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Author Topic: RF loss in cable vs air  (Read 10811 times)

Jason Glass

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Re: RF loss in cable vs air
« Reply #20 on: March 06, 2014, 06:41:15 PM »

A follow up...
Did another NHL gig and used the same setup with log antennas at the boards and 200' RG8 with amps at the head end.
Worked very well. MUCH less RF congestion in Vancouver as compared to LA!
However, using the calculator that Jason provided, it looks like I would have come out a few db better using helical antennas 150' away from the rink and only 50' of coax,  (not including the amplifier gain)
So the question is, would it be better to have a setup where amplifiers are not required?
The amps make up for cable loss but also raise the ambient noise floor and, in my limited understanding, can make the system a bit more sensitive to IM artifacts.

Hi Keith,

You're on the right track in that it is generally better to keep the noise floor as low as possible by using antennas with higher axial gain rather than lower gain antennas with amps.  That is, if the passive option is sufficient.  Most systems can tolerate a few stages of high-quality gain, though, when the ambient conditions aren't too severe and you're not wrangling dozens of channels.

It's wise to be conservative when entering any gain specs for calculations, and to use figures at the low end of spec'd tolerances.  I use 9-11dB of gain for PWS helicals in the UHF-TV band.  This coincides with my own observations and with NEC models of the antenna.  It might bring your comparison results closer together or even tip it the other way.

Keith Broughton

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Re: RF loss in cable vs air
« Reply #21 on: March 08, 2014, 08:45:38 AM »

Filter for the bandpass..
Good point but, for this application, the Lectro receiver had to work in 21 through 26 blocks.
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Keith Broughton

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Re: RF loss in cable vs air
« Reply #22 on: March 08, 2014, 08:48:45 AM »

Hi Keith,

You're on the right track in that it is generally better to keep the noise floor as low as possible by using antennas with higher axial gain rather than lower gain antennas with amps.  That is, if the passive option is sufficient.  Most systems can tolerate a few stages of high-quality gain, though, when the ambient conditions aren't too severe and you're not wrangling dozens of channels.

It's wise to be conservative when entering any gain specs for calculations, and to use figures at the low end of spec'd tolerances.  I use 9-11dB of gain for PWS helicals in the UHF-TV band.  This coincides with my own observations and with NEC models of the antenna.  It might bring your comparison results closer together or even tip it the other way.
That's kind of what I thought but wanted some opinions.
The LA gig would have been better without the amps as the RF environment was very hostile.
The Vancouver gig was much cleaner so the amps worked out.
The big issue with this particular gig was the fact that I couldn't get antennas anywhere close the "best practice" locations.
Thanks for everyones input :)
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ProSoundWeb Community

Re: RF loss in cable vs air
« Reply #22 on: March 08, 2014, 08:48:45 AM »


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