Receiver antenna length, 27, 35, 40 50 and 72 mhz

On Fri, 01 Jul 2005 00:14:56 GMT, snipped-for-privacy@bellsouth.net (Frank Schwartz) wrote in :

Well, you've bracketed the target frequency (35 mHz) in your samples (from 27 to 72 mHz), so you've probably already got your answer.

Ah. I see the problem.

This site says that this is the formula for wavelength:

wavelength = 300 / frequency in MHz

So the one-meter antennas come close to 1/8 wavelength for

Truly optimizing a receiver antenna is beyond my skills and equipment. You'd have to put some test equipment on the receiver itself to see what is really happening.

Marty KC2NEB (lowest HAM rating)

How about someone who is involved in the project just asking the JR contact who is coordinating the equipment to check the length in their technical database? Then you don't have to rely on speculation.

Carrell

| This site | says that this is the formula for wavelength: | | wavelength = 300 / frequency in MHz | | 300 / 35 = 8.57 meters | | 300/ 72 = 4.17 meters | | So the one-meter antennas come close to 1/8 wavelength for | 35 mHz and close to 1/4 wavelength for 72 mHz.

For the record, the it's 1/4 wavelength that you're usually looking for in a whip antenna.

And your line of reasoning is correct, however if you look at the `serious' R/C radio equipment around the globe, on all the bands (except for the 900 or 2.4 gHz bands), the antennas are all about one meter in length. I can't claim to have checked much stuff outside the US, but in the US, 27 mHz, 50 mHz, 72 mHz and 75 mHz all usually has antennas right about one meter in length.

So if the antenna is one meter in length, and the frequency is not 72 mHz, there's two possible explanations --

I think it's usually #1 for most of the good R/C equipment. (I'm not talking about cheap Radio Shack-ish R/C `toys', or things like the Hitec Feather.) They probably stick with the standard one meter because 1) 3 meters for the 27 mHz band would be too long, and 2) it's easier to stock one length of antenna than several different lengths.

| Truly optimizing a receiver antenna is beyond my skills and | equipment. You'd have to put some test equipment on the receiver | itself to see what is really happening.

It's not so hard to make a good effort. In the absence of a matching network, the antenna should be about 95% of 1/4 wavelength. (The 95% is to cover the electrical length of the antenna vs. it's physical length.) The only real difficulty is determining if there is a matching network or not.

As for determining range, you don't need fancy equipment for that either, but it can make it easier and more accurate.

| KC2NEB (lowest HAM rating)

The level of your ham license doesn't really say anything about your skills. Many `techs' know a lot more than many `extras' ...

Its more thqan likley his whip is bottom loaded. It will need to be changed.

No, I don't think his whip is bottomloaded....my main concern is to find out if I am correct in assuming that almost all r/c receivers, be it 27, 35, 50 or 72 all come with 1 meter long antennas, give or take an inch or so.... Frank

Not at all.

My JETI REX 4's come with less than 20", on 35Mhz, and the micron range of home built's state 'anyhing from 10" to 50" depending on range required' but advise sligthly retuning the input RF coil for a new length.

I fly with whatever bit of wire comes to hand frankly, but then I domn't expect full range and I am not flying a 200mph 12lb model that costs a couple of grand in front of spectators...

all this stupidity about 1m=tuned at 72Mhz is just that - stupidity. That appliesd to proper whips with ground planes in otherwise free sapce. You may get close to that in a transmitter: You certainly do not in a receiver. Wires are run up and down and around past various metallic objects.

IF your mate gets a decent reciever he should be up for 500-600m easily, which is a lot of range really. I reckon if you can get 60m on the ground with a collpased TX antenna you should be OK for a km in the air.

Futaba provide :

For further information refer to articles at =

regards Alan T. Alan's Hobby Web Links

Good stuff here. But I would be concerned about blind spots with a large metalic fuse.

According to Hitec, their 72Mhz receivers use a 42inch antenna. This is also the same length used on 36Mhz (for Australia). I would suspect that 35Mhz is close enough that you can use your standard length 72Mhz antenna.

Hitec list a different length for 27Mhz, can't remember the exact length but it's listed in their receiver FAQ. Should be the same for most other brands.

On Fri, 01 Jul 2005 03:38:23 GMT, snipped-for-privacy@frenzy.com (Doug McLaren) wrote in :

It is a violation of netiquette to ruin theoretical arguments with the assertion of mere facts. :-P

AH! Now you're talking! I knew that there was some way of adjusting receivers to less-than-optimum antennas.

That was kind of my guess. As the Labatt bear used to say, "Crose enough!"

Makes sense. And it would be harder to mess up both in production and repair of the receivers if they all just have a standard-length antenna in stock.

OK. I can just about visualize what you mean.

That's definitely above my pay grade. :-O

I failed in my first attempts at RC in the 60s with Galloping Ghost equipment in part because I didn't understand "tuning" the receiver. The guys in the club I joined weren't able to help me, either, although they knew it was necessary. My used RX had no tuning core and I couldn't find the manufacturer to get one, so they wouldn't fly my airplanes for me. I went off and "flew" by myself. After a while, I got tired of wrecking and rebuilding the planes and went on to other hobbies, until I returned to RC in 1995.

I guess I'm still trying to fill in the blanks from what I didn't learn in the 60s.

I'm not one of them. I'm fully qualified for the lowest rating. :o)

Marty

I will go along with this comment. The whip is optimised to work with the USA receiver. The whip is *not* optimised to work at 35 Mhz.

Reg G4N callsign

Perhaps I should also have stated.. The whip is somewhat different to a straight piece of wire. It will be more critical of loading.. it is itself a shortened, usually helically wound aerial.

Reg