[Elecraft] TX Test Mode garbage

[Bob McGraw K4TAX]

Hasn't anyone done any real measurements of this phenomenon? Just 
because it is heard doesn't make it bad or in violation of the FCC 
Spectral Purity of Emissions.    And it is generally reported to be 2.7 
kHz wide, i.e. the same as the SSB filter.

In measuring my K3S, s/n 10163, the worst case is - 42 dBm at the test 
frequency.  I did check several bands and found the same result.  In all 
cases, it is evident the low pass transmit filter is doing its job as 
there is more TX noise below the transmit frequency than above.  My 
measurement indicates the noise is in the -60 dBm to -70 dBm range, 
depending on band.    There are some other emissions which are -85 dBm 
{~15.9 MHz}  and -91 dBm {~31.9MHz}.  These are seen within a span of 
1..0 MHz to 50 MHz on the HP spectrum analyzer, connected directly to 
the output of the transceiver, ANT 1 port.  The K3S is in CW mode, Test 
Mode, keyed with a straight key.   As to seeing power on an external 
device, at these levels, it likely won't be observed.  Further I observe 
when the PWR is reduced to zero watts, the emissions do not change 
except at the point when the KPA switches out {~ <12 watts} , there is 
about a 10 dB decrease as expected.

All in all, I'd say the radio is quite clean with regard to my 
measurements and spectral purity.

73

Bob, K4TAX


On 7/26/2017 10:00 PM, EUGENE GABRY wrote:
> Out of curiosity I just checked this with my K3S and found the same oddity. During CW key down into a dummy load in TX Test mode the K3S draws 2.5 amps from the 1 amp in RX, and the hash signal heard in another receiver into a different dummy load appears to be 2.7Khz wide. Starts out as full scale signal in the receiver and drops quickly to S5 but never goes away during key down. Cant detect any power indication on the dummy load power meter during key down. Maybe a pre driver stage getting bias in TEST MODE?
> Interesting...
>
> Gene
> N9TF
>