2 antennas on tower question

[Thunderknight]

The base radio kenwood tk 7180 coming off the other antenna works fine.

I do use a MCA204M
VHF/UHF Receiver Multicoupler - 25 MHz to 1 GHz
For the scanners

Swap the scanner antenna onto the Kenwood temporarily and if it still works fine, you know the antenna is good.
Same thing with the multicoupler...try with and without it to make sure it's not the problem. (or being overloaded...I don't have one, but if it is amplified, it could be overloaded too).

 

[prcguy]

I would definitely use vertical separation with your most needed antenna on top and use a mount that would place the lower antenna a good 6ft out from the tower at a reasonable distance below the top one.

My big question, what is that tower made from? It looks like two sections of Rohn 25 mounted on top of a steel plate on top of a larger series of tower. If so, that can't be right, the leverage on the steel plate would be tremendous and you would never want to climb that thing. I don't think I would want to stand near it.
prcguy

 

[jonwienke]

Here's an example of a recommended dual-antenna setup. The top antenna is an Ed Fong dual-band J-pole, and the lower antenna is an Antennacraft ST-2 mounted 10 feet down and 5 feet out horizontally.

 

[N4GIX]

Remember this: A happy tower will stay up for years whereas an unhappy tower will result in a tangled mess of metal on the ground, always keep your tower happy, the more antennas the meerier.

That is not very good advice. The more antennas the more likely it is to exceed the wind loading capacity of the tower.

In fact, that particular tower is already compromised in terms of safety. Overloading it will only hasten it's potential failure.

 

[KC4RAF]

Prcguy brings up a valuable point.

How is that upper tower secured to that steel plate? It seems to be a tragedy just waiting to happen!
If that upper tower had been down inside the lower unit and secured by weld or very strong bolting system, then it might be ok. But the way it is...I wouldn't climb it for anything, or live under it. Just my .02 cents.

 

[N4GIX]

Probably with a Rohn tower base plate (which is intended to be secured to a concrete base), that is bolted to the top of the larger tower's steel plate.

This means that the top sections are only secured with six bolts to the three 4" long tubular fingers welded to the steel plate. This is why I said it's already compromised.

 

[prcguy]

The interface plate seems to be specific to or custom made for the larger bottom tower section. Could have been a rotor plate or similar. Either way, not a good idea to bolt another tower to the top of it.
prcguy

Probably with a Rohn tower base plate (which is intended to be secured to a concrete base), that is bolted to the top of the larger tower's steel plate.

This means that the top sections are only secured with six bolts to the three 4" long tubular fingers welded to the steel plate. This is why I said it's already compromised.

 

[nick223]

Thanks for all your concerns with the tower but I was just trying to troubleshoot the reception issue. I don't think the tower has anything to do with it. It's bolted and welded to the bottom half and hasn't fell over yet and we've had 50+ winds. Also everything is done by crane or a boom so no need to climb it

 

[nick223]

I always tell everyone I know with a VHF scanner/receiver to put a cheap FM notch filter in the antenna line even if they think they do not have a problem. Even those who think they did not have a problem have found it works miracles as nearby FM broadcast stations were simply de-sensing the receiver without giving a hint otherwise that they were doing that. In addition, I use paging filters-VHF paging needs to die.

Does the filter go inline before the polyphaser or after?