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
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.
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.