[Moon-net] 2 receivers with the same antenna

[Edward Cole]

At 09:38 AM 11/17/2007, Edward Cole wrote:
>At 07:44 AM 11/17/2007, Gabriel - EA6VQ wrote:
> >Hi,
> >
> >Might be this is a silly question, but I can't find very much information
> >about this subject using Google.
> >
> >What is the right (lowless) way to connect two 144 MHz receivers to a single
> >antenna?
> >
> >I want to make some tests comparing the reception of my usual receiver
> >against an SDR-IQ receiver. What kind of splitter should I use?
> >
> >73. Gabriel - EA6VQ
>
>Gabriel,
>
>I tee the output of my second preamp (which is in the shack) and run
>two RG-58 lines: one to the FT-847 and the other to the 2m/28 MHz
>converter in front of my SDR-IQ.  The mismatch doesn't bother the
>sensitivity of the radios due to 31 dB gain of the two cascaded
>preamps that precede them.  My mgf-1801 (0.15 dBNF, 16.8 dBgain)
>preamp is at the tower-top and the ARR P144VDA (3SK48) (~1 dBNF, 14
>dBgain) is in the shack with 170 feet of LMR-400 between the two
>preamps.  My 2m converter is the DEMI 144/28 xvtr. with about 1 dBNF
>and 15 dBgain, followed by a 18 dB gain wide-band IF amp before the SDR-IQ.
>
>
>73,
>Ed - KL7UW
>======================================
>   BP40IQ   50-MHz - 10-GHz   www.kl7uw.com
>144-EME: FT-847, mgf-1801, 4x-xpol-20, 185w
>DUBUS Magazine USA Rep dubususa at hotmail.com
>======================================

One more comment, Gabe,

I measured the sensitivity of both radios in this setup by inserting 
a signal generator in the input of the second preamp with a 66 dB 
attenuator so I could get low enough signal levels to resemble 
eme.  I found the FT-847 system sensitivity to be - 152 dBm using 
SpectraJT to display the signal.  The SDR-IQ sensitivity was -166 dBm 
with similar RBW running winRad.  But, operationally, I do not run 
the SDR-IQ RBW that narrow for eme.

This was the subject of my paper for CSVHF this year:
http://www.kl7uw.com/SDR.htm

So in general the two receiving systems are equally sensitive to eme 
signals.  I generally find my lower signal threshold is about -28 on 
JT65B and this is typically produced by a single-yagi station with 
600w.  This is about equivalent to my station ERP.  My "normal" eme 
reception limit is about 1kW for single-yagi stations, (typ -27 to 
-25 on JT65B).


73, Ed