Batboard

Can you pau an amp after the duplexor?
What i mean is can there be an amp between the line in from the antenna and the duplexor?
I'm scared to put it between the Flexar and the duplexor for fear of the amp having too much power for the duplexor.
Any ideas?
Tyler

On 2002-03-22 10:59, Trm70c wrote:
Can you pau an amp after the duplexor?
What i mean is can there be an amp between the line in from the antenna and the duplexor?
I'm scared to put it between the Flexar and the duplexor for fear of the amp having too much power for the duplexor.
Any ideas?
Tyler

No, by putting the amp between the duplexer and the antenna you would not receive any signal into the repeater. When the amp senses the power input from the transmitter it trips the T/R relay thus opening the receive path thru the amp.

Are you sure? I use the same type of amp in a mobile setep with my ht-750 and it workd fine. I was planning on using a tpl amp and maybe putting a few fans on it, our raio doesn't get all that much traffic.
Tyler

On 2002-03-22 11:30, Trm70c wrote:
Are you sure? I use the same type of amp in a mobile setep with my ht-750 and it workd fine.

Yes, I'm sure. In your mobile setup you are not receiving AND transmitting at the same time!!

so if I put it between the flexar (repeater and the duplexor would it work? on the tx line, the rx line would be left alon
Tyler

On 2002-03-22 12:08, Trm70c wrote:
so if I put it between the flexar (repeater and the duplexor would it work? on the tx line, the rx line would be left alon
Tyler

Yes, putting the amp between the TX output of the repeater and the duplexor would work.

On 2002-03-22 10:59, Trm70c wrote:
Can you place an amp after the duplexor?
What i mean is can there be an amp between the line in from the antenna and the duplexor?
I'm scared to put it between the Flexar and the duplexor for fear of the amp having too much power for the duplexor.
Any ideas?
Tyler

Hi:

If I read you correctly, you want to place a
Power Amp between the Duplexer output and the
antenna in a Repeater Application ; If that is the case
<b><h2>Don't</b></h2>

If you have a Duplexer stright inline with
the transmission line leading to the Antenna,
it will not work properly since the " Reciever Port will be disabled in transmitt.

A simple Handie-Talkie does not have to
RECIEVE and TRANSMITT at the Same Time like a
Repeater !

Installing a Power Amp always goes from the
<b> Output Port</b> of the Transmitter, <b>TO</b> to the <b>Input Port</b>of the
Duplexer where is says ( TX )

ALSO, be aware that YOUR DUPLEXER MUST have
the Power Handling Capicity of the Amp.

Using a 100 Watt Power Amp on a Small Mobile
Duplexer will cause to to FAIL...

Most Mobile Style Duplexers are limited to
30-40 Watts MAX, and the small little Flexar
Duplexer is really limited to 25 MAX

Monty

<font size=-1>[ This Message was edited by: [email protected] on 2002-03-22 13:17 ]</font>

thanks for the good info, what does a good used / tuned duplexor cost? 451.***/456.***
tyler

Just wondering... is your repeater accessed using HT's or mobile rigs? How much power do they run?

Before cranking out the TX power amp, you might want to check the following...

Feedline/Coax: what type is it? How long is the run? How old is it? Are the connectors installed correctly?

Antenna: Is it tuned? Is it in good shape?
How tall is it mounted?
How much gain is your antenna rated at? (this is very important for the repeater recieving a weak signal clearly)

The Flexar isn't all that bad of a repeater. It has all Maxar guts. The Maxar series are quite modular in design, and were made at the climax of crystal rigs in the 1980's.

See, one can have 110W PEP TX from the repeater, but if the reciever is deaf, and can't pick up a decent signal, one really can't really benefit from the extra transmit range. Do I make sense?

We use both mobiles and portables, the mobiles get out decent, maybe ten to fifteen miles, we run 40watt maxtracs and 50-75 watt mitreks. The moto tech told me that our repeater was putting out 15 watts out of the duplexor which is about right since the repeater is only thirty watts. The antenna heighth is 75 ft. Big fat coax, it's a big whit antenna, i'm guessing it has decent gain the fcc license says our repeater has an erp of 83 watts, so it's got to be gaining somewhere. Though i don't really know what erp means. Keep the good info coming! Tyler
I was just thinking that a little more power might improve our coverage, and nobody say add antenna heighth, this option has been discussed and is very expensive.
Tyler

ERP means Effective Radiated Power.
To figure the ERP you need to know the antenna gain vs: isotropic, feed line loss(s) and accual transmitter power into the feed line.
15 watts out of a duplexer into the feed line with two db loss and a six db gain antenna would be about 40 watts ERP.
To get a realy noticable increace in range the accual power must be trippled. If you have thirty watts out of the transmitter (Flexers are only 15 watt tx) and only 15 out of the duplexer, either the duplexer is de-tuned badly or has a very poor insersion loss. Consider a pass/notch duplexer of professional quality, four cavitys minimum. That would help BOTH the transmit and receive range much better than adding a power amp, plus you will need a better duplexer to handle the increaced power.

On 2002-03-22 18:45, Trm70c wrote:
...Though i don't really know what erp means...

ERP is how much power is really being radiated. TPO is transmitter power. So ERP is "TPO minus line & duplexer loss plus antenna gain"

Let's see here... 83W ERP...15W out of the duplexer...I'm guessing your antenna must have around 9dbi to 10dbi of gain.

_________________
Jonathan KC8RYW
<small style="color: springgreen; ">I'm voting Green in 2004! <a href="http://www.takethepledge.com/">www.take ... /a></small>

<font size=-1>[ This Message was edited by: KC8RYW on 2002-03-22 19:48 ]</font>

Another problem that no one has mentioned yet is the white noise that all solid state amps today create. The wide band width in todays amps with no tuning circuits, make them more prone to generating more wide band white noise into a system.

This broad band noise generally requires more and better filters in the duplexer. Some of the newer solid state transmitters available today make a very poor repeater. They just generate too much wide band noise.

You need to be careful when talking about adding a solid state power amp to the output of a transmitter in the repeater service. Yes you may gain more talk out, but it will be at the loss of hearing the weak signals trying to get into the repeater.

You will do better in trying to improve the antenna system, reduce feedline loss and duplexer loss. Maybe a pre amp on the receiver. Only problem is that this too is prone to creating problems on the receiver side.

Make sure that all the coax jumper cables in the system are heliax style or double shielded. You can't use RG-8 type cable for repeater service. The shield is only 50 to 70%. This allows way too much leakage in the repeater system.

Don't just go and start changing coax cables on the duplexer. All those cables are of a critical length. Their length is determined by the operating frequency.

Hope this gives you some thoughts to consider.

Jim