Setup: Flex 5000A, Power SDR 2.0.16, Win XP/SP2
I use my Flex 5000A now and then on AM when I don’t feel the urge to
fire up my big plate modulated rigs. Naturally, I was curious how the
Flex looks on my scope in the AM mode. I was pleasantly surprised at how
the Flex could handle the asymmetry in my voice and produce very healthy
looking positive peaks without nearing the baseline. Performance on the
test bench was equally impressive. The Flex 5000A passes triangle waves
cleanly from 10 cps to over 5000 cps in the AM mode. My plate modulated
rigs can’t do that! The biggest surprise came when I ran a 1000 cps sine
wave through the Flex. It cleanly reaches 125% in the positive direction
before it reaches the baseline. Normally, an AM transmitter will reach
100% positive and 100% negative simultaneously when fed a sine wave.
Broadcast stations use expensive processing equipment to limit negative
peaks to achieve asymmetry like this. I’m not aware of any Inovonics
processing equipment inside my Flex 5000A, so this has me wondering how
the asymmetry was achieved. Note that the Power SDR compander and EQ
were not active during the triangle wave and sine wave measurements.
1. Is this asymmetry common in all Flex 5000A’s or is mine extra special?
2. Is this a result of hardware or software?
3. Is this a symptom of possible I/Q imbalance?
Don’t get me wrong, I like the concept of asymmetry in the AM mode (as
long as it’s heading in the positive direction) and I don’t view this as
a problem. I’m just curious how it was achieved.
73,
Rob W1AEX
Picture sine wave test:
http://members.cox.net/w1aex.fn31/flexsine.jpg
Picture triangle wave test: http://members.cox.net/w1aex.fn31/flextri.jpg
Video sine wave test: http://www.youtube.com/watch?v=1gNsWl8BBD0
Video triangle wave test: http://www.youtube.com/watch?v=UpoCipk-U08
--
One thing I'm certain of is that there is too much certainty in the world.
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