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How to know if I'm on 1.2 or 2.4 GHz

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In trying to improve the range of a cheap hongkong made wireless video system, I have built 2 collineair antenna's.

- 1 for 1.2 GHz

- 1 for 2.4 GHz

I lost the manual to my wireless video system so I don't know if it's 1.2 or 2.4 GHz. I was trying to see which of both antenna's gave the best result in order to determine the frequency range of my equipment before getting involved in more complicated antenna's.

The problem is both antenna's work just as well on the receiver. How can this be? Is it because 1/1, 1/2 or 1/4 wavelength all will work in an end fed vertical colineair? I used 3 segments (1/2 L , 1/2 L and 1/4 L , separated by 2 loops of 1/2 L )

Are there any other ways to determine if my TX/RX is working on 1.2 or 2.4 GHz that do not need specialised equipment? (I was thinking of doing stuff involving the microwave oven, but I suspect this is radiating on a quite broad spectrum)

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I bought it on eBay but the item is no longer listed. It is similar to the one pictured in attachment, but with the folowing differences:

- the receiver is white instead of black

- it has the letters ZTV written above the text "radio av receiver"

- it has an audio output next to the video output

But since these units are around on both frequencies, I would like a way to test the freqeuncy band instead of predict it.

post-2-1159027783_thumb.jpg

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The one you show is 1.2Ghz I think.

The long aerials and the tuning knob point this way.

A frequency counter is the best way to pin point it if you are making aerials but Im sure you know that.

A possible way to test is to set up the transmitter and receiver at a distance that shows a poor picture the then use a 6" square of metal to act as a reflector behind the receiver aerial. Move this metal slowly closer to the aerial and see what distance gives the best picture. 60mm would indicate a 1.2Ghz system and 30mm a 2.4Ghz system.

Terry

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Ok, so I did a few experiments. The weird thing is that the refelctive sheet of metal behind the antenna didn't seem to help reception at all.

The antenna was pointing up, the sheet of metal was behind and parallel to the antenna. The transmitter antenna was also vertical.

General conclusion of the experimentation was that reception was always worse with the metal sheet behind the antenna then without it. The distance didn't seem to matter much: the closer the sheet was held, the worse the reception became.

Any other idea's?

Would using a 1.2 GHz double biquad on a 2.4 GHz receiver still work? After all, it's twice as large :)

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Thats very odd, I have used this test in the past to help judge the effectivness of various aerials and it improved the signal a lot.

For what its worth I still think you have a 1.2Ghz system, what is the length of the elements in your TX and RX aerials ?

The 1.2Ghz biquad on 2.4Ghz would not be effective.

Terry

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The TX aerial is 11 cm, the RX aerial (incl. enclosure) about 15 cm.

Tx aerial can of course also include the PCB of the TX itself, in which case the total is 14 cm.

I will try the reflector-sheet test again but fixing the sheet instead of hand-holding and attaching an extension cord to the monitor. In this way I can move my own body further away from the rx to avoid interference.

I have to add that to perform the range test I "hide" the TX inside my house (concrete and iron) so I don't need to move away that far. I never tried direct line of sight tests (ground - to - ground) since I don't have an open space that's big enough.

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Ahh, that may be the problem. You need to do the test in the open.

Find a park or field, you must have one somewhere close by ?

Terry

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I now repeated the test with the antenna and the sheet of metal on a fixed support. I couldn't replicate the "best reception" scenario.

However, I have a very good "worst reception" test:

1) switch on TX with antenna vertical

2) switch on RX with antenna vertical

3) walk away until reception becomes bad

4) walk back a few meters until reception is good again

5) fix RX antenna/receiver on tripod

6) fix sheet of metal behind and parallel to receiving antenna

7) move metal sheet to different distances between 1 and 50 cm.

result:

- between 14 and 16 reflector distance the image becomes very blurred

- between 28 and 31 cm the image becomes quite blurred

- all other distances give the same good reception as without the reflector

My conclusion is that putting the refelector at 1/2 wavelenght would effectively cancel the incoming radiowaves since they are bounced back 180 degrees out of phase. (distance antenna-reflector-antenna=1 wavelength). A similar result should occur at 1/1 wavelength but less pronounced (since the metal sheet isn't infinately large and isn't positioned perfectly, some of the waves don't get reflected)

This is exaclty what I'm seeing in this test, so I would assume that 15cm = 1/2 wavelength, which would mean I have a 1.2 GHz system.

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Yes that sounds right, all the things you say point to it being a 1.2Ghz system. Odd the test did not work better, I did the test myself yesterday when I was working on a corner reflector aerial and it worked well.

Terry

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