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Idiot's guide to Power supplies
If you're planing to power your transmitter from batteries, than skip this section! You might want to read it to get an idea of what others do.
Most home-built and small power hobby transmitters need a good 12-15 volt, 2 (Minimum) - 8 (Future expansion) Ampere Stabilized power supply.
Note stabilized was printed in bold type, meaning output voltage is regulated and stabilized to spefic value.
Wall-wart types are usually not of this type. They can output even 20V when in load-free mode and only go down to rated 12V under substantial load. This is
not what you want to use as it may damage your transmitter and will definitely present as a strong 100Hz hum on your signal from the lack of proper
stabilisation. Short circuit protection is useful, but not mandatory. A fuse serves well instead of protection and you should definitely use one. They cost 5 cents
and a final RF transistor can cost you more than 100 US$/Euro. Do your math.
Adjustable output voltage gives you an additional feature, you will be able to change your transmitter's output power by changing voltage of your power supply.
Not bad. You can sometimes squeeze more power out of your transmitter if you raise voltage over rated voltage for your transmitter just a little bit. But be careful,
this is likely to destroy your output transistor, sometimes blow some electrolytic capacitors or cause excessive heating.
Importance of proper power supply is often underestimated. Poor power supply can cause several serious problems; add hum to your signal, cause interference to
your neighbors (typical for AM systems where RF leaks into power lines), low current rating, unstable operation under RF field etc. Complicated laboratory
power supply units with lots of un-shielded electronics are often susceptible to RF fields meanning they can uncontrollably raise their output voltage or
short-circuit protection can trip when the current is not even reaching 10% of the limit. A good power supply for transmitters should be RF shielded.
Radio Shack is a good place to look for cheap stuff, as well as ham stores and ham fests.If you prefer to build your equipment by yourself, get
your soldering irons and check out these projects below:
Adjustable 1A power supply
This is a simple variable output power supply. Now, left of this circuit would be standard line voltage transformer (110-220/18V) and a standard
gretz rectifier with smoothing caps (10000uF or even better more). The heatsink of the 317 regulator must be isolated from the ground
(aluminum heatsink).
3A 13.8V fixed-voltage power supply;
This is a pretty strait-forward circuit. You might need to bypass C5 with a bigger
capacitor (10-100uF). Diode D makes up for the BE loss of 0.7V of the 2N3055 transistor. If you need higher voltage, use 7815 instead
of 7812 and connect pin 3 directly to ground. This will give you 14-14.3V on the output. I built several power supplies like that
for my CB/ham stations and they work very well. Of course you have to add mains transformer and rectifier bridge + smoothing caps,
just like above. Caps should be as big as possible (20000uF or more).
28V high-current power supply for 40-200W RF power amplifiers;
This design is from the ARRL handbook 2005, we recommend this book to anyone as it covers all aspects in RF design including antennas, transmitters, basic electronics, filters, amplifiers and others. This power supply is very convenient for 40-200W RF amplifiers which often operate from 24V. Check ARRL handbook for PCB layout and additional details. We even have a link to this book in our Recommended reading section.
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