Low Power RTTY Output

[Nelson Moyer]

When I connect my Hal DXP38 AF Out to the K3 Line In, I get a maximum of 20
watts RF output, even when the TX Level pot on the DXP38 is set for maximum
output, MIC SEL is set to Line In, PWR is set to 100 watts, and Line is set
to 60 (max setting available). I see no ALC bars.

When I connect the DXP38 AF Out to the rear mic jack, I get 100 watts RF
output and 6 ALC bars with MIC SEL set for rP.L, PWR set for 100 watts, and
the mic gain set to 15.

Apparently the K3 Line In is designed to support sound card digital inputs,
so if you're using an external box for AFSK RTTY, you may have to use the
rear mic input to get full RF power output. I didn't try the front mic
input, but presumably it would be the same as the rear mic input.

I reported the low power problem using Line In for RTTY to Wayne a couple of
weeks ago, but I didn't get a response. I'm curious about why there is such
a difference between the maximum achievable RF output on RTTY when using the
line input (max line gain of 60 for 20 watts RF and no ALC indication) vs.
the rear mic input (mic gain at 15 for 100 watts RF and 6 bars of ALC). The
output level from the DXP38 is the same to both ports, so obviously, the K3
Line In has a much lower maximum level than the Mic In. Is this something
that can be addressed in a software upgrade?

Nelson, KU0A

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[MontyS]

Your conclusions are right-on.  Because so many more of us use soundcards
than DXP38s (which were designed to plug into mic jacks) I hope there will
be no firmware change forthcoming.  Two different source levels, 2 different
inputs. You have 2 mic jacks so you can have your mic on one and the DXP38
on the other.

73 - Monty  K2DLJ

Apparently the K3 Line In is designed to support sound card digital inputs,
so if you're using an external box for AFSK RTTY, you may have to use the
rear mic input to get full RF power output. I didn't try the front mic
input, but presumably it would be the same as the rear mic input.

I reported the low power problem using Line In for RTTY to Wayne a couple of
weeks ago, but I didn't get a response. I'm curious about why there is such
a difference between the maximum achievable RF output on RTTY when using the
line input (max line gain of 60 for 20 watts RF and no ALC indication) vs.
the rear mic input (mic gain at 15 for 100 watts RF and 6 bars of ALC). The
output level from the DXP38 is the same to both ports, so obviously, the K3
Line In has a much lower maximum level than the Mic In. Is this something
that can be addressed in a software upgrade?

Nelson, KU0A

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[Iain MacDonnell - N6ML]

Nelson Moyer wrote:
> When I connect my Hal DXP38 AF Out to the K3 Line In, I get a maximum of 20
> watts RF output, even when the TX Level pot on the DXP38 is set for maximum
> output, MIC SEL is set to Line In, PWR is set to 100 watts, and Line is set
> to 60 (max setting available). I see no ALC bars.

OK, so you're not supplying enough audio.


> When I connect the DXP38 AF Out to the rear mic jack, I get 100 watts RF
> output and 6 ALC bars with MIC SEL set for rP.L, PWR set for 100 watts, and
> the mic gain set to 15.

Now you are supplying enough audio.


> Apparently the K3 Line In is designed to support sound card digital inputs,

Yes.


> so if you're using an external box for AFSK RTTY, you may have to use the
> rear mic input to get full RF power output. I didn't try the front mic
> input, but presumably it would be the same as the rear mic input.

If your external box is designed to drive a mic-level input, then it
needs to be connected to a mic input. If you only have the line-level
input available, you might have to look at an audio pre-amp to bring
the level up.


> I reported the low power problem using Line In for RTTY to Wayne a couple of
> weeks ago, but I didn't get a response. I'm curious about why there is such
> a difference between the maximum achievable RF output on RTTY when using the
> line input (max line gain of 60 for 20 watts RF and no ALC indication) vs.
> the rear mic input (mic gain at 15 for 100 watts RF and 6 bars of ALC). The
> output level from the DXP38 is the same to both ports, so obviously, the K3
> Line In has a much lower maximum level than the Mic In. Is this something
> that can be addressed in a software upgrade?

It's not an RF level issue - it's an AF drive level issue. I'm sure the
mic input on the K3 goes through a pre-amp that the line-level input
does not. I don't know if there's any room for more gain in the line in
or not, but the real answer is to either use the Hal box with the mic
input as it was designed to be used, or use an external pre-amp, IMO.

     ~Iain / K6IAM

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[KK7P]

The LINE IN has a hardware attenuator so that soundcard outputs won't be
set to very low levels. This is to help protect against noise pickup on
LINE IN.

If the DXP-38 can't drive the K3 LINE INPUT, then you either need to
boost the signal or use a mic input with proper precautions for ground
loop isolation, etc. The DXP-38 may have an option via internal jumper
to increase its output level.  My DXP-38 and its manual are outside my
lab at the moment so I can't easily check this.

73,

Lyle KK7P
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[KK7P]

> ...Do I use O.C. or +5V for the FSK setting?

The K3 would like to be driven with an open collector.

73,

Lyle KK7P
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