In the interest of sharing - poor signal strength issues with Beverages are
most likely attributable to the balun and/or feed system rather than feed
line losses. Low SWR is not an indication of high transformer efficiency.
I have found through trial & error that baluns with low efficiency at the
frequency of interest will really kill the signal strength.
It is also important to eliminate the possibility of the feed line acting as
a BOG (Beverage-on-ground) antenna which can significantly degrade the
antennas performance. IMHO, best to wind Beverage baluns as
autotransformers (input windings separate from output windings) instead of
feedline transformers and ONLY ground the feed line at the station side
(grounding the coax shield at the antenna creates the BOG. Also if the
antenna is in an area with poor ground conductivity, be sure the antenna RF
ground is adequate - on both ends (may need some radials in addition to the
ground rod).
With respect to the noise/loss question, in general, the ability to receive
is all about S/N ratio. AGC in the receiver compensates (to some limit of
course) for low level signals. The noise is there all along - but when
there is significant signal loss then S/N is significantly decreased, AGC
kicks up, and we begin to hear that noise that would otherwise be buried
(well down) in the presence stronger signals....
Hope this info is of use.
Matt
KM5VI
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of David
Gilbert
Sent: Tuesday, May 13, 2014 11:18 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Beverage Layout Problem
Can you come up with a scientific explanation for why lossy coax picks up
more noise than does a lower loss coax? I can't.
And if you are able to do that, can you come up with a scientific
explanation for why less than a db difference in loss would make several
times that many db difference in the amount of noise it picks up? I can't.
There's something very fishy here.
Dave AB7E
On 5/13/2014 9:07 AM, Edward Sawyer wrote:
>
>
> You're going to have to explain that some more for it to make any sense.
> The total cable loss for 200 feet of RG-213 at 7 MHz is about 1 db.
> It seems to me that you'd have to have some really horrible impedance
> mismatches for the difference between RG-213 and LDF4 to even be
noticeable.
>
>
>
> The best clue that something is skewed, though, is your comment that
> the noise floor changes a bunch and the signal level not so much. That
> sounds like a termination problem of some sort, or more likely some
> kind of open shield in the RG-213.
>
>
>
> 73,
>
> Dave AB7E
>
>
>
> RESPONSE - That's because its not about loss differences. Its about
> the lossy coax also picking up sufficient noise to be amplified by a
> preamp and create noise floor. If you don't believe it. Lay out 200 -
> 300 ft of RG8x or Rg6 on the ground and connect a 20dB preamp to it
> and see if you hear anything with a good receiver - mine's a FT1000MP
> Mk V (and supposedly that isn't even any good - although I never seem
> to have problems hearing more than most other people). Then do the
> same thing with LMR600 or LDF4. All I can say is - there's a
> difference. And when you then connect a long beverage to it, you can hear
more than with lossy coax.
>
>
>
> Possibly if the pre-amp were mounted on the beverage feeds, you
> wouldn't hear as much noise pick up. But with 5 beverages, that's a
> lot of preamps for me.
>
>
>
> Ed N1UR
>
>
>
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>
>
>
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