Hi John,
In a message dated 96-03-22 10:50:48 EST, you write:
>Here are some thoughts as to why Beverages can underperform:
>First, they may be too close to other antennas, causing their
>directivity to be degraded by coupling to those antennas.
>The F/B on my European Beverage was only mediocre until I
>relocated it away from my verticals. Ideally the separation
>should be a couple wavelengths or more, which can be a problem
>for space-limited situations.
That makes sense and it's a good point. My Beverages were around a half mile
to a mile from my transmitting antenna, in the middle of an open field. The
closest power lines were about a half mile away, in the direction of my
house. The house was SW of the receiving antenna field.
>Next, it is my experience that impedance matching to the receiver
>makes a big difference.
That agrees with my feelings. I used ferrite transformers designed and tested
with an RF bridge. I'm always careful to nearly perfectly match my systems,
but since the feedline was so long I used a line amp with a pair of push-pull
high power low noise CATV transistors to drive the 1/2 inch hardline from the
receiving antenna control box. The amp was switchable (via tone controls) in
and out, and I could select a remote attenuator and up to 32 antenna ports
also.
>One must also be careful to avoid stray pickup on any vertical
>downleads from the Beverage to ground, at the termination end
>for example. I use shielded leads for this purpose.
A single conductor lead can not be shielded from electromagnetic fields
unless special conditions are met. The requirement is that the shield and
center conductor carry equal amplitude and exactly opposite phase currents.
That's nearly impossible to accomplish when feeding a single wire antenna.
Unless there is an "electrically correct" counterpoise at the height of the
antenna, the vertical feedline will always "pick up" signal, shield or no
shield.
>Incidentally, I have never found that anything better than a
>simple ground rod (8 foot long) is needed for my Beverages.
>This is a high impedance antenna, so ultra-low ground loss
>is not a critical requirement. I suppose in situations,
>like rocky ground, where one cannot drive in ground rods,
>some radials could be used instead.
I've found just the opposite, and let me explain why. The feedline can be an
antenna. It can receive noise or unwanted signals, just like an antenna
laying on the ground will. The feedline can also conduct common mode
interference from noise sources to the antenna location. If any parallel or
common mode currents exist on the cable, they can "pump" the ground system up
and down with unwanted RF. Another way to view this is the feedline acts like
part of the ground system, with the power dividing in proportion to the
ratios of the resistances of the ground and the common mode impedance of the
line.
Unwanted signals can also couple via radiated field effects to the antenna!
Even if the antenna has a high impedance, it does not eliminate this problem!
The only ways to eliminate this problem are to:
1.) Install decoupling common mode chokes on the feedline and ground the
feedline at several points on the way to the antenna with independent ground
rods.
2.) Use a feedpoint transformer that has independent secondary and primary
windings. Never connect the feedline shield to the Beverage ground rod.
Ground the feedline to it's own ground several feet away.
3.) Improve the Beverage ground until it is of much lower impedance than the
common mode impedance of the line. Then the Beverage does not try to ground
through the feeder.
If this isn't done, the feedline can easily be part of the Beverage system
and decrease performance!
>In conclusion, I find my Beverages are absolutely essential to
>doing serious weak signal DXing on the low bands. (Fred, I
>have to confess that it was hearing the Beverages working at
>your QTH over 10 years ago that motivated me to install mine,
>so I find your comments a bit ironic!)
Beverages work well here too John, it's just that other antennas work a bit
better. 3-4 dB improvement on a quiet night is a lot of receive improvement
for an antenna so simple to install! But a four element phased array will
improve things 6 or 8 dB under the same conditions!
On a noisy night, if the noise happens to be coming from a null in the
Beverage pattern, things can improve by 20 dB! But phased antennas, when
properly installed, can provide 40 dB (or even much more) improvement!
73 Tom
>From Michael H Bragassa <bragassa@hal-pc.org> Sat Mar 23 04:14:43 1996
From: Michael H Bragassa <bragassa@hal-pc.org> (Michael H Bragassa)
Subject: setting pier pin for 45G
Message-ID: <Pine.BSF.3.91.960322220734.20741A-100000@hal-pc.org>
Hello Rev!
I did a similar thing there in Casper, when I set my tower on the patio
cement. I drilled the required number of holes into the cement with a
rented hammer drill. Don't EVEN think about doing it w/ your hand drill
es carbide bits! Took 1 minute to drill each hole!
Then I placed my bolts in these holes , threads up, and cemented them
with a mixture of sulpher and ????. Call W7PSO / K7GLL /K7FE: One of them
gave me the idea of the mixture??? It will hold...forever! Maybe, 'today'
an epoxy of sorts would work just as well?
Hope you are 'reading' these good 'posts' on Beverages...for the ranch?
Hello to all in 'The Windy'.
73 mike R3/AA5NK
On Fri, 22 Mar 1996 Mortonwg@aol.com wrote:
> Gentlemen: My old Rohn HDBX-48 bit the dust this past winter and I am
> replacing it with 80 feet of rohn 45. The base is very large for a guyed
> tower set up, however I still need to set the pier pin in the existing base.
> What kind of bonding agent have some of you used to bond the pier pin to the
> base. The pin is 12 inches in length and the hole I will drill will be
> approximately 7-8 inches in depth. So, how do I keep my 4 year old from
> reaching in and pulling the pin? 73's es DX , Rev Morton WS7W
>
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