xpyttl wrote:
Hi Jason

Nice questions, let me try to answer a few ..

wrote in message
ups.com...

1. i've seen transmitter schematics that were simple, and others
that
were complex. as a general rule of thumb, are the more complex ones
trying to compensate for frequency drift, or maybe eliminate higher
harmonics? how efficient and/or stable are the simple transmitter
schematics?

One obvious thing is that CW transmitters tend to be simple, SSB
transmitters complex. But there are a thousand design variables.
One big
one is the complexity of the ICs employed. Today you can have a very
stable
VFO with just a few parts. You tend to pay a little bit of a price
in phase
noise, but frequency drift is not an issue. With an analog VFO, you
can add
a lot of complexity trying to get around frequency drift, but phase
noise is
never an issue. Years ago, all you had was analog. A few years ago,
DDS
(direct digital synthesis) was complex and expensive. Today, analog
VFOs
tend on the expensive side! It is similar with amplifiers. In many
radios,
all, or most, of the PA is in a single brick, instead of a fistfull
of
parts. Ditto with almost everything up and down the chain.

Frequency is also an issue and again that is changing with
technology. A
few years ago, it was hard to get directly to VHF. You typically had
several oscillators getting mixed up, frequency multiplied, etc.
This was
especially true if you had an analog VFO because it is very hard to
get
stability at VHF, and multiplying the frequency also multiplies the
drift in
an analog VFO. There are still reasons you might want to do some
mixing up
to get to VHF with a DDS VFO, but DDS parts up into the gigahertz
range are
now cheap parts.

It was only a few years ago that a DDS VFO cost hundreds of dollars.
Today
you can buy a chip with a VHF synthesizer and amplifier and modulator
for

Good info to know. I was kinda looking around to make a (mostly) IC
transmitter like that... (anything 70cm and under). Are you aware of
any chip PN's or schematics I could dive into to learn?

Thanks,
Dave

"dave.harper" wrote in message
ups.com...

Good info to know. I was kinda looking around to make a (mostly) IC
transmitter like that... (anything 70cm and under). Are you aware of
any chip PN's or schematics I could dive into to learn?

Analog Devices' parts are favored by hams. The greatest number of projects
out there use the AD9850, but that part is a little older, and does not
provide modulation input. Also, it is really only good up to about 30 MHz,
you can push a bit past that but the power requirements explode and the
noise goes up. Without any component changes it will go down to 1 Hz.
Newer AD98xx parts are starting to get more attention, and some of those are
useful up into the low 100's of MHz. The 99xx parts have more features yet.

TI has a TRF4400 which is a 440 MHz synthesizer with modulation and an amp
(not much of an amp, tho!), and the almost identical 4900 for 900 MHz. Some
folks have used these down to 6 meters. The TI parts have greater channel
spacing than the AD parts, but that also reduces the frequency of the
crystal or oscillator, which has a big effect on the power consumption. TI
also has a 2050/1/2 which are synthesizers (I don't recall if they have
modulation) up into the gigahertz range. I've been toying with using one of
the TI parts as a VFO for an HF rig by using a prescaler to divide down the
frequency (and consequsntly the spacing).

The AD parts are pricey, but AD is very good about samples. The TI parts
are all in the five buck neighborhood. There are a zillion projects/kits
out there based on the AD parts.

If you've ever built an analog VFO, these DDS parts are like black magic.
They take little in the way of support circuitry, no fretting about layout,
no spending weeks trying to work out the temperature compensation, no moving
around because you breathed on it, you just dial in the frequency you want
and you are spot on.

...

Does anyone here remember the simple CW transmitter that used a 6146 as a
keyed ocillator? It would put out about 60 watts. There was a very low
current light bulb in series with the crystal to limit the current that
could flow in the crystal circuit. I think it was in the 1959 or 60
HANDBOOK. I used a gaseous regulator tube on the screen. It didn't chirp too
badly.........Analog VFO's yes now there is a fun project!


"xpyttl" wrote in message
...
"dave.harper" wrote in message
ups.com...


If you've ever built an analog VFO, these DDS parts are like black magic.
They take little in the way of support circuitry, no fretting about
layout,
no spending weeks trying to work out the temperature compensation, no
moving
around because you breathed on it, you just dial in the frequency you want
and you are spot on.

..