RE: [BYUARC] Antenna farm, a proposal: comments please
Jim Manookin
First off, Thanks Brent, for doing all this research and motivating all of us to think about the WSC antenna situation, and hopefully DO something about it. Your proposal sounds to me like a great idea, particularly to help facilitate future antenna projects.
I would like to propose a slight alteration to Brent’s suggestions.
· Keep the 2m repeater antennas on the main tower.
The rationale behind this recommendation:
· Having a bunch of 2m (or for that matter, any common-band omnidirectional) antennas on one mast can (and almost certainly WILL) lead to major problems with using more than one of the 2m services. The repeater will interfere with the Diamond and/or J-pole and vice-versa, since those antennas would be in close proximity to each other, and radiating directly into each other.
· On the other hand, if we keep some lateral distance between in-band transmitting antennas, we have a hope of using multiple radios simultaneously (we can expect about 35dB isolation between antennas, due to free-space loss). Orienting antennas with their null axes aligned with each other also improves isolation – that is why the 2m repeater antennas are mounted back-to-back.
· Tower placement of the 2m repeater antennas will possibly give us slightly better coverage patterns for the repeater than the pipe mast.
· I would like to investigate an alternate mechanism for tower-mounting these antennas – the present yardarms will attach only to the upper section of the tower, but in order to service the tower-top-mounted antennas, the tower needs to telescope all the way down. I think that with a suitably thin attachment system (perhaps something akin to a pipe clamp? or maybe something that attaches to the rungs, rather than the posts, of the bottom tower section?), a yardarm can be mounted to the main (bottom) tower section and still leave room for the telescoping section to be lowered.
· Also, having all the repeater antennas on one tower (which, by the way, will place them higher than they could be on the pipe masts) will free up the pipe masts for more frequent modifications of the more casual antenna systems. I think it is fairly important to maintain our repeaters as consistently as possible, for the longest term between service episodes. The pipe masts are much more friendly to casual and frequent antenna alterations/modifications: they don’t require climbing equipment or special skills to service; they telescope down to roof level fairly easily; they can be easily accessed from the penthouse roof and/or the Skyroom roof.
· The pipe masts may not extend high enough to allow the high gain 2m repeater antennas (or their replacements) to clear the roof; having the repeater transmit antenna accessible to the reach of casual (and possibly un-initiated) rooftop workers may be an RF burn hazard. At the very least, it places that critical antenna in a vulnerable location.
One more question:
Brent, do you have antenna models in mind, and/or price estimates for the 2m and 70cm repeater antenna replacements?
Jim Manookin
BYU Office of IT
Design Engineer
BYUARC Advisor
2306A ITB
Voice: 801 422 7547
Fax: 801 422 0767
Email: jim_ma...@byu.edu
Email: n7...@byu.edu
From: byu...@googlegroups.com [mailto:byu...@googlegroups.com]
On Behalf Of Brent Smith
Sent: Sunday, May 20, 2012 10:45 AM
To: byu...@googlegroups.com
Subject: [BYUARC] Antenna farm, a proposal
Sorry but this is going to be a bit long.
As most of you know, all of the antenna on the roof of the Wilk need some work.
Jim has an antenna analyzer which he has used to check all of the antenna we have up.
All of the antenna need to have their coax replaced and some of the antennas need to be replaced.
We really can't tell if the antenna are good or bad until the coax has been replaced.
The following is the list of antenna assets we have.
1. The Diamond VHF/UHF high gain on the very top of the tower, connected to the Yaesu mobile.
2. The tri-band beam HF, with rotor, connected to the HF rig.
3. A 40 meter inverted V only half deployed, connected to the HF rig.
4. A new 40/80m inverted V, in the shack.
5. The 2m high gain repeater receive.
6. The 2m high gain repeater transmit.
7. The 70cm high gain repeater transmit/receive.
8. A home made high gain VHF/UHF J pole.
9. 2 azimuth/elevation rotors assemblies.
10. 2 2m circular satellite antenna.
11. 2 23 cm circular satellite antenna.
12. 70cm circular satellite antenna.
13. The main tower.
14. The East Ibeam mast.
15. The West Ibeam mast.
Part of the challenge of the working on the antenna is that all of the functioning antenna are on the tower, which means that when we want to work on anything we have to work on everything.
Jim (N7XGA) has mentioned on several occasions that it would be a good idea to move some of the antennas off of the tower on to one of the masts.
So here is my proposal for the new antenna/tower/mast configuration as we work on things this year.
Comments Please.
1. Bring up one set of satellite antenna on the East Ibeam mast. This would consist of a rotor, 2m circular, 70cm circular and 23cm circular antenna.
2. Change the top of the West Ibeam to a T bar on the top and then mount 4 antenna on it. 2 above the T and 2 below the T. These would be the 2m repeater transmit, the 2m repeater receive, the diamond and the J pole
3. Mount the 70cm repeater antenna on the very top of the tower with the tri-band beam just below and the 40m/80m inverted V underneath.
As part of this I would suggest that we buy 3 new antenna to replace the 70cm repeater, 2m repeater transmit and 2m repeater receive.
Comments Please.
Does this sound acceptable?
Does this sound reasonable?
Does this sound doable?
Alternate suggestions?
Comments Please!
Brent Smith
N7TOT
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