Building of the WT40 Transceiver will begin with the Audio Amplifier module and proceed "backward" through the modules until we get to the antenna connection.
For just about everything you do in electronics there are at least two ways to do it; sometimes there are dozens of ways to accomplish the same thing. This means choices must be made. For the purpose at hand, I have made some of those choices for you. I have chosen to use discrete components for the Audio Amplifier because I think discrete components are easier to work with.
The audio module for the WT40 is a relatively simple, low-power circuit, shown in a photo of the prototype, below.
The red jumper wires on the circuit board are for distributing 12 volts to power various parts of the board.
The blue wire is a jumper to carry the signal from the output of the preamplifier transistor to the base of the amplifier transistor.
The "legs" on the 2N3053 transistor are pre-formed before the heat sink is mounted, then the transistor placed on the circuit board, as shown in the photos, below.
The photo on the left shows the legs formed to spread them to accommodate the parts layout, and to make the transistor and its heat sink more stable.
In the photo to the right, notice that the 2N3053 stands about 3/16 of an inch above the surface of the circuit board.
Resistors and capacitors mount flat against the circuit board.
More about this when we get to Part 5: Building the Audio Amplifier.
A simplified diagram of the Audio Amplifier module is shown below.
This is a generic module with Power, Input Signal (from the Product Detector module), Output Signal (to Headphones and/or an OPTIONAL Speaker), and, of course, a GROUND connection - the one connection that all modules must have.
Speaking of the speaker, this audio amplifier is more than adequate for headphone use, but is not suitable for direct connection to a speaker. Yes, it will drive a small speaker directly, but the performance will be marginal, at best. A separate, amplified speaker unit, such as the ones pictured below, is recommended.
The SONY speaker shown in the photo, was once part of an old PC audio system. These units can sometimes be purchased in "thrift" stores for a couple of bucks (that's where I got this one).
This Sony unit measures about 6 3/4 inches tall by 2 3/4 inches wide by 4 3/4 inches deep. The unit is powered by either four "c" cells, or a 6 VDC "wall wart". This is a nice little speaker unit, and I have used it several years, both on my workbench and at my Ham radio station.
The SONY unit is powered by either four "C" cells, or a 6 VDC "wall wart". This is a nice little speaker unit, and I have used it several years, both on my workbench and at my Ham radio station.
Or, you can build such a device to drive an external speaker, such as the one in the photos below.
The amplified speaker shown in the photo above was build (almost) entirely from junk box parts. For scale, the speaker is about 2 1/2 inches in diameter, and was salvaged from a discarded CB radio. I purchased the "box to put it in" at the same thrift store for $ 0.25. Yep, for a quarter, I got a fine little box to house an auxiliary speaker.
(Thrift stores are one of my favorite sources for parts!)
Be that as it may, I used this speaker unit with an earlier version of the transceiver we are building here.
More about speakers when we get to Optional Features, later in this series.
Meanwhile . . . it appears that I have run up against some sort of limit for blog content, bandwidth, or some such thing.
In any event, Google won't let me add any more graphics to this entry, so I'll continue Part 4 on the next entry.
See you there . . .
73 for now
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