Hi Wayne, That gives me almost exactly the overhead I need if my neighbor buys an amp--or puts up a beam. Thanks!
73 Eric WD6DBM On Tue, Jun 23, 2020, 8:39 PM Wayne Burdick <[email protected]> wrote: > 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]
