A simple substitute of the RD15HVF1 for the IRF510 (different pin-out!) makes the rf amp capable of at least 30 MHz. ?The IRF510 becomes very inefficient over about 20 MHz.?
Dr.?William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ
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Big Signal Ranch ¨C K9ZC
Staunton, Illinois
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Villa Grand Piton - J68HZ
Soufriere, St. Lucia W.I.
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On Oct 28, 2017, at 12:28 AM, John Backo via Groups.Io <
iam74@...> wrote:
Smitty:
Yes; it can be done.
Check each and every band for birdies.
Check out the HRI DDS v.4 for a dual mcu DDS
that uses the second mcu to control bandswitching.
You will have to modify that for the Si5351 instead of the
AD9850 for the DDS. But you are not alone.
With the present BITX40 board configuration, it is unlikely
that the IRF510 will go very well above 17m or so.
Figure out a layout with a separate PA and relay controlled
LPFs. The BPF configuration is much simpler...probably
one or two circuits will do.
Check out the Minima and uBITX designs to see what problems
have already been run into...designing a multi-band superhet is
not exactly simple. There are a lot of variables.
But it can be done with a BITX40 board as the basis. Go for it.
Build and MEASURE; work with blocks that fit together for a whole.
The easiest thing to do is design everything with a 50 ohm in/out
impedance. Then everything matches.
john
AD5YE
K9HZ