TK-890H and RF exposure

[LakeMan2]

I was thinking of using a TK-890H in a vehicle. Then I started thinking of transmitting at 100W with an antenna only a few feet from people in the vehicle. I used an RF exposure calc and it does not look good unless I am missing something. Even using the 40W low power on the 890H still is relatively high RF close by.

Can you tune the 890H to go below 40W and still have the PA function as intended. I am not sure what happens if you run a PA lower then its designed low point.

 

[kayn1n32008]

You should be fine if you mount the antenna on the roof

 

[LakeMan2]

You should be fine if you mount the antenna on the roof

But why?

I was thinking of installing in a jeep such that the antenna would be mounted on top, but on top of a roll bar because there is no metal roof. So if one has to rely on a metal roof to attenuate the signal, I won't have that. If the vertical pattern of a 1/4 or 5/8 UHF whip is poor enough that attenuation is high below horizontal, then I may be ok. I am trying to find some vertical radiation pattern documentation, but so far am still looking.

Thanks

 

[mm]

That radio has already been tested at a FCC authorized facility for MPE with numerous antennnas taking into account occupants inside and outside of a vehicle.

The following is From OET 56 mobile two way radios RF emissions to occupants in the same vehicle:

There is no evidence that there would be a safety hazard associated with exposure
from vehicle-mounted, two-way antennas when the manufacturer’s recommendations are adhered to.


Your radio has already passed FCC MPE tests, as long as you use any of the Mfg recommended antennas you are fine.


Quarter wave, 1/2 wave 5/8th wave antennas were in the original MPE tests..


For your jeep install if you elevate the antenna and mount it on a metal ground plane that is situated above the roll bar then you would be close to the Mfg test in a metal roof vehicle.

 

[LakeMan2]

For your jeep install if you elevate the antenna and mount it on a metal ground plane that is situated above the roll bar then you would be close to the Mfg test in a metal roof vehicle.

So assuming that the radio was tested at full power (100W) and passed on a metal roof, with the open roof I could cut it down to 40W and probably be ok. Would the metal roll bar be enough of a ground plane?

 

[kayn1n32008]

So assuming that the radio was tested at full power (100W) and passed on a metal roof, with the open roof I could cut it down to 40W and probably be ok. Would the metal roll bar be enough of a ground plane?

Run it at the low power setting and use a 1/2 wave and you will be fine.

 

[cmdrwill]

2.5 Antenna Installation IMPORTANT NOTE: To assure optimum performance and compliance with RF Energy Safety standards, these antenna installation guidelines and instructions are limited to metal-body vehicles with appropriate ground planes and take into account the potential exposure of back seat passengers and bystanders outside the vehicle.

NOTE: For mobile radios with rated power of 7 watts or less, the only installation restrictions are to use only approved antennas and install the antenna externally on metal body vehicles. For mobile radios with rated power greater than 7 Watts, always adhere to all the guidelines and restrictions in Section 2.5.1 below.

2.5.1 Selecting an Antenna Site/Location on a Metal Body Vehicle 1. External Installation - Check the requirements of the antenna supplier and install the vehicle antenna external to a metal body vehicle in accordance with those requirements.

2. Roof Top - For optimum performance and compliance with RF Energy Safety Standards, mount the antenna in the center of the roof.

3. Trunk Lid - On some vehicles with clearly defined, flat trunk lids, the antennas of some radio models (see restrictions below) can also be mounted on the center area of the trunk lid. For vehicles without clearly defined, flat trunk lids (such as hatchback autos, sport utility vehicles, and pick-up trucks), mount the antenna in the center of the roof. BEFORE INSTALLING AN ANTENNA ON THE TRUNK LID, - Be sure that the distance from the antenna location on the trunk lid will be at least 85 cm (33 in.) from the front surface of the rear seat-back to assure compliance with RF Energy Safety standards. - Ensure that the trunk lid is grounded by connecting grounding straps between the trunk lid and the vehicle chassis. NOTE: If these conditions cannot be satisfied, then mount the antenna on the roof top.

4. Mounting restrictions for certain radio models - For all VHF and UHF models with the output power set to 30 watts or higher, the ¼ wave antenna shall be mounted only in the center area of the roof, not on the trunk lid, to assure compliance with RF Energy Safety standards.

7. Make sure the mobile radio antenna is installed at least 30 centimeters (1 foot) away from any other antenna on the vehicle.

 

[LakeMan2]

Anyone happen to know how low a power you can run the 890H at (without any negative effects)? I know the specs say 40W, but can you tune it below that say to 25-30W? I know that if you really want that power you could just use a 890, but a 890H is what I will have. I will have everything I need to test it myself, just trying to get a heads up on the probability of it working. I also don't "think" it will hurt the radio to tune/run it at lower than 40W, but just in case someone knows otherwise, I want to ask before I break something..

 

[mmckenna]

Service manual says to set the low power to 40 watts.

I'd be reluctant to tell you to set it any lower without having the correct test equipment. I don't know about the TK-x90's, but I do know that some of the Motorolas will go unstable if you turn them down too far.

If this is a concern, you can pick up other lower powered radios used quite cheap, even the non-H model TK-890's.

And I agree with the others, high RF too close to occupants isn't a good thing. CMDRWill posted what I would have. There's documents like this for a reason. Most of them are for occupational exposure, as in police officer on 10 hour shifts sitting close to the antenna. For amateurs, hobbyists, etc, you may choose to ignore the recommendations, but I wouldn't advise it.

 

[LakeMan2]

Yep, thanks. I have some concerns with the higher RF given that I do not have a full metal roof. Hence my post. The inputs here pretty much say that it is a tough call and it may or may not be an issue, but definitely something to think about.

I will just have to try the lower power on the H and see. I have a service monitor, so I can look at it. I have a 100W MTR2000 that I run at 25-30W and it has been fine but then again the MTR2000 is speced down to 25W. It just depends if that 40W lower limit is hardware limited or more marketing due to the fact that the low power version goes up to 40W.

If I can, I like running the higher power units at much lower power (rather that using a lower powered rated unit) because I operate them in 100+ degree summer temperatures and with the additional heat sinks etc will hold up better.

 

[LakeMan2]

To close this out, I tuned the TK-890H down to 30W and it appeared to run just fine. Power, freq, and deviation looked stable. I did not try to go lower, I just stopped there.