[Moon-net] Array Deterioration

[Lance Collister]

Bernhard E. Keiser wrote:
> John, I've experienced the same problem (not hearing well), and am looking 
> for the solution.  However, all my coax connectors are covered with 
> Coax-Seal.  Were yours?
> 73,  Bernie. W4SW
>   
Hello Bernie,

I think a critical question to ask at the beginning of the investigation 
is what kind of antennas are exhibiting these problems.  For tropo or Es 
or strong local signals (which is for most antenna users), this hearing 
loss would probably not be so apparent.  However, when it comes to EME, 
the slightest degredation is immediately apparent to the operator. 

Some antennas (at least the older M2 models) created a connection by 
crimping aluminum rod down on copper wire inside the connector block on 
the driven element.  This connection is very prone to corrosion by 
virtue of the contact between the dissimilar metals, and the result is a 
buildup of resistance between the two metals.  As you can find from a 
simple internet search, this phenomenon takes place regardless of 
whether the connection is sealed against the air and water or not, 
although it is accelerated if exposed to moist air and/or water. 

This corrosion is not easily noticeable on transmit, since with high 
power, the resistance is easily overcome.  However, the result on 
receive is that weak signals simply disappear entirely.  I don't know if 
this manufacturing procedure is still currently used at M2 or not since 
it has been a couple years since I looked into this  (a simple solution 
is to crimp the aluminum over copper tinned with lead bearing solder), 
but the driven element connections on many dozens of M2 yagis that have 
been used on EME have had to be rebuilt to correct this problem.  W5UN 
discusses one solution on his website, which was to use a special 
brazing alloy to braze the copper wire to the aluminum.  W1JJ replaced 
the lower T match bars with copper tubing so they could be soldered to 
the copper wire inside the connector blocks (be sure, however, to tin 
the copper tubing where the aluminum T match shorting bars contact them). 

If it is some other type of antenna (commercial or homebrew) which is 
causing the problem, the concept is still something to be carefully 
addressed. Good luck and 73, Lance

-- 
Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8)
P.O. Box 73
Frenchtown, MT  59834  USA
QTH: DN27UB
TEL: (406) 626-5728
URL: http://www.bigskyspaces.com/w7gj
2m DXCC #11/6m DXCC #815