Posted by
k6dgw on
Apr 16, 2017; 6:08pm
URL: http://elecraft.85.s1.nabble.com/OT-operating-QRP-at-same-park-tp7629369p7629373.html
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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