On 11/8/2017 11:03 AM, Jim Thomson wrote:
But when the ICOM
756 Pro 2 and 3 folks start TXing, I can hear all sorts of crud on
the ICOM rigs..go figure.
Don't know about this rig, but retired broadcast engineer W4TV has
identified one cause of this as the method used for ALC within the rig,
and they do it all the time. It has nothing to do with ALC from the amp,
and also occurs with the rig running barefoot. I've observed this on 6M,
called the station to let him know, and they've told me the rig they're
running and that they're barefoot. The times I remember the rig was an
el-cheapo Yaesu.
On 11/8/2017 10:21 AM, Gary Schafer wrote:
he easiest way to observe splatter is to switch your receiver to the
opposite side band and listen for the crud.
and
On 11/8/2017 11:03 AM, Jim Thomson wrote:
That will only work.... provided there is nobody within 6 khz of you.
In the example I used below, if you are listening on 3800..and switch to
USB, you will then hear everything from 3800 to 3803.
Another easy way to observe this is with one of the better spectrum
displays that is of instrumentation quality, or even a decent SDR. Like
any instrumentation, we must make certain it is not being overloaded.
When looking at a good spectrum display, it's easy to see the splatter
and identify it as coming from a specific signal because the splatter
correlates with peaks of the signal generating it. And, of course, the
correctness of any measurement is no better than the technical
capabilities of the person making the measurement.
The Elecraft P3 is an example of a very good spectrum display, and when
fed by the IF of an Elecraft K3 or K3S, the combination is quite linear
and can be calibrated to input voltage at the antenna input. SDRs like
the ANAN 10e (a 10W transceiver, $950) and RX only SDR Play and the
FunCube Dongle Pro+ (under $200) all have 100x greater frequency
resolution than my HP 8590D and very good dynamic range. The 8590D
doesn't have nearly enough frequency resolution to show the bandwidth of
CW or SSB signals, while all of these spectrum displays -- the P3 and
the three SDRs, can get down to 2 Hz resolution.
VE7RF has correctly observed that TX IMD is relatively high in the
Elecraft K3 when run at full power, and, like many rigs, increases when
power supply voltage falls below 13.8 V, which is where most rigs are
designed to operate. K3 RX IMD is quite low, and TX IMD drops
significantly when it's running at the 50W level needed to drive most
power amps to full output. K6XX showed all of this in the slides for
his talk to NCCC several years ago, which are on my website (link posted
yesterday). My own measurements are here, along with a full description
of my measurement setup and method.
http://k9yc.com/P3_Spectrum_Measurements.pdf
I'm an EE by training, retired from a career in broadcasting and pro audio.
73, Jim K9YC
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