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How much gain do I want?

Joined
Jun 21, 2016
Messages
71
Location
New York, USA
#1
I'm fairly new to radios, I know that the higher the gain on an antenna, the more the radiation pattern is horizontal and less vertical, but how much gain do I really want, and how much of an effect could it have on our signal quality?

I'm on GMRS, we have a repeater just above tree line (highest I can go without it being too expensive), and that has a +5db gain antenna on it. The repeater is running at 35 watts right now, and can go up to 50. The trucks can switch between 15 and 25, or 25 and 50 watts and so far they have a few cheap 4db antennas. Were in a suburban area with buildings every couple hundred to few hundred feet, and quite a few trees. Not too sure what else would need to be bought into consideration.

Most vehicles, I can put the antenna right on top in the middle, but there's a couple cars that have FD antennas there so I have to put the GMRS one on the trunks. Oddly enough, one of those cars seems to have better connection when the vehicle is pointing towards the repeater (from a distance), as opposed to away where the antenna would be less obstructed my the body of the vehicle.
 
Joined
Jul 27, 2005
Messages
9,905
Location
Point Nemo.
#2
If the terrain is relatively flat, higher gain antennas can certainly work better.
However, you won't see huge increases in range. With a low repeater antenna and mobile antennas, you're really limited by line of sight. Line of sight with that setup will probably be a few miles at best. A bit more if topology works in your favor.

I used a 5/8th's wave UHF antenna for a while on top of a full size truck. After a while, I swapped it out to a quarter wave and could not tell the difference in performance except when really way out on the fringes.

You can experiment with both and see what works for you. Personally I prefer lower profile 1/4 wave whips.

For trunk mounts, see if you can find an elevated feed antenna, this gets the radiating element above the roof line and can help performance. Your experience with the directionality of the trunk installs is typical, offset ground planes can do that.
 
Joined
Jun 30, 2006
Messages
7,284
Location
So Cal - Richardson, TX - Tewksbury, MA
#3
I would consider a higher gain antenna on the repeater itself. How long is your 5dB gain repeater antenna? Many antennas have bogus gain ratings and a UHF antenna with 5dB gain over a dipole will be a good 7ft tall. I've seen some little 4ft jobs that claim the same gain and its a lie.

Going from a 5dB gain antenna to a 10dB on the repeater is a significant improvement and worthwhile if you can afford it. It sounds like your repeater is not on a high hill top so higher gain antennas on the mobiles would also benifit.
 
Joined
Jun 21, 2016
Messages
71
Location
New York, USA
#4
I got this GMRS HAM UHF +5dB gain Repeater Base Antenna | eBay on the repeater. I don't have a picture of the inside, but theres a 2 conductor wire (kind of like a speaker wire) inside it, one connected to the center of the connector, one with a couple notches cut out of the wire connected to the outside of the connector. It does seem to work significantly better then the last couple high gain antennas I got (one was about the same price, the other was almost free).

And no its not really on a hill, everything is fairly flat around here, highest point of town is like 50ft above sea level, tower is 49½ft high and 40ft above sea level. Problem is trees are almost that height, some of them higher. Right now we can cover this town and the surrounding ones (so long as were using the vehicle radios), but if i could push that a little further for a couple friends I'd like to. I cant go to 50ft or higher though or i'd need permits and inspections and what not, it would cost too much for us.
 
Joined
Jun 30, 2006
Messages
7,284
Location
So Cal - Richardson, TX - Tewksbury, MA
#5
That's not a 5dBd gain antenna, more like 2dBd at best. Its probably a 2 element colinear J-pole made of 300 ohm TV twinlead. If you can get a real antenna like a surplus 10dBd stationmaster or DB Products DB420 or similar, you will do back flips over the increased range and static free signals within the weak range you have now. A major portion of a repeater system is the antenna and that can make or break coverage. Height is also a major factor in range so if you can increase the height it will be noticed at a distance.

You might try looking at your local Craig's list ads for UHF antennas, sometimes big ones show up for cheap.

I got this GMRS HAM UHF +5dB gain Repeater Base Antenna | eBay on the repeater. I don't have a picture of the inside, but theres a 2 conductor wire (kind of like a speaker wire) inside it, one connected to the center of the connector, one with a couple notches cut out of the wire connected to the outside of the connector. It does seem to work significantly better then the last couple high gain antennas I got (one was about the same price, the other was almost free).

And no its not really on a hill, everything is fairly flat around here, highest point of town is like 50ft above sea level, tower is 49½ft high and 40ft above sea level. Problem is trees are almost that height, some of them higher. Right now we can cover this town and the surrounding ones (so long as were using the vehicle radios), but if i could push that a little further for a couple friends I'd like to. I cant go to 50ft or higher though or i'd need permits and inspections and what not, it would cost too much for us.
 
Joined
Jun 21, 2016
Messages
71
Location
New York, USA
#7
Is craigslist a good place to find those antennas in surplus? Or is there anywhere else you know of where I can look around?

and I am using LMR-400 with N connectors, along with this lightning arrester in the middle (by the base of the tower connected to the block with the lines to the 4 ground rods)
 
Joined
Jun 30, 2006
Messages
7,284
Location
So Cal - Richardson, TX - Tewksbury, MA
#8
I've seen them on Craig's list in my area but I also see them at a ham radio swap held every month near me. Over the years I've picked up several UHF Celwave PD-201 style Stationmasters, several DB Products dipole arrays and a couple new in box 15ft long 7.5dB gain sticks from Antenna Specialists at the swap meet, all really cheap. Somewhere near you there are big surplus UHF antennas wanting a new home, you just have to sniff them out. If you were local to me in So Cal I could hook you up with something.

I'm not sure that lightning arrestor is doing anything for you except for providing a point on the coax shield to connect a ground wire. If you get a direct hit it will be all over for whatever equipment is connected to the antenna, including anything plugged into AC outlets on the property. Are the ground rods bonded to the buildings main electrical panel per NEC Article 810?




Is craigslist a good place to find those antennas in surplus? Or is there anywhere else you know of where I can look around?

and I am using LMR-400 with N connectors, along with this lightning arrester in the middle (by the base of the tower connected to the block with the lines to the 4 ground rods)
 
Last edited:
Joined
Jun 21, 2016
Messages
71
Location
New York, USA
#9
No these ones are just for the tower. The garage it is part of, and the main building, have their own ground rods to the panels.

The arrester does have a little thing inside it, like a glass tube like thing under one of the larger side bolts, but I know it is cheap. I was told nothing could protect a direct hit anyway.

Sorry i am a bit new to the radio world. I always liked them but only recently i really started to get involved with them.


I've seen them on Craig's list in my area but I also see them at a ham radio swap held every month near me. Over the years I've picked up several UHF Celwave PD-201 style Stationmasters, several DB Products dipole arrays and a couple new in box 15ft long 7.5dB gain sticks from Antenna Specialists at the swap meet, all really cheap. Somewhere near you there are big surplus UHF antennas wanting a new home, you just have to sniff them out. If you were local to me in So Cal I could hook you up with something.

I'm not sure that lightning arrestor is doing anything for you except for providing a point on the coax shield to connect a ground wire. If you get a direct hit it will be all over for whatever equipment is connected to the antenna, including anything plugged into AC outlets on the property. Are the ground rods bonded to the buildings main electrical panel per NEC Article 810?
 
Joined
Jun 30, 2006
Messages
7,284
Location
So Cal - Richardson, TX - Tewksbury, MA
#10
According to the National Electrical Code, any ground rods you add, even on a remote tower, must be bonded to the main electrical panel with no less than #6 copper wire, and if the run is over a certain length you must upsize the wire. Do a search on NEC Article 810.

The glass thing is a gas discharge tube that conducts when it sees over 90volts or something around there.

No these ones are just for the tower. The garage it is part of, and the main building, have their own ground rods to the panels.

The arrester does have a little thing inside it, like a glass tube like thing under one of the larger side bolts, but I know it is cheap. I was told nothing could protect a direct hit anyway.

Sorry i am a bit new to the radio world. I always liked them but only recently i really started to get involved with them.
 
Joined
Nov 18, 2008
Messages
429
Location
Campbell County, Wyoming
#12
For the most part, Power over about 20 watts will have little or no effect. You may actually improve things by lowering the repeater below the trees if the foliage is almost solid. antenna gain figures are more for advertising than anything else. Most squelch circuits take 3-5 db to 'open' so for the most part if you are using the squelch you are dealing with 'strong' signals anyway. The antenna pattern for vehicles will likely favor the direction of the most metal rather than be circular. That means that your 'best' direction will be a line form the antenna 'through' the engine.

Propagation is as much an art as a science unless you figure everything so experience will be your best guide.
 
Joined
Jun 30, 2006
Messages
7,284
Location
So Cal - Richardson, TX - Tewksbury, MA
#13
If you increase repeater power from 20w to 100w with everything else equal, the range of the repeater will increase and noisy areas will become less noisy. Going from 20w to 50w might go unnoticed in some directions but it will still give slightly better performance. That of course will not help mobiles getting back into the repeater. Raising the antenna above trees will increase range, as foliage will attenuate signals and getting above them can provide an angle down and through less trees, less buildings, etc. Antenna gain figures when using the same reference will indicate which antenna will have greater range under the conditions the OP is using them. Start with a 3dBd gain antenna 50ft in the air and go to a 10dB gain model and you will see instant and measurable improvement.

Been doing this for 40 years installing repeaters and owning a commercial repeater business. In just the last month playing with a UHF amateur repeater at my house with friends monitoring at various distances I've swapped antennas several times with people noticing instant and positive improvements with higher gain antennas. I've raised and lowered the antenna from 15 to 40ft with huge improvements in range. Gone from 20w to 100w with "wow" comments on the other end with people going from some noise to full quieting, etc. Bottom line is all the suggestions above should help improve range.

For the most part, Power over about 20 watts will have little or no effect. You may actually improve things by lowering the repeater below the trees if the foliage is almost solid. antenna gain figures are more for advertising than anything else. Most squelch circuits take 3-5 db to 'open' so for the most part if you are using the squelch you are dealing with 'strong' signals anyway. The antenna pattern for vehicles will likely favor the direction of the most metal rather than be circular. That means that your 'best' direction will be a line form the antenna 'through' the engine.

Propagation is as much an art as a science unless you figure everything so experience will be your best guide.
 
Last edited:
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