Building a Repeater

[sfd119]

I have kind of a weird question to post, and I"m not sure where to post it. I figure here would be the best spot as it relates to amateur radio stuff.

I'm looking to build a simply repeater out of stuff I have already.

Could you, in theory, take two say Yaesu radios and link them up using the pinouts of the mic cables? You know, as one receives the other transmits what the first one receives? (I know I would need a duplexer to accomplish this).

Is this actually possible? I know there are real repeater linking cables, controllers, etc but am curious if my idea would work.

Thanks!

 

[zz0468]

Is this actually possible? I know there are real repeater linking cables, controllers, etc but am curious if my idea would work.

It could be made to work, but barely. Some sort of minimal interface circuitry between the two radios would probably be required. Is this something you really hope to accomplish, or is it an academic question? Are you willing to settle on something with no controller, no id'er, and probably lousy sounding audio, or is there an expectation that it actually work good? So, the short answer to the question of is it possible? Certainly. But would you want to? It's not at all how I'd go about it.

 

[sfd119]

I do what to accomplish it...by no means does it need to be crystal clear audio, I just sort of want to do something for fun.

 

[davidgcet]

the RX radio must have a means of outputting a COR which the TX radio would see as PTT. you may have to use a switching transistor to accomplish this, i've done it before using part of the squelch circuit to turn the transistor on and issue PTT.

do you have schematics for the radios?

 

[sfd119]

I don't have a schematic on them. I do have these radios:

TX: Yaesu FT-2500M with the MH-36C mic.
RX: I'd like to use a scanner, but if its got to be a radio, that's not a problem either. RX Radio could be a Yaesu FT-2400 or a Yaesu FT-2200.

 

[davidgcet]

since it is a unidirection repeater all you need is RX audio to Mic Hi, common ground, and somethign from the RX to act as PTT. you will need to figure out how to issue the PTT, so schematics are a must unless someone has instructions for doing it with your exact units. also, if you need repeat hang time your ptt will have to hold for a second or two after RX stops.

 

[sfd119]

By schematics what do you mean? Of the whole radio or just of the mic?

 

[sfd119]

Here's a FT-2500M schematic for the TX Radio: http://www.iw2nmx.it/Yaesu/FT-2500M/FT-2500M Schematic.pdf

 

[KAM101]

and don't forget the TX and RX bandpass cavities, they allow the the receive signal to pass, and block the transmit frequency, without them you end up with inter-modulation distortion.

 

[sfd119]

and don't forget the TX and RX bandpass cavities, they allow the the receive signal to pass, and block the transmit frequency, without them you end up with inter-modulation distortion.

Yep, I'm aware of that. I'll either get a duplexer or have the freqs far enough apart with two antennas, rx on top, tx on bottom.

 

[davidgcet]

if this is a same band repeater the antennas may require a much larger vertical seperation than is possible. find a duplexer and have it tuned to your freqs. unless you own a service monitor or good spectrum analyzer and frequency generator you won't tune them properly.

what about PL/DPL, is your scanner capable of it? if you run it CSQ you will be open to all sorts of skip. plus a scanner has such a wide front end that it won't give the best results and could suffer from blanking when the TX keys up.

i'm not trying to discourage you at all, i just want to make you aware of things that go into repeater system design.

 

[n5ims]

One other issue is the radios you're planning to use aren't designed for a very high transmit duty cycle. Since a repeater transmits for fairly long periods of time with only short periods of downtime you'll need to closely watch the transmitter's heat level and most likely run it at half (or less) of it's maximum rated power level. Otherwise it'll overheat and may blow the finals (or at best the radio will automatically switch to a lower power until things cool down enough).

 

[sfd119]

Scanner has PL/DPL/NAC availble along with the RX & TX radios mentioned above. I will get a duplexer if I can get this working easily enough. I would like to just figure out the appropriate pin outs from either the scanner or an rx only radio to the tx portion. If I get all this setup, I'd be happy to order a duplexer.

I understand you guys are all giving me constructive criticism and I appreciate it greatly!

@n5ims, Again, this wouldn't be a highly used repeater, I'm really just building it for fun at this point.

@n5ims

 

[sfd119]

FT-2400 Schematic: http://www.studio70productions.com/misc/ft-2400.pdf

Edit: What about this: http://www.synergenics.com/sc/

Could I use a computer to connect the scanner (or RX radio) & TX radio together and use that software to handle everything else? Is this achievable with using the LINE OUT from a sound card and have it go to the MIC INPUT on the radio??

Edit2: Here's the MIC schematic on the FT-2500M http://imgur.com/bo6gB.png


I guess the question now is, I'll use the SCANNER as the RX devices (inputs into the LINE IN on the computer) and then the FT-2500 as the TX devices (coming from the LINE OUT on the comptuer). I just need to know the pin outs at this point from the LINE OUT on the computer to the correct pins on the 6pin connector to the radio's mic spot. Anyone got any ideas or know if this is possible?? Thanks!

 

[n5usr]

Some radios are MUCH easier than others to use. In my case, I used some Alinco single-band mobile rigs as they have every signal required to do a full repeater on the back of the radio on a DB9 connector. You can literally hardwire the DB9s together (in the right wiring pattern, of course) and have a minimally-functional repeater!

Some other rigs do too, the Yaesu FT-8800 and 8900 I know (I have them as well) although in some cases you have to reverse polarity of the COR (gives an "active high" but needs "active low" to TX or vice versa). The audio even matches, they have "9600 baud data" pins that have matched in/out levels.

I have a 220MHz repeater that used (and may well go back to) two Alinco rigs for the TX/RX. Audio was excellent - not so happy with the audio of the real repeater I recently got, thus may go back!

As for the two radios you mention, the hardest part as already mentioned is getting a proper COR (carrier operated relay) signal to key the transmitter when a received signal is heard. One option that springs to mind is to buy a (CTCSS) tone decoder board, connect it to the audio output of the scanner, and use a tone to control the repeater. If the scanner filters the low frequencies too much, you may have to connect the tone board to the discriminator audio of the scanner (be the same as connecting a "discriminator tap" for software such as UniTrunker used by many here).

Power level is an issue, I ran my Alinco 220 xmtr at 5W, it was only warm as long as I kept a fan going on it. Otherwise even at that level it got VERY hot. The 2M remote base xmtr I could run at higher power, since it only transmitted when I did - basically like I was using it directly.

Realize that duplexers can be the single most expensive part of a repeater system unless you find a good deal on used ones somewhere. If I were going to buy duplexers at anywhere near new prices, I'd go ahead and get some radio gear that would be easier to use than what you have first. Especially for the receiver, a scanner's front end is typically nowhere near as good as a real radio. (Although some ham rigs have such a "wide open" receiver range they aren't much better!)

It is also helpful to have a proper repeater controller in the system as well. The wiring I mentioned above simply allows automatic retransmission of audio. No control of the system is possible, though. Unless you are present with the repeater you would have no way to shut it down if something started going wrong. There are various repeater controllers available in the ham world, some very basic others quite fancy. Mine is an Arcom RC-210, it has a few extra features - thus a higher price tag.

One option for a tone decoder: TD-5 Subaudible Tone Module

They also have a basic controller too: COR-4 Module

 

[n5usr]

I guess the question now is, I'll use the SCANNER as the RX devices (inputs into the LINE IN on the computer) and then the FT-2500 as the TX devices (coming from the LINE OUT on the comptuer). I just need to know the pin outs at this point from the LINE OUT on the computer to the correct pins on the 6pin connector to the radio's mic spot. Anyone got any ideas or know if this is possible?? Thanks!

You still need a way to key the transmitter. You could use some sort of computer program to "detect" an active signal, but it will need to control a relay that is connected to the PTT of the mic. Typically via a serial or parallel port interface.

At its simplest, you just connect the "hot" (center) pin of the line out jack to the "hot" pin of the mic input. Same thing for ground. However, you may find it difficult or impossible to get the audio level set properly (it may be very very quiet or extremely loud and distorted) especially if the impedances are significantly mismatched. You may need to put some sort of interface circuitry between the line out and mic. These can take different forms, depending on what needs to be done. If the audio is way too hot / loud, a simple resistor pad can cut the signal down. Too low, you may need a preamp. And it is often useful to use an isolation transformer to break ground loops which induce low-frequency hum.

 

[kpoe_28]

I have kind of a weird question to post, and I"m not sure where to post it. I figure here would be the best spot as it relates to amateur radio stuff.

I'm looking to build a simply repeater out of stuff I have already.

Could you, in theory, take two say Yaesu radios and link them up using the pinouts of the mic cables? You know, as one receives the other transmits what the first one receives? (I know I would need a duplexer to accomplish this).

Is this actually possible? I know there are real repeater linking cables, controllers, etc but am curious if my idea would work.

Thanks!

The easy way.... I've got one of these and works just fine, easy plug & play.
Good luck 73's

 

[sfd119]

Yeah, I have seen that, It's looking like I"m going to end up getting that.

I was just trying to do things my own way, like always.

 

[sfd119]

Okay. So I have it wired up right now so that It will pass the audio from the scanner to the Yaesu, and if I hold the TX button, it'll transmit the audio on the different freq.

However, what voltage, wire, or external component will allow it to do it automatically??

 

[n5usr]

Again, that's the COR circuit. The simplest way - is there anything on the scanner that indicates it is receiving something? Ideally an LED. If so, you can pick the voltage that turns that on, and use it to turn on a relay that is wired across the PTT connection.

But most scanners don't have anything discrete like that. Next simplest is something that can "listen" to the audio and generate the keying signal. Something that could detect audio is doable, but could be touchy - it may drop out mid-sentence when people are not talking if the received signal is very quiet. The tone board I mentioned earlier would work more reliably, as subaudible tones are continuous when keyed up, but of course would be another purchase.

There is going to be someplace in the scanner's circuitry where a voltage changes based on received signal - that's how it knows whether to unmute the speaker - and you may be able to find a trace on the PC board and tap it. But that would require the schematic and some investigation.