Did the audio go through a LPF for the phasing unit?
Remember that a square wave is made up of the sum of many harmonics -
most of these will have been removed and the amplituyde of the
fundamental may not be that large.

Richard


andreas magun wrote:
Hi,

I have assembled a T2 phasing exciter (KK7B) and looked
at its output spectrum with a spectrum analyzer.

When pumping the exciter with quadrature sine wave signals it
works as expected (output power roughly 3 mW, sideband supression
better than 40 db).

However, when pumping with quadrature squarewave
signals of approximately the same power, the output power
drops by a factor of at least 20 db! I would have expected
much more power, similar to that obtained with sine wave pumping.

The quadrature phase signal was generated with a 74F74, the
quadrature signals being attenuated to give a power of approx. 10 dbm
and output impedances of approx. 50 Ohms.

There must be an explanation.

Thanks
Andreas

Thanks for replying.

The problem, was that I had not enough LO-power from the 74F74 outputs.
I have buffered them with a 50 Ohm TTL Driver 74AS804 that could deliver
plenty of current into the LO-inputs. I have limited it to approx 10 mA
by a series resistor of 300 Ohm. At a voltage drop of approximately .550
mVpp across the LO-inputs (approx. 5 mW) the exciter works now as expected.

Andreas

Richard Hosking wrote:
Did the audio go through a LPF for the phasing unit?
Remember that a square wave is made up of the sum of many harmonics -
most of these will have been removed and the amplituyde of the
fundamental may not be that large.

Richard


andreas magun wrote:

Hi,

I have assembled a T2 phasing exciter (KK7B) and looked
at its output spectrum with a spectrum analyzer.

When pumping the exciter with quadrature sine wave signals it
works as expected (output power roughly 3 mW, sideband supression
better than 40 db).

However, when pumping with quadrature squarewave
signals of approximately the same power, the output power
drops by a factor of at least 20 db! I would have expected
much more power, similar to that obtained with sine wave pumping.

The quadrature phase signal was generated with a 74F74, the
quadrature signals being attenuated to give a power of approx. 10 dbm
and output impedances of approx. 50 Ohms.

There must be an explanation.

Thanks
Andreas

On Mon, 07 Mar 2005 17:47:56 +0100, andreas magun
wrote:

Thanks for replying.

The problem, was that I had not enough LO-power from the 74F74 outputs.
I have buffered them with a 50 Ohm TTL Driver 74AS804 that could deliver
plenty of current into the LO-inputs. I have limited it to approx 10 mA
by a series resistor of 300 Ohm. At a voltage drop of approximately .550
mVpp across the LO-inputs (approx. 5 mW) the exciter works now as expected.

That is good to hear. I've had excellent results with T2 using
squarewave drive.

Allison