On Fri, Feb 6, 2009 at 9:17 PM, Richards <jruing@ameritech.net> wrote:
> The flap over the correct balun / unun / transformer sure soured my
> impression of Array Solutions and Zero-Five. Their handling of this
> situation reminds me of the way Intel handled the situation with its
> broken Pentium chip.
You know something?
There's no good purely technical/performance reason for everyone to want
one of these antennas. The basic theory, if you can call it that, is that
you can build a mediocre but simple to install antenna system by slapping on
some not-necessarily-well-chosen transformer and using coax cable loss to
increase power "handling" capability on the lower bands.
Zero-Five was first. It was very popular because it was easy to install,
and didn't work that bad (can you measure, say, 6dB without setting out to
really try? I can measure that, but not unless I try, and it's an amount
that really matters : http://n3ox.net/files/6dB/). Maybe you only get 3dB
or 4dB down, and on some bands the loss tends toward totally negligible...
so the antenna, qualitatively, works pretty well to make DX contacts. I've
taken my base matching network for my 1/2 wave vertical on 40m out of line,
loaded it and the coax up with my little MFJ-941E tuner, resulting in a loss
of about 10dB as measured by strong, steady received stations, and then gone
down to 40m CW and busted pileups with 100W input. 10W ERP. Got through
the C57R pileup. And that's pretty much the WORST length a coax fed random
antenna can be. I didn't have any transformer at all, just a half wave wire
coax fed at the bottom, and low power.
The antenna approach is simple, doesn't totally suck for the average user,
and is fairly easy to produce, so other companies jumped on the 43 foot
bandwagon as it got REALLY REALLY popular to own one.
So we get different versions.
DX Engineering.
MFJ and Hy-Gain, if there's even a distinction.
I've got nothing against any of these companies; they all make products that
the ham radio community wants. I'm impressed with many of the products Zero
Five / Array Solutions and DX Engineering have. MFJ is there to pick up the
budget end of the market, and that's useful too. I'd be happy to patronize
any of them when I need their products. But the reason why they're all
selling 43 foot verticals is because people want them, and want to believe
they're negligibly different on all the listed bands than something that
requires a complicated tuning scheme.
And yeah, you put down 7000 feet of radial wire and run hardline to the
thing, and it'll work out OK, though I have it on good authority that you
might find that the UNUN or BALUN or whatever doesn't quite cut the mustard
if you actually manage to shove 1400W of your 1500W through it on 80 and
especially 160. The feedline loss may be crucial to the power handling of
these antennas. Running 1500W into a 43 foot vertical on 160m even with a
good air core loading coil is kind of a difficult proposition. Running an
actual 1500W through a ferrite cored UNUN into a 43 footer? Not likely.
Again, people point to their good DX contacts that they've made with this
antenna, but even at 20dB down you'd be radiating 15W of your 1500W on
160m. Is 15W ERP enough to make 160m DX contacts? Absolutely. I'm up to
102 countries worked this season, and my OPTIMISTIC estimate of my effective
radiated power is about 25W. 10W is probably more realistic, but, like many
people, I just can't get my head around the fact that I have a 60 foot
antenna on a 50 foot square radial patch, no amplifier, and often get really
great reports from Europe, so I try to find a reason why the antenna is lots
better than -10dBi, when in fact, it might not be.
And running a full 1500W even with a good loading coil? A couple of years
ago I asked this forum about base loading coils for a 40 foot antenna on
160m, and one person responded that he did it, and it worked OK, but he
started a grass fire with it once when he ran high power. But I don't
hear anyone setting grass fires with their 43 footers.
There are plenty of people who've published analyses of these antennas
assuming PERFECT 4:1 transformers that show that you're giving up a couple
dB here and a few dB there, and 10dB on 80m and 20dB on 160m with reasonable
lengths of normal coax. So why get bent out of shape when one of the
manufacturers quietly starts replacing the wrong transformer they shipped
for a while? It doesn't really matter to the basic technical validity of
this system. On 80m and 160m, the really effective way to use a 43 foot
radiator is to cancel all that capacitive reactance with the best inductor
you can find. BALUN or UNUN or whatever makes little difference on those
bands, it's just bad bad bad.
And besides, it is possible that for a lot of folks, the BALUN caused
ABSOLUTELY NO ISSUE. If they favored a band where their coax feedline
presented a high impedance common mode circuit, they wouldn't have even
noticed the problem.
Pick the company you like with the service you like and the quality of
construction you like. Pick the price you like, but don't get "soured" on
any one in particular for making a poor technical choice regarding the
transformer, because the *good* technical choice is essentially to stop
selling a very popular stick of telescoping aluminum to people who want
one. Even with a perfect, lossless, transformer the system is, in my
opinion, technically questionable no matter who sells it.
73
Dan
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