Re: [Repeater-Builder] "Rusty bolt" help!!

[Dick]

Fraser:   If it is a "rusty bolt" effect, it an be a bear to find the particular offending item.  Typically, a "rusty bolt" will generate more than just a single frequency.   The actual effect is interesting.  The "rust" can also be another kind of corrosion that forms an oxide between the bolt and the material it's fastening.  Of course, rust is also an oxide.  The result is a crude semiconductor that gets saturated with RF and generates RF noise that's rich in harmonics.   I had a similar problem when I was an EE at the Lockheed Skunk Works. I used a signal generator and a spectrum analyzer and pumped RF into what seemed like a zillion fasteners.  At the same time, we listened with the spectrum analyzer until we found several fasteners that resulted in a lot of RF peaks when excited with RF.  We replaced the fasteners and all was well.   As you can see, this is a long, tedious project, but it does work.  In your case, you can use a scanner tuned to a harmonic of your repeater's output frequency.  Make sure that what you're hearing on the scanner only happens when you key the repeater and make sure the repeater itself isn't generating the harmonic you hear.   If you find that it's a fastener causing the problem, make sure that the replacement process includes oil on the threads and a good sealant around the fastener head and where the nut goes on.   As someone else mentioned, it could also be intermod.  If it is, you'll need a list of all XMTRs at the facility and some intermod software to see if your RPTR XMTR is mixing with another signal and coming out on your RCV freq.   Feel free to email me off list.   Dick W1NMZ Manager (Retired) Electromagnetic Environmental Effects Lockheed Skunk Works   ----- Original Message ----- From: Fraser Stuart To: Repeater-Builder@yahoogroups.com Sent: 20 February, 2006 05:38 Subject: [Repeater-Builder] "Rusty bolt" help!! We have a 145 Mhz 600khz split repeater running 25 Watts output up LDF 450 coax to a three element commercial beam at 25 Metres above ground mounted on a metal 35 Meter tower,,, We are trying to identify the problem of what could be a "Rusty Bolt effect" the effect is that it will wipe out a signal on the input of all but the very very strong signals it sounds just like a heavy crunching sound,,,,it does not become worse with rain, wind,cold,or heat,,,,,we have changed the Tx/Rx set up, and changed the Wacom Duplexer..added extra bandpass filters   We have another beam 3 Meters below, run the system on this with the same effect, have run the repeater with two antennas and extra filtering,  also the effect is present with only 1 watt of RF output,,,,   one other effect the noise can be heard on the Tx carrier ie no through audio,,   To investigate the mast will cost money for an insured rigger,,,   idea's where or what to try next would be greatfully recieved,,   rgds Fraser YAHOO! GROUPS LINKS  Visit your group "Repeater-Builder" on the web.    To unsubscribe from this group, send an email to:  [EMAIL PROTECTED]    Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.