facing a problem with Loop feed for 21 cm hydrogen line

[NISHANTH D]

I have managed to construct my loop feed from Alex's design for the hydrogen line observation, but I can't solder the copper loop to the N-connector with normal soldering (for some reason, they don't go together ). I think soldering doesn't work well with copper and stainless steel. How do I do it...?

[Alex P]

Hi Nishanth,

Its typically not steel, but nickel plated brass.  ( as you can see in the shield cut out area

Just sand it a bit to get to the brass color .. 

HOWEVER, it does take a  large soldering iron to get that amount of metal up to temp !

( or practice a bit with one of those mini butane torches & use that )

You might want to solder the loop before you attach the N adapter to the dish to eliminate that as another heat sink,

and Clean and Pre-tin the loop ends & N connector before joining them.

Another Idea : make a  cut-out into the shield side of the N connector in which to insert that end of the loop

for a better solder connection.

Alex

[NISHANTH D]

Thanks Alex, I will try to do as you said but I'm not sure about heating the N connector with butane torch to attain a temperature suitable for pre tinning, I am afraid that I might melt the teflon inside.

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[b alex pettit jr]

Solder should flow ~ 400-500F  & Teflon can survive ~ 800F.

Focus the heat on the Copper loop as it is much more thermally conductive than Brass.

I've done this frequently .. and All Survived 

Another Idea : remove the excess brass so the shield connection has less material to needing to be heated.

- Alex