[TenTec] PC generated noise & the pegasus serial cable

[Guy Zebrick]

Hey all - I found a problem, and then the solution, to a noise issue I discovered on 15 and 40 meters. I was doing some testing on my Pegasus the other night, and when I was on the dummy load, I found I had a S-5+ noise level on 15 and 40 meters. the other bands were quiet. Turning off the connected laptop PC eliminated the noise.

I have an ICOM 740 (now resting in a comfortable retirement mode) right next to the Peg, and it was NOT effected by the noise at all.

Turning on the laptop again, the noise returned to the Pegasus, BUT when I disconnected the serial cable, the noise went away again. I should also note that I have been battling a cracking noise coming into the accessory input when running PSK or SSTV using the speaker-out on the laptop. 

The noise was coming in through the cables, not 'over the air'!

The solution was simple. I ran a ground wire from my grounding post on the back of the Peg to one of the  screw terminals on back of the laptop that is used to secure a parallel port cable. This eliminated the crud on 15 and 40 meters, as well as the crud on the speaker output. Seems that I may have had some sort of ground loop going.

Funny thing is I am using a commercial RS232 cable to connect the laptop to the serial port on the Pegasus, so I thought the grounds would be common through the 9-pin cable.. but I guess not.

Anyway, just wanted to share. Still think the Pegasus is one of the best bargains in Ham Radio along with Carl's N4PY's software.

73's
WD5ACP