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RF connections aren’t the only important connections in an antenna system

– Posted in: 630 Meter General Topics, 630 Meters

I’ve been very fortunate.  I have had very few problems with my station over the years.  Part of that is because I’m very Type-A and like my equipment overbuilt, even if it looks like I just threw it together.  My 630-meter station was built using the “Rube Goldberg” method, as if it were something out of a Frankenstein movie with lots of switches, meters and procedures for operating the station written on note cards as if I were executing a space shuttle mission.  NASA would be proud!

In preparation for my evening CW sked with Steve, KF5RYI / WG2XIQ/1, I was checking receive antenna positions that might be most advantageous for making the QSO a  pleasant, arm-chair, copy experience because there was a cold front in the Midwest that generating lots of lightning noise.  I switched the transmit antenna to the detune position to avoid coupling noise into the receive antenna system and the receiver noise vanished.  I flipped the switch a few times and the receiver noise was back.  Probably just a dirty contact in the switch.  Steve begins calling and I returned to him only to notice almost immediately that I had zero ohms of base current and the scope match waveform looked crazy.  I was definitely not at 50 +j0 ohm match to which I was accustomed.  Uh oh.  Remaining with our earlier NASA theme, “Houston, we have a problem.”

I sent Steve a text message to let him know what was going on and immediately began investigating.  I checked to make sure I had not lost a top loading wire, the ATU looked normal and even checked the vacuum relays at the feed point.  Everything looked OK except for the control voltage to the relays.  There was a tremendous amount of voltage sag for the amount of load I was presenting with the three vacuum relays that are switched in parallel.  Its worked for years now but I was measuring 5 volts on a 12 volt system.  I recall the sag being something like 11.5V at the feed point.  I have had very good success over the years using small control wires even up to 1000 foot long that performed ok, albeit slowly, with 12 volts.  Wire size was not the problem.

A few weeks earlier I had found the band switch for 160m / 630m to have a bad solder joint and I re-soldered it.  The process should have been easier than it was but it seems a few years of sitting in my very dusty shack resulted in a surface that would not take solder well – bring on the flux.  Flux solved the problem and the switch seemed back to normal.  Perhaps the DPDT switch had a bad contact.  I tend to re-purpose switches so there was no telling how many cycles it had seen.

I was able to get the system settled down where I could at least run WSPR for the night.  The problem was either in the band switch or the “detune enable” switch or something in the control line.  I had added a few 25 pair control cables a few years earlier to various distribution points around the property for dry contact and power to be used with antenna projects.  Surely it could not be the control line!

My morning CW sked with Steve went well.  No problems were experienced and in hindsight it was because I did not touch the switches on the console.  I spent a few minutes investigating outside after first light only to find that the relay controls wires had never been switched to a new trunk line.  I was using some old multi conductor antenna rotator wire that had been spliced together using terminal blocks.  Its a wonder this thing worked at all!  I traced each terminal block and while the first looked OK, the second one looked like this:

RF connections arent the only thing that is important

RF connections aren’t the only thing that is important!

The block had been placed into a Tupperware bowl and “sealed” from the environment inside of a shrub in the front of my house.  I had completely forgotten about it.  Spring 2015 was very rainy, in fact, we had 100-year flooding here in the Dallas area.  The Tupperware was full of water, the drain holes were plugged and once again, its amazing that the system worked at all!

I immediately “punched down” the control line from the shack into a distribution point with a new pair going to the antenna and abandoned the old control line.  Now the system appears to be working and switching well and I am seeing 11.5+ volts at the feed point distribution for the vacuum relays.

I like using plastic containers for weather proofing but the take home message should be that they need to be checked regularly and ventilated to minimize moisture accumulation.  Contacts and wires need to be observed as well.  This particular corroded block has AC and DC on it so there is no telling what kind of noise I may have just cured by removing the cruddy junction from the system.  I had forgotten about this old control line run so it was unintentional and its my guess that the only thing holding the relays closed was sealing current.  When I touched the terminal block above, the wires disintegrated in my hands.

As an aside, the combiner made a great buffer between my amplifiers and the mismatched load.  The amps continued to make power but all of it was going to the reject load, which was nice and toasty after just a few moments of transmitting before I realized there was a problem.

With winter approaching in the northern hemisphere, check those connections!  Its a lot easier doing this kind of troubleshooting and repair when its above freezing!