Hi Randy,
You do realize that an 8 bay antenna at VHF is going to be around 45 feet in
length? That is going to consume almost 1/2 of your tower. The effective
height of that antenna will be at its center point.
Also the gain figures that you were looking at were for one direction-
offset pattern. You have to look close at those graphs that they give you as
at first glance it appears to have gain in all directions but in fact may
have loss in some directions. You have to find the zero db circle on the
graph. I don't think the pdf on the site has enough resolution to see it.
As for the duplexer, the first thing to do is find out from the repeater
manufacturer how much tx to rx isolation is required at the frequency
spacing you are going to use. Then look at a duplexer that will provide that
amount of isolation. Getting a duplexer with less isolation will not do the
job and getting one with more is a waste of money.
As for the hybrid ring, Sinclair radio was famous for that for their close
spaced duplexers many years ago. There have been improvements in cavity
coupling and loop designs since and you don't see that used much anymore.
73
Gary K4FMX
> -----Original Message-----
> From: towertalk-bounces@contesting.com [mailto:towertalk-
> bounces@contesting.com] On Behalf Of Randy Molyneaux (ve5 rjm)
> Sent: Saturday, January 06, 2007 10:04 AM
> To: TowerTalk@contesting.com
> Subject: [TowerTalk] RE- best repeater configuration - Looking for
> moresuggestions
>
>
> ******************************************************
> I beleive I will be going with a lower power repeater, and higher gain
> antenna?
> one question I have is the pattern of radiation.
> The way I see it, there will be a small null but not huge (most omni when
> all bays are placed in one direction)
> when you place the bays in opposite directions, you lose gain, and the
> radiation pattern seems to be more
> oblonged, or oval in shape.
> I need to cover more of a 280 degree area mobile anyways...
>
> I would like to thank everyone for their comments, and have made a
> decision, on power / antenna.
> - (30 - 40 Watts with 8 Bay Dipole Antenna (11 dbd gain)
> the next thing, I would like if anyone has had experience with the
> following equipment...
>
> would like comments on anyone having experience in using the following:
>
>
> Antenna's I am considering to use:
> a.. Comprod 878-70
> http://www.comprodcom.com/english/pdf/base/BaseStation2005-Full.pdf
> b.. Bluewave http://www.bluewaveantenna.com/products/pdf/BSE139LH0.pdf
> c.. Other suggestions are welcome
> Repeater's I am considering to use:
> a.. Kenwood TKR750 Rev 2 -
>
> http://www.kenwood.com/i/products/info/pmr/tkr750_850/index.html
>
> b.. Vertex VXR-7000
> http://www.yaesu.co.uk/vertex/base/vxr7000/vxr7000_1.htm
>
> c.. Icom apparently has one available that I have heard good comments
> about also.
>
> d.. Other suggestions are welcome
>
> e.. (looking for easy programming - great performance - SUPPORT very
> important to me)
> Duplexer's I am cosidering:
> a.. CP66-13-44 (621-90) 6 cavity, 4", 138-174 MHz
> http://www.comprodcom.com/
> b.. CP66-113-44 (620-90) 4 cavity, 4", 138-174 MHz
> c.. CP66-13-76 (621-90) 6 cavity, 7", 138-174 MHz
> d.. Other suggestions are welcome - (looking for best isolation (I can
> not seem to find a hybrid ring type duplexer, if anyone knows of one to
> purchase let me know.
>
> 73's
> Randy Molyneaux(VE5RJM)
> Michelle Molyneaux (VE5MDM)
> EchoIRLP Node 1710 & 1858
> EchoLink Node 48431
> ve5rjm@hotmail.com
> http://parc.sasktelwebsite.net
>
>
>
> ******************************************************
> As I recall - every 3 db is a doubling of power - SO:
>
> 50 watts into 11 dbd antenna - 630 watts
>
> 100 watts into 8 dbd antenna - 631 watts...
>
>
> OK - they are about equal...now what about maintenance, cost of antenna,
> etc. The 11db antenna would probably have a sharper pattern, and require
> a
> larger rotator. But then there is the cost of the amp, etc.
>
> At this point - it is probably just an economic decision, as well as a
> "hassle" question - which is the least hassle to set up and maintain.....
>
> Scott, aka KB0FHP
> Well, with a 4 bay dipole, over a 8 bay dipole ( I think in chosing which
> antenna, I
> will be going with the 8 Bay (11 dbd gain) and not going to purchase the
> amplifier.
> the cost cancels each one out.
>
>
>
>
> ******************************************************
> Just my guess... but the 100 watts is probably going to talk better
> than it hears -- since most folks will be transmitting to the thing
> with 50 watts or less. I'd vote for the better antenna.
>
> Our local 2m repeater actually is a 100 watt GE radio -- but
> we have it turned down to 50 or 60 watts, because the extra
> 40-50 watts really doesn't buy much.
> This is exactly what I suspected.
>
> --
> Dave N0RQ
> http://www.powerlinenoise.com
>
>
>
> ******************************************************
> One consideration often forgotten in the dB arguement is the benefit on
> the RECEIVE side as well. I would rather have 100W into a 3el yagi than
> 1000W into a dipole in most cases. Then there is the antenna pattern
> noise/QRM rejection as another plus.
> ( I am looking for the best omni direction I can get, so when you are
> mobile will get into the repeater)
> note: about 240 degrees require to access repeater from at least 40 miles,
> the null part of the antenna can be less obviously.
>
> Arne N7KA
>
> ******************************************************
> You didn't say what band the repeater would operate in? - VHF (TX: 145.250
> MHz RX: 144.650 MHz)
> With 145 feet of cable I would assume that the antenna would be something
> less than that in height above ground? (150' 1/2" Hard Line Heliax -
> Antenna Height side mounted 145')
>
> The higher gain antenna will give a little better performance on the
> receive
> side of the repeater. But if this is going to be at VHF that size antenna
> will be a handful on the tower.(commercial grade tower) It will handle it
> since their is only 1 other antenna
> positioned right at the top.
>
> 73
> Gary K4FMX
>
> ****************************************************
> Reading this I'm assume that you are talking about a repeater installation
> -correct
> and not an installation for working the repeater. I'm basing that on the
> remark that the area is fairly flat over a 60 mile radius.
>
> IF that is what you are asking then things are a bit more complicated.
> what is 145' of minimum loss 1/2" coax
> How high will the antenna be? -Antenna height will be 145' 1/2" hard line
> Heliax 150'
>
> You also refer to 4 and 8 bay dipoles. How will they be configured?
> Generally when all are mounted on one side of the tower they have a deep
> null off the back. You can basically get a circular pattern by mounting
> half
> on one side and half on the other side of the tower. If there is an area
> where the null can be tolerated then of course you mount them all on the
> same side.
> -
> The way I see it, there will be a small null but not huge (most omni when
> all bays are placed in one direction)
> when you place the bays in opposite directions, you lose gain, and the
> radiation pattern seems to be more
> oblonged, or oval in shape. ( I have no choice, the antenna must be side
> mounted- for my situation)
> Sharing tower space (160')
>
>
>
> *****************************************************
>
> Randy:
>
> That extra 3 dB of gain from the 8 bay dipole array works on receive,
> too. FWIW.
>
> 73 de
> Gene Smar AD3F
>
> ****************************************************
> -------------- Original message ----------------------
> From: "Randy Molyneaux (ve5 rjm)" <ve5rjm@hotmail.com>
> > I was curiously seeking info on a new repeater and came across many
> sites, and
> > formulas
> > and one in choosing the best overall system for the cost. What would it
> be.....
> >
> > Let's say in choosing equipment everything is fairly close in
> camparison.
> > 50 Watts (100 % duty cycle)
> > Let's not disucss options...especially right now?
> > 145 feet of 1/2" coax line...(Minimum loss)
> > the question is?
> >
> > Would you consider an amplifier pushing out 100 Watts at 100 % duty
> cycle over a
> > 4 bay dipole antenna (8 dbd gain)
> >
> > or
> >
> > Would you consider 50 watts over a 8 bay dipole antenna (11 dbd gain)
> >
> > overall the area within an 60 mile radius is faily flat.
> >
> > All suggestions are welcome
> >
> >
> >
> > 73's
> > Randy Molyneaux(VE5RJM)
> > Michelle Molyneaux (VE5MDM)
> > EchoIRLP Node 1710 & 1858
> > EchoLink Node 48431
> > ve5rjm@hotmail.com
> > http://parc.sasktelwebsite.net
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
>
>
>
>
>
>
>
>
>
>
>
>
>
> 73's
> Randy Molyneaux(VE5RJM)
> Michelle Molyneaux (VE5MDM)
> EchoIRLP Node 1710 & 1858
> EchoLink Node 48431
> ve5rjm@hotmail.com
> http://parc.sasktelwebsite.net
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
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