my experience is not all npo caps are created
equal. I suspect many are mismarked as happens with nuts and bolts. Mono caps or
cog as they are sometimes called exhibit better stability.
?
My beacon is mounted at the center of my dipole,
temp here has been from 100 degrees F daytime to 75 or so at night. My beacon
will shift about 25 to 30 hz. this fall I may have to take it down and reset it.
I have a 7805 regulator down in the shack, power is fed to beacon through rg59
coax and? f? connectors. I could replace the 7805 with an LM 317 and
limit the voltage to 6v and trim the freq by adjusting the voltage. also the led
may shift somewhat due to temp change, I have found this the case when using
varactors to tune vfo's. Those in cooler climates may want to put a heat source
in the case if the beacon is to be remote mounted. a small incadesent lamp or
led or resisor? and lots of insulation on? the beacon. would
help.
?
Drift is a minor problem.
?
Paul k5wms
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----- Original Message -----
Sent: Thursday, June 17, 2010 11:24
AM
Subject: [QRPLabs] NP0 Caps
?
Greetings from sunny England,
Those of you who have built the beacon
kits will have noticed that we do not use NP0 caps. In fact I cannot remember
the last time I used them. Yet these beacons are very, very stable in output
frequency as are my other projects. Which makes me wonder if modern caps are
much less temperature sensitive than they were in times of yore and question
why people still use them.
What do you guys
think?
Regards,
Steve G0XAR
