What is the minimum length of coax required to operate a 102' G5RV?
On what band?
A 102', center fed doublet with 35' of parallel feeder (ideally about 600 ohm stuff)*, will work pretty well for 20 meters with any length of 50 ohm coax connected at the end of the parallel feeders. For any other band, the answer is -- it depends.
*And that is the essential definition of a "G5RV" antenna. It's 3/2 wavelengths on 14 MHz, the way Varney intended. That it "works" on other bands is more or less a bonus; it doesn't work really well on any other band.
Experiment with YOUR antenna and find out what works for YOU. My first suggestion would be: Leave the coax out completely and run the parallel line directly to a good tuner.
The minimum length of coax to use with a G5RV is whatever it takes to get to the transmitter. The coax part isn't a part of the 'matching' scheme, that ladder line is.
- 'Doc
jazzsinger,
I don't see where we are disagreeing on anything. Everything after that SO-239 is part of the antenna -system-, and can affect the resulting impedance seen by the transmitter. No disagreement there. But, the length of the coax part of the feed line isn't critical at all. Sure, that length can affect things to some extent, but if the rest of the antenna system has been done correctly, the extent of the coax length should have very little affect. So, it isn't part of the impedance matching network/device. Right?
- 'Doc
The g5rv is non resonant antenna,by that very definition there will always be standing waves on the feedline be it coaxial and/or twin feeder,therefore the length of coax will act as an impedance transformer to some extent and is exactly the reason the g5rv must be used with an atu. you can't change the laws of physics just to suit hams because an antenna is popular albeit very misunderstood.The whole system is brought to resonance by an atu,that includes the coaxial portion.
I'm using a stupid tuner (mfj) so it's all good.I beg to differ,anything after the so239 on the back of the radio is considered a part of the antenna system,as the transmitter will see it all combined,not individual parts.
The TRUE G5RV is indeed a "resonant" antenna, for 20 meters, where it's 3/2 wavelengths long. The 35 feet of parallel feeder is a matching section, again for 20 meters only.
The "tuner" does indeed transform whatever complex impedance the transmitter sees into a conjugate match so that maximum power can be transferred from the transmitter to the antenna system (which includes everything downstream from the antenna connector/terminals on the tuner), but it doesn't do anything at all to any mismatch there might be at the feedline-to-antenna junction. If there was a 6:1 SWR without the tuner, there will still be a 6:1 SWR, even though the tuner might show zero reflected power. The system will still have the losses caused by the SWR.
That one must be for your cb radio/Iam using one of those antennas in my bed room have it in a upside down v works awsome! its the only antenna I have seen that actually works in a apartment. I have purchased a ton of other ones but this is the one that works as advertised
how many people exactly use a g5rv as a single band antenna? to call an antenna that is used on many bands by 99.9999% of people a resonant antenna because it is resonant on one single frequency is ridiculous.