OK, It looks like I am going to have to eat some words here. Either I
didn't use the same type of tape as before, or something else was
different. Anyway, I checked 2 different traps (P/N 878749 - 10m, and
878637 - 15m DE) in our trap test oscillator, with varying amounts of black
electrical tape wrapped on the plastic outboard cap. Both 3M Tartan(TM)
brand Vinyl Electrical tape and generic black electrical tape (listed 906B
flame retardant, 600V) were used without a noticeable difference.
10m 878749 trap:
3 wraps, covering all of the cap: freq shifts down 15 KHz from nominal
cap removed from trap: freq shifts up 20 KHz from nominal
15m 878637 DE trap:
3 wraps, covering all of the cap: freq shifts down 12 KHz from nominal
cap removed from trap: freq shifts up 102 KHz from nominal
No "Q" measurements were performed. This will have to be done at a later
date with a different test setup.
As a result of these tests, I am now recommending the use of black vinyl
electrical tape wrapped on the trap caps to protect them against UV
exposure. However, do not close any water drain holes in the cap or trap
while doing this. As the tape may unwrap with time, you may wish to secure
the last wrap with a small tie-wrap.
73 Roger WB0DGF
Telex Communications, Inc.
http://www.hy-gain.com
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|