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[TowerTalk] Steve Best on Mismatch loss, transmitters andtuners

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Subject: [TowerTalk] Steve Best on Mismatch loss, transmitters andtuners
From: w5rz@troi.csw.net (Dennis Schaefer)
Date: Thu, 23 Jul 1998 21:23:58 -0500
At 11:11 PM 7/22/98 EDT, T93m@aol.com wrote:

>and on the end  I must say that I learned more in couple of months on this
>reflector than in 5 years on HAm antenna reflector....so keep up good work...
>the more YOU argue about, the  MORE I will laugh..( or I  should say
>learn).....
>
>73 de Danny /T93M

Danny,

I took this message as being facetious ("the MORE I will laugh").  If so,
I'll give you the benefit of the doubt and assume it was a reaction to
perceived criticisms of your company.  To Cushcraft's credit, Steve Best
seems to be taking a gentlemanly approach to the discussion.

The whole thing started with Steve's seemingly radical statement:

    "The above statements are perhaps the biggest misconception in the 
     amateur hobby regarding antennas.  Antenna VSWR does reduce antenna 
     gain.  No question.  If you feed an antenna with a 20:1 VSWR you will 
     give up 7.41 dB of radiated power.  VSWR results in a mismatch loss 
     regardless of cable attenuation."

THIS STATEMENT WAS MADE AS AN ABSOLUTE.  THERE WERE NO QUALIFIERS.
Since this conflicts with almost everything written by other "antenna
experts" (DeVoldere, Orr, Moxon, ARRL, etc.),  of course it evoked some
lively comment.  In the course of that discussion, there are naturally some
questions by those new and less informed.  That does not negate the
comments of the truly learned (including yourself).  I have learned a lot
from following the discussion.

The ARRL Antenna Book says:  "For example, 100 feet of 300 ohm receiving
type twin lead has a loss of only .18 dB at 3.5 Mhz, as shown in Chapter
24.  Even with an SWR as high as 10 to 1 the additional loss caused by
standing waves is less than 0.7 db."   


Danny also says:
"5. I won in couple of contest not because good setup and matched antennas, IT
WAS PURE LUCK!!!"

Our Field Day group operates one CW transmitter and one SSB transmitter.
This year, our CW station used two 40 meter Extended Double Zepp antennas
tuned with a Johnson Matchbox tuner.  That was all - no beams or coax fed
antennas.   I didn't model the impedances, but I'm sure the mismatch was
horrendous on most bands.  (we used it on 80 through 10).  We made 1148
QSO's on that one station, which surpassed any previous efforts, even when
using a tribander (Cushcraft!) and good dipoles.  Was this antenna better?
Antenna evaluations are usually very subjective,  but  I can say it sure as
heck didn't have 7.41 dB of radiation loss compared with previous resonant
antennas.

There are good reasons for Cushcraft and other manufacturers to produce
antennas that match "50 ohm" coax.    If Cushcraft starts making EDZ's,
they will need to include a matching network or recommend a tuner.   And -
a Cushcraft or homemade EDZ with a good link tuner such as a Johnson
Matchbox (No baluns) will put a stronger signal into a distant location
(broadside) than a perfectly matched, coax fed dipole.  

The X-7 and X-9 seem like tremendous products.  I am tempted to buy one.  I
really hope I misinterpreted your message, and the powers-that-be at
Cushcraft are paying attention to some of the real knowledge present on
Towertalk and are not entirely smirking at our "funny" ideas.

I have been in military communications and have worked closely with the
state OES and other govt.agencies.  Design considerations are vastly
different than for ham radio.  Our state OES office has a huge discone-type
antenna for HF, which I think cost $250,000.  "Eyeball analysis" tells me
that it was designed to work over a large frequency range, and also that it
has little gain.  The new HF protocol calls for some sort of rapid
frequency hopping, so tuners probably aren't practical.  This antenna is
probably a great design for its intended purpose.    For a spot frequency,
a dipole would probably kick it's butt in the favored direction.  They
simply don't have the luxury to build an antenna that will deliver "maximum
smoke" to a given area  on narrow frequency bands.  On several occasions
during emergency exercises, a ham HF station has relayed for an Army
National Guard HF station running a KW.  Again, the same circumstance.  The
ham station was optimized for 3.9 Mhz and it worked better ON THAT
FREQUENCY than the multi-thousand dollar setup right next to it.

I know, some scientific types will scoff at my "anecdotal" evidence.  Wanna
challenge our CW tent to a head-to-head next Field Day?

(All offered in the spirit of lively discussion - hope no one is offended)
73,
Dennis,  W5RZ
 
     



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