I have an extremely limited time budget and when something that appears as a mystery (eating into that time) it creates a sense of terrible frustration. I had such events over the past couple of days.
All of us have seen the phenomena where you connect the antenna, and the atmospheric noise is present. Disconnect the antenna and the noise goes away. In fact, that is a simple test once you have homebrewed a rig to see if the receiver is working even when the band appears totally dead.
I have also noted that when connecting the coax cable that when the center pin 1st hits the connector lots of signal but upon full engagement you only hear the band signals for that band.
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At times with the Arduino and no antenna connected you faintly hear the clock noise as the code cycles through the loop. Connect the antenna and magically that faint noise disappears.
Now the tale of woe. Using the Ten Tec 150A described earlier on this blog, with the antenna connected I could hear the Arduino and connecting the radio to the antenna OR the dummy load there was no change in the background noise -- we still heard the code cycle. Now how could that be?
Wow, we had a Ghost in the Machine. So how to attack this problem? The first step in the fault tree analysis is to separate whether the problem is the Radio itself OR Everything beyond that. Step 1 is to disconnect the coax at the radio. The atmospheric noise disappeared, and the only noise was the faint clock cycle.
The conclusion was that the problem was everything else. The fact that you could hear the atmospheric noise suggests that we have an open connection somewhere in the coax.
We have the classic PWP event! PWP = Problem Was Pete. If you look at this coax connector soldered by me, you will see pieces of braid not soldered to the shell. In a couple of other holes, the solder was a cold joint and actually broke away from the hole.
I found this by accident as I bumped a short piece of coax when connected to the dummy load and the radio went quiet. A bit of wiggling and I could make the noise appear/disappear on demand. That was the problem -- bad solder connections by me.
It has been hard to tell how long it has been this way but sure showed up with the Model 150A. The Coax is RG-8 (real stuff) and hard to solder and not very flexible. A replacement with a short chunk of the smaller diameter RG8X is a temporary fix.
The very astute blog reader would ask how come you are just now finding this issue? The answer is I have two operating positions and a two-position coax switch. Most of the time when I build and test stuff it is at the other bench. This bad piece of coax is located at the secondary position which is not used as much as the primary one.
Lesson learned: check all of your coax connectors and recognize you may have a lot of skills but soldering connectors to RG-8 is not one of them. Let's see, type in DX Engineering and whip out the plastic. RG-8 previously bought at Amazon sucked big time!
SHOCKER: This is like getting hit in the cajónes with a bowling ball. A 6-foot length of RG-8 built with connectors is about $7 a foot from DX Engineering. This might be a good time to improve my coax soldering skills and fix the connector. Nothing like a dose of reality to improve one's mind!
73's
Pete N6QW