Wattage to Miles Ratio

[WRVG593]

Hey there, I was thinking about this while sitting at work. Obviously half watt radios are not going to get very far, and an "emergency amatuer radio" that Transmits 100 watts on GMRS frequency is going to reach much farther. And line of sight has the biggest factor when it comes to the GMRS channels especially. But let's say a clear highway, completely straight, or even a field completely flat, was to he utilized.

How far does that Half Watt Walmart FRS Radio transmit? 1 mile? 3 miles for the horizon? 35 miles to a mountain? How far does the 25 watt go? 50? How much does it matter for How much juice you're getting? It's not like amatuer where you get 1500 watts. Does 5-50 really change alot?

[bd348]

FRS is 2 watts now.  In suburbia I get .75 to 1 mile, or 1.5 to a mobile unit with its better antenna.  Going to 5 watts GMRS with a half-wave antenna goes a bit further.

[MichaelLAX]

If you are going to compare a HT with fixed rubber Duckie antenna to a mobile higher powered rig with an external antenna; there is just no comparison, whether or not either or both are on VHF or UHF.

The mobile is always better in that situation. Irrespective of the difference between 2 to 50 watts, the fixed HT antenna to mobile external antenna, is going to be a big differential. 

I am not aware of Amateurs who use 1,500 watts for VHF/UHF unless perhaps some sort of experimental transmissions to a NASA interstellar vehicle.

The major advantage of 2 watt FRS radios are that they are easily purchased on the way to a field trip by a road group and GMRS users can communicate with them.

For the most part GMRS users cannot communicate with MURS that easily.

[gortex2]

It all depends on line of sight. When we scout repeater sites for our SAR stuff we actually used FRS radios alot. My opinion is if I can talk on 2 watts from a mountaintop to a handheld in an area I need coverage a 25 watt repeater will be more than suitable. I have UHF SAR repeaters running 25 watts that can hear a 4 watt portable fine from 40 miles out. But you can see the tower from 40 miles. 50 watts is max on GMRS. I have never needed that much power for anything I do on GMRS and both my Jeeps have the MTX Midland at 15 watts. Never had issues with either talking to who I need to.

BTW.. there is no such thing as a "Emergency Amateur Radio". If an amateur radio is being used they have different licensed frequencies for power levels. Amateur Radio frequencies are not GMRS and amateurs cannot use 100 watts on GMRS just becasue.

[WRVG593]

57 minutes ago, gortex2 said:

It all depends on line of sight. When we scout repeater sites for our SAR stuff we actually used FRS radios alot. My opinion is if I can talk on 2 watts from a mountaintop to a handheld in an area I need coverage a 25 watt repeater will be more than suitable. I have UHF SAR repeaters running 25 watts that can hear a 4 watt portable fine from 40 miles out. But you can see the tower from 40 miles. 50 watts is max on GMRS. I have never needed that much power for anything I do on GMRS and both my Jeeps have the MTX Midland at 15 watts. Never had issues with either talking to who I need to.

BTW.. there is no such thing as a "Emergency Amateur Radio". If an amateur radio is being used they have different licensed frequencies for power levels. Amateur Radio frequencies are not GMRS and amateurs cannot use 100 watts on GMRS just becasue.

Technically per the FCC, are we not able to use any radio on any frequency in the case of an emergency or life saving event? That is what I mean by emergency amatuer that can broadcast on those channels. I know they can't just do it just because. 

[gortex2]

That's an incorrect statement. They are allowed to use any Amateur Radio Frequency only. I'm sure this will spark a debate but that's the rules. Most hams will bend them to allow them to talk on public safety and other frequencies claiming the rule. 

[WRVG593]

33 minutes ago, gortex2 said:

That's an incorrect statement. They are allowed to use any Amateur Radio Frequency only. I'm sure this will spark a debate but that's the rules. Most hams will bend them to allow them to talk on public safety and other frequencies claiming the rule. 

So there's NO way even during a forest fire that people could use a Ham Radio to talk on GMRS in the event to be saved? There's no statue in the FCC rules allowing and turning their cheek to this? 

[wrci350]

49 minutes ago, gortex2 said:

That's an incorrect statement. They are allowed to use any Amateur Radio Frequency only. I'm sure this will spark a debate but that's the rules. Most hams will bend them to allow them to talk on public safety and other frequencies claiming the rule. 

No debate from me on the fact that what the rule says is that hams can use any *amateur* frequency in an emergency.

I will, however, disagree with your assertion that "Most hams" think otherwise.  Some?  Oh definitely.  But not most.

[gortex2]

21 minutes ago, WRVG593 said:

So there's NO way even during a forest fire that people could use a Ham Radio to talk on GMRS in the event to be saved? There's no statue in the FCC rules allowing and turning their cheek to this? 

There is no rule stating you can use another service with an approved device in another service. So yes. Does it happen. Probably. Is it right. Not by the rules. To be honest I'm not relying on any radio in an emergency. Way better stuff to rely on. 

[bd348]

To get back to the original question, one person's take is at:

GMRS Radio Range Chart

 

[KAF6045]

There are too many variables involved to formulate a "power <-> distance" relationship.

A 1W radio can reach LEO satellites, maybe a bit more power for the ISS. In totally bare regions, the same is likely limited by horizon distance (well, if just skimming the horizon, maybe 2X horizon distance -- radio to just above horizon to receive radio). Frequency -- VHF tends to work better in foliage, UHF in urban areas (the shorter wavelength can get through window and door frames which may appear as Faraday cages to longer wavelengths). The rare tropospheric ducting can pass signals for miles (Hawaii to California has been known to occur).

 

[OffRoaderX]

The official answer is "It depends" ...

[SteveShannon]

12 minutes ago, KAF6045 said:

There are too many variables involved to formulate a "power <-> distance" relationship.

A 1W radio can reach LEO satellites, maybe a bit more power for the ISS. In totally bare regions, the same is likely limited by horizon distance (well, if just skimming the horizon, maybe 2X horizon distance -- radio to just above horizon to receive radio). Frequency -- VHF tends to work better in foliage, UHF in urban areas (the shorter wavelength can get through window and door frames which may appear as Faraday cages to longer wavelengths). The rare tropospheric ducting can pass signals for miles (Hawaii to California has been known to occur).

 

7 minutes ago, OffRoaderX said:

The official answer is "It depends..."

Both of the statement above, by @KAF6045 and @OffRoaderX are correct. The rest of my post is useless except as a geeky point of interest. 

There is a calculation that can be done to determine theoretical loss at given distance, but it assumes perfect conditions, i.e. "Free Space."  That could useful for establishing an absolute outer limit for distance.  Great for space travel. The equation looks like this: 

d is the distance between the receiving antenna and transmitting antenna.

f is the frequency in Hertz

c is the speed of light in the same units your distance is in.

Gt is the gain of the transmitting antenna

Gr is the gain of the receiving antenna

Here's a calculator built to use it: 

https://www.pasternack.com/t-calculator-fspl.aspx