DIY Repeater Icom 5021

brandonmckinney · #1 (**permalink**) 07-25-2012, 12:15 AM

I am building a repeater for my fire department. I have connected or linked two Icom 5021 radios with all the proper programming to function as a repeater. Field testing with two antennas has proven successful. Next step is purchase of a duplexer. Does anyone see the need for a repeater controller in this case?

Thanks

gewecke · #2 (**permalink**) 07-25-2012, 12:23 AM

Quote:

Originally Posted by brandonmckinney

I am building a repeater for my fire department. I have connected or linked two Icom 5021 radios with all the proper programming to function as a repeater. Field testing with two antennas has proven successful. Next step is purchase of a duplexer. Does anyone see the need for a repeater controller in this case?

Thanks

How do you intend for the repeater to ID itself?

A very basic controller with DTMF control and CWID can be had cheaply here,

Integrated Control Systems

73,
n9zas

n5ims · #3 (**permalink**) 07-25-2012, 1:03 AM

A repeater controller generally also provides a time-out timer, which is especially important when standard radios are used to build the repeater since their duty cycle (the required non-transmit time following a defined transmit time, often 2 1/2 mins transmit followed by 5 mins of not transmitting) is nearly always well below the 100% duty cycle time of repeater transmitters.

Failure to respect the duty cycle will cause transmitter failure, which isn't something you want on a repeater that handles critical traffic for a fire department. Because of the duty cycle issue, you really should give serious thought to reducing the power output of the transmitter, which will help extend the duty cycle and lifetime of the transmitter.

mmckenna · #4 (**permalink**) 07-25-2012, 1:30 AM

I agree. Consider using the mobile radio as an exciter to drive a continuous duty RF amp. Turn the transmitting mobile down to 5 watts or so and you will have a happier radio. A forced air flow over the heat sink is a good idea either way.

Also, double check how the system performs after a power outage. Do the radios turn back on when power is restored? Do they come up in the correct mode?

Some pictures would be nice...

I'll also agree that a purpose built repeater is better suited, but when money is tight, you have to make do. Good luck!

brandonmckinney · #5 (**permalink**) 07-25-2012, 2:04 AM

I can activate the time out timer on the radios so I do not believe I will need a repeater controller to perform this task.

The reason I am asking specifically about the controller is that I was told by a radio tech/salesmen that I needed one for my system that I a building. Something along the lines of the repeater controller is going to keep the PL Tones from running into each other. Still haven't figured out exactly why I need it. I don't have the funding right now to purchase it anyway.

Thanks for the feedback!!

mmckenna · #6 (**permalink**) 07-25-2012, 2:32 AM

Now THAT is creative!

kayn1n32008 · #7 (**permalink**) 07-25-2012, 6:09 AM

Wirelessly posted (Mozilla/5.0 (BlackBerry; U; BlackBerry 9780; en-US) AppleWebKit/534.8+ (KHTML, like Gecko) Version/6.0.0.600 Mobile Safari/534.8+)

One other thought, do not run the transmitter at any more than 50% of its rated output, even with cooling fans.

cabletech · #8 (**permalink**) 07-25-2012, 6:55 PM

Per FCC rules, you need to be able to control the equipment at any time from any where.

That being said, a control board will a) do PL/DPL b) do fcc mandated IDing c) allow for remote control of the equipment.

You can find inexpense control boards and diplxers on the net

12dbsinad · #9 (**permalink**) 07-26-2012, 5:46 PM

Quote:

Originally Posted by cabletech

Per FCC rules, you need to be able to control the equipment at any time from any where.

You can find inexpense control boards and diplxers on the net

I think what you meant is a duplexer...

Im not sure I understand where this FCC ruling comes from... control it from anywhere?

ramal121 · #10 (**permalink**) 07-30-2012, 10:18 PM

Here's what a repeater controller will provide for you (basic functions)

1) Automatic identifier - nice but not needed. The user can ID in plain voice as long as FCC regulations are followed. Minor training.

2) Time out timer - this is already provided in the transmit radio and is programmable to your needs. I have yet to see a radio where you cannot tack on a TOT to a PTT input.

3) Squelch tail - a controller will provide a transmission hang time after the receiver clamps. If you are hooking the COR line to the PTT line directly there will be zero squelch tail. Again, nice but no deal breaker.

4) Level setting - if you hook receive audio directly to the mic input and it sounds OK to you, you're in good shape. If transmit audio is too low or too high and distorted, there is no way to adjust it. Only a controller with gain controls can solve this (or some kind of outboard level adjustment).

5) Audio shaping - if you are using mic input for transmit (which pre-emphasizes the audio), you will want to use de-emphasized receive audio for it to sound correct with the right response curve. This configuration will also strip the receive PL and not be a problem with the transmit PL. The other way around is to use raw discriminator audio in the receiver hooked to a flat response transmit input, but this WILL pass receive PL out to the transmit and cause problems. A high pass filter will have to be inserted in the line to prevent this. A good controller will have the option to use filtered audio, or discriminator audio and do the required de-emphasis to provide proper (PL free) audio to the mic input.

6) Remote control - Better controllers provide remote control via DTMF, but if this is for part 90 service it certainly is not required.

Can you screw two mobiles back to back and make a repeater out of them? Sure, have done it many times. Just watch that you don't get too talky on it and burn it up. Also the duplexer is a great idea, reduces the hair pulling trying to get split antennas to work.

brandonmckinney · #11 (**permalink**) 07-31-2012, 1:59 AM

I have a talk-out-timer already set in the transmitting radio. I have a good squelch tail and hang timer already in the transmitting radio. My audio sounds awesome and does not need any adjusting. I believe my PL tones are set correctly and do no seem to be interfering with anything. I have ordered the duplexes and am just waiting in it to arrive. I think as of right now I am going to hold off on ordering a repeater controller.

jim202 · #12 (**permalink**) 07-31-2012, 6:13 AM

Having spent some 35 years with the fire service I can understand your interest in moving this project forward. There have been a number of people before you that have sort of laid down the railroad tracks that your following. However, you need to walk a careful line here and make sure your moving forward in a legal and technical fashion.

The first word of caution is that you have a station license for the fire department that has a repeater class shown on the frequencies your planning to use. You haven't mentioned this in any of your comments so far. The second concern is that you will be operating this home brew repeater in the narrow band mode come the 1st of January, 2013. Last major comment is that you have measured the deviation of the transmitter and the frequency to make sure that the radio is operating to the correct specifications for the frequency you are planning to operate on. This all requires the use of a service monitor that has been calibrated to measure both frequency and deviation.

Being that this is being used for life safety communications, you have made sure that the radios and power source are backed up in case of a prime power failure. There is nothing worse than relying on a repeater and it isn't there just when you need it the most.

I also have to support the others that have voiced their comments of relying on a mobile radio transmitter for repeater service. You can't control the amount of transmit time when the chips are down during an emergency. Radio traffic will spike way beyond your expectations and be totally out of control for maybe the first 15 to 30 minutes when this all takes place. That will cause most transmitters to max out on heat generation in just a short time.

Having said this, I noticed that you have mounted the radios inside a computer case. This may look great, but is probably the worst thing you could do for removing the transmitter heat that will be generated. You have minimal heat removal with this package.

I am not trying to be negative. But just pointing out a number of areas that seem to be on the weak side of your plans. Over the 45 years that I have been working with public safety radio systems, I have seen a bunch of red neck hook ups. Just trying to prevent yours from becoming another one.

As much as you would like to put this into action, you should take a break and step back from the project. Take a breather and evaluate what you have, what the intention is and if your going to have the desired results. You may not have the funds to work with at this point in time, but just maybe they will become available in the future. There are a number of sources for grant money in the fire service. It may take 2 years to get there, but you will be much better off using the radio equipment designed for repeater service than jack legging it with your package.

What does the fire chief think of this endeavor? He is the ultimate one that will have to answer if your repeater fails during an incident.

NZ0J · #13 (**permalink**) 07-31-2012, 10:41 AM

I would like to add one thing here. I have an Icom 6021, which is the UHF version of your radios. My 6021 is a great radio, but it does heat up faster than any radio I've ever been around. I think in a repeater set up you're just asking for problems with these radios. I think if your serious about doing a repeater for your F.D., I would look at other avenues rather than using these radios. I would seriously look at buying a repeater with the duty cycle you need rather than building one.

brandonmckinney · #14 (**permalink**) 07-31-2012, 12:08 PM

I greatly appreciate everybody's feedback. This is awesome! It is all very useful information.

My fire department like every other government agency right now, broke. My chief is very much aware and in support of the project. We discussed our project goals and objectives with a radio engineer who estimated $20-$30,000 for the project. This is simply just unrealistic for my department. So far I have put together this repeater with no cost to my department using radios that are already sitting on the shelf. Due to the bureaucracy of government I have been forced to take my time buying one part or component at a time.

Because of our tight budget, my chief has been very cautious in buying parts for this project. I do not have a unlimited budget and every time we get a new component we test out the repeater to make sure it's still worth moving forward with.

To test the project we have been using two antennas and a repeater pair license to our county. A duplexer is on order to allow us to use one antenna and further test some potential repeater sites.

Frequency coordination and licensing will be one of the last things we do. This is because we are not sure whether the repeater will work like we want it to or not and the cost associated with it.

I completely understand and agree with the concerns regarding the duty cycle and heating up of the radio. The repeater would not be used much but could receive heavy use at time for a few minutes. I would like to find a repeater site and antenna that would allow us to turn down the tx radio to 25 watts. Ultimately I would like to have a repeater radio with 100% duty cycle. The old computer tower that I am using as a housing unit is only temporary, but surprisingly has a lot of airflow because I kept all the fans and removed all the electronics. It is connected to a UBS which is connected to our stations generator.

I am treating this project as somewhat of a pilot. I would like to show the potential of the repeater to my administration and convince them to add it in the future budgets to replace and update components as the budget allows and is necessary.

Thanks again on the feedback. I will continue to post as the repeater comes along. I am by no means an expert and can use all the tips and knowledge anyone would like to share.

Thanks,

Brandon, K7KLA
Firefighter/Paramedic
Walla Walla Fire Department

brandonmckinney · #15 (**permalink**) 07-31-2012, 12:22 PM

As to a few of the suggestions and concerns previously posted.

The radios are narrowband capable.

Our members and personnel will be trained on the functioning of the repeater and radios. Portable and mobile radio programming will be adjusted so that in the event that they cannot get into the repeater they can easily switch to simplex/talkaround mode and bypass the repeater with the push of a button.

I plan on purchasing a much more suitable enclosure if we decide to go completely through with the project. One that is designed for the radios and allows for good cooling.

brandonmckinney · #16 (**permalink**) 08-19-2012, 8:43 PM

How hot is exactly too hot?

shockhazard69 · #17 (**permalink**) 10-09-2012, 8:14 AM

Quote:

Originally Posted by brandonmckinney

How hot is exactly too hot?

Do you burn your hand touching the Tx radio? If so, that is too hot. I would say anything more than warm is too much.

stevelton · #18 (**permalink**) 10-10-2012, 3:21 PM

We have a repeater I built from 2 Icom F221s mobiles for our county ARES group. The TX radio is set to Mid power (about 25w). That in turn drives an Amp which puts out 100w with 25w drive. For daily use our setup works great, but I have noticed that during times of high use the TX radio gets very hot after transmitting for an hour straight. But if we set the TX radio at Low power (about 10w) it can run all day long non stop with not one issue. Driving the amp with 10w gets us about 50w. We have had this repeater on the air with daily use, some of it heavy, for over 3 years now.

brandonmckinney · #19 (**permalink**) 10-29-2012, 3:26 PM

Have you noticed any decrease in the signal strength or quality since you have started using this repeater? This sound promising. The chance of us using this repeater non-stop for an hour or more is almost zero. I would estimate that typically it would receive about 15-30 minutes of high use age and would only be transmitting probably half of the time during that period. I do have fans on it and have good airflow around the radios.