need help-info on grounded antenna-Marconi
 

I need some help as I am not real kean on antenna's.
If I were going on two meters, I would go buy a little vertical or
something, but this is not the case.

Hypothetical example.

Suppose a metal pipe was stuck up in the air 50 feet. We want to operate
on two meters. We measure from the top downward for 1/4 wave length and
calculate and decided on this for a proper length.

Can this 1/4 w.l. point downward from the top then be used as a terminal
point for coax shield while tapping upward to the 52 ohm point for
matching?


Can the rest of the pipe or metal support running downward be ignored as
for length, or must it be a given length? This is the part of the answer
I am interested in.

Can a MFJ-259B help with this? Does this instrument have a long learning
curve?

Thanks for any help on this.

Phil............. K9DNH (havent been on air for a long time)

"Phil Sisson, Litchfield Aerobatic Club" wrote in
message ...
I need some help as I am not real kean on antenna's.
If I were going on two meters, I would go buy a little vertical or
something, but this is not the case.

Hypothetical example.

Suppose a metal pipe was stuck up in the air 50 feet. We want to operate
on two meters. We measure from the top downward for 1/4 wave length and
calculate and decided on this for a proper length.

Can this 1/4 w.l. point downward from the top then be used as a terminal
point for coax shield while tapping upward to the 52 ohm point for
matching?

if there is an insulator there to separate the top 18" from the rest of it
you could feed the top part by attaching the center of the coax there and
the shield to the rest of the pipe.the impedance wouldn't be that close to
52 ohms though, to bring the impedance down some you could add some radials
sticking out attached to the bottom section.

another option is to add a gamma match to feed the top section, or turn it
into what is called a J-Pole, that kind of looks like a gamma match but
doesn't need a capacitor.



Can the rest of the pipe or metal support running downward be ignored as
for length, or must it be a given length? This is the part of the answer
I am interested in.

yes, if you have a proper feed mechanism for the top the length of the rest
would be irrelevant.


Can a MFJ-259B help with this? Does this instrument have a long learning
curve?

maybe, i don't know the frequency range of that off hand.


Thanks for any help on this.

Phil............. K9DNH (havent been on air for a long time)

An MFJ-259B is very easy to use. As far as your design the matching
of your antenna will be the most difficult. You may be best served to
create your antenna independant of the pipe and mount it on top.

I know you are not "keen" on antennas but the Ringo (AR-2) can be
found used for next to nothing and work pretty good. They are also a
very low profile with no radials. The reason I suggest this one is I
have used it and get clear across our local with it at 15 ft in the
air.

Homac



"Phil Sisson, Litchfield Aerobatic Club" wrote in message ...
I need some help as I am not real kean on antenna's.
If I were going on two meters, I would go buy a little vertical or
something, but this is not the case.

Hypothetical example.

Suppose a metal pipe was stuck up in the air 50 feet. We want to operate
on two meters. We measure from the top downward for 1/4 wave length and
calculate and decided on this for a proper length.

Can this 1/4 w.l. point downward from the top then be used as a terminal
point for coax shield while tapping upward to the 52 ohm point for
matching?


Can the rest of the pipe or metal support running downward be ignored as
for length, or must it be a given length? This is the part of the answer
I am interested in.

Can a MFJ-259B help with this? Does this instrument have a long learning
curve?

Thanks for any help on this.

Phil............. K9DNH (havent been on air for a long time)