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HAM RADIOS
By nchecchi, Section Homebrewed Electricity Posted on Fri Apr 16th, 2004 at 07:39:07 PM MST
INVERT DC TO AC

I am doing a project for college, and we need to set up an emergency communication system. We ran into a problem though. We need to have a mobile radio a our base station. At this station, we have a mobile radio connected to a TNC which is then connected into a PC. The problem is, we need to be able to plug the radio into the wall outlet. This doesn't work because the radio is DC power and we need it to be AC. Our professor does not want us to buy a converter, but rather use diodes, capasitors, resistors, etc.
Noone is our group has ever done this. Our plan is to use the 12+/- volts from a computer power supply since the radio is 12 volts. If anyone has any idea on how to do this, I would really appreciate the replies.
Thanks

HAM RADIOS | 9 comments (9 topical, 0 editorial)

Re: HAM RADIOS (none / 0) (#1)
by kell on Fri Apr 16th, 2004 at 09:24:04 PM MST
(User Info)

The best I can gather from your posting is that the radio you have requires 12 volts dc.

So you need a 12 volts dc power supply. Of course a lot of mobile ham radios actually run on 13.8 volts (nominal), not 12, because they need to be compatible with car electrical systems -- which are not really 12 volts. They are a little higher when the car is running.
In any event, the easiest type of power supply to build uses a transformer, bridge rectifier (diodes), filter capacitor, and linear regulating circuitry to keep the voltage steady.
If your professor wants a bunch of you kids with no electronics experience to build a dc power supply, he has high standards for you and you have a job to do. You should ask him for leads on where to find the information you need... but I would suggest finding a copy of the ARRL Handbook, which the American Radio Relay League (the national Ham organization) puts out every year. Some libraries have it. Doesn't matter what year Handbook you get, it will have several power supply projects set out very clearly, along with tons of instructive text, chapters explaining practically anything you could want to know about electronics as it relates to Ham Radio.

Re: HAM RADIOS (none / 0) (#2)
by drdongle (Dr.Dongle1@juno.com) on Sat Apr 17th, 2004 at 06:15:17 AM MST
(User Info)

Several good point made by Kell. I just want to add that using the computers power supply to power the radio is probably not a good idea. The is a good chance that when transmitting the radio will exceed the wattage capacity of the PC supply ( in conjunction with the PC).

Dr.D
Carpe Vigor, Dr.D

Re: HAM RADIOS (none / 0) (#5)
by nchecchi on Sat Apr 17th, 2004 at 04:53:45 PM MST
(User Info)

Thank you for all your help. I understand what you are saying, and for the comment about running it from the battery because it is an emergency is what we told our professor. I think he wants us to do this mainly for the experience, but also incase the power is still available.
The mobile ham radios are mostly used with the electonics of a car, but the way he wants us to do it, is with a comp. power supply. These power supplies are available to us quite easily, and it is a comp. sci. class. Also, he wants this this because once we figure out the wireing, we need to box this up and be able to carry it around.
The computer power supply can be wired to keep a consistant 12+/- volts and the radio will work with that. As of right now, we are trying to find a way, to run the power supply without the motherboard. There are ways to trick it into thinking that, we are just having a hard time doing that. If anyone knows of a way to do that?

Thanks,
Nichole

[ Parent ]

proper supply (none / 0) (#7)
by wdyasq on Sat Apr 17th, 2004 at 08:35:01 PM MST
(User Info)

Get an older "AT" or "XT" supply

Ron
Adventure is just bad planning." -- Roald Amundsen
[ Parent ]

Re: HAM RADIOS (none / 0) (#3)
by pat (see my site for writing me) on Sat Apr 17th, 2004 at 08:19:54 AM MST
(User Info) http://www.sirpaddington.com

drdongle is right, the PC 12v power supply is not going to be powerful enough to transmit. But it might be possible to use it to charge a small motorcycle battery or nicad battery pack. Depending on your standby/transmit cycle, this might work.

Your other option is to make a power supply. You need the good number of turns on each side and diodes to rectify the AC into DC on the 12v side.

PAT
VA2ZY

Re: HAM RADIOS (none / 0) (#4)
by wooferhound (tim((NoSpamAt))wooferhound.com) on Sat Apr 17th, 2004 at 11:28:15 AM MST
(User Info) http://wooferhound.com

You could always use a Car battery or jumper some wires to a battery in a car.
If it's an "Emergancy" communication system, then you need to run the entire system off of a battery anyway...

}=- W o o f -={

Re: HAM RADIOS (none / 0) (#6)
by KHB1 on Sat Apr 17th, 2004 at 08:15:14 PM MST
(User Info)

If pc power supplies are available you can stack 3 of them using the 5 volt outputs like batteries = 15 volts a cheap 7812 for a buck and you are in business.
Also check around for a local ham operator or a ham club I haven't met a ham that wouldnt be glad to help out and teach you the basics.
KHB1
As you slide down the banister of life may the splinters point the other way.

Re: HAM RADIOS (none / 0) (#8)
by drdongle (Dr.Dongle1@juno.com) on Sun Apr 18th, 2004 at 06:45:45 AM MST
(User Info)

If the transmitter is any thing over about 5 watts, a 7812 will pop as soon as they hit the "transmit" key, it's only rated at 1 Amp. Figuring in inefficancies and the fact that the various circuits in the radio will contribute to the total power consumption, a 5 watt out put radio could draw as much as 15 watts total.
However a 7812 driving several 2N3055's will likely handle the load.

BTW Ham gear usually has a very high tolerance for voltage variations, as a general rule 10-18 volts is exceptable, ( unless the manual says other wise).

Dr.D
Carpe Vigor, Dr.D
[ Parent ]

Re: HAM RADIOS (none / 0) (#9)
by DakotaSIG on Thu Apr 22nd, 2004 at 07:28:23 PM MST
(User Info)

Have a look at this:
http://web2.murraystate.edu/andy.batts/ps/powersupply.htm
Make sure you check with your prof. before opening up a PS!

HAM RADIOS | 9 comments (9 topical, 0 editorial)

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