The Harris DX design, first released in the DX10 in the late 1980s, used
inexpensive plastic switching FETs and was essentially a giant digital
to analog converter. The audio is first converted into digital, some DSP
magic applied, and then a whole lot of series connected modules generate
the carrier directly by turning on and off to create steps. More steps
are on for the positive peaks of carrier frequency and so forth.
Filtering into RF waveform is in the output. The audio is applied to the
gating of these switches, so as to create amplitude modulation, not just
steady carrier. Somewhere I had papers on this;
A basic 1500 watt block had 8 FETS, so at 200 kW they used about 1800
FETS. Combining five of these they made a 1 MW rig and combined two of
these for 2 MW. But the bread and butter design was the 50 kW DX50 which
has morphed into a more recent version as others stated here.
Nearly 100 MW of long wave and medium wave RF power has been supplied
with DX-type transmitters by Harris, according to Tom Yingst, former CEO
of the division. However, this technology has not been extended up into
HF range, as the transistors are not capable of switching at those
rates, at least not economically.
Harris has the honor of owning the DX design; their competitors use PDM
in their SOTA MW transmitters.
John
K5PRO
On 12/18/16 12:28 AM, amps-request@contesting.com wrote:
Message: 2 Date: Sat, 17 Dec 2016 22:57:44 +0000 From: Steve Thompson
> I believe, in transmitters of this type, that the modules aren't
combined in the same way we're used
to in the likes of Quadra, PW-1 or SPE type amps - in the AM txs I think it's
more like the module outputs are connected in series akin to
stacking PSUs to get a higher voltage. Steve
>> That is becoming common practice. Modular transmitters. Just
plug in the modules you want to get the power you want and I
believe they have been hot swappable for some time. .
I had never thought of switching the modules in and out, but at
250 W per step it'd be a pretty smooth transition, albeit they
may do some filtering. I wonder about switching pulses?
73
Roger (K8RI)
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|