[TenTec] dual receive

[Kevin Purcell]

Yes, it's all in the loop design.

The Elecraft K2 is rather smart about this in moving in big steps and  
them tweaking the PLL reference (using a DDS) to move the PLL between  
the big steps.

The RX320 (and I presume the Pegasus and Jupiter?) already uses a  
"big (2.5kHz) step in the PLL" approach which should help them  
tighten up the loop and then fine tunes by moving the passband around  
in the DSP.

But there must be some other changes. I Jupiter schematic would be  
rather helpful!

I was looking at the Sherwood Receiver Test table today

http://sherweng.com/table.html

and noticed that the TT-340 (another similar design, I think) is  
right near the bottom unlike pretty much all the other TT rigs. It  
has a terrible close-in IMD (46dB SFDR) with 5kHz separation. With a  
wide (100kHz - outside the roofing filter) spacing the IMD is very  
good (93dB SFDR). The LO phase noise is not that good either.

This is going to wrap badly ... but the tabs did line up.


MDS	AGC Th	AGC Cmp	BDR	Sens	LO	Spcing	Front End	FiltUlt SFDR-W	Spcing	 
SFDR-N	Spcing
dBm	uV	dB	dB	uV	dBc	kHz	Selectivity	dB	dB	kHz	dB	kHz

Ten-Tec 340	
-123	0.5	3	109	0.4	113	10	B 0.5 Octave	70	93	100	46	5

Ten-Tec 340 preamp on and measured with SSB filter
-133ab	0.13			0.14	


On Oct 3, 2007, at 11:32 AM, Duane - N9DG wrote:

> The same MC145140 PLL chip is used in the 320 as the Pegasus
> (Jupiter too I presume). I think a very similar if not the
> same PLL is used in the Elecraft K2. It's phase noise
> behavior is largely determined by how it is configured. The
> Jupiter was also notably better for phase noise than the
> Pegasus per the ARRL tests. But I've also noticed that my
> early S/N Pegasus does not have the tuning "tick" every 2.5
> kHz like the newer S/N's ones do, or that has been reported
> by Jupiter users. My speculation is that the PLL
> configuration was tweaked slightly to improve phase noise
> performance but in so doing introduced the "tick".

--
Kevin Purcell
kevinpurcell at pobox.com