GMRS Repeater Antenna

[WRVY769]

I upgraded antenna from tram 1486 to comet gp-9nca antenna because it had double the gain. and my tram 1486 antenna was 30ft off the ground and the comet antenna is 62ft off the ground and I'm not seeing any difference in range. What range should I be expecting.

[AdmiralCochrane]

If your physical location is high on a hill, there may be no difference.  Line of sight rules over height.  Likewise to the station(s) you are communicating with, if they are hilltop both antennas would be line of sight to the other station. 

[BoxCar]

8 minutes ago, WRVY769 said:

I upgraded antenna from tram 1486 to comet gp-9nca antenna because it had double the gain. and my tram 1486 antenna was 30ft off the ground and the comet antenna is 62ft off the ground and I'm not seeing any difference in range. What range should I be expecting.

Is the height difference the mast or antenna length? Unless the mast height changes you won't see much if any difference in the coverage.

[WRYW415]

1 hour ago, WRVY769 said:

I upgraded antenna from tram 1486 to comet gp-9nca antenna because it had double the gain. and my tram 1486 antenna was 30ft off the ground and the comet antenna is 62ft off the ground and I'm not seeing any difference in range. What range should I be expecting.

Is the comet tunable? I see that it's only designed to be used up to 450MHz.

[WRVY769]

yes its 11.9 db gain on 462MHz

[Radioguy7268]

It's advertised as 11.9 dBi

In a typical vertical collinear antenna, you can gain 3dB of gain every time you double the number of stacked elements  -  or you can just tell the advertising guy to add 3 more to the gain number by stating gain measured as dBi.

dBi is gain measured against a theoretic isotropic antenna - which isn't the real world.

[gortex2]

Did you add cable to raise your antenna ? If so you have loss there that you did not have before.

 

[MarkInTampa]

I was running a Comet GP-6NC (MURS/GMRS) antenna with really good results at around 35ft with 50ft of LMR-400. Swapped it out a month or two ago with a Comet GP-9 and am disappointed. VHF performance went up just a tick but UHF/GMRS performance went DOWN. I mean noticeably down. One repeater I use 35 miles away went from full signal strength to about half. Other than the occasional band opening, I don't think I've ever heard anybody hit that repeater in my neck of the woods and folks on the repeater were amazed that I was hitting it at all much less full quieting. I was kinda proud of the GP-6's performance. The repeater can't be heard on a J-Pole at all. Don't know if its the radiation pattern of the GP-9 vs the GP-6, the height of the antenna, the huge oak tree 30ft away from it, my terrain or a combination of those and other factors. This mornings project is putting the GP-6 back up.  

[SteveShannon]

If you’re mounting the GP-9 in the same place as the GP-6 was, I would suspect that the flatter propagation pattern of the higher gain GP-9 simply misses the repeater.  I assume that the GP-9 is tuned correctly etc.

[MarkInTampa]

23 minutes ago, Sshannon said:

If you’re mounting the GP-9 in the same place as the GP-6 was, I would suspect that the flatter propagation pattern of the higher gain GP-9 simply misses the repeater.  I assume that the GP-9 is tuned correctly etc.

It's not just the one repeater, the performance is off on most of the more distant (greater than 15 miles) repeaters. My terrain is is such that I know I'm not getting very far going to the north or north-east but any other direction should be fine. The GP-6 had no problem hitting another repeater 46 miles away in another direction but the GP-9 doesn't like it at all. The GP-9 is tuned OK for GMRS, around a 1:1.2 SWR at 467MHz, the GP-6 is is outstanding with a 1:1.05 SWR at 467MHz. I'm in the Tampa area, pretty flat for the most part.

[SteveShannon]

1 hour ago, markskjerve said:

It's not just the one repeater, the performance is off on most of the more distant (greater than 15 miles) repeaters. My terrain is is such that I know I'm not getting very far going to the north or north-east but any other direction should be fine. The GP-6 had no problem hitting another repeater 46 miles away in another direction but the GP-9 doesn't like it at all. The GP-9 is tuned OK for GMRS, around a 1:1.2 SWR at 467MHz, the GP-6 is is outstanding with a 1:1.05 SWR at 467MHz. I'm in the Tampa area, pretty flat for the most part.

Yes, higher gain means that the signal is more concentrated in some directions and weaker in others.  For an omnidirectional antenna that typically means thinner vertically, which may make it easier to miss repeaters. Like a pancake compared to a donut.  If the antenna is mounted too low the narrower signal might angle more upward, in a kind of shallow cone, angling over the repeaters you’re trying to hit.

I would stay with the GP-6.

 

[SteveShannon]

13 hours ago, WRVY769 said:

I upgraded antenna from tram 1486 to comet gp-9nca antenna because it had double the gain. and my tram 1486 antenna was 30ft off the ground and the comet antenna is 62ft off the ground and I'm not seeing any difference in range. What range should I be expecting.

It’s simply not possible to answer your question without knowing a lot more.  What’s the terrain like?  What buildings surround you?  What cable are you using?

If you’re surrounded by buildings, hills, or leafy trees, your signals may be attenuated such that you just can’t get through.