Martin,
Over the past 13-14 years of hearing comments from K9AY Loop users, plus my
own experience, here is what I've learned...
1. If the loop works well with only a ground rod, don't install radials. I
have seen worse performance with radials on my own loops. When radials are
added to a "good" loop the rearward null is at a higher angle and generally
less effective. (Depends on the length of the radials, too.)
2. If you choose to install radials anyway, the optimum terminating
resistance will change, but there will be a value where a null is obtained.
3. A larger loop is OK on 160M. I have used loops 25% larger than the
published design. Signal level is a bit higher on 160M, but they don't have
as good F/B on 80M. A different resistor helps on 80M, but a resistor +
inductor or capacitor is really needed to get a deep null. Maximum size with
just a resistor is about 1/4-wave of wire -- the original design had 85 feet
of wire and was OK, but not optimum on 80M.
4. There are always some local variables in ground quality, but performance
seems to be quite consistent wherever there is "real dirt" of some sort. It
is more difficult with the extremes of salt water, or rocks and sand!
73, Gary
K9AY
...Sunday afternoon i added 3 Radials for each leg of the loop and a short
> ground rod, abt. 1m only.
> There was no improvement , it made things worse instead . Well at least
> i feel so.
> Without the radials and ground rod, i feel that the directivity is a lot
> better. OTOH, on AM-BC, the directivity is impressive with the ground
> rod and radials.
>
...Is the size of the loop critical? Mine is a bit bigger (abt 2 or 3m)
> than the original design by K9AY cuz i goofed with the math...
>
...The coax is not grounded at the switch-box (it shouldn't be, right?).
> The radials are just as long as the leg of the loop,
> one is under the wire , 2 more split about 30-40 degrees each side.
>
...If i optimize the Resistor for best Null, will it work for topband only?
>
.> Martin DM4iM
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