Maximum safe signal input level for Whistler scanners?

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prcguy

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Would it be possible for Whistler to comment on the maximum safe signal input level their scanners can withstand without damage? This is not for causing interference or degrading reception, this would be the point where the scanner could be damaged.

The reason I'm asking is because there are a lot of scanner users that also run 2-way radios in the same vehicle or house with their transmit antennas very close to the scanner antenna. This can couple a lot of power from the transmit antenna to the scanner antenna and in some cases there can be several watts of power fed into the scanners antenna connector.

It would be nice to have a "not to exceed" level and its also not difficult for many scanner users to put a wattmeter and load on their mobile or base scanner antenna to measure what is being picked up and fed into their scanner from the nearby transmit antenna.

This may also help Whistler by informing customers and preventing scanner damage which can save on warranty returns, etc.

Hello Wendy, can you help us?
prcguy
 

Machria

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Interesting question... but is there "really" actual power put into the scanner? Isn't it just a strong "signal" that would make the radio be over modulated... hmmmm, just thinking out loud. I do have this problem on my boat, if I key up my VHF radio while my Sat TV receiver is on, the Sat receiver blacks out for a few seconds and has to re-establish the signal to the sat. BUT it does not damage it, just makes it loose reception temporarily.

My VHF is 25 watts, and is 2' from a 12" Sattelite dish, so I'm sure it get considerable "signal" from it.

Anyway, just thinking out loud.... Has anyone ever damaged a scanner this way?
 

BrianG61UK

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Interesting question... but is there "really" actual power put into the scanner? Isn't it just a strong "signal" that would make the radio be over modulated... hmmmm, just thinking out loud. I do have this problem on my boat, if I key up my VHF radio while my Sat TV receiver is on, the Sat receiver blacks out for a few seconds and has to re-establish the signal to the sat. BUT it does not damage it, just makes it loose reception temporarily.

My VHF is 25 watts, and is 2' from a 12" Satellite dish, so I'm sure it get considerable "signal" from it.

Anyway, just thinking out loud.... Has anyone ever damaged a scanner this way?
In this case the frequencies evolved are massively different. The satellite antenna will barely work at VHF and any initial out of band signal rejection will also massively reduce the signal. In fact I'd guess the problem you have is probably the cable to the dish picking up the VHF signal and injecting it in common mode so that it disturbs some sensitive part (could be almost any part) sensitive part of the receiver.

Now two similar VHF or UHF antennas side by side on the side of a house and one transmitting say 20W, I'd say the other could easily pick up a watt of power, which could easily do damage.
 

prcguy

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It would be power or RF voltage X current into whatever impedance the scanner presents at that frequency. At some point you would exceed maximum ratings of front end components in the scanner and damage would occur.

I don't know if that happens at 20mw into the scanner or 100mw or 1/2 a watt, etc.I can't imaging being able to shove several watts of power into the scanner and have it survive and with some users setups you can easily do that.
prcguy

Interesting question... but is there "really" actual power put into the scanner? Isn't it just a strong "signal" that would make the radio be over modulated... hmmmm, just thinking out loud. I do have this problem on my boat, if I key up my VHF radio while my Sat TV receiver is on, the Sat receiver blacks out for a few seconds and has to re-establish the signal to the sat. BUT it does not damage it, just makes it loose reception temporarily.

My VHF is 25 watts, and is 2' from a 12" Sattelite dish, so I'm sure it get considerable "signal" from it.

Anyway, just thinking out loud.... Has anyone ever damaged a scanner this way?
 

Machria

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In this case the frequencies evolved are massively different. The satellite antenna will barely work at VHF and any initial out of band signal rejection will also massively reduce the signal. In fact I'd guess the problem you have is probably the cable to the dish picking up the VHF signal and injecting it in common mode so that it disturbs some sensitive part (could be almost any part) sensitive part of the receiver.

Now two similar VHF or UHF antennas side by side on the side of a house and one transmitting say 20W, I'd say the other could easily pick up a watt of power, which could easily do damage.
Gotcha, good point. And my cables do run right along side each other for 20' or so...
 

popnokick

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prcguy's original question... which BTW applies to all scanner mfrs, not just Whistler... has still not been addressed in this thread. His question was simple: "... comment on the maximum safe signal input level their scanners can withstand without damage". HIs question did not ask about preventing or limiting potential damage, but rather at what point does it occur?
If scanner / receiver manufacturers are doing this testing, they are certainly not publishing the results. I would think (hope) the answer would be in watts (rather than milliwatts). But I see two possible types of damage (and there are references elsewhere in RR and other published tests) referring to damage -
Type 1 Damage- Something goes "pop" or fails completely during a surge of RF and the receiver goes dead permanently. Doesn't matter where in the front end or what component elsewhere in the receiver has failed... the result is when you turn on the receiver it no longer works.
Type 2 Damage - After a surge of RF coming into the antenna, the scanner / receiver is "wounded" in a way that reduces its sensitivity. It still works, but with the receiver sensitivity impaired from where it was prior to the surge of RF.
Based on my experience with mobile VHF / UHF FM transmitters operating with antennas within 3-5 feet of the scanner receiver antenna (a variety of Uniden models over the years)... I'm thinking this is going to be a rather high wattage before Type 1 or Type 2 damage occurs. I frequently have my scanner on and it WILL blank out or directly receive the signal from my FM transmitter.... but I have not seen evidence of permanent damage. I've read accounts where persons claim otherwise.... even with scanners that are shut off / not powered on. Have also read accounts of CB radio receivers being damaged in this manner. But prcguy's "not to exceed" RF input level at the antenna would be a useful figure for EVERY manufacturer to include in their specs.
 

BrianG61UK

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My guess would be 0.1W probably okay 0.5W definitely be worried, but may not cause damage. 2W lucky escape if you don't cause damage.
 

Chronic

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Gain

Antenna gain is going to complicate your calculating. Seeing how a rubber duck antenna is basically a glorified dummy load , adding a aftermarket or external antenna is going to change the calculations. what method is going to be used to determine the exact amount energy going into the antenna connector on the scanner? What about driving past a AM broadcast station running 50 or 100 KW , would that not certainly be enough to induce damage?
 

popnokick

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The test would not use antennas at all. The transmitter would be connected directly to the antenna input and initially set to very low power. Power would be increased in increments until a Type 2... and eventually Type 1 failure occurs. And has been noted in this thread, it may be frequency-dependent, so tests should be done using different transmitter frequencies as well. This will of course "burn up" a lot of scanners in the lab.... which is likely why it (apparently) is not being done. And no.... strong AM or FM broadcast transmitters in the vicinity of a mobile scanner don't damage them. They will come in on CloseCall.... or sometimes cause receiver desense temporarily. Which is why I wrote it takes pretty high wattage at the antenna input to cause damage. The original question was, "How much?"
 

Chronic

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The test would not use antennas at all. The transmitter would be connected directly to the antenna input and initially set to very low power. Power would be increased in increments until a Type 2... and eventually Type 1 failure occurs. And has been noted in this thread, it may be frequency-dependent, so tests should be done using different transmitter frequencies as well. This will of course "burn up" a lot of scanners in the lab.... which is likely why it (apparently) is not being done. And no.... strong AM or FM broadcast transmitters in the vicinity of a mobile scanner don't damage them. They will come in on CloseCall.... or sometimes cause receiver desense temporarily. Which is why I wrote it takes pretty high wattage at the antenna input to cause damage. The original question was, "How much?"
I think you missed my points.
i talking about the scanner user , how are they going to know how much power is entering there scanner antenna jack with say a 50 watt 2 meter rig with a antenna 3 feet away from the scanner antenna ? is 50 watts at 3 feet much different than say that 100 KW station at a 1000 feet away ? Energy coming through the air and then through the antenna then into the scanner is much different than a direct connection to the scanner . directly touching a 2m antenna transmitting at 50 watts will certainly give you rf burns on sensitive skin, but then take the scanner antenna off and hold the connector to the same sensitive skin and put it in close proximity to the transmitting 50 watt antenna and there will be much much less rf. and as far as my point of how is that amount of power that will cause damage to a scanner going to be measured , how is it going to be measured by the average scanner user ? instead of a number in Watts or Volts , maybe it would be more informative for whistler to say no antennas transmitting 50 watts or greater any closer than a specified number of feet from the scanner antenna .
 

jonwienke

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You can't do that, because the degree of coupling between two antennas depends of the radiation/gain pattern of each antenna, vertical and horizontal distance between antennas, and how each antenna is tuned.

The only way to measure is to connect a wattmeter with a dummy load to the RX antenna (connecting the RX antenna to the TX input on the meter, and the dummy load to the meter output), then key up the transmitter and see what reading you get.

I don't have any idea what power level is safe for Whistler scanners, but my 436 handles 500 milliwatts of VHF coming through the antenna regularly without damage. YMMV.
 

prcguy

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All I'm looking for is for the mfr to provide a "not to exceed level" into the scanners antenna connector and from that point the user can calculate or measure their setup so see if its within a safe range. A gain antenna has specs that can be entered into a calculation to approximate the users potential level he might put into the scanner.

This not to exceed level would be mostly for people who have external scanner antennas mounted very close to VHF/UHF/800 transmit antennas where the scanner would be most susceptible to damage within that frequency range.

Driving past a 50kW AM radio station would not be of any concern since the scanner antenna at AM broadcast frequencies is such a small fraction of a wavelength it would not pick up enough to damage anything. I believe most scanners have high pass or band pass filters that reject some out of band signals, providing further protection from AM broadcast, HF transceivers, etc.

If the scanner mfrs cannot provide a "not to exceed level", then I would assume I can mount my high gain scanner antenna 3" from my high gain UHF antenna fed with 300w and no damage will occur. If my scanner does break because of this I will assume I can send it in under warranty because I have not done anything the scanner mfr has warned me not to do.
prcguy




Antenna gain is going to complicate your calculating. Seeing how a rubber duck antenna is basically a glorified dummy load , adding a aftermarket or external antenna is going to change the calculations. what method is going to be used to determine the exact amount energy going into the antenna connector on the scanner? What about driving past a AM broadcast station running 50 or 100 KW , would that not certainly be enough to induce damage?
 

jonwienke

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All I'm looking for is for the mfr to provide a "not to exceed level" into the scanners antenna connector and from that point the user can calculate or measure their setup so see if its within a safe range.
Providing that spec would be good. But the only way to see if you're approaching or exceeding it is to hook a meter to the scanner antenna in situ and see what wattage hits the meter. There are too many variables to dumb it down to a simple "X feet between antennas at Y power level"
 

prcguy

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The scanner user can look up a simple RF path loss calculator with a google search and there are lots of them. Inter your frequency range, power level, known antenna specs, distance, and you have some good information.

The ONLY thing a scanner mfr can do is research the components in the front end of their scanner, or do destructive testing and from that determine a not to exceed level. It would probably be a statement something like "within the frequency range of X to XX, do not exceed XXdBm into the scanners antenna connector, otherwise this will void your warranty."

It would then be up to the user to determine if his or her setup is within a safe range. There are lots, and I mean a whole lot of people who use their scanners mobile with an external antenna mounted within a few feet or less from their high power VHF/UHF amateur transmit antennas. What about TV/radio/newspaper employees with scanners mounted in their vehicles with company transceivers and antennas mounted very close?

I would think there is an amount of radios sent in for repair because they were damaged by high RF levels into the scanner. But maybe not? We don't really know unless the scanner mfr states input level specs or lets us in on how many scanners get returned and it turns out the front end is toasted. Don't hold your breath on that last one.
prcguy


I think you missed my points.
i talking about the scanner user , how are they going to know how much power is entering there scanner antenna jack with say a 50 watt 2 meter rig with a antenna 3 feet away from the scanner antenna ? is 50 watts at 3 feet much different than say that 100 KW station at a 1000 feet away ? Energy coming through the air and then through the antenna then into the scanner is much different than a direct connection to the scanner . directly touching a 2m antenna transmitting at 50 watts will certainly give you rf burns on sensitive skin, but then take the scanner antenna off and hold the connector to the same sensitive skin and put it in close proximity to the transmitting 50 watt antenna and there will be much much less rf. and as far as my point of how is that amount of power that will cause damage to a scanner going to be measured , how is it going to be measured by the average scanner user ? instead of a number in Watts or Volts , maybe it would be more informative for whistler to say no antennas transmitting 50 watts or greater any closer than a specified number of feet from the scanner antenna .
 

jonwienke

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Perhaps it would be helpful if someone who fried their scanner with too much RF did a post-mortem with a meter to see exactly how much RF at what frequency was required to damage their scanner or other radio.

That would at least establish some upper limit to avoid.
 

NM9X

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Perhaps it would be helpful if someone who fried their scanner with too much RF did a post-mortem with a meter to see exactly how much RF at what frequency was required to damage their scanner or other radio.

That would at least establish some upper limit to avoid.
I have an old uniden portable 80 ch. scanner I could experiment with that I wouldn't miss. I'm sure the front end of that differs from the 436 so not sure if it would be a particularly useful sacrifice.
 

KR3LC

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My experiences...

My current situation has a mobile scanner antenna mounted the width of the trunk of my Mustang away from a dual band amateur antenna. I run 35-50 watts and have never had a a scanner fail. The scanner does go pretty deaf when I transmit but always returns to normal. The broadcast radio goes silent when I transmit and returns normal afterward too.

Now in a another vehicle situation I had a portable scanner with the rubber duck on the instrument panel about 18 inches line of site from a dual band amateur antenna mounted on the front fender and that scanner eventually went deaf.
 

jonwienke

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I have an old uniden portable 80 ch. scanner I could experiment with that I wouldn't miss. I'm sure the front end of that differs from the 436 so not sure if it would be a particularly useful sacrifice.
AFAIK no manufacturer is providing this spec. The fry point is going to vary between manufacturers and models, but having any data is better than the nothing we have now.
 
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