[Amps] Alpha 87 (not 87A)

[Jim Brown]

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