Backpack portable radio

I'm looking into building a backpack radio. I will be using a metal frame to house a ICOM 7000, IT-100 tuner and a Lithium battery. The frame will be placed in a military surplus backpack, likely a surplus backpack from a PRC-117.

I have seen others create backpack radios from FT-857s and other radios of similar power output. With the FT-857, ICOM 7000 and other similar radios being able to produce high wattage rates. HF 100 watts, VHF 50 watts and UHF 40 watts.

My question is what wattage is safe to use when the backpack radio is being worn by the operator and/or placed on the ground near the operator?

What wattage rates have you safely used when the transmitting antenna is very close to yourself or others?

Thanks in advance,
Ray

Here are several guides and info regarding RF exposure and safety (both govt and non-govt):
RF Exposure

The most detailed info is in FCC/OET Supplement B 1997 titled "Guidelines for Human Exposure to Radiofrequency Electromagnetic Fields - Additional Information for Amateur Radio Stations", and includes freq/power tables for Power Thresholds for Routine Evaluation of Amateur Radio Stations.

The Icom 7000, IC-706MKIIG and similar radios are not good candidates for portable battery operation due to excessive current draw on receive. These radios can use close to 2A receiving and the 7000 is known to be finicky when the voltage gets below about 12v. The Yaesu FT-857 is popular for battery backpack use because the receive current is a more reasonable 600ma or so.

The frequency range of 3 to 30MHz is not as strict as 30MHz and above for exposure limits and SSB or CW (Morse) is less than 100% duty cycle, so higher levels can be used compared to published limits. There is also whole body vs partial body exposure depending on antenna placement which can skew the outcome of the exposure calculations. Remember, the exposure limits are averaged over a 6 minute time period.

The few times I've worked the calculations a 100w backpack rig with antenna starting at shoulder height and extending above was not a problem with 100w anywhere in the HF amateur bands.
prcguy

Thank you to all for your replies and information!

@prcguy, you stated "Remember, the exposure limits are averaged over a 6 minute time period"

Just so I'm understanding correctly this means that the RF exposure is measured over an average of 6 mins. Meaning you could transmit once for 20 seconds within 6 mins or transmit multiple times for a total of 4 mins withing 6 mins. Is this correct? Or is it stating continuous non-stop transmitting for 6 mins?

Thanks for the HF calculations. I will have to calculate FM at 144 mhz and 50 watts per the info "popnokick" attached.

Im not an expert in RF exposure although I have done a lot of compliance measurements. My understanding is for a given occupational level of say 5mw/cm2 at 10GHz, you would be allowed that level for up to 6m continuous or less level for more time or more level for less time.
prcguy

B5496RR said:

Thank you to all for your replies and information!

@prcguy, you stated "Remember, the exposure limits are averaged over a 6 minute time period"

Just so I'm understanding correctly this means that the RF exposure is measured over an average of 6 mins. Meaning you could transmit once for 20 seconds within 6 mins or transmit multiple times for a total of 4 mins withing 6 mins. Is this correct? Or is it stating continuous non-stop transmitting for 6 mins?

Thanks for the HF calculations. I will have to calculate FM at 144 mhz and 50 watts per the info "popnokick" attached.

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