

GL, 73, Rich, K3VAT

I stand corrected, didn't understand it without a picture - hi.  thanks.

Steve,
Yes, the premier of autotuners comes from Germany, the AT615B.  Rock solid in every detail; highest reliability, great customer service see: http://www.hamware.de/hardware/tuner615B/at615B-e.htm but you must be willing to pay top dollar ($2200 +).

GL, 73, Rich, K3VAT

Thanks Dale, but now we have separate two antennas - a parallel or fan dipole with a 65' (40M) piece of wire and another wire of 22' (15M).

I believe that the poster "[wants] to use a 40M dipole on 15M".  If a 40M dipole allows one to adequately load up on 15M, perhaps a decent match across most of the band, so why go to the trouble of adding a second piece of wire; what is really gained?  Adding the 2nd wire will produce a very noticeable interaction unless the arrangement is configured as a 90 degree fan dipole.

thanks, 73, Rich, K3VAT

I have not vertically stacked a HexBeam Antenna, but plenty of yagi arrays.

First, vertically stacking, while not exclusively done, is mostly relegated to monobander antennas.  This is because the 2nd antenna is tuned to the 1st to take advantage of the reinforcing amplitudes generated by each antenna.  The distance between them is primarily determined by which band you select and secondarily to the the antenna's gain figures.  To produce the additional gain (a maximum of ~ 3db) requires a specific RF relationship between the two antennas.  For example two M-Square 4 element 20M yagis have a stacking distance around 56 feet; other M-Squared 4 element yagis have significantly different stacking distances based upon their frequency of operation.

Moving the stacking distance a few feet either side of the recommended stacking distance will not substantially hurt their performance; but, if you stacked those 20M yagis (cited above) at 15' apart, they would not work properly and would actually perform worst than a single yagi.

I've read about a few operators who have stacked triband yagis (10M, 15M, and 20M) at a distance apart based on 15M operation and they have reported "very good" performance on 15M and "decent" performance on 10M and 20M.  IMHO, I don't think that you'd see this when using a HexBeam.

Perhaps G3TXQ will chime in on this ... he's much more familiar with HexBeams than most of us (especially me - hi).

GL, 73, Rich, K3VAT