[Elecraft] XV-144 with high NF?

[Don Wilhelm]

  Bob,

Armed with that information, you might want to re-visit the calibration 
data for your NF measurement equipment - the two measurements do not 
support each other.

73,
Don W3FPR

On 12/5/2010 9:14 PM, Bob DeVarney W1ICW wrote:
> I guess I'm not going to worry too much about it.
>
> I just did a MDS measurement with my HP Service Monitor. MDS was 
> around -157 dBm in 400 HZ bandwidth. Preamp on, AGC off. My HP 8921 
> only goes down to -137 dBm do I added a 20 dB pad in line to get down 
> to -157 dBm. Still barely audible in the headphones at that level.
> I set the rf preamp bias to 40 mA=188 mV at TP2, and tweaked C1 for 
> best S/N at -157 dBm and I think I'll call it good.
>
> Thanks for the sanity check, Don.
>
> I've been trying to find a culprit for missing a couple juicy EME 
> dxpeditions lately, but I guess I can't blame it on the receiver just 
> yet.
>
> 73,
> Bob W1ICW
>
> On 12/5/2010 7:50 PM, Don Wilhelm wrote:
>>  Bob,
>>
>> I do not have calibrated Noise Figure measurement tools, so I do a 
>> quick assessment of the XV transverters using the calibrated 
>> attenuator output of my HP8640B signal generator, which will go down 
>> to -140 dBm.  I view the K2 output on Spectrogram and use a 400 Hz 
>> bandwidth.  With a properly functioning XV144, I normally can see the 
>> signal at 10 dB or more above the receiver noise floor.
>>
>>  MDS = -174 +10(log Bandwidth) + NF + SNR
>>
>> If I assume the SNR is zero (yes that will give the worst case NF)
>> The 10(log Bandwidth) value is 26 dB for a 400 Hz bandwidth
>> The implied MDS of a signal seen 10 dB above the noise floor is -147 dBm
>> That measurement further implies a NF of less than 1 dB, which is 
>> within specification.
>>
>> I would suggest you do a similar MDS measurement as a quick sanity 
>> check on your NF measurements.
>>
>