[TenTec] RX input Orion 1

[Martin AA6E]

Larry Menzel wrote:
...
> So, what to do.  According to Paul, W0AIH, the solution is really very 
> simple.  He inserts a lamp holder, like from a boatanchor radio dial light, 
> and puts a #47 bulb in line with the receive antenna line.  Simply take a 
> piece of coax, cut it and solder the braid and center conductor to the lamp 
> holder tabs, and VIOLA, a cheap and totally reliable fuse in the receive 
> line.  Paul insists that using a WIDE spaced lamp element, as with the #47 
> bulb, is very important, and NOT to use a "grain of wheat" style light bulb 
> which has the two poles of the filament holder too close to provide enough 
> protection from arcing across. Although I submit that if one is only running 
> 100 watts or less, that that would be sufficient. But running 1500 watts is 
> a whole 'nother kettle of RF. HI.
> 
...

A #47 acting as a _fuse_ isn't going to do much.  It takes milliseconds 
to get hot and melt.  Your front-end can blow in a few microseconds.

If you look at the schematics, you will see that the Orion front ends 
are protected by (1) a 1 mH RFC to ground, (2) a spark gap to ground, 
and (3) diode clamps to +/- 5 volts.  For 160 M work, I expect #3 is 
your defense.  The question is how much juice can you dump into the 
front end before those diodes blow?

Back to back diodes at the Rx input aren't a great idea, because they 
will conduct and cause IMD and harmonic problems if there is any strong 
out of band RF in your area. The only "good" answer is a switch ahead of 
the Rx that is shut off _before_ any RF is generated.

73 Martin AA6E