459mhz TX antenna

[Peter]

I would like to try out the new EZUHF 459MHZ but finding a suitable TX antenna seems to be an issue?  One solution offered in the forums is to tune a Diamond or Nagoya antenna with the help of a local HAM using a SWR meter or a spectrum analyzer with VSWR brdige.  Anyone know a HAM that would help or possibly know of another solution?

Cheers,

[Coyote]

418 Mhz antennas as well as a lot of 433 Mhz antennas frequency range extend too 458 Mhz

If you check the antenna length for 458 Mhz you come up 16.4cm. This is what length antenna you get supplied with Dragonlink and Chainlink receivers as standard so the original antennas work straight out the box

[Peter]

According to http://www.crompton.com/wa3dsp/hamradio/antcalc.html antenna length calculator there's almost 2cm in difference.   

459MHZ 12.235294117647058 Inches  or 31.1cm
433MHZ 12.969976905311778 Inches  or 32.9cm

Would this difference reduce reliability, if I trim to the correct length will this improve performance?

[Coyote]

See the 433 antennas are 16.4 per 1/4 or 32.8/9cm so only 10mm each element on the rx antenna. You could always trim the antenna, it would improve it, but only slightly

[Devonian]

Personally, I'd trim the antenna to around 164mm for a quarter wavelength on the Tx.

Make a half wave for the Rx with each 'leg' a quarter wavelength, therefore a total of 328mm.

If you have access to a decent VSWR meter that can work at UHF, then use it to 'tune' the antennas to your particular Tx and Rx.

Nigel.

[Peter]

Is there any advantage using quarter wavelength over half wavelength for the TX? I was under the impression the latter improved gain?  

[Coyote]

With higher gain you change the transmitted pattern from the antenna, it gives you a little gain, but changes your pattern from a more practical almost shpere pattern ( looks like a doughnut ) to a disk like pattern. For contact with a moving rx antenna more con`s then pro`s

On 459 Mhz the wavelength is that large even on low power rating your still broadcasting miles of signal

[Devonian]

Use a single quarter wave on the Tx as it matches the feedpoint impedance better (50 Ohm).
A single half wave will need some jiggery pokery to get it to match.

A half wave dipole, on the other hand, will match 50 Ohms quite well on the Rx (as it is 2 quarter wave elements).

Nigel.

[thundead]

I use the BEVRC 1/2 wave antenna on the openLRS running @ 459Mhz and is working great :D