[TowerTalk] Beverage doubts.

[Tom Rauch]

> Date:          Wed, 22 Apr 1998 11:21:16 -0400

Hi JP,

> On certain occasions, the beverage might be better, but not enough
> to warrant the construction and maintenance.

I've been keeping a running total of mornings my Beverages are better 
than my 160 4 sq. The Beverages are better about 1/3 the time during 
darkness, and nearly 100% of the time after daylight or before 
sunset.

However, by using a system similar to the MFJ-1026 (with beefier 
and lower noise internal amps) to phase the Beverages as pairs (I 
have two groups separated about 300 feet apart) or phasing one or 
both pairs against the  4 square, I can pick up a few more dB S/N.   

Under ideal conditions phasing all the antennas together improves 
S/N about 6 dB or so, and that is substantial!

> My experiences with LONG beverages are limited to a few stints 
> as the 80 meter op at K1KI's multi/multi.  Tom has a 4-square
> that really kicks butt. On 80, I had a selection of beverages,
> most of them 5-600 footers, but one 1200 (!) footer to Europe.
>The 1200 foot beverage was incredible, allowing me to pick out
>signals that were barely audible on the 4-square. 

I had the selection of 2 wl or  same direction 1 wl Beverages on 
160. I never found a case where the 2 wl Beverage was any better. 
Others (like W8LRL) report the same thing.

But if I don't terminate a Beverage, or terminate it incorrectly, the 
extra length makes a big improvement in F/B and often in S/N. That's 
because the F/B ratio of a long wire is directly related to the 
return loss of the antenna, and the longer antenna has more return 
loss when the system is improperly terminated.

I measured current in several Beverages over the years. At the end 
of 500 ft on 160, with a 7 ft high antenna, 25 to 50% of the current 
is gone at the far end. That's 3 to 6 dB of power loss, and 6 to 
12 dB of return loss.

Measurements like mine are confirmed in textbooks, where long wires 
close to real earth have been measured.

> Someone else made a comment disparaging pre-amps in general on
> beverages, but I can't agree.  At the KE2NL station, we successfully
> pre-amps on
> the 580 foot EU beverage.  However, the primary transmit antenna is
> a pair of phased dipoles, and doesn't have the F/B and F/S of a
> properly functioning 4-square.

There was considerable discussion of this on the topband reflector. 
The fact is the atmospheric noise level on 160 and 80 is so high you 
hardly need worry about system noise figure.The system requires just 
enough gain to keep the AGC working, but the noise figure can be 20 
dB or more in many cases with no S/N degradation.



At my very quiet rural location, a 20 dB nighttime system noise 
figure is enough and an external preamp is unnecessary (even though 
my Beverage feedlines have 5-8 dB loss). It's only during daylight I 
need pre-amps, and even then a 5 dB noise figure is plenty.

MMIC's used in some pre-amps are very prone to overload. The 1 dB 
noise figure is a great thing at UHF when pointed at the sky, but on 
160 and 80 totally unimportant. It would be much better to give up a 
bunch of that ultra-low noise figure for more power handling 
headroom, since the pre-amp must handle the accumulated power of ALL 
signals passing through. Many of those signals are strong enough to 
drive a set of headphones to fair levels, with only a diode between 
the headphones and antenna! 

MMIC's have the advantage of being easy to use, but offer poor 
performance in HF receive applications. If I connect an IMD-prone 
MMIC preamp to my Beverages, receive system performance deteriorates 
(just like the other guy observed). 

73, Tom W8JI
w8ji.tom@MCIONE.com

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