Multi Dipoles Vs 1 Colinear

mrtor · Post by **mrtor** » Sun Jan 18, 2004 6:06 pm

Good afternoon group

I'll say upfront, I'm no engineer so if I am asking a basic question fundemental to the rules of engineering I appologise right here and now.

My situation:

I am being granted temporary access (1 month) to a communal repeater site for a job we are going to do in a few months time.

The site admin. has told me I need to supply 4 folded dipoles and harness etc for my 5 watt base as well as the necessary diplexer, cavities etc.

Normally I would use a 3db Colinear for such a job, and indeed do not have said 4 folded dipoles.

Why would someone request 4 folded dipoles which are going to (A) cost me more inc. harness (B) take up a lot more room on his tower versus a simple colinear ?

Bottom line, I guess if that is his rule, and I want access to his tower I have to play by his rule or bugger off somewhere else, however it begs the question Why ?

Are the 4 dipoles going to give less interference to his existing customers or better coverage for me ????

Your thoughts appreciated
Thanks
Mike

mastr · Post by **mastr** » Sun Jan 18, 2004 7:57 pm

FWIW, folded dipoles (such as the db-224) are DC grounded. I don't know if your colinear would be or not. A 4 bay dipole offers about 6db gain in most cases.

PETNRDX · Post by **PETNRDX** » Mon Jan 19, 2004 10:10 am

And it could be that he wants you to mount on the side of the tower leg, not on a pipe mounted to a "bay" or side mount like you would have to do with a colinear. He might be trying to save mount space.

mrtor · Post by **mrtor** » Mon Jan 19, 2004 5:45 pm

PETNRDX wrote:And it could be that he wants you to mount on the side of the tower leg, not on a pipe mounted to a "bay" or side mount like you would have to do with a colinear. He might be trying to save mount space.

Hi Petnrdx

He does want me to mount it on the side, however I have to provide all the out riggers and hardware anyway.

It just seemed a bit odd to me. Having taken a long hard look at the tower now, it's about 30 metres tall and only has multiple arrays of folded dipoles, yagis and 2 small microwave dishes on it, not a colinear to be seen

Space is not really an issue as he has heaps of room on the tower.

Obviously just one of those things, maybe he has shares in the company that I will ultimately have to buy the dipoles from

mrtor · Post by **mrtor** » Mon Jan 19, 2004 5:47 pm

mastr wrote:FWIW, folded dipoles (such as the db-224) are DC grounded. I don't know if your colinear would be or not. A 4 bay dipole offers about 6db gain in most cases.

Thanks for that, I was under the impression that dipoles only offered unity gain, so there you go I have learnt something.

It's just going to cost me about $1000.00 Australian for the 4 dipoles and the wiring harness when I already have the damn colinears available..

Bugger !

bernie · Post by **bernie** » Tue Jan 27, 2004 3:51 pm

My two bits worth:
I would assume that the reason is "No reason, Company policy"
Given my druthers I would go with a co-linear any day.
The main problem that we have in this environment (Hawaii) with dipole antennas is the eventual degradiation of the insulators, and the resulting site noise.
We have removed almost all of the multi-bay dipole antennas installed here over the years due to arching.