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[TowerTalk] Mosley Antenna Question

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Subject: [TowerTalk] Mosley Antenna Question
From: "Jim Thomson" <jim.thom@telus.net>
Date: Fri, 20 Feb 2015 10:25:19 -0800
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Date: Fri, 20 Feb 2015 08:02:43 -0800
From: Jim Lux <jimlux@earthlink.net>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Mosley Antenna Question

On 2/20/15 7:28 AM, Ed Sawyer wrote:
> It seems to me quite clear as to what Mosley's strategy is.  "Make my HF amp
> happy and let me crack most pileups in a reasonable amount of time and I am
> a happy DXer".  That means the lowest SWR at the output of the amp for the 3
> bands - period (think dummy load).  All of their trap design materials are
> design to be lossy and inexpensive and to balance with the lack of matching
> network at the feedpoint (again inexpensive).  The gain claims are legendary
> and ridiculous to the point of the strategy being that if someone really
> knows the theory - they will know this isn't real as a free space gain and
> waive it off anyway.  But a good portion of the market won't know any
> better, like the match, and as long as they get through to the DX will be
> happy.
>


It might also be that the perceived advantages are not so much in 
forward gain, but in the "shape" of the pattern in terms of side/back 
lobes.

When trying to make marginal contacts, or be louder than everyone else 
in a pileup, a few dB might be useful. Operating technique might 
actually be a bigger effect. Timing (when to make the call, either 
during the pileup, or with respect to propagation path availability) has 
a huge effect.

Suppressing undesired signals might also be very useful.  An antenna 
with good directivity and poor gain (e.g. lossy) might work really well, 
especially if you're in an area where that would help.

Imagine a couple scenarios:
1) You're the only ham for 1000 miles and there's no thunderstorm 
activity anywhere near you, etc.
2) You've got a lot of other hams around, and there's thunderstorms 
everywhere, particularly in the direction opposite your desired DX.

The ability to suppress the extra signals in scenario 2 might be more 
useful than a few dB of absolute radiated signal strength.


Lots of people claim that 0.5 dB makes a difference when you're close to 
the noise floor, and I believe it, and that's where skill and experience 
helps.  BUT.. to make the QSO, you need BOTH ends of the link to work. 
Are you presuming that the ham on the other end is also working against 
a 0dB SNR and is very skilled, so that boosting your Tx power (and their 
received signal) by 0.5 dB makes a difference?  Are they optimizing the 
passband of their IF, listening to SSB through a 1kHz wide signal to 
double the SNR over a 2kHz filter.

Or, are they receiving you with 10-15 dB SNR with a wide open receiver, 
because they're out in a RF quiet area, and 2 or 3 dB signal strength 
one way or the other makes almost no difference.


Hams focus a lot on gain and VSWR claims.. They're single numbers, so 
it's easy to rank performance.  They're also not necessarily indicative 
of actual operating performance.

Jim Lux 

 

#####  Nobody ever busted through a pileup.... cuz they had 40 db FB +  60db 
FS. 
Its ERP on TX....and nothing else.   Where the extra .5db or 1-3db of ant gain 
helps
is in busting a pile up.   If the DX station hears 100 guys calling him..and 
they are all exactly
S9.... and the 101st fellow comes along and is S9 +2db... guess who gets 
through. 

## Of course, ERP on TX  is the sum total of everything from feedline loss,  TX 
power measured
at the feedpoint, ant gain, and how high the ant is, take off angle, etc, etc. 

##  How u achieve your ERP on TX is up to you.  You can only do so much.  But 
when u start losing
a few db  from your trapped mosely, that stings.   If a 3 el 20m monoband yagi 
is say 5.3 dbd,
and your CL-33 is 2-3db down from that... that’s a huge amount.  That’s over 
half the gain of the
monobander right there !   Ditto with feedline loss.   Say u had 2 db of 
feedline loss to ur mosley.
Now u have lost a total of  4-5 db.   If all u have is a SB-200, you just lost 
another 3 db. 

##  If anybody thinks  there is minimal difference between a TA-33jr  and a 
hygain 204BA, try the test
yourself.   Put up 2 x  50  ft towers, 200 ft apart, side by side..and equal 
length feedlines.   Both ants
pointed at EU... then compare.    Forget the test range, the only range that 
counts is the one between
your back yard and downtown EU..or anywhere else.    The difference will make u 
gag.   The 33jr works on 15+10M...
and the 204BA  doesn’t.   The tribander has  a huge advantage with extra band 
coverage.... which
is its only advantage. 

Jim  VE7RF
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