Hooking up big azz knife switch today for that buzzardly look

[N3DRB The Derb]

Phred sent me a giant dpdt knife switch some time ago and I'm just starting to feel like I'm coming out from under the primary workload with both FT-101's fixed and working.  So I'm gonna mount the thing on the wall  and use it to switch feeders and or setups. As a bonus, I should be able to mount my RF ammeters in line so I can watch the munky get funky. 

think I'm just gonna order another 7FG ant for 40. I got the holes through the wall now, may as well use them.

[W2VW]

Watch out for QRO if the base is made from that black rubber looking stuff.

I tested mine on 20 with a kw carrier and it was OK. Next 160 season my SWR started drifting. After a long QSO I walked by the remote tuner and found the base boiling. There was a trail between 2 posts of cooking material.

I have several more knife switches I'd like to use but won't until the base gets swapped out to thick plexiglass. 

[W7TFO]

Another trick on the old switches is to raise the metal parts via some small porcelain insulators and keep the original base.  If those insulators have lots of ribs it looks even more terrifying.

[K5UJ]

Watch out for QRO if the base is made from that black rubber looking stuff.

I tested mine on 20 with a kw carrier and it was OK. Next 160 season my SWR started drifting. After a long QSO I walked by the remote tuner and found the base boiling. There was a trail between 2 posts of cooking material.

I have several more knife switches I'd like to use but won't until the base gets swapped out to thick plexiglass. 

Ah yes, meeting the demands of AM    Somewhere around here I have a dpdt knife switch I bought at a hamfest around 37 years ago and used as a t/r switch believe it or not back when I was a novice.  I used it with coax but it was fine on the low bands where I operated.  It was also fine because I didn't know any better hi hi.   The Knight T60 didn't care.  Its blades are around 3 inches long, spaced apart 3 inches and the blades and contacts are all mounted on porcelain posts a couple inches tall.  it looks like some kind of Dr. Frankenstein's basement thing with Grandpa and Herman.   The way it's spaced it would be pretty good with my ladder line.  I was thinking the other day I ought to use it to switch the line from shack to ground outside.

Rob K5UJ

[W1QWT]

Ah Yes, Nothing like an old buzzardly big AZZ shank switch.
I have the plus 2 Db version here made by Electroswitch Corp:




I am using it to switch the feedline into the house or into a strapping circular ground system so those sparks don't find their way to me inside during those
nasty tundering storms.

Regards
Q, W1QWT

[wb1aij]

Watch out for QRO if the base is made from that black rubber looking stuff.

 After a long QSO I walked by the remote tuner and found the base boiling. There was a trail between 2 posts of cooking material.

Another solution has to do with "Duty Cycle"  The switch does not heat up during periods of receive, only transmit. When you smell smoke it's time to pass it on. Kind of like the 10 minute timer.

[ka3zlr]

..........Nice............


73
Jack.

[Opcom]

Hey Deb, can you shew us a pic of that knife?

[K9ACT]

Watch out for QRO if the base is made from that black rubber looking stuff.

 

A friend gave me one with a slate base and the thought never even occurred to me that there could be a problem.

This is a big hummer.... about a foot long and half as wide and weighs about 5 lbs.

It didn't boil or cook like a previous bakelite one but the slate base got very hot after long transmissions.  It broke my heart but I replaced them both with 1/2" PVC and have no more problems.  These may have worked for Frankenstein stuff but the do not like high power RF at all.

js

[N3DRB The Derb]

Another trick on the old switches is to raise the metal parts via some small porcelain insulators and keep the original base.

Thats the way mine is. everything is riding on 4" long and 2" square porcelain standoffs. Fiberglass base.


yeh, installation is being a pain     - I'll post a pic when it's fully installed. Should be later today.......

[Opcom]

I did not think about slate as being unfriedly with RF.

[K9ACT]

I did not think about slate as being unfriedly with RF.

It was the last thing I suspected but there was nothing left to suspect.

Apparently all rocks are not equal.

It's hard to think of a rock as being anything else but slate is metamorphosed shale and the oil shales seem to be a possible source for oil.  Probably not PCB transformer oil but obviously the stuff, even after metamorphosis is porous.  So it's not the slate but whatever it has soaked up over the eons that causes the problem.

js

[K9ACT]

I think I blew it.  According to:  http://www.asiinstr.com/technical/Dielectric%20Constants.htm

Slate has a dielectric constant of about 7 and the PVC I replaced it with is about 3.

I am now thinking that I should have tried baking the slate in the over for a few hours before giving up on it.  It could be just a matter of moisture.

js