[Elecraft] KX3 and FLDIGI

[Mark]

Lyle KK7P wrote:
"The IQ output is not processed by the DSP.  A signal above OR below the 
carrier will show up.  There is no opposite sideband rejection."

I think the point of Lyle's response was missed.  Signals in both sidebands will be displayed on the FLDIGI waterfall! 

What does this mean?  If you have the KX3 tuned to 7.100, and you see a signal on the waterfall at 7.102, that station may actually be on 7.102 as displayed on the waterfall, which is OK since FLDIGI will then transmit back to the station on that frequency.  But if the station is actually on 7.098, it will still be displayed at 7.102 on the warerfall, but FLDIGI will then transmit on 7.102 since it doesn't know which sideband the signal is in.  You will end up transmitting 4Khz above the other station's frequency.

Why doesn't SDR software have the same problem?  Because SDR software uses the phase information in the In-phase and Quadrature signals to determine which sideband the signal is in.  

Using the phone jack for FLDIGI allows the SDR routines in the KX3 DSP to do this, thereby eliminating the signals in the unused sideband.

I hope that makes some sense.  Unfortunately, this can be difficult to explain via email.


Mark
KE6BB

-------- Original message --------From: Lyle Johnson <kk7p4dsp at gmail.com> Date: 12/2/16  12:57 PM  (GMT-08:00) To: elecraft at mailman.qth.net Subject: Re: [Elecraft] KX3 and FLDIGI 
Kevin,

The IQ output is not processed by the DSP.  A signal above OR below the 
carrier will show up.  There is no opposite sideband rejection.

A signal from the headphone jack will have the opposite sideband removed 
or significantly reduced in amplitude.

73,

Lyle KK7P


> On 12/2/2016 2:43 PM, Kevin - K4VD wrote:
>> When using the KX3 with fldigi can I use the RX I/Q output from the 
>> radio
>> to the computer? I can't find any reference to i/q in the fldigi docs so
>> I'm assuming the answer is no but thought I'd ask before giving up.

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