----- Original Message -----
From: "W7CE" <w7ce@curtiss.net>
To: "W4ZW" <w4zw@comcast.net>; <towertalk@contesting.com>
Sent: Saturday, August 19, 2006 7:15 AM
Subject: Re: [TowerTalk] small antennas
> Having a 402CD 14' above the SteppIR (less than 0.3
> wavelength) will most likely reduce the F/R performance of
> your SteppIR.
The 40-2CD normally stacks well with a tribander, but may
affect 18 and 24 Mhz. It can also affect 10, 15 or 20 if an
"unlucky" length of feedline is dangling off the 40-2CD's
driven element.
The easiest way to check for interaction between two
antennas is to do a quick front-to-back experiment with a
local ham, who is located 200 meters to several miles away,
with line of sight. If two antennas are interacting, front
to back ratio is the parameter that is degraded most, and is
therefore the most sensitive indicator of degradation.
To do the experiment:
1. Point your antenna away from the local ham.
2. Have him transmit a brief key-down signal.
3. Note the s-meter reading.
4. Point the antenna toward the local ham.
5. Have him transmit another signal.
5. While he is transmitting, crank in fixed attenuators
until the s-meter reading returns to the level noted in step
3.
6. Read the front to back ratio from the attenuator setting.
Precision attenuators are nice, but the fixed
attenuators/IPO/AIP on most rigs are fairly accurate, and
should give you a good idea whether the front to back ratio
is reasonably good.
Sometimes just changing the 40-2CD's feedline, or
shorting/opening its feedline when the antenna is not being
used will solve interaction problems.
Dave Hachadorian, K6LL
Yuma, AZ
.
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