Hi Dave, Thanks for your input to my problem. I will break out the prints and start looking for any signs of instability in the power supply filtering. If I can figure it out I will let you know how it turns out. Thanks again..
LOUIS, KD5GM in EL29kq CW, The original digital mode AMSAT #37061: FIST #3606 ----- Original Message ----- From: "David Palmer" [email protected] To: "Louis House, KD5GM" [email protected] Cc: [email protected] Sent: Thursday, January 20, 2011 04:31 PM Subject: Re: [amsat-bb] Tone interference
Hi Louis,
I have seen a few (rare) postings about the LM7806 voltage regulator in the G-5500 not having enough bypass output filtration, and thus becoming unstable.
Reportedly the '7806 regulator needs a 0.1 uF output capacitor for stability, and the G-5500 uses a 0.01 uF cap instead. An unstable regulator can either generate RF noise (as you describe) or the voltage output can become inaccurate as the system warms up, leading to subtle (less than 10 degree) positioning errors. For example:
http://www.mail-archive.com/[email protected]/msg01702.html
I was noticing a slight drift in my display readings as my '5500 warmed up, so I checked the ouput of the 7806 in mine with a scope and saw it was oscillating (about 200 mV at 5 MHz). I simply soldered a 0.1 uF tantalum capacitor, in parallel, to the leads of the exisiting (0.01 uF) cap ... and that removed the oscillation entirely. Meters then had nice stable readings after that too. I never noticed RF noise, but the fix should be the same for both.
Hope this helps,
73 de Dave KB5WIA / CM88 AMSAT #38466
I have discovered a pulsating tone (about 600 HZ) in my 910H receiver when I am tuned to 145.900 MHz (working the Linear birds VO-52 etc). The tone stops when I power off the G-5500/LVB tracker. All equipment is grounded and ferrite core filters are on all of the cables to solve this problem. Aside from moving all equipment across the room from each other, what might I be missing? Any help will be appreciated Thanks, LOUIS, KD5GM in EL29kq