Optimal Arial Lenghts for TX

[John Young]

Thank you John..... very nice attachment.

Question: Full lenght (2,35443m) vs 1/4 wave (588,6mm), any prefrences or do they work equally well

My pleasure Iceman.

Morph is right – a full wave length is preferable. Just ensure that it is vertically polarised [most or nearly all A/C have antennas pointing up vertically] as opposed to horizontally polarised.

Furthermore, for line of sight, a vertically polarised antenna is more efficient as it radiates 360° versus a dipole or horizontally mounted antenna.

73's de John ZS5WG

PS: These comments apply to a groud station as queried by Iceman.

[John Young]

How do I measure this My whip is mounted on a base with a little spring point, is it from the pivot point or from the little grub screw holding the whip.

Do I assume correctly, that to cover all bases, 555mm seems a good average for the arial

There are other factors that come into play, one being known as “the end effect”- “how much the radio “senses” after the actual end of the antenna”.

It is not possible to accurately measure in millimetres what your radio “sees or senses” without a SWR meter.

I can’t see how you could go wrong at 555 mm though. Our puny power allows for some flexibility regarding the SWR.

[IFLYHI]

Sorry I type slowly

Last question

vertically polarised [most or nearly all A/C have antennas pointing up vertically]

My aerial is mounted slightly back (for more speed ) should I have it as upright as possible or does that not matter

[John Young]

My aerial is mounted slightly back (for more speed ) should I have it as upright as possible or does that not matter

The more vertical, the better – remember the attitude of the M/L in flight. In other words, in flight, the antenna will “lean back” even more.

Whenever I pass a microlight with the antenna leaning back, I gently encourage the owner to adjust the antenna to a vertical position, and if necessary, explain why.

[Henry6iix]

I dont have a trimming chart with me here but John is right 588mm.

If the spring on the bottom of the antenna is about 13mm in diameter the u cut the antenna from the hole to the tip 588mm

73 de Henry ZS6IIX

[Duck Rogers]

Now this is exactly what this forum is all about :D
I LEARNED something today :D
I always neglected to use the compensating factor of 0.93
Thank you, all you clever dudes

Duck Rogers

[ACE]

Now this is exactly what this forum is all about :D
I LEARNED something today :D
I always neglected to use the compensating factor of 0.93
Thank you, all you clever dudes

Duck Rogers

Ditto from me, have saved the spreadsheet too.

Well done and thanks.

Charles Tiddy.

[alan]

Last question about this very interesting and informative topic. I was told to face the aerial away from the trike so that it is at right angles to the aerofoil tube. The theory is that the aerofoil tube acts as the ground plane. Is this correct?

Thanks John and others for the useful advice

[John Young]

I was told to face the aerial away from the trike so that it is at right angles to the aerofoil tube. The theory is that the aerofoil tube acts as the ground plane. Is this correct?

Hi Alan - no, it is not [entirely] correct.

The entire M/L would act as something of a ground plane, but you would achieve a much better “punch” with a vertical antenna. Remember that your best signal [TX] would be at right angles to your vertical quarter wave.

Consider it another way. The TX signal from a vertical antenna is roughly the shape of a round cake tin some 50 NM wide. Now it’s not hard to visualise that if you tilted your antenna at 45 degrees or more, the “cake tin” [signal] would now be aimed at the floor, sky and either side, but not all around as intended.

Regards to all – John

[ICEMAN]

Can someone pls pm me their email address and help place a photograph for me

I want to place a photo of the "ATC tower" that got this post started.... :D

Tx
Stan

[Morph]

Send the email to me by pressing the button at the bottom of this message

[ICEMAN]

Tx....... sent

[alan]

Thanks John

If nothing else then at least I won't get poked in the eye by the antenna sticking out at 45 degrees when I push the trike out

[krusty]

John,

My 29Mhz base station here at home as an ant that I estimate to be about 4m long. It is a telescopic antenna which was supposedly supplied already tuned correctly. Reception on the antenna is BAD and I'm not sure about transmissions yet (need to do more testing).

That seems to be double the optimal length?

Is that correct, or am I being dumb?

[John Young]

John's posted an Excel Spreadsheet to use when determining antenna length

http://www.gregperkins.co.za/flying/dow ... ulator.xls

Hello Krusty,

Just read about Microwave – EISH !! - suddenly other issues appear completely unimportant.

Krusty, by following the link above, an optimum full-wave would measure some 9.62 metres.

For info, a half-wave would measure 4.81 metres and likewise, a quarter-wave would be 2.40 metres.

The 29MHz in question is probably for ski-boat or 4X4 – both should be horizontally polarised which would make a half-wave vertical dipole a tad impractical.

Regards