While Potato Country is a rather large (and vague) area, knowing a bit more closely about the conditions around and more importantly, BETWEEN the two (or more) houses that you want to communicate with is the main factor... And this goes for ANYONE wanting to communicate with the other locals in your group.
Ask yourself these questions:
- Can I physically see (with your eyes, binoculars, or a telescope) the other locations from my house (even if this is only when standing on your roof)?
- Can I guarantee that there is only trees and other houses between my house and the other houses?
- Do I know for a fact that there is actual Earth between me and the other houses?
The Earth is NOT Flat, nor is it perfectly round. It's rather lumpy, even on the supposedly flatter or rounder parts. Even the ocean gets an attitude and stays rough. That being the case, and added to the fact that everything that is matter works against a RF signal going from one point to another (including atmospheric air), anything between you and the other houses is going to attenuate (reduce) the signal. If you reduce it too much, then you won't have enough signal level at the far end to make the connection reliable. And adding to that fact, the issue that different frequencies are attenuated by different matter, at different amounts (but USUALLY, the lower the frequency, the lower the attenuation).
So let's get a bit technical for a moment. I won't go into too much detail, but lets look at the science behind the signal for a moment. Radio communication is basically a transmitter that produces a signal on a certain frequency (in Hertz (Hz), or a multiple of that KHz, MHz, GHz (Kilohertz Megahertz, Gigahertz)), at a certain power level (watts or milliwatts (thousandths of a watt), that is received some distance away by a receiver that has a certain threshold above the noise level to overcome before it can actually detect that wanted signal. The receiver's sensitivity to incoming signals is usually in microvolts (millionths of a volt). Radio receivers are a rather sensitive lot, they don't take much of a signal to get them to work. That being said, a LOT of things are working against the whole process of getting that signal from your mouth to someone else's ear. The total attenuation from losses inside the transmitter, to losses in the coax feed lines both at the transmitter site, to the receiver's site, as well as antenna losses (or gains), receiver sensitivity and losses, and the attenuation of all of the matter between the antennas, is called "PATH LOSS". We can control some of the factors, but not all.
Before we dive deeper, I want to mention that the math is MUCH easier if we convert the details to decibel form. For example, the sensitivity of most current receivers runs around .1 to .5 microvolts, but the transmitters run from 500mw to 1500 watts. If you convert the receiver sensitivity from .3 microvolts to -118dB/m, and then convert our mild FRS radio transmitter at 500mw ( 1/2 watt ) to 27dBm. You can use the chart at (
http://wa8lmf.net/miscinfo/dBm-to-Microvolts.pdf ) to convert the receiver sensitivity, and the website at (
https://www.pasternack.com/t-calculator-power-conv.aspx ) for the transmitter watts to dBm. What this does is allow you to use simple math now to check and see how much overhead you have on your signal to see if the path loss is going to kill it. 27dBm - (-118dBm) =
145dBm of signal to play with before you can't communicate at all.
The air attenuates HF, VHF, and UHF frequencies at ground level (less than 1km above sea level) at around .06dBm/km. Trees and forests nail the signal a lot harder than just air, but the attenuation varies with the frequencies of the signal involved. HF signals (3MHz to 30MHz) travel
fairly well through forests, losing about 3-12db per km depending on how thick the forest is, how wet it is, and whether you are trying to transmit through the trunks or the canopy. This loss increases to 15-85dB per km at VHF frequencies (30MHz to 300MHz), and up as high as 160dB per km for UHF frequencies. This is why CB radios at 26-27MHz (HF Frequencies) work MUCH better than FRS/GMRS radios at 462-467MHz (UHF frequencies), and MURS and 2meter Amateur work somewhere in between the two (they are in the middle of the VHF range). Earth (Soil/Dirt/Rocks...) doesn't pass much in the way of HF, and even less on VHF and UHF. Attenuation of the Earth is WAY up there and not even worth trying to make work.
Going back to the example of the FRS walkie talkie with 500mW of power on 462-467MHz, with a signal overhead of 145dBm, we can see that the signal is not going to make it more than a km through the woods (unless they are mighty thin and you are transmitting through the trunk area and not the canopy) since a dense canopy can eat 160dBm of your 145dBm overhead. So a cheap FRS radio is not going to make it even the first kilometer through. BUT, if there was no forest (say, mountaintop to mountaintop), then that signal could go (145/.06)=2416km. This is why there are many reports of people with cheap FRS/GMRS walkie talkies being heard hundreds of miles away (and why things in space can pickup those signals with ease...). This is all great you say, but you don't live on mountaintops, and neither do your friends you want to talk to. OK, back to the problem at hand. We either need to raise our power levels at the transmitter site, raise our antennas over the obstructions (trees or Earth), OR change our frequencies to see if that helps. Let's kick up the power at first. Let's upgrade the 500mW FRS radio to a 5 watt Baofeng. Now we are cooking with 5 watts (37dBm) instead of 27dBM. 37dBm-(-118dBm)=155dBm overhead at 5 watts transmit power. Better, but still less than the 16dBm of signal eating forest attenuation. OK, so 10 times the power didn't help. Let's change the frequencies down to CB land...
CBs have a power output of 4 watts on AM, or if you have a SSB capable one 12W on SSB. PLUS, the attenuation at HF frequencies is a LOT lower. 4 watts is right at 36dBm, 12 watts is close to 40.8dBm (still not that much more usable power than the 5 watt handheld at 37dBm). But, as we said earlier, the attenuation at these frequencies is MUCH better. Let us estimate the losses of one km of forest at around 10-12dBm. I will leave the receiver sensitivity the same as the other radio as they will be close enough for the "back of a napkin" math. Next we figure the AM transmitter overhead at 36dBm- (-118dBm)=154dBm. And the SSB transmitter overhead at 40.8dBm- (-118dBm)=158.8dBm. It doesn't look that much better than the FRS at this point, but wait... At 10-12dBm per km, you are now looking at 154/12=12.83km before signal loss at the worst for AM, and 158.8/12=13.23km before signal loss using SSB. So a few kilometers COULD be done through the woods with CB, but not FRS/GMRS. Now, these calculations are only working with the space between the antennas Path Loss, and none of the other losses or issues so this is no guarantee either way but at least a good baseline.
My suggestion, go with SSB CB, or try to get above the treeline or the Earth's horizon. The better suggestion would be to get your Amateur radio license (and every one else in the group the same), and that way they can run with 50 watt mobiles, or use handhelds and the already exiting repeaters.
Loup
www.wearecb.com
