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Old 05-17-2017, 10:50 AM
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Default Less sensitive with AC power?

I have a client who reports that his WS-1040 is much less sensitive when connected to AC power thru the regular Whistler power adapter than when operating off batteries.

I have never seen this occur with any of my Whistler/GRE/RS radios including the similar PRO106 and PSR500.

Has anyone else seen this occur and does anyone know a way he can run the radio off AC power without the degraded sensitivity?

Thanks!
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Old 05-17-2017, 11:20 AM
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I have experienced this. I believe it is due to increased radio interference (possibly being generated by the adapter). At one time, I spliced in a couple of chokes in series with each wire from the adapter to eliminate most of the problem.

Shawn
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Old 05-18-2017, 12:41 PM
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I have the same problem with my TRX-1. I am in a high RF environment near FM and TV transmitters. The TRX-1 seems to have good front end that eliminates the desense problems I had with my PSR-500 as long as the TRX-1 is run on the internal batteries. But, with the provided USB cable, as soon as it is connected to any external device, it goes to 5 bars of noise on the RSSI indicator on VHF and somewhat less on UHF and has severe desense . I tried an additional ferrite choke on the scanner end of the cable and it did not help. It appears that the ambient unwanted RF that the TRX-1 front end blocks gets in through the charging circuit when it is connected.

It was not an apparent issue with the PSR500 since that scanner was desensed to the point of uselessness on VHF in this environment even without external power.

I have found no solution to run the TRX-1 from external power without severe degradation and I assume the WS-1040 has the same issue.
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Old 05-18-2017, 1:19 PM
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There's no reason why that should be the case. As mentioned I'd be highly suspect of interference. These radios come with a linear power supply so it won't make any radio noise. However, any number of other items in one's home may. This is an ongoing and increasing difficulty for those in the 'radio arts' such as ham operators. Cell phone chargers, computer monitors, ethernet routers, TV sets, washing machines, some LED and CFL lamps, battery chargers, and on and on, anything with a switch mode power supply is a potential noise maker. It's not uncommon to find several problem items. Sometimes this noise gets into your power system where it can be passed into your sensitive radio when plugged in. Other times it's radiated.

One solution may be to wind the wire several times through a ferrite toroid (mix 43 would be a good choice to start) to choke this noise. The best course is to find the noise source and stop it. That's a discussion in itself.

Another possibility is the power supply or radio is defective. It's rare but a bad diode in the supply can cause noise as can a bad rectifier in the radio. This noise would typically be in the audio frequency range. The way to test is to plug the radio in away from home, friend's house.

Yet another possibility is overload. It's also rare but being near a broadcast station transmitter can induce enough RF into your power system that when you plug in it's like attaching this re-radiating antenna to your radio. Typically this would be with a full power AM station but can certainly happen with FM. Again, try away from home. My furnace re-radiates WLS 890.
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Old 05-19-2017, 9:19 AM
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Quote:
Originally Posted by AC9BX View Post
There's no reason why that should be the case. As mentioned I'd be highly suspect of interference. These radios come with a linear power supply so it won't make any radio noise. However, any number of other items in one's home may. This is an ongoing and increasing difficulty for those in the 'radio arts' such as ham operators. Cell phone chargers, computer monitors, ethernet routers, TV sets, washing machines, some LED and CFL lamps, battery chargers, and on and on, anything with a switch mode power supply is a potential noise maker. It's not uncommon to find several problem items. Sometimes this noise gets into your power system where it can be passed into your sensitive radio when plugged in. Other times it's radiated.

One solution may be to wind the wire several times through a ferrite toroid (mix 43 would be a good choice to start) to choke this noise. The best course is to find the noise source and stop it. That's a discussion in itself.

Another possibility is the power supply or radio is defective. It's rare but a bad diode in the supply can cause noise as can a bad rectifier in the radio. This noise would typically be in the audio frequency range. The way to test is to plug the radio in away from home, friend's house.

Yet another possibility is overload. It's also rare but being near a broadcast station transmitter can induce enough RF into your power system that when you plug in it's like attaching this re-radiating antenna to your radio. Typically this would be with a full power AM station but can certainly happen with FM. Again, try away from home. My furnace re-radiates WLS 890.
Very thorough and detailed post!
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Old 05-21-2017, 2:23 PM
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I'd guess it's more likely due to detuning of the antenna with the power cord connected, as the cable becomes apart of the antenna system / ground reference when connected to the scanner; I've experienced this as well on various handheld radios. You can replicate this by attaching a way too long of "tiger tail" to the BNC ground, which will have similar effects of detuning the antenna (sometimes it helps, sometimes it doesn't depending on a ton of environmental variables).

Even though the power supply is DC isolated from mains voltage, doesn't mean it is RF isolated, which means that the radio's RF ground reference will now be coupled somewhat to the home's electrical system (which can induce a lot of RF hash as well). The last thing you want for an antenna system is for your home's electrical system to be the ground reference... As mentioned, adding a lot of chokes in a loop on the power cable can help to isolate the radio's RF ground from the home's electrical system by acting as an impedance to RF current flow.

On battery power, the scanner is essentially floating at some arbitrary voltage where the RF ground is coupled to your hand that is holding the radio (i.e. your body is acting as the other side of the antenna), which is commonly the scenario portable antennas are tuned & designed for. For portable transmit antennas, this matters a lot more & can drastically effect antenna tuning / SWR.

Last edited by SPL15; 05-21-2017 at 2:33 PM..
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