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Three antennas, same problem

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JimTailor

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I have an Icom pcr100 fed through a switch by three different antennas - a discone and two long wires each pointed in different directions. Reception seems to be of the same poor quality no matter which atenna I switch to. Local AM and FM stations sound garbled and shortwave is a tough catch no matter where I tune. I know there are lots of factors affecting the shortwave reception but, again, if I do catch something, shortwave reception sounds the same off of all three antennas. I connected long wire directly to the pcr100 and FM reception is fine, AM is okay and I get more shortwave than with any of the three outdoor antennas and this wire is just running across the floor of my basement not really even stretched out very much. I've checked the integrity of the switch and the wire between the switch and the pcr100 with an ohm meter. Its a good quality switch bought a few years ago from a friend in the "business". Because of lots of rain, I haven't gotten outside to look at the connectors on the three outdoor antennas but the chances of all three being funky are slim. I also use the discone for another scanner without a problem. Any ideas?
 

Al42

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JimTailor said:
I've checked the integrity of the switch and the wire between the switch and the pcr100 with an ohm meter.
DC resistance has nothing to do with how the switch will work at RF.
Its a good quality switch bought a few years ago from a friend in the "business".
He was in the business or he gave you the business?
I also use the discone for another scanner without a problem. Any ideas?
You're talking about short wave - a discone is about as useless as a light bulb at low (below around 100 MHz) frequencies. A discone that would work decently at 30 MHz would have 8 foot long radials and a huge disk.
 

gcgrotz

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Quoting Al42:

"You're talking about short wave - a discone is about as useless as a light bulb at low (below around 100 MHz) frequencies. A discone that would work decently at 30 MHz would have 8 foot long radials and a huge disk."

I saw one of those once at the Canadian Navy station outside Halifax NS. Pretty cool.

My suggestion would be to try bypassing the switch since it is common. Also the jumper from the switch to the radio. I'd still suspect one of them since the wire on the basement floor seemed to work.
I would also verify the RX. Have you tried it at another location - firend's house etc? And verify your audio since that seems to be the root of the problem too - garbled audio. Is it connected to your sound card? If so - mike or line input? Try using headphones direct to the RX.
You'll find it, just use some detective work and start eliminating things one at a time. If you think you've found the problem, put it back and make sure the problem comes back.
 

kb2vxa

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Hi Jim and all,

First of all a "long wire" which in most cases turns out to be just a random length wire (the term often misused) has no particular directional characteristics so you can eliminate one. They require no transmission line whatsoever so coax actually is superflous unless it just happens to be an inverted L and a remote ATU but I'm getting off topic.

If you can receive SW on a discone there probably is a ground fault in the antenna or coax, a discontenuity making part or all of the coax into an antenna. This severely degrades the antenna's performance as you may be experiencing but haven't mentioned.

For VHF/UHF work you need a coaxial switch, not a coax switch, a completely different design. Alpha Delta, Daiwa, MFJ and others make excellent ones good up to about 500MHz or so, HF coax switches get flaky above about 30MHz. One thing that may be confusing you is the fact that HF switches have virtually no port to port isolation so you could be picking up "phantom HF signals" on the discone's port, crosstalk from the long wires' ports.

An ohm meter is as good as any for checking DC continuity but the center conductor is only half of the transmission line, the shield is the other half. Any discontinuity from one end to the other spells disaster so ring it through as well as checking for shorts, I'll bet you find an open somewhere between the far end and the receiver itself unless you have just realized you're using the wrong kind of switch.

There is also the off chance that the ground connection inside the receiver opened, I have seen it happen. Sometimes vibration strain causes the connection to the board to be lost, even the board can be damaged so that's another place you can check if all else fails.

As Sherlock Holmes said, "Once the impossible has been eliminated, what remains however improbable is the solution." Process of elimination my dear Watson, "The truth often hides in plain sight."
 
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