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HELP WITH DIPOLES AND INVERTED V'S
- Thread starter TonyV225
- Start date
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.
20 meters is good, reason I asked is I put it up and had 100' of the stuff and just slapped some ends on and never got around to doing anything else with it up to now.
It's up 35' or so and the end of the twin lead 300 ohm is at 24' where it connects to the coax, I have no other choice in the mounting scheme other than to bring it to the tuner with coax so I guess I will just bring the extra coax in and clip it there and put a new end on and call it good.
Thanks for the info.
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.
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
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.
An antenna tuner (ATU) never makes an antenna resonant. It can certainly do some impedance matching, which is not the same thing as 'resonance'.
As it was originally designed, a G5RV is a resonant antenna. It was not designed as a multi-band antenna. It can be used as such, but that wasn't why it was made at all. There are several antennas that can be used as multi-band antennas, and none of them, except for 'loaded' antennas, are resonant on other than their original design frequency. That's by definition of resonance.
A quick-n-dirty way of determining if the length of feed line contributes to impedance matching is to change that length. In the case of the G5RV, the only place that will not make a difference in the SWR you see will be at it's design frequency. On a harmonically related frequency feed line/coax length definitely will affect SWR or impedance matching.
SWR has nothing to do with resonance. Impedance matching (tuners) has nothing to do with resonance. The impedance at resonance can be @#$ near anything, and rarely the 50 ohms that's normally associated with antennas.
- 'Doc
All of this assumes that you are talking about the original, 'classic', G5RV antenna, except for the resonance and impedance matching part, which is true for all antennas.
As it was originally designed, a G5RV is a resonant antenna. It was not designed as a multi-band antenna. It can be used as such, but that wasn't why it was made at all. There are several antennas that can be used as multi-band antennas, and none of them, except for 'loaded' antennas, are resonant on other than their original design frequency. That's by definition of resonance.
A quick-n-dirty way of determining if the length of feed line contributes to impedance matching is to change that length. In the case of the G5RV, the only place that will not make a difference in the SWR you see will be at it's design frequency. On a harmonically related frequency feed line/coax length definitely will affect SWR or impedance matching.
SWR has nothing to do with resonance. Impedance matching (tuners) has nothing to do with resonance. The impedance at resonance can be @#$ near anything, and rarely the 50 ohms that's normally associated with antennas.
- 'Doc
All of this assumes that you are talking about the original, 'classic', G5RV antenna, except for the resonance and impedance matching part, which is true for all antennas.
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.
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.
re bazooka
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
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 on bands OTHER than 20M without a tuner? Not all that many, I'd bet.
As far as "calling" it a resonant antenna, let's define resonance, shall we? It means that the antenna, at a given frequency, exhibits equal amounts of inductive reactance and capacitive reactance. ANY antenna that exhibits this characteristic IS RESONANT at that frequency. A true G5RV is indeed resonant on or near 14 MHz.
The G5RV was designed from the ground up as a 20 meter antenna, and, as I said earlier, the fact that it can be used with a tuner on other bands with passable results is just a bonus.