Hi folks
I would like to add some comments to receiving antennas issue. Any resonant
thing (wire, cable, rotor cable tower, TX antenna...) will interact with the RX
antenna if they are in the same polarity, different polarity has 27 dB or more
of isolation due the polarization itself.
The inverted L is easy to detune, just open the wire from the coaxial and check
the noise on the EWE. The noise on the RX antenna needs to decrease one or 2 S
units. However, it is possible you will not see any difference. The reason is
that you may have another point where common noise is deteriorating the
directivity of the RX antenna. If it work, just add a relay for detuning the
Inv L during RX.
The integration with the inverted " L " TX antenna is the easy one do fix the
others resonant "things" could be difficult to recognize. Example, if you have
a low dipole or elevated radials, these "things" will destroy any directivity
of nearby RX antennas, and nearby distance on 160m means 300ft or more, one
wavelength. Rotor cable, VHF or other's 120ft feed lines could be resonant and
a good reflector for noise and re-radiate them too.
Lack of good ground (or no ground at all) is receipt for failure on RX. Running
the cables outside the tower and far from the ground is the preferred way to
screw things up.
I am following every installation of my WF's and there is an issue very
frequently found. It is bad connectors contact with the cable shield. Cold
solder, no solder, little copper wire on the braid. One single point with a bad
shield can ruin you RX system.
Doug Waller when he build the first WF was very disappointed with the results
until he found a RCA connector with one RCA ear not contacting the preamp
input RCA female. Just one little gap in ear with no contact was enough to leak
noise into the preamplifier input. After fixing the bad contact, the RX antenna
started to work with good directivity. PL259 or a F connector with bad contact
with the braid can cause several S units of noise.
Spending big money on the radio and do not care about the quality of the
connectors used for RX is no sense.
Open frame relays (not coaxial relay), open contact switches, plastic boxes are
the most common points to add noise and destroy the directivity pattern.
Running cable outside de tower and ground them at the base is not a very
popular solution. It is hard to run the cables inside the tower they say. As a
result RF is everywhere in the shack. No solution for that too.
I am just trying to help, there is no free beef regarding good RX systems.
73's
JC
N4IS
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