[Elecraft] N-gen question

[Robert Friess]

oops, Alan is right.  Brain not engaged.

Bob

On Mon, Dec 31, 2012 at 3:41 PM, Alan Bloom <n1al at sonic.net> wrote:

> Matt,
>
> -174 dBm is the noise of a resistor at room temperature in a 1 Hz
> bandwidth.  In a 500 Hz bandwidth (which seems to be the standard for
> receiver measurements) you get 10 * log(500) = 27 dB more, or -147 dBm
> thermal noise.
>
> So 35 dB excess noise is -147 + 35 = -112 dBm in a 500 Hz bandwidth. With
> a 2.7 kHz SSB filter, it should be -104.7 dBm.
>
> The KX3 S meter may not be accurate for noise.  I expect the AGC tends to
> respond to peak signal level rather than RMS.  That would give a higher
> than expected S meter reading, which is what you observed.
>
> The way to measure the N-gen output is to turn off the AGC, reduce the
> signal level so the audio output is not distorting (using attenuator or
> whatever) and measure the audio output with an RMS voltmeter.  Then connect
> a calibrated signal generator and adjust its output level for the same
> meter reading.  If you don't have a true RMS voltmeter you'll be off a dB
> or two, but it should be in the ballpark.
>
> Alan N1AL
>
>
>
> On 12/31/2012 2:33 PM, Matt Zilmer wrote:
>
>> Couple of questions on the N-gen:
>>
>> 1. The instruction sheet gives "35 dB" of Excess Noise Output.  Is
>> this referenced to -174 dBm or some other?
>>
>> I'm seeing S0 on a KX3 with the switch OFF, and S5-6 with the switch
>> on.  Seems usable.  I have S5 at -97 dBm, S6 at -91 dBm.  So the
>> reference level is around -132 to -126 dBm, if I read this spec
>> correctly.
>>
>> 2. Can someone reference a data sheet for the MAR-1 MMIC?  I'm going
>> to search for it, but thought someone might have it around.
>>
>> The N-gen makes a nice 30 minute build, and is fun.  Parents are still
>> giving me kits even though I'm 55 y/o - because they want to watch me
>> build them - yes, right on the spot in their living room in Tucson.
>>
>> I restrained meself until we got back to SoCal and I had my wrist
>> strap on.
>>
>> Happy New Year to All.
>>
>> 73,
>> matt W6NIA
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