Topband: Re: phased beverages
Fri, 23 Apr 1999 10:18:52 -0400
> I have used the RG-58 cable but the loss was very high ( the distance from
> shack to the feed point is abt 300 m ) this is to avoid the interaction
> with the vertical transmitting an. I would like to replace it now wit low
> loss cable used for sat tv ( 75 Ohm ) Should I transform from 75Ohm to
> 50Ohm on the separate receiving ant in my IC-756 ? or just simly connect
> the ANT to the RCA socket ? Does the mismatch have gerat influence on the
> overall receiving performance ?
In this application it won't make much difference. You have a lot of
headroom on 160 meters, unless the feedline is miles long small
cables are fine. Also, there is very little difference in loss unless
you go up to a large cable. As pointed out, cable loss is mostly
due to conductor resistance loss until extremely high frequencies
A small additional loss from mismatch won't matter either.
> I am considering to build a phaised two Beverages in one direction where
> my space is limited, however I would like to use the Beverages for
> multiband operation 80 to 40 m. Any suggestions on the spacing ?
It would have to be fairly close for multiband operation. I have
successfully used multiple Beverages in a 160/80 array, but never
on 40. For 160 and 80 a 70 foot stagger and 30-70 foot broadside
spacing can be used to enhance performance, but that stagger
gets too much for 40. If you stagger less than 70 foot, 160
performance will deteriorate.
> Can I use the TV Ant splitters for the phaised Beverages ? If not what is
> the phasing method for multiband operation ?
CATV splitters generally fall apart on upper HF, very few work well
below 10 or 20 MHz.
It is easy to build splitters, I build my own. Wind a center tapped
bifilar winding on a high ui core, and connect a resistor twice the
value of each split port across the entire winding. Take the
common from the center tap, and step it up with a 1:2 transformer
(5:7 turns ratio autotransformer). 73 material cores will work well,
but the core isn't critical.
The problem is phasing. You can use a delay line equal to the
stagger distance in electrical degrees. Invert one antenna 180
degrees at the feedpoint, and insert the delay line in the feed to the
REAR element. The result will be frequency independent phasing
that enhances signal in the direction of the element without the
I'm giving a talk at Dayton in the antenna forum on this type of
73, Tom W8JI
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