I recently built a copy of the 'Edison Fong' 2m/440 dual band roll up antenna... I am a little confused about tuning it...
J-Pole Antennas
J-Pole Antennas
-
You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
-
A Winner has been selected for the 2025 Radioddity Cyber Monday giveaway! Click Here to see who won!
how do you tune the 300ohm, 2m/440 dual band j pole
- Thread starter mr_fx
- Start date
Looks like you move your coax attachment points. See the SWR and Final Installation instructions here:
2 Meter Slim Jim Antenna - 300 Ohm Twinlead Version
73,
RT307
2 Meter Slim Jim Antenna - 300 Ohm Twinlead Version
73,
RT307
It isn't difficult to tune a 'J'-pole of any kind, but it can certainly be a bit different depending on how it's made.
There are two steps in that tuning process, one deals with resonance, the other with impedance matching (SWR). Each of those steps is done differently and don't 'mix', if that makes any sense.
Resonance is controled/adjusted by changing the length of the '1/2 wave' section of the antenna, the long leg. That's measured by the amount of power radiated by the antenna and isn't very exact using any of the common means of measuring power that people have. It's 'ball-park'ish, sort of.
Adjusting the SWR, impedance matching is done by sliding the feed line's attachment point up/down the antenna. (Keep the attachment points on the long leg and the short leg parallel, or the same distance from the bottom. That keeps any 'unbalance' out of it which can cause several sorts of complications. Later, if you want to see what those 'complications' are, try it with the attachment points at various places.)
That help any?
- 'Doc
There are two steps in that tuning process, one deals with resonance, the other with impedance matching (SWR). Each of those steps is done differently and don't 'mix', if that makes any sense.
Resonance is controled/adjusted by changing the length of the '1/2 wave' section of the antenna, the long leg. That's measured by the amount of power radiated by the antenna and isn't very exact using any of the common means of measuring power that people have. It's 'ball-park'ish, sort of.
Adjusting the SWR, impedance matching is done by sliding the feed line's attachment point up/down the antenna. (Keep the attachment points on the long leg and the short leg parallel, or the same distance from the bottom. That keeps any 'unbalance' out of it which can cause several sorts of complications. Later, if you want to see what those 'complications' are, try it with the attachment points at various places.)
That help any?
- 'Doc