Dual Yagi Antennas

[CFP387]

Guys, quick question:

I am using a directional yagi antenna to monitor about five tower sites on VIPER, North Carolina's statewide system, on a 436. Is it possible to add a second yagi, pointed in a different direction, to monitor additional tower sites? In theory, I would run a separate coax from two antennas into one "T" and then into the scanner. Would this work or has anyone here tried this method?

 

[majoco]

A "T" won't be the best as half the signal from one antenna will go straight out the other, after all, there's no difference between a receiving antenna and a transmitting one. You need something like a two-port combiner which has isolation between one input and the other - you could call it a splitter backwards! Even so, there's no guarantees - a yagi might have most of it's reception from one direction but it's certainly not exclusive - there's sidelobes off the main lobe that might just cancel out a transmission from the other antenna. How much signal have you got to play with? An all-round antenna might just do the job with a small amplifier up at the top.

 

[teufler]

if you have simulcast issues, the other beam will get signals from an other tower .if you run a second coax, possible to run another scanner tuned to whatever direction the second antenna IS. OR A 2IN 1 OUT ANTENNA SWITCH. ONE WAY YOU CONCENTRATE ON ONE DIRECTION AND A SWITCH TO THE OTHER FOR THE OTHER DIRECTION. BOTH ANTENNAS WILL PICK UP STUFF YOU WANT and the signals you don't want. And the stuff you don't want . a stronger and a weaker signal at the same time. you possibly will detect and echo.

 

[CFP387]

Thank you for the information. With the yagi in place as it is now, I'm monitoring around five tower sites and there is no simulcast distortion. I have specific talk groups programmed per site and I just scan those. These sites are all to my north and east; but I would like to scan sites to my west and south. In order to do that, my thinking was to install another antenna (on the same pole) pointed in that direction. Since I'm only scanning specific talk groups on specific sites, to keep it simple, should I just have one antenna per scanner?

 

[garysvan]

i am using a yagi antenna pointed north to receive minneapolis 20 miles away and over a hill from me.
my main simulcast local site is about 5 miles to the south east of me . they do not transmit the same talkgroups and i have my scanner programed like yours with sites and talkgroups in separate lists.
with just the yagi my local site cuts in and out so i am using a mag mount omni 800mhz cell phone antenna on a pie tin with separate coax from the two antennas into a "T" and then into the scanner.
it may not be ideal but it does work good the majority of the time. i may build a antenna switch between the 2 antennas or both.
a combiner for 800mhz is kind of hard to find or expensive if you do. i may try a high quality tv splitter and see how that works.

 

[majoco]

should I just have one antenna per scanner?

That's a much better idea! Two ears - two radio - it's natural really!

 

[Project25_MASTR]

A "T" won't be the best as half the signal from one antenna will go straight out the other, after all, there's no difference between a receiving antenna and a transmitting one. You need something like a two-port combiner which has isolation between one input and the other - you could call it a splitter backwards! Even so, there's no guarantees - a yagi might have most of it's reception from one direction but it's certainly not exclusive - there's sidelobes off the main lobe that might just cancel out a transmission from the other antenna. How much signal have you got to play with? An all-round antenna might just do the job with a small amplifier up at the top.

I am thinking a simple co-phasing setup would work. Theoretically, a co-phasing harness consists of two odd-quarter wave lengths of 75Ω coax T'd into a 50Ω device and functions as a simple, coax based, power divider. So in theory, one could simply obtain something like a mini-circuits divider to perform a two into one conversion. I actually know an SMR doing such a thing on his receive antennas since he's using 3 90º sectors for that function.

Of course, this is all relative depending on the equipment being used as it may not actually be practical.

 

[CFP387]

The sites I'm monitoring are within a 30-40 air mile radius. Would an omni antenna be my better choice for monitoring 700-800, and, if so, what brand or type?

 

[prcguy]

If you combine two identical Yagi antennas pointed at the same source and phased at the perfect distance apart and use a combiner, you will get a narrower beam width and up to 3dB gain.

If you combine two identical Yagi antennas pointed in completely different directions where their patterns don't intersect you will loose at least 3dB of signal over a single Yagi due to combiner losses.
prcguy