Beverage Experts -
I have been giving some thought to the beverage situation at my station in
Barbados. The last few time I have been there, I have put up an 800 foot
beverage toward the US with mixed results. On 160, the beverage is much
better than the transmit antenna (inverted V) and is probably the difference
between hearing and not hearing for at least a quarter of the QSO's. On 80,
it adds no value at all over the transmit antennas.
One area that always bothered me is the sloppy job I have done with the
grounding. The earth there is coral and pounding a ground rod more than a
few feet is a Herculean task. This is particularly bad on the feed end but
the termination end is only slightly better. Typically, I have sunk a
couple of shallow rods at the feed and one at the termination. One's
intuition would be that the coral is a poor ground but it is possible that
the embedded salt could be factor. I have no idea.
This year I was contemplating drilling holes at both ends. Actually 4 ends
since I wanted to have an EU beverage as well. However, my skepticism about
the effectiveness of the ground rods made me wonder if I was better off with
radials instead. In the archives is a statement from W8JI that a good
ground rod still had 100 ohms impedance on 160. Since I did not have
anything that could be called good, I am wondering if my ground rods are
doing anything at all. Instead, I modeled the antenna with a single 1/4
wave radial for 160 and it modeled as expected. I added a 1/4 radial for 80
as well and once again the model and source impedance were what I was
expecting. This seemed like a reasonable solution for use on 80 and 160.
The same exercise was done on the termination end and the results again were
as expected.
The surprise here was when I removed the far end terminator and the source
impedance went sky high, which is not my experience with unterminated
beverages. This made me question the accuracy of the other findings.
My questions are part theoretical and part practical. First, is my line of
thinking valid in terms of using radials to provide low impedance points at
the source and termination ends? Is there an even better idea? From a
practical perspective, is there a significant advantage to adding more 1/4
wave radials (it is already a fair amount of wire)? Do the radials pickup
signals from unwanted directions if they are above ground? Is there a
preferred orientation to the radials? Should I use any ground stake at all
on either end?
Any other guidance would be welcome either on or off line.
Thanks and 73, Tom W2SC
--- StripMime Report -- processed MIME parts ---
multipart/alternative
text/plain (text body -- kept)
text/html
---
|