06-30-2015, 03:10 PM
John and others,
Background, late 1940's early 1950's:
The G5RV was designed by Varney as a 1.5 wavelength radiator for the 20 meter band, hence the 34' matching section to provide a resistive load on the 20 METERS.
Varney also never ran any coax after the matching section but connected the antenna directly to the tank circuit of his transmitter.
Pretty much what is called a Center Fed Zepp.
Pure resistive load, matched at the transmitter results in no feedline radiation.
Fast forward to the 21st century.
102 ft flattop, 34' matching section, coax fed antenna (G5RV)operated far from the antenna's design frequency of 14 mHz.
So for giggles lets say you want to operate your G5RV on 80 meters, (or any frequency other than 14 mHz. )
Once the current and voltage are pushed either up the stub or down the coax, due to the wide departure from the design frequency, cancellation does not occur. Hence the stub and feedline radiate and as we all should know feedline radiation is BAD.
This radiation will become harmonic in nature and that coupled with the blocking due to unfiltered receivers, loud phase noise from nearby transmitters and a myriad of other random noise all adds up to greater interstation interference.
A center fed dipole with open wire line from the feed point to a link coupled tuner (Johnson style matchbox) in the shack would be much better than the G5RV antenna with stub and coax feed. With that type of antenna and tuner you maximize the "Q" of the antenna reducing any feedline radiation, production of harmonics and radiated hash.
Folks who operate a G5RV at home with a single transceiver never see the problems of interstation QRM since they only run one radio at a time.
Our goal needs to be zero or close to zero interstation interference.
Without that being accomplished operating is more of a job and not fun.
A modern, 2015 model sensitive rig will die a quick and unrecoverable death in the environment we presently operate in.
Study all that you can about success SO2R (single op, 2 radio) and multi-multi station engineering. They have already done it, no need to reinvent the wheel.
Again just my .02 cents.
Dave
W1CTN
Radio Ansonia
Background, late 1940's early 1950's:
The G5RV was designed by Varney as a 1.5 wavelength radiator for the 20 meter band, hence the 34' matching section to provide a resistive load on the 20 METERS.
Varney also never ran any coax after the matching section but connected the antenna directly to the tank circuit of his transmitter.
Pretty much what is called a Center Fed Zepp.
Pure resistive load, matched at the transmitter results in no feedline radiation.
Fast forward to the 21st century.
102 ft flattop, 34' matching section, coax fed antenna (G5RV)operated far from the antenna's design frequency of 14 mHz.
So for giggles lets say you want to operate your G5RV on 80 meters, (or any frequency other than 14 mHz. )
Once the current and voltage are pushed either up the stub or down the coax, due to the wide departure from the design frequency, cancellation does not occur. Hence the stub and feedline radiate and as we all should know feedline radiation is BAD.
This radiation will become harmonic in nature and that coupled with the blocking due to unfiltered receivers, loud phase noise from nearby transmitters and a myriad of other random noise all adds up to greater interstation interference.
A center fed dipole with open wire line from the feed point to a link coupled tuner (Johnson style matchbox) in the shack would be much better than the G5RV antenna with stub and coax feed. With that type of antenna and tuner you maximize the "Q" of the antenna reducing any feedline radiation, production of harmonics and radiated hash.
Folks who operate a G5RV at home with a single transceiver never see the problems of interstation QRM since they only run one radio at a time.
Our goal needs to be zero or close to zero interstation interference.
Without that being accomplished operating is more of a job and not fun.
A modern, 2015 model sensitive rig will die a quick and unrecoverable death in the environment we presently operate in.
Study all that you can about success SO2R (single op, 2 radio) and multi-multi station engineering. They have already done it, no need to reinvent the wheel.
Again just my .02 cents.
Dave
W1CTN
Radio Ansonia
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