[NLRS] (Fwd) WR90 dummy loads

[Dr. Gerald N. Johnson]

I have some but they are in use for experiments. And I'm not in the Metro.

WA5VJB has written about making waveguide loads, either in the technical 
collection at NTMS or on Kent's web page.

Basically a workable 10G waveguide load can be made from wood by cutting 
a piece a few inches long to fit the .4 x .9 waveguide inside and 
tapering the side that will see the RF to a knife edge probably on the 
.4" dimension with a taper at least a couple wavelengths long. Can be a 
single or double sided taper in one plane or both planes. Some 
references have indicated the sharper the point the better the match. 
Some references from MIT used resistive plasters or glue with carbon 
mixed in and liked to taper both planes like by letting the glue set 
with the waveguide on a corner and then sloping.

Kent has also suggested carving a similar piece from a scrap of truck 
tire tread. The wood has worked better for me than the tire rubber.

The longer the taper the better the match.

I have a WR62 termination that has a 1.68:1 SWR at 12.4 GHz butted to a 
WR62 slotted line. I suspect the resistive internal loss element has 
been replaced with black plexiglass. I may try spraying the plastic with 
graphite paint (as used in farm grain wagons to make the grain slide out 
better) available at some farm stores. The spray can I have is EZ-SLIDE 
that I bought to replace graphite on bad remote control buttons.

A guide wavelength in WR90 at 10368 is 3.733 cm. A taper 4 guide 
wavelengths isn't excessivly long unless your available guide isn't that 
long.

73, Jerry, K0CQ

On 12/14/2017 7:53 PM, tom ring wrote:
>
>
>
>
> Resending because it seems to be working after I re-subscribed.
>
> ------- Forwarded message follows -------
>
> Is there anyone in the metro that has 4 WR90 dummy loads, or some combination
> of things that would do the same, that I might borrow for a short period of
> time?
>
> And given I need 4, maybe more than 1 person...
>
> I could deal with it if they were 10 dB or so pads. I just have to make sure
> the transmitters don't see an empty waveguide to air. That might actually be
> better since they'd be able to see each other.
>
> Thanks.
>
> Tom
>
>
>
> ------
> Tom Ring K0TAR EN34hx
>
> 2010 Jetta 2.5 - MAC #42 HS - Don't Panic!
> 1985 Westfalia Vanagon Camper
>
> "It is better to go into a turn slow, and come out fast, than to go into a
>   turn fast and come out dead." Stirling Moss
>
> Autocross saves gas.... I no longer brake for turns.
>
>
> ------- End of forwarded message -------
>
>
> ------
> Tom Ring K0TAR EN34hx
>
> 2010 Jetta 2.5 - MAC #42 HS - Don't Panic!
> 1985 Westfalia Vanagon Camper
>
> "It is better to go into a turn slow, and come out fast, than to go into a
>   turn fast and come out dead." Stirling Moss
>
> Autocross saves gas.... I no longer brake for turns.
>
>
>
>
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