Hello, name here is Sean
Callsign is Kd4adv
QTH is Amelia, Virginia (FM17a)

I am constructing a 1/4-wave vertical groundplane receiving antenna for the
UHF 225 - 400 MHz band aka the Military aircraft band.

I found the center frequency for the civilian aviation band between 118.0
and 136.0 is around 127.75 Mhz (AM)

Who can tell me how to find the center frequency for the UHF mil-air band,
and/or, any other band?

(I have a guess that it's around 32x.xxx MHz)

Here's a formula that I found in the ARRL Handbook that I can do after
finding the center frequency. (ref. 33-26) circa 1994

234 / freq (MHz) is used to find the length in feet.

2808 / freq (MHz) is used to find the length in inches for the vertical
element

2950/ freq (MHz) is used to find the length of the radials in inches.

Thank you,
sean

Unless you plan on trnasmitting, don't worry.
I have built GP cut to each end of the mil-air
band and they both worked fine across the band.
Try something like 9.5" with radial about 10".
Construction, esp water proofing is much more
important. Any water that can sneak into the coax
will kill your signal!
I use an ancient Tandy Disckone, the one without
the vertical "stinger", for almost all of my VHF/UHF
reception. I was given a Uniden Marine VHF 2way
and use it as a dedicated WX receiver and with
it connected to the GP antenna that I built for the 70cM
ham band I pick up wx stations in hundred mile radius.

Take car builing it, use good materials, use a good
sealant, I like GE aquarium sealant. And I let it cure for
a week before placing it in service. Antennas that I
have built this way have lasted for over 20 years.
I used to use SO-259 connectors mounted upside down.
But I use hermetic female "N" connectors now. I apply
the silicon to the threads on the male connector, then
tighten it down. The advantage of this style construction
is you can mount it IN a piece of 1/2 EMT conduit with the
conduit junctions. I seal everything up with silicon. The parts
are so inexpensive that I don't plan on repair or salvage.
I do like to spary the vertical element with a silicon
"encapsulating" spray so help the conductor avoid corrosion.
I have even built several of these for cell frequencies before
the ECPA was enacted.
I bend my radials to about 60 degrees and feed the antenna
with the best low loss foam TV coax I can get. Yes it is 75 Ohms,
and the antenna be something close to a 50 ohms, but for
receiving it doesn't mater. By using TV coax I can use "F"
static blocks where it enters the house to stay legal (compliant
with the NEC which our county uses).

Terry

Alright.
Thank you

Sean
wrote in message
ups.com...
Unless you plan on trnasmitting, don't worry.
I have built GP cut to each end of the mil-air
band and they both worked fine across the band.
Try something like 9.5" with radial about 10".
Construction, esp water proofing is much more
important. Any water that can sneak into the coax
will kill your signal!
I use an ancient Tandy Disckone, the one without
the vertical "stinger", for almost all of my VHF/UHF
reception. I was given a Uniden Marine VHF 2way
and use it as a dedicated WX receiver and with
it connected to the GP antenna that I built for the 70cM
ham band I pick up wx stations in hundred mile radius.

Take car builing it, use good materials, use a good
sealant, I like GE aquarium sealant. And I let it cure for
a week before placing it in service. Antennas that I
have built this way have lasted for over 20 years.
I used to use SO-259 connectors mounted upside down.
But I use hermetic female "N" connectors now. I apply
the silicon to the threads on the male connector, then
tighten it down. The advantage of this style construction
is you can mount it IN a piece of 1/2 EMT conduit with the
conduit junctions. I seal everything up with silicon. The parts
are so inexpensive that I don't plan on repair or salvage.
I do like to spary the vertical element with a silicon
"encapsulating" spray so help the conductor avoid corrosion.
I have even built several of these for cell frequencies before
the ECPA was enacted.
I bend my radials to about 60 degrees and feed the antenna
with the best low loss foam TV coax I can get. Yes it is 75 Ohms,
and the antenna be something close to a 50 ohms, but for
receiving it doesn't mater. By using TV coax I can use "F"
static blocks where it enters the house to stay legal (compliant
with the NEC which our county uses).

Terry