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Skywave · 13th Sep 2010, 1:57 pm

Pete - G4MRU

I like the idea of a screened earth - but isn't there a potential problem with this arrangement at frequencies above, say, 10 MHz, if the coax needs to be of any appreciable length - say 20 feet for example? Taking velocity factor of the co-ax into account, a quarter-wavelength at 10 MHz is about 21 feet - producing in a high-impedance at the 'receiver' end of the co-ax.

Afterthought - I do accept that at this freq. & up, earthing of RF aerial currents ceases to become important - for reception purposes, that is; transmitting arrangements are a totally different matter!

Al.

13th Sep 2010, 1:57 pm	#21
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Re: Gutter aerial Pete - G4MRU I like the idea of a screened earth - but isn't there a potential problem with this arrangement at frequencies above, say, 10 MHz, if the coax needs to be of any appreciable length - say 20 feet for example? Taking velocity factor of the co-ax into account, a quarter-wavelength at 10 MHz is about 21 feet - producing in a high-impedance at the 'receiver' end of the co-ax. Afterthought - I do accept that at this freq. & up, earthing of RF aerial currents ceases to become important - for reception purposes, that is; transmitting arrangements are a totally different matter! Al.