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BevFlex-4X Installation Manual Rev 2.23 November 2019
32. Why are the coaxial feedline connections reversed for the EWE, FLAG, and VE3DO antenna system
configurations?
The EWE, FLAG, and VE3DO antenna configurations operate with the received signal transformer at the end of the
antenna wire toward the direction of reception. The Beverage and BOG antenna configurations operate with the
received signal transformer at the end of the antenna wire away from the direction of reception. The EWE, FLAG,
and VE3DO configurations operate as a pair of top coupled, phased, vertical antennas while the Beverage and BOG
configurations operate as resistively terminated traveling wave antennas.
33. How do I measure the impedance or resistance of the various components of the system when
troubleshooting?
The end termination units and the feed-point unit all utilize RF isolation transformers between the various segments
of coaxial transmission lines. Resistive measurements with an Ohm meter are of little value other than determining
if there is a broken connection. The DC resistance measured across either of the feedlines to the shack will be a
low value equal to the DC resistance of the coaxial cable in series with the DC resistance of the transformer in the
feed-point unit. The DC resistance measured across either end of the coax used as the antenna will be a low value
equal to the DC resistance of the coaxial cable in series with the DC resistance of the transformer in the end
Terminator Unit.
You can use an Ohm meter to verify the terminating resistor values in the control box. This is done by measuring the
resistance across the A or B inputs to the control box. The A input should measure 75 Ohms with the switch in the
Forward position. The B input should measure 75 Ohms with the switch in the Reverse position. The only way to
accurately measure the rest of the components of the system is to use an RF antenna analyzer to determine the
actual RF impedances of the parts of the system you are troubleshooting.
34.
What can an RF antenna analyzer tell me about the operation of my BevFlex-4X?
If all the connections are intact, and the correct impedance taps are selected on the end termination units, you
should see a VSWR of typically less than 2:1 (referenced to 50 Ohms) across a frequency band from 1.8MHz to 10.0
MHz when you look into the “TO RX” connector of the control box with an antenna analyzer. As the frequency is
swept across this range of frequencies, there should not be a large variation in the VSWR reading
35. I want to avoid running multiple pairs of coaxial cables to my operating position. Can I control multiple
BevFlex-4X antennas from a single control box?
Yes, you can use a remote coaxial cable switch. Many companies produce them, including DX Engineering, MFJ,
etc., but they may require modification.
For proper operation, the unused direction coax must be terminated with a 75 ohm non-inductive resistor. Most
commercial antenna switches made for transmitting either leave unused ports open or short them to ground. Some
switches designed for Beverage antennas terminate unused ports. You will have to determine if the switch you plan
to use provides proper 75 ohm termination, and make modifications as necessary.
Coaxial switches that isolate the shields of the connecting cables are preferred. Most commercial coax switches use
connectors mounted in metal cases, shorting the outer connections together. Shorting the shields from multiple
receive antennas may introduce common mode noise. Multiple loops of the coax through a large, low frequency,
ferrite toroid at the switch may resolve this problem.
You can also make your own remote switch by mounting DPDT switches in a water tight case. eBay and
Amazon.com sell very inexpensive DPDT relays mounted on circuit boards with screw type terminals that will work
well.
