Antenna DB upgrade

[WRXQ831]

I've got a repeater set up at my house. My antenna was damaged but I was able to fix it. I'm looking at replacing the antenna anyway. It's currently rated at 7.5db. I can get a comet that is rated at 9db for around 150 quid.

I'm going to replace it either way, I'm just wondering if the extra DB and a half will make a noticeable improvement. I want to get the highest performing antenna I can under, say $200. It seems like there's an astronomical increase in price above 9db. The cheapest 10dbi can find is $2,000 it goes from $150 to $2,000.

The antenna is mounted as high as I can get it and I've replaced the coax. I found a deal on 1/2 inch heliax. 

[Socalgmrs]

I use a comet 712efc. It’s awsome from my location with a 20w radio 200 miles is no problem.    I also have a 9nc with a 50w radio.  Not much difference in distance just more clear but boy can I hear everything much more clear.  I always say get the highest gain you can.   I have no negative effects in close.  

[kidphc]

If your antenna is 100 feet in the air an additional 1.5 db might be worth it.

As you increase db the antenna's radiating pattern on an omni-directional antenna gets flatter. It sends more of it signal to its horizon. I would recommend plugging the info into a one of the free typographical antenna coverage calculators to quickly ascertain if it is worth it.

They changed this tool it seams. It use to allow you to map it out and set each site differently with gain and antenna values. This is what I use to recommend. https://www.scadacore.com/tools/rf-path/rf-line-of-sight/

Have you thought about a yagi on with a TV rotator?

Sent from my SM-S901U using Tapatalk

[LeoG]

I have the 712efc and the paperwork that came with it claims 9.8dBi.  It's on the bag and in the paperwork so that's what I assume it is.  So it's even bigger than 7.2

[nokones]

4 hours ago, WRXQ831 said:

I've got a repeater set up at my house. My antenna was damaged but I was able to fix it. I'm looking at replacing the antenna anyway. It's currently rated at 7.5db. I can get a comet that is rated at 9db for around 150 quid.

I'm going to replace it either way, I'm just wondering if the extra DB and a half will make a noticeable improvement. I want to get the highest performing antenna I can under, say $200. It seems like there's an astronomical increase in price above 9db. The cheapest 10dbi can find is $2,000 it goes from $150 to $2,000.

The antenna is mounted as high as I can get it and I've replaced the coax. I found a deal on 1/2 inch heliax. 

Some times deals are not deals. What brand heliax are getting a such a deal on?

[WRKC935]

Couple things to point out.

dBi and dBd are two different values.  dBi is going to be 2.5dB less than dBd.  Because the dBd "d" stands for dipole.  Which has 2.5dB of gain above a isotropic radiator.  Which is the 'i' in dBi. 

I don't own the Comet that others have talked about.  The circles I run in and company I keep gets me DB-408's and DB-420's for my stuff.  Those of course are the 2K dollar antenna's you mentioned. 

But a guy in Columbus put one up on his repeater and it was a night and day difference between the 6dBi antenna he got with the repeater and that one.  It probably added 5 to 10 miles of range or better to his repeater, all other things being the same.  No change in mount height.

Now, be aware that you can have too much gain if you have a lot of height.  The realized gain in an antenna is accomplished in moving the radiation pattern.

Think about it like a 100 watt lightbulb.  If the light is going all directions, at all angles, no specific direction or angle gets any more light then another.

To create gain, an antenna take the unused light radiating up and down and points in to the horizon.  The more this is done, the higher the gain.  When you get the gain high enough, there isn't much radiation down.  So with a bunch of height, you overshoot the signal where you want it to go. Mind you it requires a LOT of height.  But if you are on a mountain, and get a super high gain antenna, the valley below will NOT see much if any signal.

Just be aware of that.

 

[LeoG]

2.15 not 2.5