On 2021-04-29, at 03:45, Griffo <scangriffin@bigpond.com.au> wrote:
> I have just completed my finale purchase inspection of a Europa
Classic.
>
> If the purchase proceeds, I will probably replace the transceiver
>
> As you will know the Europa's composite skin facilitates the
installation of an internal transceiver antenna. I this case a dipole,
in the vertical tail/fin.
>
> My question is: Is the dipole inherently "tuned" ? or could it require
SWR adjustment ?
Griffo - the nominal installed length of the dipole does require to be
trimmed to get optimum SWR across the aeronautical band. My comm radio
(Funkwerk ATR833) requires SWR better than 3 across the operating band.
The Europa build manual, appendix C, includes (inter alia) the
following:
=9CThe recommended antenna for installation is a dipole type, the
total length of which is to be a half wave length at the middle of the
frequency range (127.35 MHz if you are using a 760 channel radio). The
calculated length of the antenna would make each half of the dipole 588
mm (23.15=9D) long; however there are certain effects to be taken
into consideration before the final length is determined. =9CEnd
effect=9D makes the antenna apparently longer than it is, and so
does the =9Cdielectric effect=9D of the glass fibre upon
which it is mounted. Both of these effects require the dipole to be
shortened to bring the effective length to match the mid-frequency half
wave length. The only way to take these effects into account is by use
of a Voltage Standing Wave Ratio (VSWR) meter.=9D
However, the last sentence of that extract has been overtaken by
technology and I found that the easiest way to tune the dipole is by
using a nanoVNA. See my build journal at:
http://www.rowlandcarson.org.uk/aviation/europa_435/nanovna_final.php
<http://www.rowlandcarson.org.uk/aviation/europa_435/nanovna_final.php>
I found that the optimum frequency for the minimum SWR was not quite in
the centre of the band, but the NanoVNA made it easy to get both ends of
the band to the same SWR. It would have been quite tedious doing this
with a VSWR meter, which can only take a reading at a single frequency.
{I=99m prepared to travel (but not to Australia!) with my NanoVNA
to measure other builders=99 antennae, when COVID precautions
allow.}
If the aircraft you are purchasing has already flown, I would expect
that the builder has already done what she can to tune the antenna, and
you may not need to worry. But if you decide to replace the comm radio,
you=99ll have ready access to the antenna coax and can perform
tests at that time.
Hope this helps.
in friendship
Rowland
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