Hi Paul,
All very good questions.
You have received some replies that suggest problem areas and also possible
solutions, without being at all definitive.
However to my mind, Mark Fisher of Swift Avionics - the agents - who is a
contributor to this forum and therefore is/will be aware (9-5 Monday to Friday
only?),of your questions. It would appear very obvious to me, that Mark should
step in and give you (and us all), some open and definitive answers (and
perhaps some more general background on the topic), that are unrelated to any
commercial issues that he may have, as agent.
Over to you Mark.
Cheers,
Gary
----- Original Message -----
From: Paul Bart
To: Discussion of issues relating to Soaring in Australia. ; Chat DDSC
Sent: Sunday, April 17, 2011 12:31 PM
Subject: [Aus-soaring] Antena length for Oz Flarm
Hi
I have become concerned that the range at which my Flarm detects gliders is
not anywhere near specification. It often bypasses the green warning, going
straight to red. I understand that there are many factors in play, such as
shielding from the instrument panel, carbon etc., but I do not think that this
is the explanation in my case. So I thought I would invest in a better antenna,
but before I did that I had a look at the standard antenna provided. When I
removed the plastic covering I was surprised that the actual antenna was only
48 mm long. Yet the manual states, that the antenna at 1/4 wavelength should be
86 mm long. I also have the original Swiss Flarm (inherited from a glider
purchase from Europe) so I compared and its antenna is approximately 80 mm, but
as the cover is not removable, I cannot confirm the length of the actual
conductor.
Anyway I had a look at a few wavelength calculators on the web and given the
average frequency the Oz Flarm operates on is about 921MHz, the 1/4 wavelength
should be approximately 77mm and not the 86 indicated in the manual. I haste to
add here that I know next to nothing about antenna design, so a simple
application of the formula might not be correct.
In any case though, the length of the antenna on my Flarm is 48 mm, well
short of the manual stated 86 mm.
So I would like to ask those that know more then I on this topic
1) Is 48 mm the correct length (too long for 1/8 and too short for 1/4
wavelength)
2) If not, should it be 86mm as per manual, or 77mm as per calculated length
3) If mine is NOT an isolated case and the 45 mm length is not correct, are
we having a fleet of Flarms out there with much poorer range and hence
effectiveness that we should have.
Any help on the topic greatly appreciated
Cheers
Paul
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