Subject: Re: Europa-List: Length of Dipole Antenna
| Graham Singleton wrote:|
| >>Tony,
| >> Get with one of the local ham radio operators that has a
| >> GOOD SWR meter. Us it to "tune" the lengths to give you the best
| >> (lowest swr) reflective power over the aircraft band. I have a
| >> very nice curve which bottoms out about mid range.| >
| > Its best done with any nearby metalwork in place, ie elevator push rod
and > other hardware. rudder pushrod too. They will have an effect
| > Graham | >
|
| Sure can have an effect on tuning, but worth noting that tuning the
antenna will not likely mitigate the effect on radiation pattern caused by
nearby metal, especially near the tips.|
| To this end, there's a web site with enormous detail on these antennas,
and author sounds authoritative. He has developed a "meander line" antenna
using foil tape. He claims similar performance, with the meander line
seemingly favoring the low end of the band a bit. Mostly what it does is
allow for a shorter antenna, placing tips further away from annoying metal
elements.|
| Antenna fans can browse:|
| http://www.nancymoon.com/antennas.htm
| Regards, Fred F.
Cheers,
I followed Graham's admonition and Fred's contribution witrh
interest and then wandered off to the nancymoon site and found it
fascinating. Roy has said all the things that needed saying, and covers the
subject well. In fact those not keen on antennas can just about copy his
layouts verbatim and not see troubles found in other compromises.
A word of caution though. The proposed Antenna Analyser is the ideal
tool. However I've found it has a quirk or two. First of all, all antenna
measuring devices need to be classified as to use. Either it will accept a
limited amount of power applied to the antenna - OR it strictly won't. The
difference may be a hgundred bucks in repairs. It is very tempting to forget
the tool is attached ONLY for measuring the antenna's qualities and put a
watt through to see what the readings do - and they go doo-doo.
What effect does this have, you may ask. Well, if you put out
several hundred monetary units for the thing, loan it and the loanee blows
its guts out, your utilisation plan is shot. This happens even with the best
intensioned ham or otherwise. So the practical answer is: Have the owner do
it. That's why I suggested the local ham club. This tactic will meet with
greater glee than asking to use his. Yes, it may take some time to claw down
you quarry but it's worth it in the long run.
Second word of caution: In his soapbox diatribe on SWR he suggests a
"wallwart". For those not into the lingo, it's a transformer device which
'replaces' the battery, providing the requisite voltage in direct current
form. Some do a good job, some don't. The analyser can eat batteries at a
great rate, so the 'mains' are a good alternative - but as a precaution, you
must turn the power off, install the wallwart, THEN select power on at the
unit. The subtlety of this escaped me and I paid a price for not knowing.
The wallwart can poke a shot through the analyser for which it is not
designed. Roy, as I did, has not noted this.
So with that said, I suggest a hearty serving of nancymoon reading
if you want to avoid antenna problems of the efficiency persuasion later.
Ferg VE3LVO
Classic 914 mono
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