I have not found that to be the case. I tried a number of MMICs and
found them lacking in the kind of reverse isolation needed for this job.
I use the same device in my LP-PAN panadapter as K8ZOA uses in his
Z10000 buffer. I am seeing >100dB isolation of the LO signal from my
panadapter, which uses a mixer that is roughly similar to the SoftRock.
Since my IF is at 8215 kHz, any LO leakage would be seen at the center
of the panadapter display. In my case, the leakage signal is below the
noise floor. With a SoftRock, the leakage signal would appear 23 kHz
away from the K3 IF.
I wouldn't use a SoftRock without a buffer, and if I did, I would sure
make sure it was disabled during xmit. For reference, I measured LO
leakage of a SoftRock on the order of -40dBm, which translates to over
S9+30dB.
It was also mentioned about filtering the stuff coming out of the K3 IF
port. In my testing, I have found that additional bandpass filtering
between the K3 IF and buffer are definitely required to avoid spurious
mixing products between signals in the K3 BPF passbands and the internal
signals coming out the essentially unfiltered K3 IF port (mostly LO and
its harmonics). This is especially the case on 40m where a lot of strong
signals can appear in the passband. I have found a 4th order bandpass
filter to be acceptable for this task.
73,
Larry N8LP
Message: 48
Date: Mon, 11 Feb 2008 23:46:27 -0500
From: Jerry Flanders <[EMAIL PROTECTED]>
Subject: Re: [Elecraft] K3 if isolation of softrock lite used as
panadapter
To: "stephen pearce" <[EMAIL PROTECTED]>, [email protected]
Message-ID: <[EMAIL PROTECTED]>
Content-Type: text/plain; charset="us-ascii"; format=flowed
I assume a simple MMIC amp plus a simple resistive attenuator circuit
will provide enough isolation and also provide for matching levels
up/down as may be necessary. At least, that will be my first cut at
the problem unless somebody else comes up with a better plan before
my K3 arrives.
At down east microwave ( http://www.downeastmicrowave.com/cat-frame.htm ),
see the
<http://literature.agilent.com/litweb/pdf/5967-6159E.pdf>INA10386
(DC-2GHz, 24dBG, 3.5dB NF +14dbm 1dB Gain compression ) for only $5.
Very easy to use something like this, I think.
Depending on the signal level of the K3 IF output, we might get
enough isolation from a resistive attenuator alone and still have a
usable signal level on the softrock panadaptor.
I would much prefer a plug and play manufactured solution if it takes
more than an attenuator, but not an expensive one.
Jerry W4UK
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