I came across this while searching the internet while serching for antennas. I found it on qsl.net it was posted by kd6pag. I never tried building it yet but I figure some one would like it or modify to to work with scanners.
Triband Jpole
- Thread starter Pitachio
- Start date
- Status
I've made a J-Pole antenna or two and they work okay. There are better designs to be had as J-Pole tend to interact heavily with their surroundings. One thing I noticed about the design you posted is that it uses a separate feedline for each of the bands. That's something I havent' seen before.
nd5y
Member
That's an old design that requires a separate coax for each band. Most scanner users probably wouldn't like that.
People have disappointing results from j-poles due to trying to feed them directly with coax. A j-pole is an end fed half wave antenna with the "j" being a matching stub. However, the antenna is a balanced load and must be fed with a balun. I use coaxial baluns made from a half wave length of coax. The feed line will attach a little higher on the stub to allow the 4:1 balun to match 50 ohms. This works (despite many protests on other threads). The response on the antenna will be very flat and it will not interact with other objects.
Unfortunately, even a recent piece in QST magazine perpetuated the myth that j-poles can be fed directly with 50 ohm coax.
As for a multi-band j-pole, there are such things. Arrow Antenna makes 2 meter/440 j-poles. They also make one for 155/460. These are both direct fed from the bottom (an alternate to the balun). However, although I have seen the "copper cactus" design, it will not be very broad band outside its design center frequencies. You might make a slight sacrifice of gain for flat response by using a discone. Antenna gain is always at the cost of bandwidth and radiation angle. High gain broadband antennas like log periodics are directional and expensive.
Unfortunately, even a recent piece in QST magazine perpetuated the myth that j-poles can be fed directly with 50 ohm coax.
As for a multi-band j-pole, there are such things. Arrow Antenna makes 2 meter/440 j-poles. They also make one for 155/460. These are both direct fed from the bottom (an alternate to the balun). However, although I have seen the "copper cactus" design, it will not be very broad band outside its design center frequencies. You might make a slight sacrifice of gain for flat response by using a discone. Antenna gain is always at the cost of bandwidth and radiation angle. High gain broadband antennas like log periodics are directional and expensive.
- Status
Similar threads
