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Phenomenon? Listening to shortwave skip on my CB??

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Old 11-19-2005, 10:40 PM
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Default Phenomenon? Listening to shortwave skip on my CB??


I had some weird stuff happening on my Cobra 2000GTL tonight at my base station. I heard St. Joseph radio from Orange California transmitting on 13615khz on channel 40 full scale. The signal would drift between channel 38 and 40. I discovered different shortwave skip signals all day on my CB all over the 11 meter band on different frequencies and times. Now here is the weird part, I would only be able to here these broadcasts if the preamp on my Texas Star 250 HDV was on. The signal would bury my needle 30db over with the preamp on, But there was not even a hiss or hint of the same signal with the preamp turned off. I went in my mobile and turned the preamp on and I could not hear the shortwave skip signals at all so it is must be a characteristic of my base station set up for some reason. I tried tuning in these same shortwave signals on my Technical Materiel Corp. GPR-90, But I could not tune them in. Has anyone else ever experienced this before? Please let me know. Thanks,

UPDATE:
I was able to tune in EWTN radio on my Cobra 2000GTL with the Texas Star 250 HDV preamp on full scale on 27.425. I was also this time able to tune in the exact frequency(7570 Europe/Africa)http://www.ewtn.com/radio/freq.htm
at 2:00am this morning on my TMC GPR-90. Both my shortwave receiver and my Cobra 2000GTL were receiving the same exact broadcast at the same time so there is no mistaking it was shortwave skip. Please let me know if anyone else has experienced this.

Thanks again,
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Old 11-20-2005, 04:50 AM
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You were receiving IF images on your CB.
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Old 11-20-2005, 05:33 AM
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Quote:
Originally Posted by Highlander_821
You were receiving IF images on your CB.
Sounds like a good idea... SCI-FI channel should pick it up and call it "I-F HUNTERS"

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Old 11-20-2005, 06:50 AM
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The preamp was being saturated by the strong SW signal because it does not have a tuned input and will amplify ALL signals.The signal was so strong going into your CB it caused image freqs. to appear all across the band.The reason the mobile did not do it could be because the antenna did not pick up the signal as good or the CB has a better ability to handle big signals without producing garbage.

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Old 11-20-2005, 10:30 PM
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Most preamps built into linears are "broad-banded". SW broadcasters pump out some serious power. They can overload the radio's front end, and create harmonics. Sounds like you were listening to signals at around one-half the frequency you're tuned to.

A broad-band preamp will cause this on other radios, especially the HR-2510, and some old 23-channel radios I've seen.

Some external (stand-alone) preamps have tuned circuits in them that will help reject this kind of signal. The preamps built into linears nearly always broad-banded, and will pump up a 13.5 Mhz signal as well or better than the 27 MHz you're listening to.

Some antennas will pull in those frequencies better than others. An antenna with a gamma match is less likely to do this than one that is fed directly.

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Old 11-21-2005, 07:21 AM
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Quote:
Originally Posted by nomadradio
A broad-band preamp will cause this on other radios, especially the HR-2510, and some old 23-channel radios I've seen.
I had switched the coax switch to use my HR-2510 to see if I could hear these shortwave stations and I could not, It seemed after switching to different radios that it would only happen on my Cobra 2000GTL. I will say it was fun SWLing and chasing Shortwave DX on my CB.

Thanks,
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Old 11-21-2005, 10:12 AM
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Over the years I've owned three Cobra 2000's and all three would receive SW broadcasts. It is this problem with the 2000 receiver that deters me from ever owning another. I now use a Cobra 2010 and am very satisfied with receiver performance. Look for a technician who can beef up the front-end of your 2000's receiver.

Good Luck!

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Old 11-21-2005, 09:53 PM
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Quote:
Originally Posted by Inspector
Look for a technician who can beef up the front-end of your 2000's receiver.
There is no problem in that department on my Cobra 2000GTL. It is actually very good. Like I said earlier, My receive is dead quiet with no hint what so ever of those shortwave signals unless the pre-amp on the Texas Star 250 HDV is turned on.
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