Subject: K2 RX performance
Date: Mon, 29 Jan 2001
From: Dan Presley <email@example.com>
For most multi conversion RX rigs their dynamic range degrades as soon as the offending signals get inside their relatively wide 1st IF roofing filters (anywhere from 10 to 25 kHz wide) and overload their following high gain stages, resulting in desense and intermodulation products. This produces a wide dip in the graph as the signals approach the desired operating frequency.
The K2 on the other hand uses a single conversion approach with its narrow
filters placed early in the RX chain. As a result the graph for the K2 only has
a very narrow dip in dynamic range very close into the desired RX signal.
Hi folks-I wanted to add some 'real world' experience to back this up. I've never been one to pay a lot of attention to receiver performance specs, in part because I never was too sure if I understood what they were saying, or what it really meant to me as a 'user'. For the past 3 years I've been fortunate to be a 'fox' in the qrp-l contest/event ( take your pick!). If you're not familiar with this, it's a 2 hour event held on 40M cw where one station is the designated 'fox', and everyone else tries to work the fox as a 'hound'. It's become very popular with upwards of maybe 2-300 hounds chasing a fox. It's the closest I've ever come to knowing what it's like to
be a dx-type station where everyone is after you. In years past I've used some 'fancy store-bought rigs' with very tight (250Hz) cw filters to sort through the pileups, but what usually happened is just what's described above-overloading, desensing of the receiver and 'blow-by', where it becomes hard to pick anyone out regardless of how tight you filter, passband shift or notch! This year, I used the K2 and noticed an amazing difference-although there were massive pileups calling me, I could hear and distinguish stations far better than in the past. I still could use more filtering; maybe an outboard DSP or audio filter, but the big difference was that as long as I could separate out a station, I could copy him without any overload, distortion, etc. My QSO rate just about doubled from my previous fox runs, and a lot of this I attribute to the fine receiver and design by Wayne & Eric!
A funny anecdote from my last fox run-Mike,KK7GG (K2 owner as well) was with me in the shack for this event, and at one point he said "I don't think you have your filter in its narrowest position (.10)-there's a lot of guys calling" So, I hit the filter switch to kick it back to the widest position. The resultant audio 'blast' caused him to fall backwards out of his chair, and 2 dogs to start barking! There were so many guys calling me that we broke down in laughter-propagation was really good that night :)
Dan Presley-N7CQR-Portland, Or QRP-L #502