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
======================================
BP40IQ   500 KHz - 10-GHz   www.kl7uw.com
EME: 50-1.1kw?, 144-1.4kw, 432-100w, 1296-testing*, 3400-?
DUBUS Magazine USA Rep [hidden email]
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