RE: [Repeater-Builder] Re: Multiple receivers one antenna ???

[Jeff DePolo WN3A]

> You can handle the impedance matching by using 1/4 wave 
> sections of 75 ohm 
> coax between the receiver input and the T. The 1/4 wave 75 
> ohm section 
> steps the 50 ohm receiver input impedance up to 100 at the 
> other end, two 
> of those in parallel at the T gets you back to 50 to match 
> the feedline. 
> Any number of receivers other than 'powers of 2' is more 
> complicated. This 
> does nothing for the loss of course.
> 
> Roger Grady  K9OPO

The math works in the case of the tee being at the antenna connection, but
the ASCII drawing that accompanied the previous email put the tees on the
backs of the receivers, sort of like old-style thin Ethernet 10base2, except
instead of having terminations at the ends of the backbone, one end is
connected to the last receiver, and the other end is connected to the
antenna.  Matching goes out the window with this design.

The problem with even doing the tees with odd quarterwave 75 ohm
transformers is that you have virtually no isolation between receivers.  If
your receivers have tight front ends, unless all of the receivers are very
close in frequency, you may end up with more than 3 dB of theoretical loss
due to phase cancellation back at the tee.  If you're really pinching
pennies, Kevin's recommendation of using 75 ohm CATV/MATV splitters is
better since they provide port-to-port isolation, and the losses due to the
impedance mismatch (50 versus 75) are insignificant (theoretically approx.
0.4 dB + normal dividing loss).

--- Jeff





 
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RE: [Repeater-Builder] Re: Multiple receivers one antenna ???

[Jeff DePolo WN3A]

> 
> It's called a Wilkinson splitter. Here is a link to some of 
> the theory.

I don't think it's fair to call it a Wilkinson without a resistor across the
output ports.  A real Wilkinson provides port-to-port isolation due to the
addition of the resistor.  A tee and 75 ohm cables doesn't provide any
appreciable isolation; it's just two transmission line transformers teed
together to yield a proper match assuming that the ends of the cables are
terminated into 50 ohm loads.  In the real world, receivers don't have 50
ohm Z across a wide range due to front end filters and other factors, so you
may end up with additional loss (above and beyond the theoretical 3 dB
power-dividing loss) due to the lack of isolation between receivers.

--- Jeff






 
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[Repeater-Builder] Re: Multiple receivers one antenna ???

[hwingate]

--- In Repeater-Builder@yahoogroups.com, Roger Grady <[EMAIL PROTECTED]> wrote:
>
> At 12:29 PM 12/19/2005, Coy Hilton wrote:
> 
> >It may sound interesting (and cheap) but the reason that no one else
> >has suggested it is because the impedance miss matches it causes.
> >That is why you need something like a multicoupler whis is first a
> >pre amp to keep the loss to a minimum then sends the pre amp to a
> >splitter that maintains the 50 ohm match required by the receivers
> >on each output port.
> 
> You can handle the impedance matching by using 1/4 wave sections of
75 ohm 
> coax between the receiver input and the T. The 1/4 wave 75 ohm section 
> steps the 50 ohm receiver input impedance up to 100 at the other
end, two 
> of those in parallel at the T gets you back to 50 to match the
feedline. 
> Any number of receivers other than 'powers of 2' is more
complicated. This 
> does nothing for the loss of course.
> 
> Roger Grady  K9OPO
>

It's called a Wilkinson splitter. Here is a link to some of the theory.

http://www.microwaves101.com/encyclopedia/Wilkinson_splitters.cfm










 
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Re: [Repeater-Builder] Re: Multiple receivers one antenna ???

[Roger Grady]

At 12:29 PM 12/19/2005, Coy Hilton wrote:

>It may sound interesting (and cheap) but the reason that no one else
>has suggested it is because the impedance miss matches it causes.
>That is why you need something like a multicoupler whis is first a
>pre amp to keep the loss to a minimum then sends the pre amp to a
>splitter that maintains the 50 ohm match required by the receivers
>on each output port.

You can handle the impedance matching by using 1/4 wave sections of 75 ohm 
coax between the receiver input and the T. The 1/4 wave 75 ohm section 
steps the 50 ohm receiver input impedance up to 100 at the other end, two 
of those in parallel at the T gets you back to 50 to match the feedline. 
Any number of receivers other than 'powers of 2' is more complicated. This 
does nothing for the loss of course.

Roger Grady  K9OPO





 
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[Repeater-Builder] Re: Multiple receivers one antenna ???

[Coy Hilton]

It may sound interesting (and cheap) but the reason that no one else 
has suggested it is because the impedance miss matches it causes. 
That is why you need something like a multicoupler whis is first a 
pre amp to keep the loss to a minimum then sends the pre amp to a 
splitter that maintains the 50 ohm match required by the receivers 
on each output port.

If this approach was workable then the cable company would NEVER buy 
a splitter but would buy TEEs

  

--- In Repeater-Builder@yahoogroups.com, Vincent Caruso 
<[EMAIL PROTECTED]> wrote:
>
> That sounds like an interesting solution, I would be interested in 
> learning more about it.
> 
> Ralph Hogan wrote:
> > Along these lines, someone on the list mentioned using coax 
multi-dropped
> > (coax tee) off to each receiver for a voter application. Can't 
find the
> > original posting. I was curious about the lengths required 
between the
> > antenna and then to each radio?
> > 
> > tnx,
> > Ralph W4XE
> > 
> > 
> > 
> > 
> > If you are able to lose  = - 6 db of the signal to
> > each receiver you could use a passive device which you
> > can build yourself and save many many dollars.
> > 
> > There is pleny of information on the web  on a 4-port
> > "Wilkonson divider ".
> > 
> > The same phasing harness is used for a 4-stack dipole
> > array so you could ask around for one or buy it off
> > the shelf-these are frequenct contious.
> > 
> > Regards
> > 
> > Bradley Glen  ZS5WT   http://members.harc.org.za/zs5wt
> > 
> > 
> >>  It's easy!  What you need is known as a
> >>multicoupler.  This unit usually comprises a
> >>preselector to limit the bandwidth of the incoming
> >>signals, a low-noise amplifier, and a splitter with
> >>two, four, or eight output ports.  The gain of the
> >>amplifier is tailored to the number of splits so
> >>that the loss in the splitter is overcome.
> >>
> >>  73, Eric Lemmon WB6FLY
> >>
> >>
> >>-
> >>  From: Repeater-Builder@yahoogroups.com
> >>[mailto:[EMAIL PROTECTED] On Behalf
> >>Of Vincent Caruso
> >>Sent: Sunday, December 18, 2005 1:04 PM
> >>To: Repeater-Builder@yahoogroups.com
> >>Subject: [Repeater-Builder] Multiple receivers one
> >>antenna ???
> >>
> >>I would like to install one antenna for four link
> >>receivers.  How
> >>complicated is this? What do I need to do this?
> >>
> >>Thanks in advance
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> >  
> > Yahoo! Groups Links
> > 
> > 
> > 
> >  
> > 
> > 
> > 
> > 
> >
>









 
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[Repeater-Builder] Re: Multiple receivers one antenna ???

[skipp025]

The below is an old Decibel Products method 
and it does works (and was used) on their 
Tx Combiners. I have one here...  along with 
some very limited paperwork on it. 

cheers,
skipp 

> [EMAIL PROTECTED] wrote:
> I've posted this a few times...
> **IF**  loss on the incoming signal(s) isn't an issue ...
> 1/2-wave (or multiple thereof) jumpers, daisy-chained
> between "T"s.
> 
> [rx.ant-coax] ->>- [T-(rx)] -jumper- [T-(rx)] -jumper- [last
> rx]
> 
> Our RXs did not exhibit problematic interactions -- used
> RG58 & PL259s.
> Seems to play nicely.  YMMV.
>  ~/ N8BQN /~
> 







 
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[Repeater-Builder] Re: Multiple receivers one antenna ???

[skipp025]

If you use any of the below listed devices, you'd 
better chuck the pre-selector (rx-filter) and 
put something better in front of the preamp. 

Been there, done that, coffee mug and tee-shirt. 

cheers,
skipp 

> "Eric Lemmon" <[EMAIL PROTECTED]> wrote:
>
> Good idea!  Here are two:
>  
> Sinclair:  http://www.sinctech.com/catalog/series.aspx?id=109
> TX-RX:
>
http://txrx.com/product/product_view.aspx?UID=50E7FFB3-54D5-400A-AFF6-6B52F7
> C54229
>  
> Other vendors are Telewave, Celwave, Decibel Products, and Angle Linear.
> Just Google " receive multicouplers"
>  
> 73, Eric Lemmon WB6FLY
>  
> 
>   _  
> 
> From: Repeater-Builder@yahoogroups.com
> [mailto:[EMAIL PROTECTED] On Behalf Of Mathew Quaife
> Sent: Sunday, December 18, 2005 2:17 PM
> To: Repeater-Builder@yahoogroups.com
> Subject: RE: [Repeater-Builder] Multiple receivers one antenna ???
> 
> 
> How about a lead to such vendors and some model numbers as well,
would be
> helpful.  
>  
> Mathew
> 
> 
> Eric Lemmon <[EMAIL PROTECTED]> wrote:
> 
> Vincent,
>  
> It's easy!  What you need is known as a multicoupler.  This unit usually
> comprises a preselector to limit the bandwidth of the incoming
signals, a
> low-noise amplifier, and a splitter with two, four, or eight output
ports.
> The gain of the amplifier is tailored to the number of splits so
that the
> loss in the splitter is overcome.
>  
> 73, Eric Lemmon WB6FLY
> 
>   _  
> 
> From: Repeater-Builder@yahoogroups.com
> [mailto:[EMAIL PROTECTED] On Behalf Of Vincent Caruso
> Sent: Sunday, December 18, 2005 1:04 PM
> To: Repeater-Builder@yahoogroups.com
> Subject: [Repeater-Builder] Multiple receivers one antenna ???
> 
> 
> I would like to install one antenna for four link receivers.  How 
> complicated is this? What do I need to do this?
> 
> Thanks in advance
> 
>    
> 
> 
> 
> 
> 
> 
> 
>   _  
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