DIY Icom Repeater

I keep seeing listings on ebay for repeaters that were made using Icom f121s and f221s. I've also found a few websites which show you how to make them yourself.

My questions though is has anyone done this using Icom F5021's? I like the idea of having more channel options in the event I wanted to use this particular setup as a base station. I also like the idea of the programming software being compatible with several handheld models.

I'm just not sure if i'm better off sticking with the f121s and dealing with the low channel capacity. Or going to the f121?

Thanks for any experience you guys have!

Keep in mind that once you change frequencies off of the repeater pair, you will need to bypass the duplexer.

The F121 and F521 (and their UHF relatives) both can hold a LOT of channels. I think the 121 can handle 128 channels. (The 121S can only handle up to 8.)
How many channels do you really NEED?


Elroy

If you need channels

If you need channels get the radio that has the 128 and utilizes two seperate antennas in your configuration. Just keep the duplexer out of the environment and you won't need to change the frequencies on the duplexer at all. Your just bypassing the device all together. The idea of the duplexer is so that you only need to use one antenna at a time. If you choose to use two antennas make sure there far enough seperated so they do not cause heavoc on one another. Wattage plays in the speration, 20 feet vertically and 40 feet horizental is what I have been reconmend.

If your receive frequencies are in a narrow range of frequencies, OR your transmit frequencies are in a narrow range, and those two ranges do not overlap, then it is sometimes possible to tune a duplexer so that it will provide good performance over several channels. The trick is to tune the duplexer so that its performance is sufficient to do the job but it isn't too sharply tuned.

I've tuned up duplexers that can deliver a -105 dB notch if tuned for maximum sharpness, but if tuned for a perfectly adequate -70 dB notch, I can spread that notch out well beyond 100 or even 200 KHz in width. This allows one duplexer to work on several different frequency pairs. This is particularly handy if your repeater is also a base station radio and you need to operate on several different channels, whether you're operating in repeater mode or not.

Elroy

Yes, you can use the F5021 to do the same thing. You need the correct OPC cable to connect the 2 together with a self made repeater cable that connects EPPT to COR and DISC to TX Audio.

I went ahead and moved forward with my project, so far as ordering what I believe are the necessary components. Here are the links to the equipment i've purchased thus far:

2 Icom F121's : ICOM F121 ICOM F121 VHF Mobile Radio [F121] : The Antenna Farm :: , Your Two Way Radio Source!

1 Repeater housing with built in fan and power supply: ICOM Repeater System Housing With Power Supply and BU - eBay (item 110575314523 end time Nov-16-10 09:30:20 PST)

1 OPC-117 Cable modified for repeater operation: GMRS Outlet LLC :: Radio Accessories :: Mobile Accessories :: Cables :: Icom Repeater Basic Interface Cable

I'm in the process of assembling these items following a guideline from this website: DIY Icom Repeater

I had a couple questions for anyone with experience doing this. I haven't completely sold myself on the idea of using a duplexer so i'm going to keep that out of the equation for now.

The fan on the housing is a CPU type fan with a red and black wire coming off of it. Where would be a good spot to pull power for this fan without feeding it the full power of the power supply?

If I wanted to use this in full duplex, what other modifications would be needed. I see in the repeater instructions that you have to solder 1 spot inside your tx radio, for full duplex would you solder that spot in both radios?

I'm going to program these radios to run at 25 watts or less, however even at this low power I still feel a fan would be beneficial. Also with the reduced power output would this allow the antennas, with say a 5mhz frequency seperation, to remain closer together?

Thanks for the help! I also ended up with a like new 121s for about $100 bucks so I may use it as the guinea pig before I put both the brand new model 121 radios into this configuration.

Buy from an Authorized Dealer if you want a warranty.

The fan can connect directly to the power supply. If you want a temperature control send me a PM and I can tell you where I used to source these from when I was making these repeaters for retail sale (I stopped selling these back to back repeaters because it was very time consuming to build these at the rate that I was selling them at).

You need to solder the F bead - yes. Duplexer, full duplex or half it will be a repeater - and in this configuration if you ever want it to repeat you need to solder that bead. I normally just do both so that it is ready for full duplex or a quick swap should the PA die in on radio. Soldering it will not have a negative impact - so just do both radios.

Almost every UHF repeater needs a duplexer. Unless you have a tower significant vertical separation between the tx and rx antenna. The duplexer will let you use 1 antenna. Beware some commercial installation sites (towers and buildings) will require a BpBr duplexer. If at a commercial site you would probably want one anyway to protect your rx unit from rf energy at the site.

PM sent

Subscribed! I am interested in doing the same thing with an Icom F510 to Rx and an F5021 to Tx. Please update the thread with your progress. I'd be interested to see how you like it without a duplexer. I think what I'm going to do is start with the basics and then determine what level of duplexer I need once I get it set up.

By the way, I'm a ham. For me this project would just be for the sake of "a good time".

To give a quick update, at this time everything is working great. I have 1 unit setup using a 121s and a 121 in a mobile configuration. Running these at half-power (25 watts) and having a 1/4 wave antenna on the trunk and 1 on the front fender I haven't currently encountered any interference.

The other unit I am still working on. I just got the info for the fan temp sensor courteousy of GMRSOutlet so i'll be placing an order for that soon. I already installed and wired up 2 121 radios. My biggest complaint using the metal housing that I linked in my first post is that the radios don't line up very well in the front of the case. If you use the factory holes that are drilled on the side of the metal box the radios sit back about an inch from the front. Functionally it makes no difference, but cosmetically it is less than desireable. There is also a 1 inch gap around the sides and top of the radios. The case that I provided the link 2 I would say is designed for using a Moto Radius or GM300. So imagine the size difference of a 121 vs a GM300 and that will give you an idea of problem i'm facing. I am thinking about trying to find some face plates to fill the voids and also some type of bracket to move the radios forward in the case.

Other than that I can't complain too much. A case with a power supply, fan, and auto battery backup for about $200 shipped is something I haven't seen anywhere else. If someone knows of a place id be glad to hear about it.

Also word to the wise, I used the smalled soldering iron I could find from radio shack. Putting a solder blob on the spot marked "F" is a little more difficult than it looks. I dont have a ton of experience soldering though so I figure if I can do it anyone can, just take your time. The cable from GMRSOutlet takes all the guess work out of connecting the two radios, and a small razor knife will take care of cutting the plastic shroud to allow the cable to exit out the rear of the radio.

I forgot to add a couple more questions regarding duplexers. I talked to my local radio tech and had a pretty lengthy conversation regarding the repeaters that Icom builds themselves using the 121s radios. During this conversation he informed me that a number of smaller agencies, many public works and schools, were using these repeaters with great success. In the discussion was the need for a duplexer and what kind of duplexer one could get away with.

The radioshop felt that for around $425-$450 they could provide a duplexer capable of 1mhz seperation if the power was limited to 50 watts. I must say I found that difficult to believe.

After leaving the shop I did come up with a few more questions about duplexers in general. I've seen 6-cavity duplexers on ebay for around $100 with free tuning, are these worthwhile for a budget repeater build?

Can duplexers be tuned to allow for transmitting and receiving on more than just 1 frequency pair. Could a duplexer be tuned so tightly that it only allowed tx and rx on 1 frequency pair. What I would like to do is be able to transmit over a 2mhz spectrum and receive on a different 2 mhz spectrum. If that makes any sense lol an example being transmit between 152-154mhz and receive between 155-157mhz.

Thanks for the help!

mjthomas59 said:

The radioshop felt that for around $425-$450 they could provide a duplexer capable of 1mhz seperation if the power was limited to 50 watts. I must say I found that difficult to believe.

Click to expand...

What's hard to believe about that? A GOOD duplexer is expensive. A 50 watt rating with 1 MHz separation would qualify as "ok". That's 1 MHz tx-rx separation, btw. Not the width of the pass band. Single frequency... pick one and stay there.

mjthomas59 said:

I've seen 6-cavity duplexers on ebay for around $100 with free tuning, are these worthwhile for a budget repeater build?

Click to expand...

Used? Caveat emptor. Duplexers can take a beating, and I've seen some "bargains" that had burned spots on the tuning shafts that rendered them useless on any frequency I would have been interested in. I've seen some mobile duplexers for that price range, but those are for wider spacing than what you're looking for. .

mjthomas59 said:

Can duplexers be tuned to allow for transmitting and receiving on more than just 1 frequency pair.

Click to expand...

Some can. Look for a mobile duplexer. Expect minimal isolation, but they can be fairly wide bw.

mjthomas59 said:

Could a duplexer be tuned so tightly that it only allowed tx and rx on 1 frequency pair.

Click to expand...

Yes. That's precisely the way the typical repeater duplexer is operated.

mjthomas59 said:

What I would like to do is be able to transmit over a 2mhz spectrum and receive on a different 2 mhz spectrum. If that makes any sense lol an example being transmit between 152-154mhz and receive between 155-157mhz.

Click to expand...

That's a pretty tall order. You could MAYBE tune a mobile type duplexer to operate that way, but the isolation would be pretty poor, and you would be severely power limited. At that point, you should be asking yourself how much desense is acceptable, because you WILL be suffering from desense.

You need to narrow down your requirements some. You either need to run a single antenna, and narrow down the frequency range to something a practical duplexer will handle, or dispense with the single antenna idea, and run split antennas. Even with split antennas, you may need filtering in addition to the isolation provided by the two antennas. You may also need to severely limit the power of this thing. What's it going to be used for?

Here is a link to the cheap duplexers i'm talking about: 50W VHF 6 Cavity Duplexer for GM300 GM3188 GM338 - eBay (item 350296179183 end time Dec-16-10 19:54:08 PST)

As far as 1mhz seperation for $450 bucks. It wasn't that I thought that was expensive, I actually thought the opposite. Most of the name brand mobile duplexers start in the $300-400 range and most of them want minimum 3mhz seperation, most of them closer to 5mhz seperation.

I really am leaning towards just running 2 antennas and using a wider seperation between tx and rx frequencies. This unit would be installed into a large box truck, so the seperation between antennas would likely be at minimum 10-15 feet. I could gather another 2 feet in vertical seperation by mounting 1 antenna into the roof of the cab and the other on top of the box. Although that really doesn't sound like much, i'm hoping that by keeping the power closer to 25 watts and using 1/4 wave antennas that I would be in good shape. Ideally I would like to run at 50 watts with a fan but I suppose until I actually install this stuff I won't know whether it will work or not.

Once I figure that part out the next step will be putting in a cross-band repeater as well.

Imagine using the roof of this box truck, say 8 feet wide and 20 feet long. The roof of the cab is about 3 feet by 8 feet. There is 1 vhf radio already installed in the truck. I'm thinking if I put the tx antenna on the back of the box and on a corner and then the rx antenna on the roof of the cab I would be ok. If I then went further and put the crossband in I would want a duplexer to feed 1 antenna, likely in the opposite corner from the other repeater tx. The other VHF mobile could then be put either on top of the cab or on one of the unused corners of the box. Max power for any of them would be 50 watts.

Thanks for the advice!

At those powers and those frequencies, I would be thinking of at least 200 feet horizontal separation, minimum.

--
Comint

Very intrested, anymore updates???

Can anyone help me solve a no audio problem, that I am having using a Ic -F121s, and a Ic- F221. I also used the GMRSoutlet radio to radio j6 junction cable. I am trying to cross band these radios. I do have bi-directional PTT and carrier, but no audio is transmitted and the carrier is very noisy. Does anyone know if you also have to solder the D junction inside each icom unit?

Noisy radios post-soldering

Cancel question, I found it to be microscopic solder splatter on the IC solder legs next to the cable connector and elsewhere on the board. Found it with a USB microscope I bought for $35 on ebay.

DIY repeater

I have built the icom f121s repeater and it works fine now I've tried it with a 121s Rx and a f1721d Tx and it transmits signal but no voice. I have gone over the programming and the connections over and over again but can't figure it out. Is there something to solder in the 1721d after all it is data enabled to start with?

I have a similar thread.

http://forums.radioreference.com/icom-land-mobile-radio/245271-diy-repeater-icom-5021-a.html