Hi Jeff Thank you and belatedly to Ian. That confirms exactly what I was thinking regarding the length. I just was not sure that my conclusions were correct.
Cheers Paul On 17 April 2011 20:47, Jeff Farrow <[email protected]> wrote: > Paul I attach an email that Ian McPhee sent to this list last year. An > explanaation for the discrepancy. Jeff Farrow > > *From:* [email protected] [mailto: > [email protected]] *On Behalf Of *Ian Mc Phee > *Sent:* Thursday, 10 December 2009 8:24 AM > *To:* Discussion of issues relating to Soaring in Australia. > *Subject:* [Aus-soaring] many OZFLARM comm (stick) aerials in use may well > be the wrong aerial (far too short) > > Been troubled by some lack of performance in OZFLARMS for some time now and > only yesterday after talking to Mark Fisher realised many of the stick > communication aerials on OZFLARMS may well be wrong frequency. I do know 4 > in our club are wrong length and the fifth glider has one of those Mobile > one long range aerial which gives you green LEDs well beyong what the eye > can see even 4 to 5 km!!! > > My calculation for 900mhz is the 1/4 wave aerial 75 to 80mm long. At our > club 4 the little white aerial say 40 mm long - far too short. It would > seem the little person in China threw all the say 900MHz and either 1800 or > 2400MHz aerials in the one box as they looks the same on the outside. > > *I urge as many people as possible this weekend pop the rubber cover off > the aerial and inspect the inside aerial length* I am predicting 50% of > the aerials will be the wrong length - far too short. Job will take less > than 1 minute. It would be easy to add a little copper wire of the right > length > > While on Flarms etc I can say GPS (flat aerial) are best placed 25cm apart > as the GPSs can interfer with each other. > > Also in motorglider if you are using the engine battery I would suggest > fitting a 22000uF capicator in the power lead near flarm > > I will be very interested to hear the results of the aerial wore length > > Ian McPhee > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 9.0.717 / Virus Database: 270.14.116/2580 - Release Date: 12/22/09 > 06:13:00 > > ----- Original Message ----- > *From:* Paul Bart <[email protected]> > *To:* Discussion of issues relating to Soaring in > Australia.<[email protected]>; Chat > DDSC <[email protected]> > *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 > > ------------------------------ > > _______________________________________________ > Aus-soaring mailing list > [email protected] > To check or change subscription details, visit: > http://lists.internode.on.net/mailman/listinfo/aus-soaring > > > _______________________________________________ > Aus-soaring mailing list > [email protected] > To check or change subscription details, visit: > http://lists.internode.on.net/mailman/listinfo/aus-soaring >
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