Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Basic Repeater Design  (Read 6650 times)
KC5HWB
Member

Posts: 18


WWW

Ignore
« on: November 19, 2013, 05:36:25 AM »

I apologize if this question has been asked before, but I did a search and didn't find exactly what I was looking for.

I'm wondering about basic repeater design - I want to do some experimenting and I have applied for trustee status in my area.

Obviously I need a radio and an antenna, but must I also have a repeater controller?  I'm not certain about how to make the radio "listen" for signals coming in, and it should be then repeating.  Several of my radios do cross-band repeat, and this requires no repeater controller, so I was hoping to be able to do the same thing with a radio that had dual VFOs, where both of them would transmit on the same band (V/V or U/U) but I don't find any documentation for this setup in the operator's manual for the radio, or by doing a Google search.

My basic question is "how do I make the radio listen on a specific frequency, and then re-transmit it on another?"

I obviously don't have any experience with these setups, this is all new to me.

Thanks.
Logged

AA4PB
Member

Posts: 12890




Ignore
« Reply #1 on: November 19, 2013, 06:16:45 AM »

Basically when the receiver picks up any signal which opens its squelch then the squelch action keys the transmitter. The receiver audio output is connected to the transmitter audio input. Some radios have cross-band repeat built in, but they must be designed to do so.

One big issue is keeping your transmitter from blocking your own receiver. One method is to use two separate bands like 144MHz and 440MHz. If you want to use a single band with a 600KHz frequency offset like most repeaters then you need a tuned-cavity duplexer to prevent the interference.

A repeater controller provides the PTT and audio coupling functions plus time-out, beep, control, auto-patch, and a variety of other functions for a standard radio. Commercial radios are often used because of their better receiver selectivity and 100% transmit duty cycle capabilities. Sub-audible (PL Tones) are often used on the receiver squelch so that only stations using the proper tone will be repeated.

Take a look at http://www.repeater-builder.com/rbtip/ and similar web sites to get ideas as to what is involved.
 
Logged
NA4IT
Member

Posts: 885


WWW

Ignore
« Reply #2 on: November 19, 2013, 03:28:43 PM »

Are you sure you want to be a repeater trustee?

The joys of being an amateur repeater Owner, Trustee, or Technician (or ALL THREE!)

So you have decided you need to become a repeater owner, trustee, technician, or even all three. Well, let me share some experiences.

First, a good friend who had been a repeater trustee for many years said "Having a repeater is a BIG pain in the $%# (posterior...)".

I have never owned a repeater, But, for a few years now, I have been a repeater technician. So I know a little about the "pain" involved.

1. You will be ON CALL like it or not 24/7/4/52/365. It doesn't matter that you are in bed at 3AM. Someone WILL call.

2. If anything at all sounds wrong to the user, the repeater is at fault. Doesn't matter that he is using a 20 year old radio, or a blown speaker, it is STILL the repeater's fault.

3. If someone can't hit the repeater, it is the repeater's fault. Doesn't matter if the are 100 miles away in a metal building and using one of those Alinco credit card HT's, it STILL the repeater's fault.

4. If someone can't get into the repeater because it is toned, it doesn't matter if that is done to keep interference out, it is because you are trying to block them from using the repeater.

5. When it comes time to clean up the tower site, EVERYONE will have something else to do.

6. When the repeater is down for repairs, you should immediately drop everything else you are doing (including any deaths, births, vacations, etc) and GET THE REPEATER FIXED. (Including your own death...)

7. When an expensive part is needed for repairs, you will always hear "Well, I paid my $20 this year, that ought to be enough." (And that repeater cost $5000...)

8. If something goes wrong and you loose your tower site, you are the one that caused it.

9. If lightning hits the repeater, you are the one that caused it.

10. If wind tears down the antenna, you are the one that caused it.

11. Just remember, if it happened, you are the one that caused it.

12. And when the repeater is down, then you will start getting the phone calls that say "If I bring my radio over there, will you program simplex for me?"
(That is because most of the repeater users are within simplex range of each other, and they also never remember where they put their radio manual.)

My friend, I ask you this solemn question.... Are you SURE you STILL want to deal with a REPEATER?
Logged
AA4PB
Member

Posts: 12890




Ignore
« Reply #3 on: November 19, 2013, 04:08:49 PM »

And when everything works exactly as it should - nobody says anything  Grin
Logged
NJ1K
Member

Posts: 330




Ignore
« Reply #4 on: November 19, 2013, 06:34:40 PM »

Are you sure you want to be a repeater trustee?

The joys of being an amateur repeater Owner, Trustee, or Technician (or ALL THREE!)

So you have decided you need to become a repeater owner, trustee, technician, or even all three. Well, let me share some experiences.

First, a good friend who had been a repeater trustee for many years said "Having a repeater is a BIG pain in the $%# (posterior...)".

I have never owned a repeater, But, for a few years now, I have been a repeater technician. So I know a little about the "pain" involved.

1. You will be ON CALL like it or not 24/7/4/52/365. It doesn't matter that you are in bed at 3AM. Someone WILL call.

Call away, I don't care.

2. If anything at all sounds wrong to the user, the repeater is at fault. Doesn't matter that he is using a 20 year old radio, or a blown speaker, it is STILL the repeater's fault.

I left the phone off the hook!!!


3. If someone can't hit the repeater, it is the repeater's fault. Doesn't matter if the are 100 miles away in a metal building and using one of those Alinco credit card HT's, it STILL the repeater's fault.


I can't hear you!!!!

4. If someone can't get into the repeater because it is toned, it doesn't matter if that is done to keep interference out, it is because you are trying to block them from using the repeater.


I AM blocking you!!!

5. When it comes time to clean up the tower site, EVERYONE will have something else to do.

6. When the repeater is down for repairs, you should immediately drop everything else you are doing (including any deaths, births, vacations, etc) and GET THE REPEATER FIXED. (Including your own death...)


It's HAM radio, I move at my own pace!!!!

7. When an expensive part is needed for repairs, you will always hear "Well, I paid my $20 this year, that ought to be enough." (And that repeater cost $5000...)


I make my own parts at my own pace.. Don't like?? Don't use it..

8. If something goes wrong and you loose your tower site, you are the one that caused it.

9. If lightning hits the repeater, you are the one that caused it.

10. If wind tears down the antenna, you are the one that caused it.

11. Just remember, if it happened, you are the one that caused it.

12. And when the repeater is down, then you will start getting the phone calls that say "If I bring my radio over there, will you program simplex for me?"
(That is because most of the repeater users are within simplex range of each other, and they also never remember where they put their radio manual.)


YUp, it's my fault that it's there and it's also my fault if it doesn't work to your satisfaction.  Again, if you don't like it, don't use it.  Hope you like listening to my phone ringing  for days on end.  It won't get you anywhere...

My friend, I ask you this solemn question.... Are you SURE you STILL want to deal with a REPEATER?


Absolutely, it's fun and rewarding. Everyone should build and own a repeater at least once.

Logged
NJ1K
Member

Posts: 330




Ignore
« Reply #5 on: November 19, 2013, 06:51:08 PM »

Now to answer the OP's question;

For a real repeater, you need a transmitter, a receiver, a duplexer and a controller.  You could also buy a pre-made repeater.  Most factory built repeaters have the TX, RX and controller built in and many of the UHF ones even have a duplexer built in.

My honest opinion of most factory built packaged repeaters is the controllers are bare bones and have few if any bells & whistles.  Things like voice ID's, timed messages, linking ports, etc.  Get a good controller intended for ham use.  Also the built in duplexers are typically notch only and don't co-exist well at a crowded site.

If you want to build your own, used commercial radios are the best option.  GE Mastr II is a very popular radio for this.  There's lots of info and support on the web such as repeaterbuilder.com.

Good controllers such as SCOM or Arcom provide lots of features for reasonable money.

Commercial duplexers such as Wacom, Telwave, TXRX are good choices.

You really are way ahead of the game if you get a service monitor.  Lots of choices out there for very reasonable money but starting at about $2000 might be too much money for most hams.  Names such as Agilent, Motorola, HP and IFR and Aeroflex are all good.

Real repeater antennas are quite expensive also.  Dipole arrays or stationmaster type are the best but for a good one, expect to spend $1000 or more.

The site is also important.  The higher the elevation, the better.  Most are not free unless you have good connections.  Don't forget electrical costs and site maintenance.

Good luck and if you proceed, let us know from time to time how you are doing with it.

Hope this helps,

Tom NJ1K
Logged
KC5HWB
Member

Posts: 18


WWW

Ignore
« Reply #6 on: November 20, 2013, 08:47:35 AM »

Your first post sounds like my normal occupational life, being in IT for the last 12+ years. I know how to deal with people who don't have a clue.  Also my phone has a really neat 'silent' setting that I normally use at night when sleeping.

I got an application from the VHF Society here in Texas, which is the group that grants trustee licenses and maintains frequencies in my area.  It seems that a site location is the first thing I need to determine.  That isn't an issue, really... but they told me there was a waiting list for 2M freqs, so I was hoping I could at least put my name on a list and decide something later.  But they also allow you to have a repeater tower at your home.  So maybe....

Coordinated or not, I really just want to build one and test it.  And do it from my home.  So the original intent of this post was to learn the technical setup, not really to become a trustee of a coordinated repeater and start a club or my own, or whatever.  I just want the experience of setting one up and toying with it.  And I would like the ability to "point" to other repeaters in the area, like an RF link.  I know this is done with a controller and that controller needs to have the capability, such as an Arcom 210.  And of course I will verify permission from the repeater trustee that I point to, if in fact I decide to do that.

So if I took a radio, for exaplme say a Kenwood V71a, and had an Arcom repeater controller, you are saying I will also need a duplexer?  I was under the impression that the radio already had this, but maybe I am wrong, at least for repeater use.

Thanks for the info.
Logged

AA4PB
Member

Posts: 12890




Ignore
« Reply #7 on: November 20, 2013, 09:49:41 AM »

The V71a will not simultaneously receive and transmit on the same band. It can only simultaneously receive on one band and transmit in the other. When working cross-band the Rx and Tx frequencies are far enough apart that a duplexer is not needed. There is also no easy way to connect a repeater controller to a transceiver like the V71a.

For a single band repeater you typically use a separate receiver and transmitter. The controller is used to connect the two. Because the Rx and Tx frequencies are only separated by 600KHz it is necessary to use a cavity type duplexer in order the keep the transmitter from interfering with the receiver. The receiver needs to be of a very good design in order to minimize the interference issues. The transmitter needs to be capable of 100% duty cycle because two users in QSO will keep the transmitter keyed for long periods of time. For these reasons, surplus commercial Motorola equipment is often used.

If you have a local club that operates a repeater you might contact them and volunteer to help out on the technical committee in order to gain some experience working with a repeater before attempting to implement one of your own.

Hamtronics is a company that makes modules for amateur radio repeaters. They have receiver boards, transmitter boards, and controller boards available. Many years ago I built the first repeater that our local club used all with Hamtronics module kits. It served us well for a number of years until we could afford to replace it with commercial Motorola gear.
 
Logged
WB6BYU
Member

Posts: 13331




Ignore
« Reply #8 on: November 21, 2013, 12:56:00 PM »

You may find it is easier to experiment on 440 rather than 2m.  There are more
frequencies available, the wider channel spacing reduces the isolation requirement,
cavities are smaller (and cheaper), etc.

Ham rigs rarely make good repeaters because they aren't designed for the service.
The amount of isolation between transmit and receive required on 2m is far greater
than most folks imagine:  it only takes a little bit of desense or phase noise from the
transmitter to wipe out weak signals in the receiver.  Some commercial sets can be
used because the RX and TX portions are in separately shielded compartments,
the TX is very clean, and the RX is not as susceptible to overload.  The power and
audio lines have to be well filtered to prevent any RF from coupling through those
paths.  Double shielded coax is common for all RF connections.

Then, of course, you end up connecting the receiver and transmitter to the same
antenna.  How can you expect the receiver to hear anything?  That's why you need
a duplexer capable of reducing the TX signal at the input to the receiver when
both are trying to operate at the same time:  the receive signal often is more than
100dB weaker than the transmit signal, but they both have to coexist on the same
antenna.

That's why you won't find a ham mobile rig that can easily be used as a repeater:
while it is possible to get enough isolation between the two signals when they are
on different bands, it is far more difficult to do so when they operate on the same
band.  Those radios that can be programmed for dual-receive on the same band
probably don't reliably receive signals on either VFO when the transmitter is keyed.

And that's why the requirements for the antenna are more severe, too:  any poor
connection in the system will generate a small amount of noise with the TX signal
applied, and that noise can be stronger than the desired signal.  A partially-cracked
weld or dirty insulator can make an antenna unusable for repeater use when a
normal ham would find nothing wrong with it because it transmits and receives
just fine - as long as you don't try to do both at once.


Linking between repeaters is typically done on a different band than the repeater
input and output, because any transmitter at the repeater has to meet all the same
requirements for non-interference.  This is another reason you need a controller board,
to coordinate the different audio sources, and to allow you to turn the link on and off
remotely using DTMF commands.


A couple folks I work with have portable repeaters for 440 made using a commercial
mobile rig, simple controller, and duplexers in a suitable package.  If you keep the power
low (2 - 5 watts) this is probably manageable without being too expensive.  But as you
try to add features and/or use ham equipment the problems can escalate quickly.
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!