On 5/22/2015 8:58 AM, Kevin Stover wrote:
There are NO 12V final amateur transceivers that make -40dB IM3, none. Never
have been, never will be. The best are at -33 to -35.
As Paul said, it can be done. Manufacturers tout receiver figures that
are nonsensical. They are real, they can be duplicated and proven, but
the gain us little to nothing as long as the bands are loaded with -30db
transmitters and worse when they are mis configured, or mistuned. From
what I've read, the 4CX1000, 4CX1500 and the Chinese FU728F should be
capable of better than -40db with a number of the larger tubes like the
4CX3000 (designed for low IM) and other commercial Tetrodes capable of
even better numbers particularly when run at amateur power levels .
Some of the big Triodes are truly impressive. So is their filament power!
As has already been noted, IM-3 is even more important for hams on the
crowded bands. As for the filters, they wouldn't need to be so robust
if the SS finals were not run so hard. Double the number of devices and
the move away from compression would already be noticeable.
That brings two problems with it. Many hams would still push it into
compression to use the new found 3 db while the FCC would balk because
of that reason. That's why the 4CX-3000 amps are not available. Of
course a $1,600 socket dampens the desire for many
Someone got the rig and manufacturers mixed up. The 990 is a Kenwood and
the Yaesu is the FT5000MP with I believe a bit better IM than the
Kenwood. The Yaesu can be run class A, for even better numbers. I run
mine Class A to drive a Tetrode for better than -40db. True, the
FT5000MP is big and heave with a built in AC power Supply and no ability
to run off 12 VDC. I believe they run 50 V on the finals.
Although it costs to add adaptive predistortion, or the fixed
distortion once it becomes commonplace with the development of dedicated
ICs the prices should come down. I doubt it'd run more than 100 or 200
dollars to add to a rig, if that. The problem is not anything the
purchaser could see, or hear unless it might be compliments.
The knowledge, technology and readily available parts are here and all
those useless features on the receivers sound great, but you can't clean
up the other guy's signal. Until the signals are cleaned up these fancy
receivers gain us little.
Instead of adaptive distortion these rigs have added features that let
hams do all sorts of things to the signal except make it cleaner. Today
there is a set of steps to set up a transmitter for ALC, compression,
and gain. Don't follow the steps and that nice sounding signal turns to
garbage.
IF and I emphasize the IF ALL new transmitters had an IM3 of -40db or
greater, how long would it be, before these fancy receivers would start
to earn their keep? 1 or 2 years, or several decades?
A few years back a new ham was complaining about the poor receiver in
his new, top of the line transceiver. Not one person in the group could
convince him that it was the other station's fault. He was so wide his
signal was in the pass bad of the new ham's receiver. He looked at the
specs and still did not, could not, understand why he still heard the
other station.
We balk at spending a little extra to clean up the bands, because it's
the other guy who benefits from our purchase. Now if he could hear the
improvement if the other guy purchased the clean rig... However, back in
the 60s a Collins station (with a clean signal)could easily run 3 or 4
thousand dollars. A good TV set ran as much as $4,000 and reliability
was poor at best with tube changes common place. BTW $4000 in 65 is
$39,798.44 today. That's just shy of $40,000. I purchased a new
Bonneville Convertible for $3,600 that weighed just shy of 6,000#
Few people would consider a $40,000 rig today. With accessories,
amplifier, tuner, tower and antenna that would push the station close to
$75,000. And we grouse about $5,000 to $8,000, but fear not. Icom now
has a $15,000 transceiver on the market. Just think of the difference
in features and what that rig would have cost back then
The band will not get better until the signals get clean.
73
Roger (K8RI)
Those transceivers capable of 200 Watts are all usinng 28 or 50V finals and
can reach -40 depending on the low pass filter used behind the PA.It's time for
the manu's to get rid of this fascination with running evberything off a
battery.
The most expensive part of any SS amp is NOT the finals themselves it's the
LPF that will take 1500 watts and keep harmonics leagl (-43db HF, -60dB 6m).
That's not IM3. Name the amp that hits an IM3 of -40. The 8877 will come close,
the Russian triodes won't, none of the tetrodes will do it.
---
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