On 8/30/13 7:18 AM, Gene Fuller wrote:
Yes. That's why ARRL will not print advertiers' "claims to gain".
sure they will, if you can back it up with antenna range measurements or
a credible simulation. Oddly, nobody seems to have that.
I think antenna mfrs are a in a no-win situation there.. If I
advertised a dipole and published the gain as 1 dBi (-1 dBd) (which is
probably about what you'd get with a typical dipole, as implemented,
accounting for copper losses, matching losses, etc), nobody would buy
it. They'd all go "I know a dipole has 2.15 dBi gain, so that W6RMK
dipole is a pile of junk". I'd have 50 reviews on eHam, half of which
would be 1s and 2s from people who hadn't even bought the antenna or
even seen it, but comparing it against the hypothetical gain figures on
the shipping carton of their wonder antenna.
"Our special matching network provides up to 12dBd gain on any amateur
band with no tuning when installed between two trees in your backyard"
(and when you ask the company about that claim they go.. Oh, it was a
typo, it should have been -12 dBd, but we already had all the boxes
printed before we caught it)
Then there's the "spec sheet prepared by someone who doesn't know what
they're doing".. A radio shack Vertical with a sort of interesting
tuning network ( couple of threaded rings that moved up and down.
essentially a tuned load.). They had the return loss and gain
backwards. No, it's not 15 dB gain and 1 dB return loss (at least if
properly adjusted)
Nope.. the best you can do is go buy the report from someone who
actually tested them.
I've been trying to convince the radio club at JPL that we should, as a
public service, do an HF antenna gain measurement festival on the Mesa
antenna range. We've got calibrated gear, multiple transmitter sites at
1200 feet, 3000 feet, and more, with big valleys in between.
What we don't have is (and this is the hard part, as the TriBand antenna
report authors will confirm)
1) A pile of antennas to test
2) A bunch of labor to run those antennas up the tower and back down. We
have a bucket truck to make that easier, but it's still a lot of work.
And in practice, you could probably get the antennas loaned, but they
come dismantled, so you need an ever bigger pile of labor to assemble
them for the test and dismantle them afterwards to ship back.
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|