Antenna height

[snapperq]

I monitor digital trunked sites on 700Mhz - 800Mhz frequencies.
My antenna is a DP Log antenna on a rotor which works fantastic. The antenna is 40 feet upon a tower. I receive these distant (45 miles away) pretty regularly.
My question is if I have another 10 foot section added so I’m at 50 feet will this improve my reception or not? I ask this because it’s about $300 to do this project.

 

[900mhz]

I monitor digital trunked sites on 700Mhz - 800Mhz frequencies.
My antenna is a DP Log antenna on a rotor which works fantastic. The antenna is 40 feet upon a tower. I receive these distant (45 miles away) pretty regularly.
My question is if I have another 10 foot section added so I’m at 50 feet will this improve my reception or not? I ask this because it’s about $300 to do this project.

does this 300 dollar expense include feedline replacement to make up for the added height?

 

[mmckenna]

If the antenna is working well as is, why do you want to raise it? Is there something you are not receiving that you want to?

Since these sort of frequencies predominately work by line of sight, here's what you'll get by going from 40 feet to 50 feet:
40 feet - 7.75 miles to the horizon
50 feet - 8.7 miles to the horizon.
Keep in mind that the actual range you'll get depends on the height of the transmitting antenna, and some messy variables that you have no control over.

So, question would be, is that extra 1 mile to the horizon worth the $300? Is what you are trying to hear that you cannot now really going to benefit from that investment?

 

[snapperq]

My reception of those stations that I mentioned in my last post are sometimes weaker than at other times. I thought by raising the height of the antenna might bring them in better. They now are about 3 bars on signal strength and sometimes down to 1 bar. The $300 cost is for another 10 foot section of tower and additional guy wires and installation.

 

[mmckenna]

My reception of those stations that I mentioned in my last post are sometimes weaker than at other times. I thought by raising the height of the antenna might bring them in better. They now are about 3 bars on signal strength and sometimes down to 1 bar. The $300 cost is for another 10 foot section of tower and additional guy wires and installation.

If you can receive the signal, but it's weak, then that's probably path loss, multipath, or a strong adjacent channel signal. Raising the antenna won't fix that as it probably isn't going to do much to increase signal strength. In fact, if it's an adjacent signal, simulcast or interference, it may actually make it worse.
I think the only place you'd see improvement is if you had some topographical shielding that that extra 10 feet of height got you over.

If it was me, I'd take that $300 bucks and upgrade my coaxial cable and/or maybe add a preamplifier. That'll help get more of the signal from your antenna to the radio. Raising the antenna on it's own isn't likely going to do that.
And depending on the length of the cable, you'll probably be able to take half that 300 bucks and put it back in the bank.

 

[snapperq]

does this 300 dollar expense include feedline replacement to make up for the added height?

I already have an additional 20ft of LMR400 cable.
What‘s the truck repair have anything to do with my question-900Mhz? Received your reply on my cell phone. Something is messed up on here

 

[TomLine]

What's different about the conditions or time when signals are good or not so good? Could you filter out noise at the radio or antenna feed?

 

[AM909]

A tower-mounted pre-amp is definitely a good solution that doesn't add extra wind load risk (even if properly designed), appearance issues, etc. If you want to tell us the site(s) you're trying to hear and where you are, we can get a better idea. If there's a hill in the way and you're just hearing a bounce, you're almost never in a position where moving up from 40' to 50' is going to help. If you're trying to clear a 50' building right beside you, it might.

 

[mmckenna]

I already have an additional 20ft of LMR400 cable.

How long is the total run from your antenna all the way to the radio?

 

[900mhz]

I already have an additional 20ft of LMR400 cable.
What‘s the truck repair have anything to do with my question-900Mhz? Received your reply on my cell phone. Something is messed up on here

I have no idea what you are talking about regarding truck repair??? Not sure what that has to do with the conversation.

 

[jwt873]

How big is your DP log antenna (can't find anything specific on the net) ? Do you need to add a full tower section, or could you just install an 8 or 10 foot mast in your rotor? If your antenna doesn't have much of a wind load, that would be easier and a lot cheaper.

FWIW, I have a 1.2 GHz rotatable beam on top of the mast on my 40 foot tower. I feed it with 7/8 Andrew Heliax to minimize losses.

 

[snapperq]

It‘s a DP Production Log Periodic antenna. They quit making them because it was cost prohibitive. Antenna is arrow shaped about 4K x 6’

 

[trentbob]

I would not waste the money for 10 ft. Just my two cents.

 

[N9JIG]

If the coax is already long enough to make up the extended height then an extra 10 feet might result in somewhat better performance. Adding a 20 foot section of coax with an associated adapter however would probably negate much if not all the performance gains.

In addition 10 more feet of mast could cause a less stable situation and increase the possibility of damage during wind, ice and snow events.

In my opinion it just might not help enough to justify the expense.

 

[n5ims]

Be aware that many 800 MHz systems (especially those that are simulcast systems) use specialized or directional antennas to shape their signals to better cover their designed area and minimize coverage in other area(s). One of the common specialization is to have the signal sent more toward the ground instead of straight out. This will better cover the area very close to the site and will help in lower areas that without this shaping may not get good coverage. In that situation, your additional height may actually make things worse, not better.

 

[trentbob]

I already have an additional 20ft of LMR400 cable.
What‘s the truck repair have anything to do with my question-900Mhz? Received your reply on my cell phone. Something is messed up on here

I have no idea what you are talking about regarding truck repair??? Not sure what that has to do with the conversation.

There is something definitely strange going on with this thread, I had a perfectly appropriate post censored, I reworded it and posted it again and so far it's sticking. My post was it's my opinion that the 10ft is not worth the work and expenditure of the money.

 

[WA0CBW]

Have you run a path profile between you and the site to see if there is a terrain issue?

BB

 

[snapperq]

Yes there’s no tall obstructions in my path. Maybe I need to download additional talk groups and see if that helps. You make good points and it probably wouldn’t help. Thanks for everyones advice!