[Elecraft] Using the"shielded" XG3

[Edward R. Cole]

I have my XG3 "packaged" in a 6x3x2 inch diecast aluminum enclosure 
with a BNC FF bulkhead adapter and short BNC cable for connecting the 
XG3.  I have not installed a small mini-phone jack for connecting the 
XG3 to computer for external control.  I will post some photos of the 
setup in a few days.

Just a quick (preliminary) test of my 2m transverter+K3 gives me some 
results for MDS:

The DEMI 144/28 transverter is spec at <1 dBNF and 17-dB conversion 
gain.  Inputing this into my pathlink analysis program gives me the 
theoretical MDS (dBm for SNR=0) as -138 dBm using 2.8 KHz bw 
(SSB).  I used -138 dBm as spec for the K3 at 500-KHz bw which 
results in a 9 dBNF for my calculations.  -138 dBm at 2.8 KHz 
compares to a system NF= 1.46 dB

I started with two 20-dB Bird coax attenuators attached to the 
shielded XG3 and determined that I needed to run -33 dBm for the 
signal to be detected, so I changed to a 30-dB JFW step attenuator 
finding that a signal with 25 dB attenuation -(107+25) = -132 dBm 
seemed near to the weakest that I could detect by ear.  With the 
cover off the enclosure I could not reduce the signal lower than that 
by adding more attenuation indicating radiation leakage.  With the 
cover on the enclosure, 30-dB attenuation results in a signal too 
weak to detect by ear - e.g. -137 dBm).

I briefly switched to CW (400-Hz bw) so confirm that improved MDS but 
did not try measuring it.

Note: that these measurements were using my un-calibrated ear as 
threshold detector; a better approach will be using the LP-Pan 
display to quantify measurements or using an audio voltmeter.  I did 
not switch off the AGC for the above, either.  But it does tell me in 
a subjective sense what I can expect from the system (afterall my 
ears do the decoding of CW).

Next step will be inserting the signal at the input of my 2m-eme 
preamps for more rigorous testing (and balancing) in the process of 
setting up dual-pol diversity reception.  With the addition of the 
preamp, system theoretical NF drops to essentially that of the 
preamp  (MDS about -155 dBm at 2.8 KHz bw)  I will need > 48 dB 
attenuation to lower the XG3 -107 dBm signal to that level.  Not sure 
that the shielding will perform that low until I try it.

One interesting sidenote, I tried picking up the XG3 at -33 dBm into 
a rubber duckie antenna held near the transverter and could not 
detect the signal indicating the shielding of the transverter is 
excellent.  My FT-847 and FT-817 clearly hear such a signal with out 
antennas connected.

summary: the XG3 is a really nice addition to my test equipment!


73, Ed - KL7UW, WD2XSH/45
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