AMD Phreak
Premium
join:2003-12-14 | reply to keefe007
Re: Min Distance from VHF Antenna
Go as far as you can, but more importantly run STP to the radios, that is if they are on the tower. Overall, it shouldnt be affected, I have experience with stuff being next to VHF, UHF, and high-power 900MHz paging and have not had any issues. |
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keefe007
Premium
join:2004-02-24
Germantown, WI
| How close have you mounted to VHF? The problem is that this antenna is near 15/20 feet tall so it's hard to avoid. It is one of those whip antennas with little ears hanging off. I would be mounting 3 120 degree 2.4 sector antennas on a pole roughly 1.5 feet horizontally away from it. |
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sporkme
drop the crantini and move it, sister
Premium,MVM
join:2000-07-01
Morristown, NJ
 ·Optimum Online
| reply to AMD Phreak
said by AMD Phreak  :Go as far as you can, but more importantly run STP to the radios, that is if they are on the tower. Curious, what's the spectrum that ethernet uses (100MB FE)? Any harmonics from nearby transmitters to look out for (meaning, do any "common" VHF bands perhaps disrupt ethernet with one of their harmonics)? |
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lutful
Premium
join:2005-06-16
Ottawa, ON
| said by sporkme :Curious, what's the spectrum that ethernet uses (100MB FE)? Fast Ethernet transmission uses 125Mbps "raw" data rate which is carried in a 62.5Mhz "MLT-3" waveform.
There is not much VHF coming out of properly twisted portions of the cable - most noise is coupled in the small untwisted section near the connectors. |
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wispman
join:2004-12-21
USA | reply to sporkme
One time I had an ethernet cable I put in at an install that ran across a desk and it went right by a police scanner. The scanner "keyed up" and was locked on something like 150-160mhz. |
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sporkme
drop the crantini and move it, sister
Premium,MVM
join:2000-07-01
Morristown, NJ
·Optimum Online
| reply to lutful
said by lutful :said by sporkme :Curious, what's the spectrum that ethernet uses (100MB FE)? Fast Ethernet transmission uses 125Mbps "raw" data rate which is carried in a 62.5Mhz "MLT-3" waveform. So you're saying that ethernet is centered at 62.5 MHz or goes from "0"-62.5MHz?
said by lutful :There is not much VHF coming out of properly twisted portions of the cable - most noise is coupled in the small untwisted section near the connectors. I was thinking more about RF from other sources getting into the ethernet cable and providing a hard to diagnose failure or near-failure.
So anything with a strong harmonic that lands somewhere below 100MHz could be bad news, right? Technically, ethernet is RF, correct? |
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lutful
Premium
join:2005-06-16
Ottawa, ON
| Here are various Ethernet baseband spectrum. Properly twisted CAT5 cable has 50-100dB VHF rejection. |
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