I'd like to build myself a small SS QRP CW TX with a broad transmit
frequency range (say 3-10 or 5-15 MHz), and clean output. Something I
could use now on the current ham bands with a CW-capable digital
portable RX, but could forget in a cupboard and use anywhere else if
the need / right arises in n year's time.

Hardwired band limits may look reassuring from a legal standpoint, yet
almost all commercial radios DO let you get into trouble, frequency
wise, so what the heck... + you don't know what the future has in
store.

I figure it would be plenty to put together the following:

- always on VFO

- a couple of quasi-linear _tuned_ (!) amp stages
built around a 3-section variable capacitor

- no bandswitching, no plug in tuning coils
or HRO-style coil drawers

- always-on buffer

- power keying on PA

- electronic QSK

- switched receive-mode VFO-offset cap,
patched it into QSK,
to kick it way off the operating frequency
( and off the _amp_chain_passband_ as well ! )
& fully kill output + avoid any issues
in isofrequency operation

- pi network, PA current meter.

I'd draw the line this side of DDS, with huff-puff to be perhaps added
at a later stage, but I'm open to convincing.

I could sure dream up a circuit, but I wonder where to look for
inspiration. I know e.g. no solid state professional transmitters of
such ilk...

1960's solid state tactical radios perhaps?

Ideas anyone?

SpamHog wrote:
. . .
I could sure dream up a circuit, but I wonder where to look for
inspiration. I know e.g. no solid state professional transmitters of
such ilk...

1960's solid state tactical radios perhaps?

Ideas anyone?

_Experimental Methods in RF Design_, available from the ARRL. Or its
predecessor _Solid State Design for the Radio Amateur_. The latter book
is out of print, but you might be able to find a used copy.

Roy Lewallen, W7EL

"SpamHog" wrote in message
oups.com...
I'd like to build myself a small SS QRP CW TX with a broad transmit
frequency range (say 3-10 or 5-15 MHz), and clean output. Something I
could use now on the current ham bands with a CW-capable digital
portable RX, but could forget in a cupboard and use anywhere else if
the need / right arises in n year's time.

Hardwired band limits may look reassuring from a legal standpoint, yet
almost all commercial radios DO let you get into trouble, frequency
wise, so what the heck... + you don't know what the future has in
store.

I figure it would be plenty to put together the following:

- always on VFO

- a couple of quasi-linear _tuned_ (!) amp stages
built around a 3-section variable capacitor

- no bandswitching, no plug in tuning coils
or HRO-style coil drawers

- always-on buffer

- power keying on PA

- electronic QSK

- switched receive-mode VFO-offset cap,
patched it into QSK,
to kick it way off the operating frequency
( and off the _amp_chain_passband_ as well ! )
& fully kill output + avoid any issues
in isofrequency operation

- pi network, PA current meter.

I'd draw the line this side of DDS, with huff-puff to be perhaps added
at a later stage, but I'm open to convincing.

I could sure dream up a circuit, but I wonder where to look for
inspiration. I know e.g. no solid state professional transmitters of
such ilk...

1960's solid state tactical radios perhaps?

Ideas anyone?


Hello,

Try to get hold of an HW8, an old Heathkit QRP CW Transceiver.

Lots of modifications and/or extensions can be found on the internet.

Use an old RC4 (Drake) for listening. With some effort, you can let those
two rigs transceive.

Plenty of projects around that idea!

Have fun.

I was poring over a HW-9 schematic already.

Very cool, cept it's anything but broad range: doubler/tripler, mixers,
LOs, all sorts of acrobatics that cut down the number of components but
make the whole more inflexible.

Right now I am thinking about using:

- a signal generator

- 1 driver and 2 or 3 massively derated finals in parallel, all AB
class or so, with broadband RF transformers, i/o at 50 ohm or so

- perhaps a bit of negative feedback

- putting all the filtering at the end, such as 3 tank circuits with
3-section VC + pi network; doing so would possibly simplify the
mechanics of providing effective shielding.

"SpamHog" wrote in message
oups.com...
I was poring over a HW-9 schematic already.

Very cool, cept it's anything but broad range: doubler/tripler, mixers,
LOs, all sorts of acrobatics that cut down the number of components but
make the whole more inflexible.

Right now I am thinking about using:

- a signal generator

- 1 driver and 2 or 3 massively derated finals in parallel, all AB
class or so, with broadband RF transformers, i/o at 50 ohm or so

- perhaps a bit of negative feedback

- putting all the filtering at the end, such as 3 tank circuits with
3-section VC + pi network; doing so would possibly simplify the
mechanics of providing effective shielding.


I have no idea in what the HW-9 differs from the HW-8 in the transmitter
stages.

I know the receiver of the HW-9 is more elaborate than the direct reception
of the HW-8.

I do not feel comfortable with broadband signal generators in transmitters
since they tend to be noisy and jittery.

To some extend, it could work on FM, but I doubt the results will be worth
anything in SSB.

Signal generators produce also lots of spurious; filtering at the end stage
will be a real challenge.

I still have the intention to use the "inj." output of a Drake R4B, mixed
with the output of an x-tal oscillator (somewhere around 6 MHz, I don't
remember exactly) to send on the frequency the R4B listens on.

With some fiddling, you could find in every receiver a frequency to mix with
a fixed oscillator to get the same effect.

The resulting signal will need filtering before any amplification, so much
for your wish to go broadband!

On the other hand, filtering over a broad band at the end stage is OK only
if you intend to use a dummy load at all times (HI). A real antenna will not
present the required impedance over the entire frequency range to the output
of your filter. The garbage you intended to filter will only be partially
taken care of.

So you see, quite a challenge!

Points taken! Never really looked at quality in a signal generator. U
never stop to learn. Signal level garbage in - AMPLIFIED garbage
out.

A clean VFO or DDS + a tank circuit ahead of the PA looks like a much
better idea.

I have looked at a number of broadband amp designs, and it seems that
they share a real concern with cleanliness:
- linear amplification
- negative feedback (some even DC coupled)
- sometimes push-pull with matched devices.

As far as antenna matching is concerned, I'd first align the cascaded
tank circuits into a dummy load, and never operate without a tuner.

All this considered it looks like broadbanding requires choices that
together lead to a low power efficiency.

------

Now, re. filtering output with cascaded LC tank circuits, I have a
question stemming from this being the toroid era.

In the old days, multiple capacitor-tuned LC circuits in series could
be aligned over broad tuning ranges by means of slug adjusted coils and
small capacitive trimmers. It was a bit of an art, but satisfactory
alignment was possible.

But you can't easily trim a toroid.

When handling say up to 5 watts RF, do I already have to fear
saturation in IF-type, ferrite-tunable canned coils?

Or, does anyone ever put a small L of that kind as an indictive trimmer
in series with a toroid?