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Low power transmission gets distorted


Rafael Diniz
 

HI everybody,

When transmitting an OFDM signal with 8W until 10W with the ubitx v6,
the output signal is crystal clear, but when I start to reduce the
signal level (from a line-out of a computer), at 6 or 4W, the signal
gets very distorted. Am I doing something wrong?

Rafael PU2UIT


 

Hi,

I would guess that at too low of audio input, you don't have enough drive for the modulator.

Instead, once you have a good level for a clean signal, you might want to try adjusting RV1 so the amp output is lowered.

73,


Mark


Arv Evans
 

What method are you using to reduce the signal output?
_._


On Fri, Feb 26, 2021 at 1:20 PM Rafael Diniz <rafael@...> wrote:
HI everybody,

When transmitting an OFDM signal with 8W until 10W with the ubitx v6,
the output signal is crystal clear, but when I start to reduce the
signal level (from a line-out of a computer), at 6 or 4W, the signal
gets very distorted. Am I doing something wrong?

Rafael PU2UIT








Rafael Diniz
 

We built a 4.7 db attenuation circuit to connect to a MRF amp. Not what
we want, definitely.
; )

On 2/26/21 6:11 PM, Arv Evans wrote:
What method are you using to reduce the signal output?
_._


On Fri, Feb 26, 2021 at 1:20 PM Rafael Diniz <rafael@rhizomatica.org
<mailto:rafael@rhizomatica.org>> wrote:

HI everybody,

When transmitting an OFDM signal with 8W until 10W with the ubitx v6,
the output signal is crystal clear, but when I start to reduce the
signal level (from a line-out of a computer), at 6 or 4W, the signal
gets very distorted. Am I doing something wrong?

Rafael PU2UIT








Rafael Diniz
 

Hi Mark,

I think you are right. What is the RV1?

(sorry the newbie question)

Rafael

On 2/26/21 6:09 PM, Mark - N7EKU wrote:
Hi,

I would guess that at too low of audio input, you don't have enough
drive for the modulator.

Instead, once you have a good level for a clean signal, you might want
to try adjusting RV1 so the amp output is lowered.

73,


Mark


 

RV1 is power output control, see PCB - not the blue twins, those are bias.

Raj

At 27/02/2021, you wrote:
Hi Mark,

I think you are right. What is the RV1?

(sorry the newbie question)

Rafael

On 2/26/21 6:09 PM, Mark - N7EKU wrote:
Hi,

I would guess that at too low of audio input, you don't have enough
drive for the modulator.

Instead, once you have a good level for a clean signal, you might want
to try adjusting RV1 so the amp output is lowered.

73,


Mark


Rafael Diniz
 

Thanks!!

On 2/27/21 7:41 AM, Raj vu2zap wrote:
RV1 is power output control, see PCB - not the blue twins, those are bias.