Hi Ingo....
Remote beverage switching is easy to do without any control cables, just by
piggybacking the DC control voltage on the feedline.
At the receiver end, a series capacitor (typically .01 mf or .001 mf)
isolates the Rx from the DC voltage on the feedline. An RF choke (typically
2.5 mh or 1 mh) connects from the feedline side of the capacitor to the DC
supply. The RFC isolates the power supply from the RF.
At the feedpoint end of the feedline, a series capacitor (same as above)
isolates the antenna from the DC voltage on the feedline. On the feedline
side of this capacitor, another RFC is connected, supplying the DC voltage
to the relay or relays and isolating them from the RF.
I have used this on feedlines over a half mile long. On long runs, I prefer
24 VDC relays and supply a slightly higher voltage (up to 40 volts) to allow
for the voltage drop of the feedline.
If you only want to switch two antennas, a single relay will do, and the
voltage may be either positive or negative. For three antennas, two relays
are used, with a series diode determining whether each relay will be
activated by a positive or negative voltage. The relay contacts are wired so
a positive voltage selects one antenna, a negative voltage selects another,
and zero voltage selects the third.
I wire the relays so unused Beverages are grounded.
I use Potter & Brumfield open-face relays with DPDT 10-amp contacts. These
are mounted in small boxes at the feedpoint, along with a toroidal matching
transformer. I've been using this system since about 1981, at two locations,
and am still using the original relays.
The relay coils should be shunted with a .01 mf capacitor and a diode to
minimize voltage transients.
ON4UN describes a similar system in his book "Antennas and Techniques for
Low-Band DXing).
The same technique may be used even if the beverage feedpoints aren't all at
the same location. Additionaly matching transformers would be needed at each
feedpoint, of course.
I've also heard about a slightly more complicated arrangement for selecting
four remote antennas. The fourth position was obtained by applying a low AC
voltage to the feedline. The rectification in the series diodes to the
relays would cause both relays to be pulled in simultaneously.
73 and see you in the CQ WW 160m DX Contest! Happy New Year
Jon AA1k
At 11:33 AM 12/29/96 +0200, you wrote:
>In preparing for the CQ WW 160 contest in January
>at SM5HJZ we would like to switch the Beverage antennas
>with a remote switch. Since the Beverage site is
>rather far away we want to keep the number of
>control leads as few as possible. Does anyone have
>any information or hint on the subject?
>
>73 de Ingo SM0AJV
>
>
>
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