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Author Topic: UHF Yagi Question  (Read 3746 times)

Posts: 146

« on: July 06, 2012, 10:53:41 AM »

  Before we spend the money my question is, will a yagi allow us to pick up a distant hand held that's inside a building that's about 2 miles away?

 We have an issue between building to building communications, I was suggestion a yagi at one station to allow easier contact. Now I know yagis are great and have great gain, We just wish to make building to building on UHF easier, if one person gets on the roof of the other building contact is 100% I just want others inputs before spending the money.

 Any ideas?
« Last Edit: July 06, 2012, 10:56:19 AM by MDNITERDER » Logged

Posts: 1003

« Reply #1 on: July 06, 2012, 11:07:05 AM »

A yagi at the outside station might help - depends how how tightly shielded the building is where the HT is located. Better improvement might be to get the HT closer to a window, if possible. Also try various bands - 220, 900, or 1.2Ghz might get through better than 440.  A yagi at one end will make a weak signal better more readable, but if there's no signal at all to be heard, it won't help. Are you using ham HT's, or is it FRS or GMRS ? Various locations in the building? How about an in-building passive repeater ? an antenna in the room where the HT is (mag mount on a file cabinet?) linked by coax to another antenna (small beam or quad) with line of sight to the other building.

Posts: 146

« Reply #2 on: July 06, 2012, 11:16:41 AM »

Our system is vertex units on the business band frequencies, we are in a manufacturing plant that has many large metal scaffolding and has the aluminum foil roof barrier. Signal is faint unless one person goes out side. Windows are not possible as our manufacturing and our shipping portions do not have them or the option to walk away to do so. one building has one radio the second has 10 radios. So we can say the one radio is a dispatch for manufacturing. If i go on the roof of our building the person at dispatch can hear me inside his building no matter where he is. So the signal is there to grab just both being in the building we are being limited. So I am thinking if dispatch had a small 3 element yagi we maybe fine.

Posts: 17413

« Reply #3 on: July 06, 2012, 12:51:04 PM »

If the signal is weak, then there is a good chance that the yagi may help.
(Especially if you can mount it on the roof and run coax down to the
radio inside, since you know you have coverage from the roof.)
It's when you can't hear the signal at all that you can't predict whether
increased antenna gain is going to help or not.

My approach in such a case is to try it and see.  That will give you an
idea of how much gain you need.  The WA5VJB "Cheap Yagi" designs
are easy to build with copper wire and PVC pipe:

Scale one of his 70cm designs to your operating frequency, hook it up
and see how it works.  You may have to rotate it around a bit to maximize
signal reflections into and out of the building.

Otherwise, if the buildings are metal and the flat side of one faces
the other, you can install a dipole or other element on the outside
using the metal as a reflector and run the coax in through the wall.

Posts: 875

« Reply #4 on: July 06, 2012, 03:55:12 PM »

Being inside a building, and being on UHF, the results will be very variable.
Moving a few feet may be a go or no-go situation, so I would recommend something more stable.
Being inside, your signal is going to be bouncing about like in a pinball machine, with unpredictable results.

KQ6Q's suggestion of a passive repeater is a good one, and should be inexpensive.
A quarter wave vertical cut to your operating frequency inside leading to a yagi outside would be a good experiment.
The main cost is routing the coax from your area to the roof or outside.
Once you have a known stable path to your target building, you can experiment with gain antennas.

Good luck,

73 - Rob

Posts: 65

« Reply #5 on: July 06, 2012, 07:59:43 PM »

If you can get a coax to the outside of the building to yagis - you will see a world of difference.  If you can get it on the roofs - it will be great.  Whether you use the radios hooked directly to the coax - to the yagis or make a passive repeater like mentioned above - you still need to get thru the wall or up to the roofs with good coax.

Good Luck, Walter  K5KNE 


Posts: 92

« Reply #6 on: July 07, 2012, 09:25:05 AM »

I worked for Ford Mo Co for 28 years in a plant and the management people used UHF HT's. There was a repeater system in that plant and it worked well. I could sit at home and copy every conversation from the plant on a HT in my basement.

A little costly though if you only use two HT's back and forth.

Posts: 146

« Reply #7 on: September 07, 2012, 12:38:36 PM »

 So far we ended up with a 0gain omni directional antenna, our HT's are able to communicate back to base that is 2miles away from inside the second building, there is minor static depending on how warm the weather gets but it works very well.
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