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Old Nov 27, 2005, 02:57 AM
Registered User
Hong Kong
Joined Apr 2005
70 Posts
Antenna wire strand count

I have recently replaced the antenna on my Hitec receiver with another piece of wire of the same length and diameter. The only difference is the strand count.
The original wire had around 30 fine strands and the new wire has only 6 thicker strands.
Will this affect reception to any significant extent?
Any input gratefully received before I engage in the field tests.

Andrew
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Old Nov 27, 2005, 06:43 AM
Jeff Carr
Ft. Mill SC / Charlotte NC
Joined Mar 2001
2,668 Posts
The wire will be fine but will break easier since it wont be as flexable. Your good to go

Jeff
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Old Nov 27, 2005, 09:41 AM
Registered User
Hong Kong
Joined Apr 2005
70 Posts
Jeff,
It'll be set into an EPP wing so should be reasonably well protected.
Thanks for the advice.
Andrew
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Old Nov 29, 2005, 01:24 AM
Registered User
Taiwan
Joined Mar 2005
36 Posts
Hi all,
This is my first post here.
I had an unstable Futaba RX, R113iP, from friend. Its antenna seems a little short. I'd like to know what is the exact length of its antenna? The RX can't receive the TX from time to time even at short distance, is it the problem for the short antenna? Or what is the possible cause? I checked the crystal is OK at another RX.
I also had a RX, SANWA RX-311, with broken antenna from the same friend. Do they have the same length of the antenna?
Any comment is appreciated!
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Old Nov 29, 2005, 01:47 AM
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United States, WA, Puyallup
Joined Oct 2004
5,965 Posts
Don't know where you are located or what frequencies you are using, but in North America almost all 72 MHz receivers use a 1 meter long antenna.

When asking radio questions, it is a good idea to let people know what part of the world you are in. You can update your profile by going to MY RCGROUPS.

Bill
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Old Nov 29, 2005, 04:56 AM
Registered User
Taiwan
Joined Mar 2005
36 Posts
Hi, all
Sorry to miss part of important information!
1. I live in Taiwan.
2. What I mentioned RXs are all 41 MHz.
3. Didn't I specify my location when I registered? I'll update it anyway.
4. Thanks for your any comment!!
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Old Nov 29, 2005, 07:08 AM
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Hong Kong
Joined Apr 2005
70 Posts
From what I've read the antenna length should generally be an even fraction of the wavelength.
1 wavelength, 1/2 wavelength, 1/4 wavelength 1/8 wavelength and so on.
The shorter the antenna the weaker the signal.
From my year 12 physics books you can calculate the wavelength as follows: wavelength x frequency = speed
Radio signals travel at the speed of light which is approximately300,000,000metres per second. In the United States they use 72MHz so a 1/4 wavelength antenna would measure (300,000,000/72,000,000)x 1/4 = 1.04 m
In Taiwan a 1/4 wavelength antenna would measure (300,000,000/41,000,000)x 1/4 = 1.83m, an 1/8 wavelength antenna would measure 0.915 m, and a 1/16 wavelength antenna would measure 0.457m.
Full range receivers would use .915m and restricted range receivers such as the GWS type from Taiwan would use around .45m.
So your antenna should measure around 915mm or 457mm but I'm sure a few mm difference won't hurt.

I hope this helps,

Andrew
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Old Nov 29, 2005, 09:38 AM
Registered User
Florida
Joined Aug 2004
4,095 Posts
crwtar, while you are correct in part, there is a lot more to an antenna than just length. From a practicle standpoint, nearly all RC receivers are set up to use approximately 1 meter long antenna regardless of frequency. This is possible because the internal circuitry that the antenna is attached to is a tuned circuit where the L and C values are set to make most efficient use of the available energy captured by the antenna. This is commonly called "base loading" or "base loaded antennas". What most people do not realize is that the piece of wire hanging off the end of your receiver is just part of the receiving system; all the other wiring in the model, especially the ground or negative side of the power supply constitutes a large part of the receiving system, you need both to get a signal.
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Old Nov 29, 2005, 07:49 PM
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Taiwan
Joined Mar 2005
36 Posts
Thanks quys!!
I know the physics and the mathematics. However, I know Logic much better than RF, because I'm an H/W engineer.
"especially the ground or negative side of the power supply constitutes a large part of the receiving system" suppose to be called "image plane", right? But, I'm not sure this applys to both AM and FM.
Maybe I just measure other 41MHz/PPM RX's antenna and get the answer.
By the way, I just find that the radio system has "glitch" problem this morning. And I finally find that the problem is from the loose of the screw of the antenna of the TX. Is this also the cause of the un-stable problem of the 41MHz/PCM RX which has shorter antenna? I don't know yet. I'll try it tonight, after work. I'll keep younformed, if you are interested. Currently I'm figuring hard how to disassemble the Futaba 3PK TX to reach that dame screw. Anyone ever do this before?
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Old Nov 29, 2005, 10:44 PM
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Hong Kong
Joined Apr 2005
70 Posts
Rodney,
Thanks for the info. on base loading. All new to me!
I read on the AirCraft website the following statement regarding GWS receivers:
"Both R4PII have a short, 50cm antennae. Range can be increased with 1M if desired."
I assume the base loading would need to be adjusted if the antenna lenth is doubled.


Chancehuang,
Sorry,
I've only ever pulled apart JR transmitters so I don't know anything about the Futaba TX. With the JR rotating the TX antenna clockwise tightens the connection - that might be worth trying.
I think your idea of measuring another 41 MHz receiver antenna sounds good.
Good Luck!
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Old Nov 30, 2005, 12:37 PM
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Florida
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4,095 Posts
crwtar, I'm afraid I can not answer your question with certainity on the GWS receiver but, in most cases, you will best be served by NOT trying to adjust the base loading components unless you have the necessary electronic measureing gear and know how to use it. There is one simple test you can do yourself. Carefully find the current range where operation becomes jittery, add the length and check again. If it improves (gives you more range) go for it and leave it extended. In most cases, you will find it difficult to improve on the original range without the proper measureing equipment.
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Old Nov 30, 2005, 03:37 PM
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Joined Mar 2004
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www.rc-cam.com He has a pretty good dissertation on antenna length.
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Old Dec 01, 2005, 08:44 PM
Registered User
Taiwan
Joined Mar 2005
36 Posts
Hi all,
Bingo! I finally found the problem of the PCM/ RX. It's the fault of TX, loose screw of the antenna.
The "slipped" screw can't hold connection wire of antenna tight, so the transmission of TX was not stable and cause the RX not functional properly. I had to AB glue the screw to keep its position, since I couldn't pull the 3PK TX apart and had a better solution. It works so far and I hope it won't have the problem again.
Next I'll measure the range of the radio, as I mentioned earlier that the antenna lenth of the RX is shorter. I'm waiting this weekend to test it in the "field". If it still has a range problem, then I have to give it a new tail.

Chance
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