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Way off topic: Radio antennas
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james89es
I know this has nothing to do with Tek-scopes (I do own a RM547, so I
do belong "in the club") but I know many of you are also into HAM radio. Here's the story: I bought my mother a new police scanner (from Rasio Shack) for x- mas. She has had scanners for 25+ years. Her old Uniden was 15 years old. The outside antenna is about 20 years old. Problem: When we plug the outside antenna into the new scanner, it CAUSES static and reduces signal strength!! I ruled out the plug on the radio itself by connecting a short piece of cable, and touching the bare wire with my finger. In this scenario the signal is stronger and there's less static when I touch the wire, as I would expect. Once I plug in the outside antenna, however, more static and less strength ... even if I leave the little inside antenna on. They replaced the coax just in case, they used the recommended 50ohm cable - a run of about 30 feet. What would explain this?? Keep in mind that the old Uniden still works fine with the outside antenna. |
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John Miles
Might be a symptom of front-end overloading. What does the "static" sound
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like -- AM-style random static, or distortion of a tonal (pager transmitter?) signal? -- jm ----- Original Message -----
From: "james89es" <james89es@...> To: <TekScopes@...> Sent: Tuesday, January 01, 2002 8:20 PM Subject: [TekScopes] Way off topic: Radio antennas I know this has nothing to do with Tek-scopes (I do own a RM547, so I |
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james89es
The static is AM style. What I did was: tune in one of the weather
stations so there was a constant signal. It was fine with the small inside ant. Then I unplugged the inside ant. and the signal got weaker and a little static was mixed in. Then I plugged in the outside ant. and the signal got very weak with much more static. The same procedure using my finger as the ant. would make the signal stronger. (I know what you mean about pager transmitter signals - it wasn't that). Note: we are NOT trying to use one ant. in two radios at the same time. We unplug from one then plug into the other. Thanks, by the way, for responding so quick. --- In TekScopes@y..., "John Miles" <jmiles@p...> wrote: Might be a symptom of front-end overloading. What does the "static"sound like -- AM-style random static, or distortion of a tonal (pagerso I thedo belong "in the club") but I know many of you are also into HAM 50ohmbare wire with my finger. In this scenario the signal is stronger cable - a run of about 30 feet. |
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Michael
Hi,
Maybe - just maybe, there is a problem with the outside antenna. Perhaps the centre conductor is open circuit at the actual antenna, and the signal you're getting from it is being picked up and fed to the scanner via the shield... Depending on the individual configuration of the two scanners' input circuitry, the Uniden may have been happy with this, the new one may not be. Especially if the new scanner has a ground connection, and grounds the antenna shield... Just 2c worth. :) Michael |
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james89es
Could you explain what "front-end overloading" would indicate?
Radio's fault or antenna's fault? --- In TekScopes@y..., "John Miles" <jmiles@p...> wrote: Might be a symptom of front-end overloading. What does the "static"sound like -- AM-style random static, or distortion of a tonal (pagerso I thedo belong "in the club") but I know many of you are also into HAM 50ohmbare wire with my finger. In this scenario the signal is stronger cable - a run of about 30 feet. |
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Don Black
I wonder if the aerial connection could be inducing hash from a switchmode
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power supply (if it has one). Is there any difference in earthing between the two sets? Don Black. james89es wrote: Could you explain what "front-end overloading" would indicate? |
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John Miles
The new scanner may be more vulnerable to overloading caused by too much
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signal from a nearby transmitter. For many years now, the trend in all types of receivers -- not just scanners -- has been toward untuned front ends, and not all of the manufacturers have responded by using the better preamps, mixers, and synthesizers you need when you don't have any meaningful preselection. It's not uncommon for older receivers to perform better in the presence of strong signals than newer ones do. Although if what you're hearing is genuine "static," that sounds like a bad connection somewhere in the antenna system. Why it would affect the new scanner but not the old one is anyone's guess... you will probably just have to take the whole antenna system apart for a careful inspection. -- jm ----- Original Message -----
From: "james89es" <james89es@...> To: <TekScopes@...> Sent: Wednesday, January 02, 2002 7:49 AM Subject: [TekScopes] Re: Way off topic: Radio antennas Could you explain what "front-end overloading" would indicate? |
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I will through in my 2 cents worth: does new scaner has 50 Ohm antenna input? A piece of wire is a high impedance ' antenna.
Regards Miroslav Pokorni james89es <james89es@...> wrote: I know this has nothing to do with Tek-scopes (I do own a RM547, so I do belong "in the club") but I know many of you are also into HAM radio. Here's the story: I bought my mother a new police scanner (from Rasio Shack) for x- mas. She has had scanners for 25+ years. Her old Uniden was 15 years old. The outside antenna is about 20 years old. Problem: When we plug the outside antenna into the new scanner, it CAUSES static and reduces signal strength!! I ruled out the plug on the radio itself by connecting a short piece of cable, and touching the bare wire with my finger. In this scenario the signal is stronger and there's less static when I touch the wire, as I would expect. Once I plug in the outside antenna, however, more static and less strength ... even if I leave the little inside antenna on. They replaced the coax just in case, they used the recommended 50ohm cable - a run of about 30 feet. What would explain this?? Keep in mind that the old Uniden still works fine with the outside antenna. Yahoo! Groups SponsorADVERTISEMENT To unsubscribe from this group, send an email to: TekScopes-unsubscribe@... Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service. --------------------------------- Do You Yahoo!? Send FREE video emails in Yahoo! Mail. |
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