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philgib

Need The Best Fixed Directional Video Tx / Antenna Inside Legal Limits

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I am setting-up a video downlink which needs to be very reliable and reach a receiver as far as 1000 meters line-of-sight away, in a heavy urban environment. It has to be strictly directional, as both transmitter and receiver will be fixed. Power consumption is not an issue.

I have already been playing for years with 2.4 ghz 400mw to 600 mw MULTI-DIRECTIONAL video downlink, along with 14db patch antenna, and I am used to it. I would gladly use the same for what I am setting up, except that 600 mw is not within legal limits, and that I do get some interferences now and then which I need to avoid.

I am going to install this system in various countries, so best would be to have some variable TX power in order to adapt to the maximum limit allowed

- Any suggestion ?

- Also any site showing max power limitations according to countries ?

- Are legal limits usually higher for directional transmition than for multi-directional ?

- Is the diversity switch a must ?

Thank you

Philippe

Edited by philgib

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I would use helicals at both ends.

Terry

Thx for your suggestion Terry. Could you please provide the pros and cons and price of same or any good internet site about it ? Also, do I need the same kind of TX power or does that allow me to reduce the T power from 500 mw to 10mw ? Maybe I am dreaming though

Do you see the need for a diversity switch ?

Best regards

Phil

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10mW is fine for a 1000 meter fixed line-of-sight installation that is using high gain Helicals. Generally speaking, diversity antennas are not needed on a fixed (non-mobile) installation.

You'll need to get the antennas well above the tree line. Foliage is not microwave RF transparent.

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Regarding power, where are you?

Then, keep in mind that the power limit includes antenna gain. So if the legal limit is 10mW, on a 10mW TX you'd only be allowed to use a dipole antenna. Any added TX gain must be accompanied by an equal reduction in TX power...

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Regarding power, where are you?

Then, keep in mind that the power limit includes antenna gain. So if the legal limit is 10mW, on a 10mW TX you'd only be allowed to use a dipole antenna. Any added TX gain must be accompanied by an equal reduction in TX power...

Thank you for the answers above.

I have asked the same question on another forum, which adressed me to the following page :

http://www.michwave.com/bbnetwork/faq/fcc.htm

From that page, being on a point-to-point scheme, I understand that I can keep my 500mw TX, and add a 14 db antenna to the transmitter and thus reach 14 watts still remaining legal with no ham license.

If anyone think I misunderstood, please shout !

Also, I already own a patch 14db antenna. Should I replace it by a helical or can I stick to it ?

Thank you

Philippe

Edited by philgib

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From that page, being on a point-to-point scheme, I understand that I can keep my 500mw TX ....

That is for FCC registered *digital* communications devices. Other countries have similar rules, but it is best to review their regs to see what is allowed. These RF devices employ spread spectrum technologies.

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That is for FCC registered *digital* communications devices. Other countries have similar rules, but it is best to review their regs to see what is allowed. These RF devices employ spread spectrum technologies.

AFAIK in Germany you are limited to 10mW EIRP for analog data, and to 100mW EIRP for digital data, at 2.4GHz.

That means including the TX antenna Gain.

Thus feel free to use a high gain antenna on the RX side, and a highly directional antenna on the TX side while "wasting" some power with (unnecessary...sigh...) long antenna cables to avoid breaking the 10mW limit.

I know that really sucks, but that's what's legal.

This calculator might be helpful:

http://www.compex.com.sg/home/WDC.asp

Edited by Hartwig

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It's the same in the UK so I guess it may be all of europe.

Terry

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