I should have mentioned that with 30 dB simulated path loss and 10 W TX, the received signal at each end is the equivalent of about +10 dBm, or "S9+83 dB". FWIW :)
73, Wayne N6KR > On Jun 23, 2020, at 8:16 PM, Wayne Burdick <[email protected]> wrote: > > 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 <[email protected]> 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" <[email protected]> >>> To: "elecraft@mailman qth. net" <[email protected]> >>> 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:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
