Space Weather Monitors- Stanford SOLAR Center

SID Monitors
DataObtaining a Monitor
For Educators
Installation and Use
The Team

Our signal is degrading. Could our coax cable be too long? and our signal is degrading?

By 'signal' I mean that when we connect the antenna/cable to the monitor, it registers at around -4.87. We can't get it to budge from that number. We move the antenna to another room (we have LOTS of cable) and we've even moved it outside and the number doesn't change. I hooked up a new antenna yesterday and began to play with the set screw at the back of the monitor and the number began to change. I have it down between -1.25 and -1.5. But I've achieved it by putting the little black 'button' on the back at 10... I know the manual says to keep it at one. The moment I put it to even 5 our 'number' goes right back to close to -5.

A weak input signal can be caused by a faulty antenna, the connection, improper RF gain setting, antenna orientation, bad location, just to name a few...

What type of wire are you using? The best wire to use is a solid wire with a PVC jacket on it. That said, I have an antenna from magnet wire (lacquer coated wire used in transformers) connected to the monitors that I test -- and it's been out in the sun, rain, wind for years without cracking or problems-- although I am told that it could happen.

However, if you have used non-insulted wire then it will not work... this is your problem. Sorry to say but you'll need to restring the antenna with insulated wire. I use a colored wire (usually red) solid #20 ~ #18 with 25 turns on a 5.5' frame and get great results. I don't know about using white wire -- it might be okay, but I worry about white because of the white wire ties become brittle after a long exposure to the Sun's UV rays and yes they DO fall apart in time-- so I use the black wire ties... some even say UV protected.

If it's lacquer coated wire, then it needs to be scraped off at the terminal connection points. Usually a small piece sandpaper will do the trick.

Otherwise, if none of the above applies, here are some antenna troubleshooting tips: You'll need an ohm meter (most digital multimeters will work fine). You will need to read low resistance values, I mention this because some meters have a manual resistance settings, fancier ones have an auto ranging function. Here's a troubleshooting procedure:

1. Check the resistance of the antenna (I'd expect 2.5 - 10 ohms) across the terminals of the antenna. Be sure to do this test with the coax disconnected from the SID monitor -- AND -- at least one of the coax wires removed from the antenna terminal block. (This assures that you only read the coil resistance w/o the coax or coax connected)

2. Check for short circuits. * The problem can be sometimes the cable inside the TNC connector can short together, this is sometimes a tricky connector to use and can fool you to make this connection... sometimes it happens to me. Measure the coax connections at the antenna end (easier to do) and again you want to make your measurements not connected to either the antenna or the SID monitor. The meter should read the same as if the probes are not connected at all.

3. Check for open circuits. * Test the resistance across the TNC connector center connector and outside shell then touch the wires on the stripped end of the coax together (form a temporary short) and see that the meter reads the resistance of the cable.

* You could also perform a continuity check for each wire in the coax. The braided copper or shield connection is connected through the cable to the outside of the TNC connector and the solid copper wire is connected to the inside electrode of the TNC connector. Put one probe of the meter (red and black) on each end, (polarity doesn't matter) and verify continuity (low resistance) through each wire -- and verify that no connections exist of any resistance, i.e. short circuit is between them.

4. Measure overall resistance Connect the coax cable back on the antenna terminal strip, but still not connected to the SID monitor... read the resistance across the TNC connector (repeat the measurement as in #3). You should see the total resistance of the coax and the antenna coil. The lower resistance value is expected, 10 ohms is okay, 50 ohms sounds too high.

5. Try for intermittent connections try moving the coax cable near the connection points by moving it a bit while watching the meter. Any change is a sign of an intermittent connection.

6. Plug the TNC connector into the SID Monitor and try it again.

7. Cable length: If you are sure you have more than enough, then try making a shorter cable. I know that 50 to 70 feet is not a problem... I haven't tested antennas with long wires, e.g. 100' but I can't imagine this is the problem until you've ruled out #'s 1-3 in my list.

P.S. If the values are increasing when the gain switch is in the x10 position, the signal is actually the ground wave (I've done it with NLK) no SID's will be recorded... just a straight line.

©2015-2018 by Stanford SOLAR Center