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Author Topic: Designing a Clean Linear Amplifier with RF Negative Feedback - Opinions Wanted  (Read 21141 times)
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K1JJ
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"Let's go kayaking, Tommy!" - Yaz


« Reply #25 on: December 16, 2005, 03:55:50 PM »

Another good response below....   

The 4CX-350 is very common comapred to the 'J' model.  Hope he's correct.

T
----------------------------


wc6w@juno.com wrote:
> Hi Tom,
>    That '5106 is probably for Cable TV use and likely cuts off around 40 MHz (on the low end!).
>
>    If I recall correctly, some of the general purpose units that go down to a MHz use numbers from CA28XX group.  They come in both single ended and push-pull versions.

CA2820 and 2830 are good ones, 0.5-1W capability and only a couple of
power line decoupling caps needed. Motorola equilvalents are MHW590 and
592 - these replaced the TRW parts after Mot bought TRW. Many other
CA28** or MHW parts will also suit, but some need external chokes or
transformers. Beware the gain - around 30dB. If you're running about
1-200mW out for linearity, it means only -10dBm in (ideal if you build
your own exciter). If you're going to do that, you could consider going
the whole hog and incorporate polar or cartesian loop feedback.

>    I've seen a few of the 350J's for sale on the web over the years.  I don't believe the demand is very high for those as they have a 26V heater and as such can't be dropped into a 4CX250B socket.  There is also the 4CX600J/JA/JB.

I'd bet that the 'FJ is barely different from a std '350 - just tested
for linearity under class A. They might be a few dB better than 'any
old' '350, but I'd be surprised if the difference was more than a few dB
- not 10 or more.

Steve
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

Wise Words : "I'm as old as I've ever been... and I'm as young as I'll ever be."

There's nothing like an old dog.
K1JJ
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"Let's go kayaking, Tommy!" - Yaz


« Reply #26 on: December 16, 2005, 05:10:20 PM »

Yet another good idea.  Your own shack "spectrum analyzer":

Dave/Ape you were axing about this the other day...

T

-------------------

Hi Tom,

You do have a spectrum analyzer in your shack! Your receiver.
Modulate the transmitter with 2 tones and tune across with your cw
filter on another receiver. Note the level of one of the tones on the S
meter. Then tune to the 3rd order product and note the level difference.
Same thing a spectrum analyzer does.
If you want to get real accurate put a step attenuator in front of the
receiver so you don't depend on S meter calibration.
Now you will have a base to work from.

73
Gary  K4FMX
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Use an "AM Courtesy Filter" to limit transmit audio bandwidth  +-4.5 KHz, +-6.0 KHz or +-8.0 KHz when needed.  Easily done in DSP.

Wise Words : "I'm as old as I've ever been... and I'm as young as I'll ever be."

There's nothing like an old dog.
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