[Elecraft] K3 if isolation of softrock lite used as panadapter

[Larry Phipps]

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 <jeflanders at comcast.net>
> Subject: Re: [Elecraft] K3 if isolation of softrock lite used as
> 	panadapter
> To: "stephen pearce" <pearce.sg at gmail.com>, Elecraft at mailman.qth.net
> Message-ID: <6.2.5.6.0.20080211233327.041bba58 at comcast.net>
> 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
>