Bob wrote:
*It seems that here we fall largely to the victim of verbal semantics.*
I thought you were going to rant about the marketing of antennas in
advertising.
I have long considered the ads and accompanying breathless "reviews" of
antenna products as the biggest swindle in amateur radio, one reason I
resist store bought antennas. It is identical to what I've seen in
Bicycling Magazine and SCUBA, too, with names changed to protect the
guilty. It wouldn't surprise me to learn that these ads and "reviews" are
all dreamed up by a small band of imagineers in a dingy office in Santa
Monica, the same outfit that writes Disney cartoons, Hanna Montana scripts
and airline ticket pricing schedules. The manufacturers insist on removing
"Once Upon A Time" from the ad copy before placing the ad.
For decades, we, especially the non-technical types, the dentists, and
lawyers and real estate brokers and office workers, have been sweet talked
into spending large sums of money in the belief that this new *DX
Pulverizer 9 Bander* with the lowest SWR from one end of the band to the
other, on every band too, even the new WARC bands, of any competitor, was
the ticket to ham radio nirvana, endless QSOs with anyone you wanted,
always S9 and usually 40 over, even without those bulky, finicky, and noisy
linears.
Almost nobody understands this stuff completely, and there is often harsh
disagreement between those who do, or claim to.
Since I moved here to the Rock Ranch, I've been spending a great deal of
time studying antennas of all types, going from website to website to
Antenna Book, to old QST articles. Often the road from ignorance to
understanding takes a detour through the dark forests of confusion, the
long way.
One disquieting aspect I have noticed is that there are a great many
designs and variations of antennas. Every now and then, someone comes up
with a "new" design, or a new variation of an old design, more likely, and
writes about his findings and the promising, perhaps even impressive,
results. Then, you run across users of the "new" design" who claim that
their antenna of that design works just fine, they have been making
contacts all over the place, their transceiver is happy with it and so are
the neighbors. No one claims that they are pile up busters, just good for
making contacts. "I can work everyone I hear!" they breathlessly write on
eHam reviews.
Pretty soon, one or more gurus come up with responses that poo-poo the
idea, explain why it can never work, that the resulting signals will be 10
db or more below a NVIS, the hapless user will be lucky to not set his
house on fire, it's nothing more than a complicated, expensive and hard to
duplicate dummy load and the feedline is doing all the work, or it wouldn't
work at all, and sometimes even offer models to demonstrate that.
I've experienced this myself. This spring I made a home brew clone of a
S9v31 vertical and made 4 Petlowany coils to use in place of radials. Several
self described experts considered the coils unusable, a waste of time,
"might as well use trash can lids!" Despite those gloom and doom
assessments, this antenna worked fairly well, surprisingly well considering
how modest it is, on Field Day. Running 5 watts, I worked from British
Columbia to Puerto Rico and San Diego to New Hampshire on 40, 20, and 15M
CW.
Somewhere in the hundreds of websites and articles I've read was a comment
from someone considered to be quite savvy on antennas that he had seen a
model that showed that a 36" rod stuck in the ground outperformed a 3 el
yagi at 60' or something like that. I wish I could find that article
again. The point was that modeling sometimes isn't always what it is
cracked up to be.
I have also had the impression for many years that a great many antennas in
use are not well installed, improperly, inefficiently, using poor or
deteriorated feedline, poor solder connections, corroded connections, and
similar maladies. Correcting those in a particular installation would gain
back quite a few of the missing dbs.
One challenge we inflict on ourselves is wanting to use the antenna for
multiple frequencies. It is no trick at all, apparently, to design an
optimum antenna for one frequency, like a broadcast band antenna. The
challenge is trying to come up with something that delivers an optimum
amount of fire on many frequencies from one wire.
Testing these concepts requires space, expensive equipment and lots of time
and energy. Read accounts of Rudy Severns' testing of verticals, laying
and removing dozens of radials of various lengths and taking readings with
tens of thousands of dollars of test gear he uses. Exhausting! I
remember participating with Wayne Overbeck, N6NB, 35 years ago or so
testing quads and yagis. He drove all over Southern California pulling a
70' crank up tower on a trailer and 2 ele yagi to do side by side
comparisons with huge antennas in place! You should have seen us putting
up a 70' crank up tower in the street out in front of this quad owner's
house!
We all know, and concede, that ~200' towers, stacked 4-6 el monoband yagis
properly installed, are effective antennas. The question is how to do the
best with a lot less, especially those who for one reason or another aren't
going to be able to put up those magnificent arrays. What compromises cost
the least in terms of effectiveness? What fundamentals do we dare not
ignore to get the best from what we can put up and use?
73 de W6OGC Jim Allen
On Mon, Sep 15, 2014 at 9:01 AM, Bob McGraw - K4TAX <RMcGraw@blomand.net>
wrote:
> It seems that here we fall largely to the victim of verbal semantics.
> Almost every radio I've owned, as well as the related printed manual, gives
> the indication there is a place to connect "the antenna". In fact, we
> don't actually connect the antenna but more correctly we connect the "feed
> line" or "transmission line" to the equipment and it is that feed line or
> transmission line that is actually connected to the antenna.
>
> In general the generic description we use, the antenna, has to do with
> the radiating part of our station, via various interconnect means, being
> described as "the antenna" and thus any tuning, more correctly matching, is
> then stated as "tuning the antenna".
>
> Yes, feed line loss due to SWR is a concern in many instances. Many
> feedline materials or choices have very low loss when operating at a
> matched condition. However we find the loss goes up rather dramatically
> when the feedline is operated at other than its design impedance. One
> needs to consult the published charts and tables to determine the matched
> loss for a given type of feedline and then an additional table to add the
> loss value when the feedline is operated with some value of SWR other than
> a 1:1 condition or matched condition.
>
> What is frequently overlooked, we take a given feedline having a loss of 1
> dB per hundred feet in a matched condition and use that feedline in a
> condition where the SWR on the line is 10:1. We then find the total loss
> is 1.0 dB plus the added loss due to SWR of 2.5 dB for a total loss of 3.5
> dB.
>
>
> 73
> Bob, K4TAX
>
>
> ----- Original Message ----- From: "Jim Brown" <k9yc@audiosystemsgroup.com
> >
> To: <tentec@contesting.com>
> Sent: Monday, September 15, 2014 1:53 AM
> Subject: [TenTec] SWR is a DUMB Indicator of Antenna Performance
>
>
>
>
>> My Ten-Tec 238 tune my 80 double ext.zepp on all bands 160-10 with a 4-1
>>> balun 182 ft of 400 ladder line then the 4-1 with 20ft of coax.
>>>
>>
>> No, it doesn't "tune" your 80 double ext.zepp, it creates a match between
>> the transmitter and the FEEDLINE that allows the transmitter to dump power
>> into the FEEDLINE. How much of that power gets to the antenna depends on
>> the mismatch between the feedline and the antenna. It's pretty common to
>> lose 10 dB between the transmitter and an "all band" dipole. 10 dB is 90%
>> of the transmitter power.
>>
>> I can make my 80M dipole look like 1:1 on 30M to my 200W amplifier, but
>> mismatch loss is determined by the match between the ANTENNA and the
>> FEEDLINE, and I would be burning 180 of those 200W in the feedline.
>>
>> Bottom line -- SWR is DUMB, STUPID, and USELESS as a measure of antenna
>> performance. I can LOAD a lightbulb, but it's a lousy antenna.
>>
>> 73, Jim K9YC
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>>
>>
>>
>
>
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