Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1   Report Post  
Old August 16th 05, 05:19 PM
Ken Bessler
 
Posts: n/a
Default Homebrew HT antenna

I just built a 1/4 wave (146mhz) antenna for my dual band
HT (Yaesu FT-51r). It's simply 19.25" of .025" piano wire
soldered into the core of a broken SO-239/BNC adapter.
The BNC center pin just sits in the socket in the radio with
a rubber bnc cap keeping the antenna load off the pin and
keeping dirt out. It's all a press fit and it seems to work great.

Comparing it to my OEM rubber duck, it's about 2-4 S units
better on 2m & 440. As I understand it, it works as a 3/4
wave antenna on UHF and should be a good match but the
radiation angle won't be perfect.

My question is this: What would be the radiation angle on 440?

I know I'm picking nits here but I'm interested in the theroy.

P.S. The FT-51R is an all metal case HT which should provide
a good capacitive couple to my hand but what about when
the HT is on the back of my backpack? What counterpoise do
I get then? Maybe from the mic cable?
--
73 de Ken KGØWX - Flying Pigs #-1055
Elecraft K2 #4913


  #2   Report Post  
Old August 16th 05, 06:00 PM
David G. Nagel
 
Posts: n/a
Default

Ken Bessler wrote:
I just built a 1/4 wave (146mhz) antenna for my dual band
HT (Yaesu FT-51r). It's simply 19.25" of .025" piano wire
soldered into the core of a broken SO-239/BNC adapter.
The BNC center pin just sits in the socket in the radio with
a rubber bnc cap keeping the antenna load off the pin and
keeping dirt out. It's all a press fit and it seems to work great.

Comparing it to my OEM rubber duck, it's about 2-4 S units
better on 2m & 440. As I understand it, it works as a 3/4
wave antenna on UHF and should be a good match but the
radiation angle won't be perfect.

My question is this: What would be the radiation angle on 440?

I know I'm picking nits here but I'm interested in the theroy.

P.S. The FT-51R is an all metal case HT which should provide
a good capacitive couple to my hand but what about when
the HT is on the back of my backpack? What counterpoise do
I get then? Maybe from the mic cable?
--
73 de Ken KGØWX - Flying Pigs #-1055
Elecraft K2 #4913


In a HT I would not worry about radiation angle.

Dave WD9BDZ
  #3   Report Post  
Old August 16th 05, 08:37 PM
Roy Lewallen
 
Posts: n/a
Default

Ken Bessler wrote:
I just built a 1/4 wave (146mhz) antenna for my dual band
HT (Yaesu FT-51r). It's simply 19.25" of .025" piano wire
soldered into the core of a broken SO-239/BNC adapter.
The BNC center pin just sits in the socket in the radio with
a rubber bnc cap keeping the antenna load off the pin and
keeping dirt out. It's all a press fit and it seems to work great.

Comparing it to my OEM rubber duck, it's about 2-4 S units
better on 2m & 440. As I understand it, it works as a 3/4
wave antenna on UHF and should be a good match but the
radiation angle won't be perfect.

My question is this: What would be the radiation angle on 440?


It's just about impossible to say. Your body is radiating at least as
much as the "antenna", and the pattern is determined the combination.

I know I'm picking nits here but I'm interested in the theroy.


The theory says that if you put any current I into the antenna, an equal
current I flows from the inside of the antenna connector shell over the
edge, over the HT case, and into any conductor it can find. The amount
of radiation from the antenna is proportional to the current on each
part of the antenna multiplied by the length of wire it flows on. The
radiation from the HT case or your body is proportion to the current on
each part of it multiplied by the length of the conductor it flows on.
Your body and the HT case follow the same rules as the "antenna", and
are at least as important a part of the radiating system. The overall
pattern is the sum of the fields from all those current-conductor length
products, from both the "antenna" and your body.


P.S. The FT-51R is an all metal case HT which should provide
a good capacitive couple to my hand but what about when
the HT is on the back of my backpack? What counterpoise do
I get then? Maybe from the mic cable?


Yes, the mic cable and case will become the other half of the antenna
system. If you unplug the mic, the current into the "antenna" will drop
(on 2 meters at least) because the impedance of the outside of the case
will be relatively high because of its short length. And only the amount
of current that flows on the outside of the case will flow into the
"antenna".

Roy Lewallen, W7EL
Reply
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
FA: VHF / UHF Antenna Assortment - starting at $5.00 Les Wilson Swap 0 March 7th 05 02:09 AM
Discone antenna plans [email protected] Antenna 13 January 15th 05 12:51 AM
Understanding Shortwave Radio Listening and Antenna Design and Construction RHF Shortwave 3 February 13th 04 08:16 AM
EH Antenna Revisited Walter Maxwell Antenna 47 January 16th 04 05:34 AM
Poor quality low + High TV channels? How much dB in Preamp? lbbs Shortwave 16 December 13th 03 04:01 PM


All times are GMT +1. The time now is 03:33 PM.

Powered by vBulletin® Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 RadioBanter.
The comments are property of their posters.
 

About Us

"It's about Radio"

 

Copyright © 2017