In article ,
Mark Conrad wrote:
Wow, thanks everyone for the great reports on
the lttle Yaesu transceiver!
I am contemplating it mainly for its ears.
I wanted to order the optional Collins 300 cycle filter
for CW work, but had hazy memories from 55 years ago
that such filters tended to cause unwanted "ringing"
of the output audio, kinda like a steady loud output "hiss".
Sharp frequency-domain filter cutoff, comes along with blurry
time-domain cutoff... you can't entirely avoid that.
Narrow-bandwidth filters aren't all equal, though, even for the same
-3 dB bandwidth. Different filter alignments cause different amounts
of frequency-domain (pass-band and stop-band) ripple, and different
amounts of ringing and phase shift. Some types seem to be easier on
the ear (and the whole ear/brain system) than others.
Another, more modern approach is to use digital filtering techniques
(either with a DSP chip, or with a personal computer acting as a DSP).
By using finite-impulse-response digital filters, you can get a wider
range of time- and phase-relative behaviors than you can with an IIR
analog filter.
When I left Ham Radio in 1955, the QRPp experts were
playing with "active filters" for low power QRP work.
If I remember correctly, such filters would block _all_ the
signal, noise and everything, then open up a 30 cycle "window"
for a brief while when the "start" of a dot or dash
was liable to occur.
The entire mess, transmitter and distant receiver was sync'd with
the WWV time signal, to open and close the receiver's active filters
during automatic CW transmission.
The incoming dot or dash audio would be re-generated artificially
by a separate audio circuit in the receiver.
QRP advocates claimed they could get on a crowded voice band,
and pump a low power CW signal through at a slow speed
of a few words-per-minute.
This sounds like the "synchronous CW" approach. As you indicate, it
requires extremely careful time-base matching at the sending and
receiving ends.
I do recall reading of some work being done with computer-assisted CW
some years ago. It seems to have lost out in popularity to other
digital modulation modes such as PSK31, which have many of the same
benefits for narrow bandwidth but which don't require
tightly-synchronized clocks.
At the other end of the speed range, are some very-high-speed CW and
digital modes used for things like meteor scatter communications.
Switching Gears -
*********
Does anyone know if the FCC still requires at least 50 RF watts
to legally drive a linear amplifier?
The current standards (Part 97, sections 315 and 317) say:
- Commercially-built amplifiers capable of operating below 144 MHz must
be certificated in order to be sold or modified.
- To be certificated, an external amplifier may not amplify the RF
input signal by more than 15 dB.
- To be certificated, an external amplifier must not amplify signals
between 26 MHz and 28 MHz at all (0 dB gain maximum).
- The above restrictions do not apply to external power amplifiers
which are made by, or modified by, a licensed amateur radio operator
for use at an amateur radio station.
So, yeah, if you want to buy a amplifier which can deliver "legal
limit" power of 1500 watts of HF, you need to plan on driving it with
at least 50 watts or so. If you want a hotter rig, you'll either have
to construct it yourself, modify a commercial amplifier, add an
external intermediate amplifier stage, or cheat.
There was talk that they might change that requirement so that
low power rigs like the Yaesu could drive an amplifier.
Well, low-power rigs *can* drive an external amplifier... just not all
the way up to legal-limit in one step. A 5-watt Yaesu could drive a
15 dB linear amp up to around 150 watts of RF output - this is more
output than most "barefoot" single-box HF rigs are capable of, and is
less likely to accidentally ignite the neighbor's cat than a
legal-limit setup.
--
Dave Platt AE6EO
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