Scanner overload?

[kodo]

If I have my BCD436HP scanner on my person and I TX with my HT, will I overload the receiver? Most our HT's are 5W max with a ~6" rubber duck.

What about if I'm using the scanner with a vehicle mounted unit? I think our work trucks have a 35w or 40w transceiver, UHF band with a roof-mounted antenna.

Just asking because I've seen some posts about the Q2 and Q3 semiconductor.

 

[cmdrwill]

We get a lot of professional two way mobile radios in for repair with burned up receiver frontend transistors due to co-located antennas that are too close. Scanners can also suffer the same problem(s).

 

[kodo]

We get a lot of professional two way mobile radios in for repair with burned up receiver frontend transistors due to co-located antennas that are too close. Scanners can also suffer the same problem(s).

Ok so it is possible. Is it likely given the conditions and power levels I'm working with?

 

[ko6jw_2]

Who knows? I have zapped scanners before and had to send them in for repair. I'm very careful now. No one can say how likely it is. There's one easy way to find out.

 

[jonwienke]

If I have my BCD436HP scanner on my person and I TX with my HT, will I overload the receiver? Most our HT's are 5W max with a ~6" rubber duck.

This scenario will not damage your scanner.

What about if I'm using the scanner with a vehicle mounted unit? I think our work trucks have a 35w or 40w transceiver, UHF band with a roof-mounted antenna.

This scenario may damage the scanner, depending on the TX wattage, scanner antenna, and distance between the scanner antenna and the vehicle antenna. I had a friend key a 75W radio once while I was standing about 10 feet from the antenna with the scanner on my belt and nothing bad happened. YMMV.

 

[buddrousa]

I would not want to transmit on my 5 watt walkie with my scanner 2 feet away either.

 

[Delta33]

I use my tk880 at 50watts next to my Gre and it rarely burps when its not supposed to.

 

[ofd8001]

Add me to the list of having a portable too close to a scanner causing scanner damage.

The truck is probably shielding the mobile radio's RF from the scanner antenna, so I doubt that's too much of a worry.

 

[jonwienke]

If you're inside the vehicle with a rubber duck antenna, and the mobile's antenna is outside, the vehicle body will provide enough shielding to prevent damage.

 

[kodo]

I'd be curious to learn what the physics are behind this.

 

[jonwienke]

The same physics that allow radio transmission. Sending an AC signal to one antenna induces an AC voltage in nearby antennas. If the transmitter signal is strong enough, and the antennas are close enough to each other, the induced voltage in the receiving antenna can be high enough to damage the RF input transistors.

 

[kodo]

The same physics that allow radio transmission. Sending an AC signal to one antenna induces an AC voltage in nearby antennas. If the transmitter signal is strong enough, and the antennas are close enough to each other, the induced voltage in the receiving antenna can be high enough to damage the RF input transistors.

Relevant formulae?

 

[buddrousa]

Basic Electronics that is taught in electronic school and then again taught when you work with RF. Study and get your HAM Lic and you will start to understand RF Theory.

 

[royldean]

Relevant formulae?

V=IR

As V goes up, if R is constant, I must go up. Too much I and you fry components in the receiver. Is that good enough? Sheesh.

 

[dlwtrunked]

Relevant formulae?

(Referring to scanner overload that will damage the receiver.)
You will not find one. The exact minimum voltage required for failure will depend on random flaws in the particular receiver components that are not predictable. And no one is going to do the required extensive destructive testing to try to come up with a good probability distribution of those--the answer to them is "just do not do it".

A similar problem is asking for a formula to give the maximum position error with a GPS. That is not possible and the best one can do is give an approximate distribution of error but the maximum error will still not be known. (Having a PhD in mathematics and looked extensively at this, I wish that it was not true.)

In addition, the voltage arriving will depend on the power transmitted (including antenna gain), the receiver antenna gain, the distance between them. There are devices sold to try to protect receivers from such. These were not lightening protection). As I recall, Grove Enterprises (gone) used to sell s small one with Type-F connectors. Also see DEO Receiver Guard 2000 Series but frequency information is not given.

My self, I unplug the mic on a transmitter when its antenna is near a receive antenna on the car and do other things like change the transceiver to a frequency that it cannot transmit on by design. But this is for very close antennas on the roof of a Corolla. Can I operate safely with the antenna spread apart on the car? I do not plan to purposely test that.

Note: Depending on the design, some lightening protectors might provide some protection but others will not. Regarding overload that will cause reception problems (not damage the receiver), that is usually measured and in the specifications.

 

[kodo]

Basic Electronics that is taught in electronic school and then again taught when you work with RF. Study and get your HAM Lic and you will start to understand RF Theory.

You should be able to find the total energy transferred over a given distance, which is an inverse square function. I1/I2=D2²/D1². Antenna efficiency and frequency used probably play a factor also.

From there it seems like the scanner should already have a pre-determined tolerance, which should have been tested by engineers at Uniden..

 

[jonwienke]

You should be able to find the total energy transferred over a given distance, which is an inverse square function. I1/I2=D2²/D1². Antenna efficiency and frequency used probably play a factor also.

Not "probably", more like "*definitely". There's also the relative orientation of the antennas to each other, each antenna's propagation pattern, constructive and destructive interference from reflected waves and their orientation to the receiving antenna, RF absorption from objects between the antennas, etc.

It's too complex and too many unknowns to calculate a minimum "safe distance" with any degree of certainty.

 

[ecps92]

Good thought, but with the Memorize the Answer study guides out there, they don't learn the basics

Basic Electronics that is taught in electronic school and then again taught when you work with RF. Study and get your HAM Lic and you will start to understand RF Theory.

 

[cmdrwill]

The same physics that allow radio transmission. Sending an AC signal to one antenna induces an AC voltage in nearby antennas. If the transmitter signal is strong enough, and the antennas are close enough to each other, the induced voltage in the receiving antenna can be high enough to damage the RF input transistors.

In simple terms, this IS dead on.