The output of the TS-64 is probably moderate to
low impedance. The input to the IDC or similar
deviation circuit is probably a much higher
impedance.
If you replace your ts-64, you'll probably have
the same results.
You need to place at least a high value series
resistor from the ts-64 output, to the IDC or
modulator (if not an IDC type) input. You'll
notice a post from Juan, which also mentions
the series resistor.
Turn the ts-64 output level pot (if there is one)
up to 3/4 or 5/8 full on.
Couple the output to your idc (modulator) through
a 250K 1/4 resistor and look at the sub tone
deviation on your service monitor. With the
MSR channel element pot set 2/3 or 3/4 cw
rotation (if not previously set), you will note
x-value of sub tone deviation.
You then change the series 250K resistor value to
change the sub tone deviation, using the ts-64
pot for very minor adjustments once you're near
the target sub tone deviation value. If you have
very excessive output level, by all means increase
the resistor to 330K or 470K.
On the www.radiowrench.com/sonic page, I've just
added a really nifty sub tone (PL or CTCSS) generator
circuit made from a 555 timer chip. Don't discount
the circuit, it's actual operation is very good.
The output level of the 555 through the low pass filter
is still overkill. I mention on the instructions, you
can replace the last 270k resistor in the output lead
with a pot and take the output through the pot wiper.
Just increasing the series 270K resistor value does
what I describe above. It's a level adjustment and
a "stage buffer" (isolator) of sorts.
If a sub-tone (ctcss) generator has more than enough
output, you can often use a resistor to reduce the
level and isolate the generators low impedance output
from the IDC (modulator). This is a general rule of
thumb.
If your circuit doesn't have enough output, you'll
need to increase its level with some type of simple
amplifier, followed by the same type of coupling -
isolation method. The resistor or resistor-cap
(the cap provides DC isolation and a bit of rc
filering) circuits are very/most popular.
cheers,
skipp
> "Army Curtis - AE5P" <[EMAIL PROTECTED]> wrote:
> Ah ha!! I have finally found the problem. Skipp and Kevin both
> suggested that I look long and hard at the channel element, and
just
> to be sure, I ordered a new one today from ICM. But that was not
the
> problem ;o) That's okay, as I really would prefer a new ICM element
> anyway.
>
> Went down to the shop tonite to conduct some tests on the channel
> element that Skipp suggested to me, injecting a high level PL tone
> into the PL tone input of the exciter. I figured I would first
> disconnect the TS-64 tone board, and monitor that point with a
scope
> to see exactly what was hitting the "splatter filter" in the
> exciter's audio chain. As soon as I plugged the radio in, I knew we
> had found the problem as the deviation increased several fold. For
> some reason, the TS-64 was pulling down the audio line. Disconnect
> it and now the modulation is clean as a whistle (grin) at 1 KHz to
> over 6 KHz deviation. No distortion is evident on the service
> monitor scope at all.
>
> In thinking back over all the symptoms, the fact that I was seeing
> increasing deviation with increasing audio frequency feeding an
> audio generator directly into the exciter should have been the tip
> off. All of the pre-emphasis I believe is done external to the
> exciter, yet I was seeing obvious pre-emphasis, and could not make
> rated deviation at 1 KHz audio frequency.
>
> I've got several brand new TS-64's on the shelf, and will install a
> new one tomorrow.
>
> To put it mildly, I am really stoked that the problem is finally
> solved. Thanks very much to those who tried to help me with this.
> Ah, life is good!
> 73,
> Army - AE5P
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