Military Antenna AT-677/VR Mod and test for ham radio VHF 2 meter use

[digitaldust]

People have stated this antenna works in the ham band , well not the whole band . I have done testing and found that it was not being all that it could be. I have installed then checked the SWR on the antenna ( Location of install , Pass Rear of Truck ). What I did find it was ok at 147.200
1.5 SWR but going to 144.555 , and 146.780- .600 this antenna was very hot ! like 2.8 . So I opened up the antenna and found.....

Nothing more then a 1/4 wave non loaded nor matching anything unity antenna of coax with the shielding stripped back and 17 inches of center conductor. So like any good ham I worked the math ((( : If you are operating on 144.5 MHz, dividing 144.5 into 468 gives 3.24 feet. To find the quarter wave, dividing 3.24 feet by 2 gives 1.62 feet for each leg. When mounting on a vehicle, a quarter wave antenna MUST be mounted on a metal base. A quarter wave antenna can be mounted on a fiberglass or plastic body vehicle with the coax connected to one end of the antenna, center lead to antenna, braid grounded, voltage fed. Taken from another ham KC9AOP )))))

So 19.3 inches is the 100% point to make this antenna work all across the ham 2 meter band.

Also a side note this is still a GREAT scanner antenna for trains and other VHF uses . It is just the TX that is being modded
My videos are crappy but there here to help under stand what is inside the antenna and its magic green pool cue.
http://www.youtube.com/watch?v=pQL3dbGGCYc&list=UUs_cShQBwRzHOw3gWI4timQ&index=3


http://www.youtube.com/watch?v=ub_1thS-V2I&list=UUs_cShQBwRzHOw3gWI4timQ&index=4
this video shows the MFJ Mighty Fine Junk meter testing
http://www.youtube.com/watch?v=qv_KxwSQY34&list=UUs_cShQBwRzHOw3gWI4timQ&index=2


Maybe this will help ya in the ham VHF play time ! 73.
!kc8dup!

 

[digitaldust]

http://www.kc9aop.net/HAM/antenna_facts.htm a fun page with great info !

 

[tennmogger]

That's really good information and a useful modification! Thanks!

That antenna design uses a bazooka, or sleeve, type match/balun. It'd be interesting to know if the lower end of the stripped-back braid on your antenna is bonded to the outer braid of the coax as in a true bazooka.

Here's some info on a bazooka:

http://www.antenna-theory.com/definitions/bazooka.php

Theoretically, you might get near perfect match if you lengthened the folded-back part of the antenna, too. As it is, the 19.3 gives you a good minimum SWR at one point within the 2 m band, but the sleeve may still be too short. Having a matching sleeve would perfect the modification and prevent coaxial radiation at 2m wavelength.

I'd just use it, considering the good results you got.

Great work!

Bob WB4ETT

 

[TxFireDeuce]

What is the brand of ant. And what is a place to buy one I am wanting to set up a 2m in my m35a2 and have been looking for a good ant. Thanks