Greg - ZL3IX wrote:
> Hi all,
>
> I have recently constructed a 2-wire Beverage at my remote Rx site.
> It's performance is fair, but the F/B ratio in the forward direction
> leaves a little to be desired, so I have been doing a couple of
> impedance and insertion loss measurements.
>
>
>
Greg,
I did some tests on a DXE two wire ladder line system and was most
disappointed that I did not take their advice on unused port termination
long ago. On my two wire systems I run two separate RG-6 lines and they
are close to 1/2 when considering the velocity factor. (The DXE
switching system with internal relay was acting up with some stray
current so I began trying everything to fix the problem.) While
listening to two AM station on 1400 Khz I noticed that while placing a
termination on the NW feedline and RX-ing on the SE feedline the traces
of the NW station vanished. (The NW station is in PR about 200 miles and
the SE station is in the Grenadines about 350 miles to the SE from St.
Croix.) I repeated these test over and over and the termination on the
unused feedline appear essential to a better f/b on a two wire
Beverage. Using the termination made all interference to completely vanish.
DXE recommends for their two wire boxes a single feed line with
switching the internal relay with a power inserter while terminating the
unused port. The KD9SV dual wire boxes, which I use for the WD-1A wire,
(the wire cost much less than ladder line and appears very rugged.)
I did however find that the RG-6 can be terminated effectively at the
shack...my test were for 1/2 wave considering the VF of 78%. But
screwing off and on a BNC connector everytime I changed the antenna
direction especially during a contest was not an option......so I came
on a simple solution:
1. Place a BNC Tee connector on each in coming two wire Beverage
transmition line.
2. Connect one side to the regular RX bank antenna switch.
3 Connect the other side of of each BNC tee to a non grounding
switch...anyone with
PL-259 and adapters for BNC will be fine. I have some three position
type F switches
that would make things easier if you don't like to crimp BNC connectors.
4. Place a single 75 ohm termination on the out put of this switch to
terminate the feedline
of the reverse direction. A three position coax switch will do 3
reversible Beverages or
allow for two with one open position as you may require.
I had a bunch of pushbutton Dynair 6x1 and 10x1 position video
distribution switches which I sold on e Bay that terminated every unused
PL-259 port in 75 ohms. I have one left that I will try to mount
somewhere. But since they have rack mount ears and take a bit of
pressure to actuate I have stayed with the rotary concoction.
My tests have proven to me that DXE suggestions of termination of the
unused two wire feed port is really important for F/B and pattern
continuity.
73,
Herb Schoenbohm, KV4FZ.
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160 meters is a serious band, it should be treated with respect. - TF4M
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