In a message dated 08/06/05 17:50:09 GMT Daylight Time, [EMAIL PROTECTED] writes:
Just a thought on dummy loads, a number of years ago I noticed my Heath Cantenna was giving me a slightly higher SWR reading instead of 1 to 1. When I measured it with a VTVM I found it was 40 ohms, not the original 50 ohms when I built it 25 or so years ago. Reply:--------------------------------------------------- There was a similar query in Radcom quite a few years back, I think in the Technical Topics column about the value of resistors changing in oil filled RF dummy loads. The answer to the problem came back from no less a person than Reg Varney, G5RV who was I understand involved in the chemistry profession at one time. Certain types of oils apparently degrade the carbon material that the resistors are constructed from and over a time alter the resistance value. Vegetable oils were particularly bad in this respect it turned out. As these vegetable oils are available cheaply in all grocery stores, this would be a popular choice for the cash strapped ham, to their eventual downfall. There are oils available that do not exhibit or minimise this effect, though probably are much more expensive to purchase and more difficult to source. Some transformer oils such as PCBs have to be avoided as they are reputed to be carcinogenic. Bob, G3VVT _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
