RadioBanter - View Single Post - j-pole 5/8 wave

Ed Cregger · October 5th 07, 08:42 PM posted to rec.radio.amateur.antenna

wrote:
On Oct 5, 11:49 am, K7ITM wrote:
On Oct 5, 6:45 am, wrote:

Higher?? You posted 6.34dBi for the half wave, and 6.58dBi for the
quarter wave GP ... Am I misreading something, or was that a typo
about which has higher gain, or what?

Dang.. I guess I had it backwards in the 2nd post...
Normally, I would think the 1/2 whip would show slightly higher,
but dunno.. Quiver in the force I guess.
I have no real problems with either type. A 1/2 wave whip is fine
if it's decoupled.
But few J pole users seem to add decoupling sections.
Most of the ringos sold for VHF lack decoupling also..
One note.. If I build a 1/2 wave, I usually prefer to feed as a ringo,
vs as a J pole..
But I still mostly use the GP's as they are simple. I've got one up
in the attic hanging from the rafters as an emergency antenna
when T-storms are in the area and I'm chicken to use my outside
antennas.
MK

Yes, BUT, the 5/8th wave radiator will put more of the signal toward the
horizon, instead of launching it at a 40 degree plus angle away from the
horizon. So while one configuration can have higher dbi ratings, it
doesn't count unless the signal goes where it will be most effective.

I have a friend (engineer) that designs and builds his boats (some
rather large sailboats) with everything quantized mathematically. I
showed up one day with a model sailboat sitting on a carry stand that I
had made. He asked me how I calculated the angles needed to accommodate
the hull accurately. He said that this problem had been bugging him for
a while. I was surprised because this guy is really smart.

I grabbed two rulers and put each one along the side of the boat and
then clamped them at that angle. I then transferred the angle of the two
rulers to a sheet of paper by simply drawing lines along the inside of
the v that was created. His jaw dropped in surprise. He was amazed at
how easy the process was and he realized that the same process would
work with his full size boats. No math required.

While EZNEC is a fantastic program, it is no better than the programmer
that wrote it. No one person can take absolutely every variable into
consideration because many of them are very, very complex and nearly
impossible to quantize.

I suggested a simple 1/2 wave J-pole antenna earlier that was easy to
make, super easy to tune and one that worked very effectively. Yet
everyone is beating their brains out trying to come up with the best
5/8th wave J-pole, even though this design will require lossy matching
devices to get the impedance down to a manageable/acceptable level.
What's up wid dat?

I do realize that figuring out such a design is fun in and of itself and
may be the real purpose of the exercise. Still, I'll betcha no one on
the receiving end of the OP's signal could tell if he was using the
5/8th wavelength J-pole or the 1/2 wavelength J-pole.

Ed, NM2K