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[AMPS] 6146 high imd/receivers

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Subject: [AMPS] 6146 high imd/receivers
From: (igor rosky)
Date: Sat, 20 Feb 1999 17:45:29 -0800 (PST)
Yes there appears to be some techniques that develop high thrid order
IMD with solid state devices. The modern trend is to use "Feedforward
rather than Feedback" Feedback  being patented back in the  1930s.

The patented feed forward method claims that the single advantage of
feedworward over feedback, is that the error(being distortion) is
corrected while it occurs, rather than correcting for an error  which
has occured and is being transmitted.

Cited advantages for feedforward methods are broadbandwith with 3rd
order imd figures of -60 being a typical minimum. As Carl has said
beeing mostly being used in the digital cell phone business.

Anyway we can just dream on about this being available in ham
equipment. It is the same problem with receiver 3rd order intercept
points, we seem to be stuck on 20dbm 3rd order intercept point. Even
the miserable scanner makers in the likes of AOR have receiver with a
3rd order intercept point of +30dbm. At the current rate of receiver
performance increase in ham equipment, most of us will be dead before
we see a high performance transceiver with a good receiver and
transmitter. Yes the FT 1000MP is lousy, so is the Kachina, sorry of
the subject.

Igor wrote:
> On Thu, 18 Feb 1999 18:09:05 -0800 (PST) igor rosky <>
> writes:
> >
> >
> >
> >I have would also be interested in this area, my 4cx10000 has superb
> >3rd order IMD. The problem is the driver,(all ham radios). My idea is
> >to use  TS830s with a modified 6146, modified for improved 3rd order
> >IMD to drive a 4cx600J(3rd order imd -46 db at 500 watts) then to
> >drive a 4cx10000.
> >
> >My question, has anyone optimized a 6146 for best 3rd order IMD, and
> >what is the typical figure. I would use solid state but typical 
> >driver
> >transistors have very low 3rd order IMD performance.
> There are some interesting developments in SS IMD performance in the
> microwave wireless industry. 
> Using circuitry to sense the IMD and then phase shifting back to the
> input, performance in the area of -50dB is attainable. I do not know
> details but understand it is somewhat involved.
> The TS-830 is a nice xcvr Igor, I use a pair of them here on VHF/UHF
> drive transverters.
> For HF you may want to add a low series R regulator to the screens
of the
> 6146's and the 12BY7A driver. It appears that you will have more than
> enough drive for the 4CX600J so consider reducing the Ep and Es on the
> 12BY7A primarily for longevity. 
> With some fine tuning of the various voltages and currents you can
> around 
> -40dB or better IMD under voice condx. The negative feedback used is
> based upon the Collins design.
> 73  Carl  KM1H
> >
> >On another note i cannot measure the improved 3rd imd of the
> >4cx10000J, its just as good as the plain 4cx10000. I use a HP141t, i
> >might be doing something wrong in the measurment prcocess. I have
> >played with numerous settings of plate/screen and grid volts, but 
> >cant
> >seem to get the improvement. The 4cx600J however is superb with
> >bypassed cathode resistor.
> >
> >Igor 
> >RW3
> >
> >
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