[Elecraft] K4 Question

[Victor Rosenthal 4X6GP]

Well, that would certainly be enough for me. I have two loud 
line-of-sight neighbors, but they don't hit +10 dBm.
Unfortunately they have "dirty" transceivers, so it doesn't matter. I 
suppose I should buy them K4s.

73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
CWops no. 5
http://www.qsl.net/k2vco/
.
On 24/06/2020 6:38, Wayne Burdick 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 <n6kr at elecraft.com> 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