[Elecraft] K2 KX1 K1 More advice sought on Elecraft radios
Happy New Year 2009 everyone! Thanks for your answers so far. Yes, I was aware that Wayne N6KR designed both the 40A and K2. I was simply amazed to receive an offline email from him, given the demands on his time! I asked Wayne if I could share the following: Wayne wrote that he “optimized the NorCal 40A for best noise figure by using ideal coupling to a gilbert-cell multiplier (NE602). Normally the exceptionally low MDS of the '40A (around -143 dBm) would be wasted on 40 m, but with short, low-gain, tuned whips, it could make a difference because the antenna is very lossy.” “Contrast that to the average 40-m station, which uses a full-length 40-m dipole, or -- noisier still -- a 40 m ground plane. In this case the noise floor is probably 15-20 dB higher than the short whip, so the MDS of the receiver won't matter. At least on 40 m.” “While the low NF of the NC40A is nice, the NE602 is a very weak mixer, so it can't be used in the front end of a high-performance rig like the K2 or K3. Thus these rigs use switching mixers. The K2 uses a conventional diode mixer and preamp, resulting in an MDS of about 6 dB worse than the 40A, but about 20 dB better dynamic range. The K3 uses a custom, low-loss switching mixer and an extremely low-noise preamp and synthesizer, so its MDS is only a few dB worse than the 40A's. But its dynamic range is 10-20 dB better than the K2, and thus 30-40 dB better than the 40A! “ What I am trying to grasp now is -- what is the relationship between the MDS and the blocking dynamic range and third-order IMD dynamic range in terms of listening experience? Also, how does the absolute IMD level, and the difference between IMD level and blocking level translate into the listening experience? Is a lower relative IMD level a quieter radio? I have the sense that the depth of the IMD level and the delta between IMD level and blocking level create a quieter experience? I’m looking at “QST Product Reviews: A Look Behind The Scenes” QST October 1994, pp. 35 figure 2 found on the Elecraft site. If two radios with the same absolute BDR and IMD dynamic range but different MDS levels would one want the lower MDS? If the 703+ has an IMD level of -50? this is between the 40A -68? and the K2(-41?)/K3(-34?) both higher, what does this indicate? Wayne also explained: “Once you have full-size antennas up, MDS will no longer be the limitation. You'll need better dynamic range “ Can someone help me understand these receiver comparison concepts? Are these right? NC40A -143 mds ? bdr 75 imd Imd level -68 Blocking level K2 -136 mds 126 bdr 95 imd Imd level -41 Blocking level -10 K3 -138 mds 140 bdr 104 imd Imd level -34 Blocking level -2 703 -141 mds 122 bdr 91 imd Imd level -50 Blocking level -19 K1 Mds 40A and K2 ? KX1 Mds 40A and K2 Best, Dan Perez AD1P ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] K2 KX1 K1 More advice sought on Elecraft radios
I can only compare the K1 and the K2. They are both great kits, but after that they don't really compare. The K2 is a full-featured rig, and the K1 is a special-purpose, trail-friendly CW rig. The K1sounds great, and has filters, and what it does, it does very well. I don't notice any difference in MDS. However, I tried, once, to use my K1 at our club's Field Day, near a high-power station. It was completely swamped by anything transmitting even two bands away. In contrast, the K2 is happy with another station on the same band, as long as the antennas aren't too close and there's some space between the frequencies. I think your numbers for the 703 are way too good. Look at the rig comparison chart on the Elecraft site -- the numbers are pulled from ARRL reviews, for the most part. Unfortunately, the K1 and KX1 aren't there, but the 703 is. Peter N8MHD ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
Re: [Elecraft] K2 KX1 K1 More advice sought on Elecraft radios
Thanks Peter, I used Lab Receiver Test Data Comparisons (ARRL QST Review Data, plus some data from Sherwood Engineering). Using preamp on and 20 kHz spacing (as 20kHz only available for 703 ip3) MDS – IMD dynamic range = IMD level [ -141 - 91 = -50 dBm] MDS – BDR = blocking level [-141 – 120 = -21 dBm RIG is 703 MDS (dBm) -131 preamp-off) -141 (preamp-on) BDR 'Desense' 95 5 kHz spacing pre-amp off 122/120 20 kHz spacing pre off / on IMD DR3 'Intermod' 76 5 kHz spacing pre-amp off 89/91 20 kHz spacing pre off / on Ip3 (dBm) +11/+1.920 kHz spacing pre off / on +56/+47 Ip2 (dBm) Out of band Signal Rejection pre off / on Best, Dan Peter Wollan wrote: I can only compare the K1 and the K2. They are both great kits, but after that they don't really compare. The K2 is a full-featured rig, and the K1 is a special-purpose, trail-friendly CW rig. The K1sounds great, and has filters, and what it does, it does very well. I don't notice any difference in MDS. However, I tried, once, to use my K1 at our club's Field Day, near a high-power station. It was completely swamped by anything transmitting even two bands away. In contrast, the K2 is happy with another station on the same band, as long as the antennas aren't too close and there's some space between the frequencies. I think your numbers for the 703 are way too good. Look at the rig comparison chart on the Elecraft site -- the numbers are pulled from ARRL reviews, for the most part. Unfortunately, the K1 and KX1 aren't there, but the 703 is. Peter N8MHD ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
RE: [Elecraft] K2 KX1 K1 More advice sought on Elecraft radios
It's true that linearity and low noise are often sacrificed for larger dynamic range. How much we sacrifice for the performance we need is a tradeoff that is has been with us for a very long time: ever since passive detectors like crystals and electrolytic detectors were replaced by the Audion and its successors. The common regenerative detector is not only wonderfully sensitive - matching most of the modern receivers available today - it produces a clean, crisp audio that is hard to beat. That is, on CW. The common form we usually see in the old handbooks was a triode grid leak detector made to regenerate. They were not very linear when demodulating A.M., but they usually sounded better than most of the superhet receivers of their day, and better than many today. The underlying problem with a regen, as with any tuned radio frequency (TRF) receiver, is that they are either fixed in frequency with exotic input filters to provide good selectivity or they are tunable with less complex input filters and have fairly poor selectivity compared to a superhet. Indeed a superhet is simply a fixed-frequency TRF receiver with a tunable converter ahead of it, and it's that added complexity that adds noise, spurious responses and most of the other ills we suffer with modern receivers. Like everything else, engineering is an exercise in compromise. Different compromises are important in different situations. Up through the 1990's large ocean-going ships had two independent Morse stations built into a common console: one was the main station and the other was a completely independent backup station. The backup station receiver was usually the one that had become obsolete as new technology became available sometime in the past. It was common to find the backup was a simple regenerative receiver. One time I overhauled the regenerative backup receiver for a ship. When I was done I installed it in the console and turned it on to show the radio officer (Sparks) that it was working. We were dockside in the San Francisco Bay and as it came alive we were greeted by an awful howl of cross mod and heterodynes produced by the powerful broadcast band transmitters that literally surrounded us all overloading it. I mentioned to Sparks that would not be the case at sea. Sparks cast a baleful eye on me, stroked his beard and said, Sonny. If'n this tubs a'sinkin in the middle of the ocean and someone's overloadin' this receiver like that, he's the ship I WANT to hear! Sometimes a critical deficiency in one application is a critical advantage in another. Getting the most out of any tool requires understanding its limitations and the knowledge to use it to its best advantage in each situation. That includes radios. Modern radios -- and the Elecraft rigs are no exception - are designed for specific applications. Then as much flexibility is built into them to take advantage of changing station environments, band conditions and operator preferences. That's why they have such a variety of filters, preamplifiers, attenuators, and other user-selected options. Understanding what they do and how to apply them correctly is essential. Ron AC7AC ___ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
