Fellows, when you read the summary that Lee so kindly provided, please
keep in mind that you can use ordinary coax as the capacitor. If I remember
correctly, solid dialectric has a higher breakdown voltage. Any handbook
will give the capacitance per foot, but I think RG-8U has about 43pf per
foot with a breakdown of about 4000 volts. More than sufficient. I use
it all the time in parallel LC networks where I feed the antenna at the
base.
As to the comments about making the antenna longer ( supposedly to raise
the impeadence) and inserting a cap in series to tune out the reactance,
that will work fine, but if you do so, keep in mind that you're only
fooling yourself. Impedence is the sum of the antenna's resistance AND
reactance. Reactance defined in general terms is "a resistance to do work )
For example. a large motor will have enormous inductive reactance, and
simply whacking the power to it probably will result only in a blown
breaker. However, if you hang a sufficient capacitive reactance across the
main windings, you cancel that "start up resistance" and the motor starts.
At some speed, a centrifugal switch disconnects the cap, and you're off
and running. Unfortunately, we can't switch our cap out...The cap will
indeed cancel the inductive reactance, but some power is lost...
This is another case of worshipping the "SWR god". Match the antenna, NOT
the coax. If you want to really raise the resistance of the inv L, make
it a folded inverted L. That will give you a step up from about 37 ohms
resistance to about 148 ohms. ( and about a 1.4 SWR using a 4 to 1 balun )
( or about 1.28:1 if you use a 1/4 electrical wave of 72 ohm coax from
the antenna to your 50 ohm line.
Using that same principal, and assumming we have a vertical height of
about 65 feet, why not make the entire antenna vertical using a folded
tripole? At about 18 ohms to start with, we increase the RESISTANCE of
the antenna to 162 ohms, with 0 reactance, ( better know as resonance )
giving us a match of about 1.4:1 with either a balun or a quarter wave..
Flames will be ignored, but honest disagreements, commentary, or antenna
discussions ( wish we had an ant reflector )are most welcome.
Ed
-------------------------------------
Name: ed sleight
E-mail: k4sb@avana.net
Time: 12:26:37 PM
This message was sent by Chameleon
-------------------------------------
>From w2vjn@rosenet.net (George Cutsogeorge) Thu Oct 17 00:57:37 1996
From: w2vjn@rosenet.net (George Cutsogeorge) (George Cutsogeorge)
Subject: Ferrite Beads
Message-ID: <M.101696.165737.37@ppp008.rosenet.net>
While looking for some split beads to quiet down an unstable signal eminating
from our fax machine, I came across some engineering samples of type "J", or 75
material that I had forgotten about. Type J is recommended by Amidon for RFI
applications below "5 to 10 MHz". The other split beads on hand are type 43,
recommended for "30 to 200 MHz". Both types on hand are the kind with 0.25"
holes and are 0.562 square by 1.125" long. I put two turns of #22 wire on each
set and checked the attenuation on an HP network analyzer. Here are the
results:
Frequency Type 75 Type 43
0.15 MHz -0.3 dB -0.3 dB
1.0 -2.4 -2.5
3.0 -6.2 -7.1
10.0 -11.0 -13.0
30.0 -16.0 -17.5
It seems there is little difference between the materials over the frequency
range we are interested in. On these two samples there appears to be a slight
advantage to the type 43. I can only assume that type 77 will fall inbetween
these results as I have no sample. If some one has a type 77 bead in the
configuration described, I would be glad to run a sweep on it.
As for the signal from the fax machine which was S3 on 20 meters; two turns of
the line cord around a large type 43 bead made it barely audible in the noise.
George
----
George Cutsogeorge, W2VJN
Umpqua, OR.
http://www.qth.com/topten
>From n4vhk@sumnet.summit.winston-salem.nc.us (HENRY HEIDTMANN) Thu Oct 17
>13:26:28 1996
From: n4vhk@sumnet.summit.winston-salem.nc.us (HENRY HEIDTMANN) (HENRY
HEIDTMANN)
Subject: DVP schematic
Message-ID: <199610171226.IAA00440@sumnet.summit.winston-salem.nc.us>
I have purchased a DVP board from LZ engineering. I am about to finish the
db15 cable, but I noticed in the schematic that there are two "mic" wiring
points. However, I dont which one goes to the rig, and which one goes to the
mic...Successive calls to LZ have gone unanswered(maybe they have left for
CQWW SSB dxpedition or something)...If anyone has made their own cable for
DVP, let me know which is which....Thanks for the bandwidth...
Henry Heidtmann, N4VHK
W4NC Multi-single Team, CQWW SSB
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