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Old 7th September 2010, 02:52 AM   #1
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Default Antenna question on the wrong website

I know this isn't a radio forum but a lot of you have experience in HAM and other radio circuits I've learned.

My question is based on previous experience producing good results.
If I use an antenna promoted by the manufacturer for 2.4ghz, to receive 260mhz, will it really be an issue?

I've done this in the past with various devices. I used an automotive car stereo whip antenna on my radio controlled RC car and it gave me the furthest range I've ever achieved. A prime example of manufacturer rated spec not hindering performance. In this scenario, I'm replacing a crappy, broken metal telescopic antenna for the wireless receiver in my wirless guitar system that transmits at 260mhz. The choice being between a near frequency CB whip antenna or, a small wireless LAN whip type antenna.

I understand the issue of wavelengths but will it REALLY create THAT much of an issue?
I've used hunks of wire for some of the best antennas I've ever owned!
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Old 7th September 2010, 03:22 AM   #2
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Yes, I build tube amps here in this forum, but in real life I am an RF engineer. Your wireless mic antenna works at 260 MHz. THe wierless LAN antenna is made for 2400MHz. This is just too different to work very well.

Any telescopic antenna of about the same length would work much better. One intended for a portable TV would be a good choice. And yes a piece of wire about 1 1/2 to 2 feet long should be OK too.
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Old 7th September 2010, 03:33 AM   #3
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Radio frequencies radiating thru the air is a real cool thing! All around us are frequencies bouncing off walls, coming thru the windows...& all of it has their own wave-length. Quite the thing..if only we could SEE these frequencies...we would all be astounded!
You have one frequency at 2400000000 Hz(2.4Ghz) another at 260000000 Hz(260Mhz)....or 260Mhz and 2400Mhz, or one is nine and a quarter times higher than the other. When one designs an antenna......size of elements is everything...when a frequency is too long to be practical for say...handheld use, you cheat, or fool the receiver, or transmitter into thinking the antenna is bigger than it is.
Ever wonder why there are these large incredibly tall "radio towers"?
A common 1/4 wavelength hertz antenna in the AM band would have an element hundreds of feet high........This same 1/4 wavelength at 2.4Ghz, would be only about Forty Millimeters high(Appx, ONE inch). These are the scales we are talking about...
For your "piece of wire" antenna....imagine this wire is probably not straight....you body just holding onto it is redirecting radio waves in all different directions, and at a great wide swath of frequencies. Recall the poor guy long ago twisting & turning with an old pair of TV "rabbit ears" trying to get a good reception....with the onlookers saying "Freeze, thats it...now just hold it there" The poor guy contorted in some goofy pose.
He was acting as an antenna himself....directing and reflecting radio waves with his body.
Yes it will be an issue with this great a mismatch of frequencies.

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Old 7th September 2010, 04:34 AM   #4
gootee is offline gootee  United States
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Yeah, it'll be a huge issue. You might get 1000X more signal with an appropriately-sized antenna. Use the wavelength as the antenna length, if possible.

Using a ground plane, and being far enough above the earth, are important, too.
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Old 7th September 2010, 06:46 AM   #5
RJM1 is offline RJM1  United States
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A 2.4GHz antenna operated at 260 MHz would have a SWR > 100 so I doubt that you would radiate any power. Using the program EZNEC Demo a 10.9 (0.277M) wire 1mm thick over a ground plane would work well at 260 MHz. (1/4 wave)
EZNEC Antenna Software by W7EL

Last edited by RJM1; 7th September 2010 at 06:49 AM.
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Old 7th September 2010, 12:27 PM   #6
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It all depends on range. A very poor antenna will still give enough signal if the transmitter is close to the receiver. As you move it away you will find a much shorter range than with the correct antenna. Roughly speaking, an antenna only a tenth of the correct size will pick up only a tenth of the voltage but will then lose most of that in an impedance mismatch so you will get maybe 1% of the correct voltage into the receiver.

Antenna performance depends on physics, not manufacturer specs. Hopefully the two are related, though.
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Old 8th September 2010, 12:46 AM   #7
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Thanks for all the very informative answers which expanded the basic understanding of antennas I already had. I suppose I've been lucky in using antennas with boldly different ratings in contrast to the applications I've used them for. At 99 cents shipped to the door, I figured I can't lose by testing a couple of these antennas out. If all else fails, I'll just build my own and cannibalize the housing of one of these cheap antennas which is largely the reason I seek to use one.

Many years ago I built a dish antenna. Looked like a mini satellite dish by the time I was done. Coat hanger framing, aluminum foil sheeting and was about 2.5-3 feet across at the open end.
Man that thing could pull in stations from Canada and sometimes Tennessee! It was mighty finicky though and I often found myself running outside to fuss with it.
With the internet being such a good source of information, I learned about wavelengths and antenna design. Bought myself a couple large steel hoops from the craft store then ran copper wire across them which created varying lengths. With it sensitive to wavelengths of a massive bandwidth range, totally blew my "trailer park satellite dish" away.

I suppose an antenna of this design might actually be applicable to multiple bandwidth applications?
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Old 8th September 2010, 02:05 AM   #8
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Fun stuff antenna. There are a lot of ways to make an antenna and many antennas work at octave intervals of the their intended frequency...though maybe not optimally. At least not without a little modification. Would really like to see an image of the antenna with the hoops you described. Receiving antenna have one job- to convert the electric (and/or the magnetic) wave into an electrical signal. Make some images and put them up. We will claim it is for audio because it receives music! HAHA
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Old 8th September 2010, 02:08 AM   #9
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Default A test!

Kudos to the first one who can tell me what this is & what its for...........

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Old 8th September 2010, 02:20 AM   #10
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