New J-pole for the barn workshop

[loopstick]

Regular balanced dipole antennas have to be fed where the voltage is highest. Problem with this is that center fed antennas being balanced require balanced feed lines like twin lead which is what most FM receiver antennas are made of. They are often folded 300 ohm twin lead types that come with your stereos when new, you know.. the old two leg types you hang up horizontally where the lead comes down the centre.

J-poles are absolutely no different, except they are fed at the END. That means they need a means to transform the current at the end into voltage at the centre.

Minimum voltage, maximum current at the center. Vice-versa at the ends:

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[BillyBatts]

I can't begin to tell you the number of J-Pole antennas I fabbed for Amateur Radio 2 meter operation. Never thought of using one for FM broadcast reception. I have a Discone I bought from Radio Shack back about 1995 for that purpose - in my attic. It's also acceptable to transmit 2 meters since it's close enough to the FM Broadcast spectrum.

May have to fab a J-Pole once again for FM reception.

Thanks for the post.

 

[EddyR]

The advantage to a J-pole is it receives in all direction equally well. That is also its downfall for some. The one thing that ruins good FM reception is multipath. Multipath is the FM signal hitting the antenna a different times. In TV it was the problem showed up as GHOSTS. The J-pole is a poor antenna in these type locations.They are hopeless in my location. The advantage to a J-Pole is it receives in all direction and if you are in the clear it may work very well for you. On paper antennas are shown receiving the signal equal all over the receiving element. In real life the antenna get more signal on it's tallest part. Many times it is easer to get a vertical or J-pole higher than a horizontal dipole so it is getting a stronger signal .
Another antenna for FM reception is the basic dipole made from zip cord,or lamp cord.Lamp cord is a almost perfect 75 ohm lead wire like coax but it has less loss and it can be connected to a dipole half wave with a no loss. It will connect to the radios 75 ohm connection will no loss. If A half wave dipole 55-58" fed with zip core will give you a lot of signal for a very little investment in time or money. Do not steal the zip cord off your wifes favorite lamp. Note Zip cord and 300 ohm feed wire can not be coiled or taped to a metal mast like coax. A J-pole can be fed with Zip cord just connect it to the same spot as the coax.
Ed

 

[darklife]

Minimum voltage, maximum current at the center. Vice-versa at the ends

Dammit I had a feeling I had those two reversed.
What can I say.. it was the end of the night and I was tired

I did forget to mention one thing and that is J-poles often have a lower angle of radiation out towards the horizon over regular dipole antennas which can cause some gain over a traditional center fed (1/2 wave) dipole.
Not sure if this helps a lot for reception but I know it can greatly benefit transmitting from one since it focuses the signal where you want it most.

Either way j-poles are simply more convenient in many cases. This is why its parent antenna the zepp was used so they could fly the whole thing out of the back of a blimp.

A few alternatives to the j-pole is the end fed dipole using a matching coil rather than the 1/4 wave J section, and a j-pole with stacked elements for more gain called the "super" j-pole.
I tried the latter once using an extra 1/2 wave section on top with a 1/2 wave phasing stub between the sections but the length of the overall antenna was slightly obnoxious for my property and the overall gain didn't seem worth it.

 

[BillyBatts]

I ran a Zepp for many years in HF Amateur Radio before changing to a Windom. Had great success with that Zepp.

I've hooked up the Discone to the FM and will experiment tonight on RX S-meter units. Tomorrow I'll hook up the J-Pole I'm fabbing and see if there is a difference, just for poops and giggles.