Hi Eric, I did a quick test using my home lab to simulate a possible FD scenario.
For this test I set up a K4D and a K3S with their antenna jacks connected directly together through a high-power attenuator. Receiver preamps were off. With this arrangement, the RX noise floor is minimized since there's no actual antenna involved. I set mutual attenuation to 30 dB, a rough estimate of the path loss using dipoles 500' apart at 7 MHz. This is a pretty wild guess, though. Loss could be much higher if the antennas were oriented to avoid coupling, and it'll vary with frequency, terrain, actual distance, etc. Of course path loss could be lower with gain antennas at either or both ends, aimed at the other. (A situation generally avoided at FD.) While transmitting with the K4D at 100 W and receiving with the K3S, I found I was engaging the K3S's carrier-operated relay. This is evidence that the path loss probably is higher than 30 dB in real-world scenarios. I dropped to 10 W on both rigs (10 dB down from 100 W) to avoid the confound. I then coupled in a weak signal at the equivalent of about S2 (-113 dBm) as indicated on both receivers. When keying one rig, there was no evidence of desensing of this signal at the other, and only a very slight observed increase in the noise floor (as indicated by the respective panadapters). Yes, the two radios have entirely different architectures. Each has pros and cons. With an SDR like the K4, the fundamental limit on narrowband TX noise performance is the DAC. The K3S, on the other hand, has to shoehorn its 8 MHz IF transmit signal through a narrow crystal filter, adding ripple and group delay to complex signals (like voice and data). It also exhibits a characteristic "pedestal" of 15 kHz DAC noise that sits maybe 15 to 20 dB above the wideband noise floor. When it comes to CW keying bandwidth, both the K3S and K4 have essentially identical (and excellent) performance due to an optimally shaped keying envelope. 73, Wayne N6KR > On Jun 23, 2020, at 3:46 PM, Wayne Burdick <n...@elecraft.com> wrote: > > Hi Eric, > > S9+65 dB is about -8 dBm. Off the top of my head, this is far, far below what > a basic K4 or K4D can handle, artifact-free, in-band, without the need for > attenuation or additional filtering. When I get back to the lab I'm going to > set up exactly this condition and get back to you. > > Of course the out-of-band rejection is even higher. > > A number of K4s will be used extensively during FD this year, including mine. > I'll be taking advantage of the K4's low current drain (for its class) by > running mine from a KX2 11 volt battery pack (3x 18650 cells). For at least > an hour or so :) > > 73, > Wayne > N6KR > > >> From: "Eric Norris" <norrislawfi...@gmail.com> >> To: "elecraft@mailman qth. net" <elecraft@mailman.qth.net> >> Sent: Tuesday, June 23, 2020 9:32:04 PM >> Subject: [Elecraft] K4 Question >> >> My foaming at the mouth over the K4 has been tempered by it having less >> adjacent channel rejection than the K3 due to the different >> architecture--at least until the K4HD comes out. I understand this, and >> the reasons why. Thanks for your answers >> >> I know I have asked this question before, but I want to be more specific. >> My QRM neighbor is S9+65 db on my K3S S-meter. If he is blasting away on >> ft8 at 7074 kHz at that signal level, how would the plain K4 receiver >> perform at 7034 kHz on CW? Would there be AGC pumping, RX desense, or >> other degradation, or would I be able to carry on a CW qso unmolested like >> I can with my K3? What about an adjacent band like 3534 kHz or 10114 kHz? >> Or is the answer I have to wait for the K4HD? >> >> No speculation, please, I'm looking for a real-world or lab-world answer. >> >> Thanks and, >> >> 73 Eric WD6DBM > > > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
