Building a repeater . . .

[Robb]

I may or may not. There a MANY repeaters where I live in the South Bay Area of CA. Many of them are open repeaters and are not very active, except for the one repeater that is part of the Winsystem. That is a busy repeater. But I still want to know how the work and how to build one for little $$ - should I for whatever reason - decide to build a repeater.

But for understanding how it can be done - and as inexpensively as possible - what does it all take? Maybe you are a new Ham and have wondered as I have. Or maybe you are just as curious as I am to know the nuts and bolts of a repeater and just how they work. Maybe you have used this method. Or a different one.

The terms/words used to describe the parts and functions of a repeater are going need more definition and explanation that I am giving it here. Feel free to jump in and add your $.02; it may well go a long way here.

The internet has different ideas as to how it can be done. There is a program called "Echostation" that I was reading about here:

(K1RFD EchoStation - Repeater-Control Software for Amateur Radio)

With an old computer running Windows 95, two radios, a power supply, and two antenna, and that program; can one put together a repeater? Did I leave something out?

I know that for it to be legal, that the area frequency coordinator would need to be contacted and a pair of in/out TX/RX frequencies chosen. The FCC would also need to be paper chased as well for a grant (have NO idea what happens with that either).

The Echostation program is free for the first month.
Dunno what it cost to pay for the license for it.

Has anyone every done/tried this?

 

[Captain Kilowatt]

You left out ID'er and cavity filters tuned to the operating frequencies. I thought about it years ago using a pair of Johnson vhf mobile radios but looked at the cost and said why bother. Oh yeah, you need a carrier controlled relay as well as an antenna changeover relay.

 

[AudioShockwav]

I helped some guys set up a 2 meter machine, the radio was a old forest service radio with a 100 Watt PA, converting it to 2 meters , you had to swap the TX and RX crystals for the repeater pair, split the TX and the RX with separate 259`s for each. Turned the radio down to 40 watts to allow a higher duty cycle, Disable the tone burst, and heat up the RX and TX at the same time.
Cat 1000 controller took care of all the functions .
Single Hustler antenna, g7 if i remember right
Duplexers, spend a little money and it is worth it.
Coax..Good coax. hard line if you can afford it, but if it is a short run you can do with good low loss coax, being on the very top of a mountain helps keep the coax short if you get that lucky
4 deep cycle battery's
50 Amp power supply
Odds, ends, cables, big diodes, charge controller, some solar panels if you want back up for the back up, beer for the guys putting the tower up.
If you already got the tower you can save money on beer ( maybe)

73
Jeff

 

[Robb]

Let's say that you have two Yaesu FT-8800's . . .

http://www.qsl.net/oares-5/em_repeater.htm

 

[Moleculo]

Let's say that you have two Yaesu FT-8800's . . .

Easy to Build Emergency Repeater

You can do it with two basic radios and a few other parts:

• Two radios
• One duplexer
• One antenna
• One power supply
• Coax (duh!)
• A way to ID - use a computer interface or use the ID-O-Matic from hamgagets for $25.
• A way to turn the repeater off - an internet IP controllable power strip will do.

That's all you really need for a basic repeater. Keep in mind that if your repeater is going to be busy, the TX radio is going to need forced air, more heat sink and anything else you can think of to keep it cool. The total cost doesn't have to be that great if you can find basic radios for a good price.

 

[Robb]

Seems that a duplexer is somewhat expensive. They are pre-tuned for a specific pair of in/out freqs too. This makes it harder to find and perhaps won't line up with the available freqs given by the freq coordinator too.

Is there a problem with making two GP 5/8 wave antenna and using them one to each radio? Since the TX freq is .600Mhz from the receive freq on the 2m band; there shouldn't be any interference. Right/wrong?

So, let's say that we are using a duplexer. How are the two radios wired together? Out of the speaker of the RX radio and then -?- into the input of the transmit radio? Or would you use a computer sound card in/out and the Echostation software to control the works?

 

[Mudfoot]

You left out ID'er and cavity filters tuned to the operating frequencies. I thought about it years ago using a pair of Johnson vhf mobile radios but looked at the cost and said why bother. Oh yeah, you need a carrier controlled relay as well as an antenna changeover relay.

Not to mention the politics and headaches associated with ownership.

 

[Captain Kilowatt]

Robb, you can't just use two separate antennas and not get interference problems. If the two GP's are mounted one above the other by a couple wavelengths you will have some isolation due to the nulls but it won't be enough to overcome desense. Desense is when the rx sensitivity is severely degraded due to the frontend being creamed by an extremely strong sigbal, which the tx would pose, and you needthe rx operating at the same time as the tx. BTW, as for duplexers, you rarely if ever get a used unit tuned for your freq pair. Most hams that have the ability to build a repeater also have the ability and equipment to retune them.

 

[fodendaf]

i found this homebrew cavity resonator by accident
www.ingenia.org.uk/ingenia/issues/issue18/david.pdf

 

[Captain Kilowatt]

i found this homebrew cavity resonator by accident
www.ingenia.org.uk/ingenia/issues/issue18/david.pdf

Yeah but by the time you empty it you're in no shape to convert it into a cavity filter.

 

[fodendaf]

not necessarily, I bought an empty one at a steel recycling yard to use as a diesel tank. I did drink the dregs out of the bottom but i wish I hadn't as it was damn nasty. goodness knows how old the beer in it was.

 

[AudioShockwav]

Most hams that have the ability to build a repeater also have the ability and equipment to retune them.

Correct, I have a set of VHF duplexers down in storage, they are tunable so you can set them for your pairs.
Cap Kilo is also correct about :

Desense is when the rx sensitivity is severely degraded due to the frontend being creamed by an extremely strong signal, which the tx would pose, and you need the rx operating at the same time as the tx.

If you re-read the link you posted there is this:

The reason the antennas are separated by 1/4 mile is so the 2-meter Tx signal does not de-sense the 2-meter Rx radio. Since Tx and Rx frequencies are typically separated by only 600 KHz, you need to either use duplexers or spatial separation to attenuate the 2-meter Tx signal at the 2-meter Rx radio enough to allow its receiver to function.

but use one or more mobile duplexer cavities to notch out the Tx frequency on the receive side. These cavities are small, smaller than a 1 lb. coffee can, and can be had at hamfests fairly cheep. I picked up a set for the 2 meter band last October in Rickreall for $50. It has 6 cavities!

You have a radio(s) that is listening at the same time it is transmitting, and life will suck big-time if the front end of the RX is being wiped out.
We encountered that with the machine we set up for the club.
and there is another reason to reduce power out put, not only to increase duty cycle of the radio, but the more RF you are stuffing up the coax while the RX is coming down, the more you will fight desense.

There are also plans on the internet, if you look, for building a 6 cavity set out of Copper tubing ( read BIG copper tubing ) but at the price of copper today that will add up quick.
I will find it and post it in a little while here.

73
Jeff

 

[AudioShockwav]

Made from 16 gallon Oil drums.

2M Duplexer

Made with Copper tubing.

Build a 2 meter duplexer

More info:
http://www.eham.net/ehamforum/smf/index.php?topic=76303.0


http://www.repeater-builder.com/pix/dupfig19.jpg

One thing I forgot, depending on how many user`s you wind up with on your machine, you will need a thick skin and a very understanding Wife.

I always thought the heart of the repeater was the crazy person who would drive up a mountain at 2 AM to fix it.

No shins, you are asleep at 2 AM and the phone rings...wife thinks some one has died because NO ONE calls at 2 am unless it is an emergency.
She answers Phone
"hello"
"What?" " who is this?" "The Radio what?"
She looks at you like she wants to rip your testicular equipment off, hands you the phone and say`s
This Radio Stuff is getting out of hand!
( at this point you are thinking " this will not end well")

You say "hello"
Your buddy says " Dude , the repeater is down, it has been down for over 45 min...what you going to do?"

Been there.

73
Jeff

 

[Robb]

Well; I wouldn't want anyone to lose their family jewels over this project. Least of all me - either. There are many considerations for doing a project like this. Having radio club members to share the responsibility would help. Including the cost. But for building an inexpensive emergency repeater, one needs to get inventive.

Since the need for a cavity duplexer has been defined in the previous posts ('desensing'), to find and incorporate a duplexer becomes a necessity.

On eBay, I found a duplexer (new) for a mobile radio equipped with N-connectors. But it should provide the same function at a fairly reasonable cost . Making a mobile repeater would also allow for the power supply part of the repeater to be dealt with. Making it mobile means that one can drive up to the nearest mountain/hilltop and make this possible repeater station effective in an emergency situation too.

Perhaps using this unit can lower the cost somewhat?
Here is the VHF duplexer, capable of handling a 50w power output - for $!00:
eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices

 

[Moleculo]

A lot of people use those ebay duplexers with a lot of success. Really the only issue with them is that they don't offer as much isolation as better, more expensive ones. If your repeater is on a site where there are a other repeaters, this could be a problem. However, if you're just building a home repeater, it will work fine. I plan on using one of those for the D-STAR repeater I'm building.