Topband: Re: phased beverages

[Tom Rauch]

Hi Dan

> 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 
are reached.

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 
delay line.

I'm giving a talk at Dayton in the antenna forum on this type of 
phasing.


73, Tom W8JI
w8ji@contesting.com


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