EasyAs Antenna

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ROCKet STAR
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EasyAs Antenna

Postby ROCKet STAR » Sun Aug 28, 2011 1:27 am

Just a quick question regarding the antenna on the EasyAs unit as my knowlege of antenna theory is fairly limited...

Out of the packet the antenna is a nice neat coil, is it important that the antenna be kept in this configuration or would it still be effective if it were straightened out? My reasoning for doing so would be to allow it to be passed through the bulkhead of a carbon avionics bay.
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Re: EasyAs Antenna

Postby Lamp » Sun Aug 28, 2011 5:54 am

That is a good question. PK as the designer would know but generally a helical configuration like that is done to make it physically smaller. Essentially a helical is a coil and it will add some inductance so straightening it will change the impedance of the antenna but I cannot say how much it would upset the SWR.
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Re: EasyAs Antenna

Postby cryoscum » Sun Aug 28, 2011 6:32 am

Chris, I've been using it both straight and coiled with no noticable difference. No doubt Pete is right and I suspect you'll find there's a minor frequency shift when uncoiling the antenna, but again no real operational difference.

PK, please confirm if correct?

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Re: EasyAs Antenna

Postby Tarpazium » Sun Aug 28, 2011 1:56 pm

Getting above the Corn!

G'Day

It's now the end of August and summers almost here. In the next few weeks they will begin planting the adjoining cornfields at the Cedar Grove launch area, if they have not already done so.

Image


I was reading about tracking beacons and getting signals above ground clutter in general and I came across the above antenna configuration. It was being used by the US Civil Air Patrol. They were using arrangement for RDF location of downed aircraft using a RF Beacon at (406 MHz). I then wonder if anyone would care to comment on the efficacy of such an antenna as compared to the more conventional 5 element Yagi's that we commonly see?

I understand that these complete RDF units are sold commercially as a L-Tronics Little L-Per and as a whole system cost 1000's of dollar.

I was however intrigued by the antenna arrangement and wondered, if it could be adapted from 406 MHz to 433Mhz.

If anyone has any input in regards to dipole antenna geometry, calculations, efficiency or informed comment, then I would be happy to hear from you.

Thanks

Tarp

P.S.

I'd be fairly certain that the elements from another $2-00 tape measure style configuration would also work equally as well in such an antenna.

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Re: EasyAs Antenna

Postby Stewart » Sun Aug 28, 2011 3:10 pm

Tarp,
The double dipole ant looks to be a "time Difference of Arrival" reciever setup, the attatched circuite switches between the left/right antennas and measures the frequency differential to determine which way to the transmitter . On this page ( http://theleggios.net/wb2hol/projects/rdf/rdf.htm ) there are 2 projects for such a setup - about 1/2 down the page.
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Re: EasyAs Antenna

Postby PK » Sun Aug 28, 2011 10:27 pm

Uncoil it. For bonus points run a 17cm wire from the -ve terminal of the battery in the opposite direction. You'll get a bit more range.
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Re: EasyAs Antenna

Postby ROCKet STAR » Sun Aug 28, 2011 11:45 pm

Ah, excellent. In that case I'll go ahead and mount it as planned. Thanks guys.
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Re: EasyAs Antenna

Postby bpratt » Sat Sep 03, 2011 9:22 am

Tarpazium wrote:
I was however intrigued by the antenna arrangement and wondered, if it could be adapted from 406 MHz to 433Mhz.

If anyone has any input in regards to dipole antenna geometry, calculations, efficiency or informed comment, then I would be happy to hear from you.



300 divided by the frequency in Mhz, multiplied by 0.5 (dipole is half a wavelength) then multiplied by 0.95


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