how to expand the range of a two-way radio (UHF)?

Good day. Please help me with my project.

My dad asked me to design a system that would eliminate "dead spot" using a two-way radio in a 4-story building and has a basement.

The two-way radio he wants to use is a MOTOROLA Model T289. Has a frequency range of 462.0 - 467.0 MHz and a power output of 0.5 Watts.

The problem is that the signal from the two-way radio can not reach the basement since it operates in a Line of Sight condition.

What should I do to make the signal reach the basement?

Is there any devices that would make the signal available in all corners of the building? Like an IBS in GSM?

Thank you in advance for helping me

Hmmm, those are cute little radios.

A different antenna would be a good place to start. You can hack into the cover and make a coax antenna.

Get some cheap 50 ohm RF coax, cut it to match your UHF frequency, about 6 inches for 460 Mhz but leave yourself an inch or two extra. You may want to get matched BNC connectors, the female to permanently fix to the radio. You would solder the center conductor of the female connector to center conductor connection on the radio circuit board. The shield pin would be soldered to ground. The BNC connector would be held in place with good epoxy to the plastic cover.

Take the coax and strip back 6 inches approx of the black or gray jacket, exposing the foil and shield. You should have an inch or two extra still jacketed. unravel all the woven shield wires carefully, leaving them uncut and unbroken. What you have should resemble a peeled bannana. Twist the lengths of shield wire together off to the side in two or three seperate "ropes" and apply solder in several locations on each "rope" to hold it together.

Take the male BNC connector and the jacketed end of the antenna. Cut back a 1/2 inch or so of the jacket, then cut back an 1/4 inch or so of the shield you exposed (approximates). Cut about a 1/8 inch of the white or clear center insulator to expose the center conductor. Solder your BNC center pin to the center conductor and apply the shield-connection body to the shield wires. Its been a while so the steps are cloudy in my mind.

You may want to reinforce this area somehow, perhaps a small hollow plastic tube to slide over the inch or so of jacket and BNC connectors.'

Now, dangle the twisted and soldered shield to the side of the radio, and the center insulator and center conductor will stand vertically as your radiator.

It doesn't matter about line of site, this antenna will most likely give you the extra range, even from multiple floors of the building. You might even get away with modifying only one transciever, as the gain achieved will be both transmit and receive.

It is late here tonight, but I'll try to upload a sketch tomorrow.

I'm surprised that you can't get reliable communication between 4 floors. Are the radios in good condition?

ke5frf said:

A different antenna would be a good place to start. You can hack into the cover and make a coax antenna.

Click to expand...

I thought for a minute you were going to suggest a "passive repeater".
A passive repeater is simply two antennas connected by a piece of low loss coax. You would place one antenna in the basement and the other on the floor you'll be using the most. The closer the radios are to the antennas, the better it'll work.

@ke5frf: thanks for the suggestion.

@kchriste: what brand of passive repeater should i use? do i have to buy a unit of base station for that?

ke5frf - Jeez Id have to give that a try just for the ingenuity of it .
A vertical with ground plane ,probably works best with the ground plane at 45degrees ?

If the floors in the building are made of bamboo then the radios should transmit through them.
But if the floors are made of steel reinforced concrete then you have a problem.

buknoy said:

@ke5frf: thanks for the suggestion.

@kchriste: what brand of passive repeater should i use? do i have to buy a unit of base station for that?

Click to expand...

A passive repeater by his suggestion will not have a brand. You can fabricate your own with the method I just described of stripping the coax and making a ground plane antenna.

You would run the neccessary amount of coax from top floor to bottom and strip back each end of the coax in the fashion I described before, except that you would not be connecting to the radio with BNC. The vertical elements could be held steady by some means, a wooden dowel vertically bolted to a structure or something similar, or a straight piece of PVC pipe. The "passive" term implies that no active circuit elements are involved.

Still don't have time to draw something but I will attempt to after thanksgiving holidays here in US if still interested.

tytower said:

ke5frf - Jeez Id have to give that a try just for the ingenuity of it .
A vertical with ground plane ,probably works best with the ground plane at 45degrees ?

Click to expand...

It is quite effective, better than the cheap stub antenna for sure.

If you can hold the braid wire stiffly, yes I would thinf a 45 degree downward slope would be good.

Does the building have a master TV antenna system? Try connecting a UHF antenna at a wall outlet in or near the basement. A set top indoor bow-tie TV antenna will do.

If it is a cable company fed system then, in addition, put a second UHF antenna on the upper floor you want coverage to and hook it to a TV wall outlet. Better if you can get them both on same branch feed from distribution amp splitter.

Keep in mind that the floors of some concrete buildings are poured on to a corrugated sheet metal surface that remains after construction further adding to the challenge of getting RF from floor to floor.

I recall someone testing the rubber duck antennas that were provided with some commercial radios that revealed relatively poor performance. Some measurements and testing might reveal an opportunity and a slight gain might give you a little boost. In simple terms the antenna on the radio did not allow the radio to run at the maximum power level and/or was a poor radiator. It could be a 0.5 watt radio but only into a proper load.

Many of those radios are intended for use with a repeater. You can google to find out more but the repeater is a receiver that hears the signal and re-transmits on a slightly different frequency. The repeater receiver could have multiple receivers and a more powerful transmitter.

Modifying the antenna of a FRS radio is illegal.
Use of a repeater is also illegal.

Family Radio Service - Wikipedia, the free encyclopedia

Defying the FCC regulations can cost you lots of money.

https://www.electro-tech-online.com/custompdfs/2009/11/DA-09-2390A1.pdf

You would be better off just using a pair of cell phones.

Good point on FRS, I just googled and see that this model is in fact FRS. The frequencies seemed to be part of commercial service where repeaters might be allowed.

Isn't GMRS such that repeaters on some frequencies are allowed? That's not of much help to the owner of FRS radios but that could be a solution.

PatM said:

Modifying the antenna of a FRS radio is illegal.
Use of a repeater is also illegal.

Family Radio Service - Wikipedia, the free encyclopedia

Defying the FCC regulations can cost you lots of money.

https://www.electro-tech-online.com/custompdfs/2009/11/DA-09-2390A1-1.pdf

You would be better off just using a pair of cell phones.

Click to expand...

I acknowledge that he should confirm the regulations that apply, but sometimes us arrogant Americans forget that this is an internationally used website and the FCC has limited authority extending only to its own borders (federal means our country and nobody else's).

I kind of assumed he was outside of the US, just judging by his screen name, but of course I have no idea.

Side note, this wouldn't preclude the use of the passive repeater suggestion. I'm pretty certain they are referring to duplex repeaters using different frequencies and power.

The passive repeater idea is the simplest and cheapest. But, in case that won't do the job, you could add an active element by inserting a bi-directional amplifier of the proper frequency range. Just don't crank up the gain more that actually required to get a satisfactory signal.

@ke5frf: i will try your first suggestion on one of the radios and i hope i can do it properly. also, i want to try the "passive repeaters" but i am wondering if I have to design an antenna that will receive only 460MHz of signal? thank you so much for giving suggestions.

RCinFLA: we do not have a master TV antenna system in the building.

BobMcC: do i have to buy that bi-directional amplifier?

I am actually from the Philippines and I appreciate all your suggestions. Thanks.