At 30-40 ft separation on 15 and 20, your two antennas are probably
within each other's near-field and each is thus "part" of the other.
The coupling in the near-field can be very high. The general rules are:
1. Separate the antennas by as much as possible, preferably several
wavelengths. A wavelength on 20 meters is ... well, ~20 meters [roughly
67 international feet].
2. Orient/position the antennas such that one is in the other's null.
For half-wave dipoles, that's off the end and FD experience suggests
colinear with each other and well separated works best. Note however, if
they are within each other's near-field, orientation may have little if
any effect [see #1 above].
During the BPL bruhaha a number of years ago, I modeled my my
non-resonant sloping-V and a couple of 12 KV distribution lines [which
would have been the BPL carrier] together using NEC-2, similar to K9YC's
suggestion, to see how badly I would disturb my neighbor's BPL I'net if
he had it. The coupling coefficient on 40 meters and higher was pretty
stable at around -30 to -35 dB. On 80 and 160, where the power line and
antenna shared a near-field, the coupling was in the -10 to -15 dB range.
As you describe them, and with perhaps 10 watts for easy math, the
received power might be one or two tenths of a watt. It's not real
surprising the receivers "cried out in pain" [:-).
73,
Fred ("Skip") K6DGW
Sparks NV USA
Washoe County DM09dn
On 4/16/2017 9:44 AM, kevino z wrote:
A friend and I both had our KX2 transceivers and some resonant end fed
antennas. He was on 15m and I was on 20m. Our antennas were placed about 30-40
feet apart, as slopers with the radiating ends up 30+ feet in the air using
Jack-kite poles. The plane of the antenna's slope were perpendicular to each
other.
We were both on 10w SSB.
Every time one of us keyed up, the other person's KX2 would experience a nasty
noise from the signal. Pre-amp was off, as was attenuator. My question is this:
Would the use of some bandpass filters have helped us? This is a situation we
are trying to resolve before operating QRP in a similar park for a QSO party.
If more distance between the antennas would have helped, what is the proper way
to determine the needed separation?
I read the other day about someone in a car using 3 or 4 Elecraft radios with
antennas on the roof, so I imagine there has to be a way.
Thanks,
-Kevin (KK4YEL)
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