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Sounds interesting! Maybe I can experiment
with this too...
73,
Steve
----- Original Message -----
Sent: Wednesday, April 14, 2004 3:42
PM
Subject: Re: [Repeater-Builder]
Hamtronics exciter
Hi Steve,
I have had good results FM'ing the TA-51 and
TA-451. See here:
http://www.repeater-builder.com/rbtip/ta-51pl_mod.html
While
this mod was only intended for FM'ing the crystal to get adequate PL deviation
with low distortion, I have recently redone my remote receiver projects for
one of my 2 meter machines (4 sites). I used the modification as above
for voice frequencies as well as PL, the difference from the stock modulator
was amazing. While the linearity of the modulator 'as designed' is of no
concern when only one frequency is applied (like a PL tone) I was surprised to
measure quite acceptable response across the entire range from about 10 cycles
to about 5500 cycles. Even though the PM modulator in the UHF exciter
shows better response because it's multiplied several more times then on
low-band or high-band, FM'ing it made it sound so much better.
Obviously, a clipper and low pass filter should be implemented when using any
modulator capable of deviating beyond the acceptable bandwidth of the
particular service/frequency spectrum.
Kevin Custer
Steve
Grantham wrote:
Well... Does anyone think it would be feasible or practical to
modify the TA-51 to implement an LC phase modulator? Just how easy or
how difficult might that be?
Steve
-----
Original Message -----
Sent:
Tuesday, April 13, 2004 9:46 PM
Subject:
Re: [Repeater-Builder] Hamtronics exciter
[EMAIL PROTECTED] wrote:
Hi Kevin,
Virgil mentioned that he had looked at
the manual and noted that the TA-51 uses RC phase modulation. A-ha! The
light went on. You can only get 90 degrees of phase shift max with an RC
circuit. Had they used an LC phase modulator, they would have
gotten 180 degrees max. That's why the deviation is low with that unit.
They don't have much deviation to start with, and as you say, if it
isn't multiplied a lot, it'll be low at the final
freq.
Tell Virgil thanks for the
investigation. Also as a side note from practical experience with
this type of exciter, and as you have mentioned before as well, the tuning
of the first stages after the oscillator are critical for good modulation,
otherwise it will be very distorted.
Kevin
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