Dodgy Radio Communications

Question

This question relates the same world discussed in this post: Horseback Travel in an Unpopulated Pacific Northwest

Two mounted patrolmen are tasked with navigating and policing a reimagined Coastal PNW, the geography of this area is incredibly vertical and heavily forested. I understand this would naturally be unforgiving to signal transmission. That said, one of the patrolmen is a Field Radio Operator, he wears a pack much like the US Army had in the 80s and is able to send and receive transmissions from their support Airship, his partner, however, only has a very short-range communicator, (1-2 miles) only able to basically "walkie talkie" with his partner.

This short range communicator is written to where it cannot reach the airship due to its power, but the serviceman with the full pack is able to pass on the transmissions from the airship through the walkie talkie to his partner, is this realistic? Would this make sense given the physical setting and technological limitations of the universe? (No satellites, no well established supertall radio masts in the region, no smart tech) I understand that the Airship would act as an excellent semi-permanent radio transmitter/ signal repeater, but I am having trouble figuring out how to limit one of the servicemen's radio capability realistically.

As they move through the region, North from Vancouver Island towards Sitka, AK, they have semi-mobile radio towers airdropped to them, these cement a radio footprint and set up an emergency frequency for the denizens of the region to call for help. Please someone with radio transmitting knowledge help me out here.

Answer 1

I believe communications range is a function of antenna size and power. (And that's without taking the geography into account). More of both means you can emit a stronger signal, which means people further away can receive it. That's because a radio signal is just an electromagnetic emission.

Think about the radio in your car or bedside alarm. It can pick up local radio stations just fine, but it can't transmit back to them. That's because receiving and transmitting are different.

So, the reason your two patrolmen have different communications abilities is because that backpack has a big antenna and a big signal amplifier. The reason both patrolmen can receive from the airship is because the airship has a huge antenna and amplifier. The reason one patrolman can only transmit to the other is because s/he has a smaller antenna and amplifier.

The particulars of the terrain then work as additional constraints on top of the basic facts about differing transmission power.

Answer 2

I have worked in the region (PNW) with hand held radios in small teams. Some places had repeaters set up. Some places we worked with helicopters. So a range of scenarios.

For radios it really depends on topography. Do you have line of sight? If you have line of sight, most other factors like transmit power, antenna placement don't really matter. The other factors matter when you don't have line of sight. But not completely blocked by hills/mountains etc.

Scenarios that are similar to what you seem to be asking about that I have personally encountered. All using the same radio equipment unless noted.

Person A needs to talk to B and C. Both B, C are 1Km away from A. But B is separated from C by 200m. Due to topography(C has dropped elevation faster then B). A can talk to B. B can talk to C. But C and A can't hear each other. B relayed messages from A to C.

Person A, B are on a 60% slope. B is higher then A by 5m vertical. B can talk to C via radio. A and C can't talk to each other via radio. Once B walked up the slope they can communicate to C as well.

Person A has a second hand held radio with a whip that has extension wire that allows it to be elevated by 3 meters on the end of a stick. The radio with elevated antenna allows an additional 500m of range on flattish terrain.

A repeater was place on a mountain top. The team was 3KM further down a Valley from the repeater. Person A could hit the repeater while they are up one of the sides of the valley. Person B in the valley bottom directly below person A couldn't hit the repeater. Person A can talk via radio to person B as they are about 400m away from each other.

Persons A, B have are within 5m on level ground. A's radio picks up conversation clearly. B's radio only picks up one weak fragment. Probably partially broken hardware.

Person A is in fixed location using a 50W transmitter. All others can hear A clearly. A can only hear two out of five of the others.

If I understand your scenario, it is common. You can achieve your scenario even if both of your people have the same hardware so as long as they are separated by some distance or better yet, by elevation. You can even have situation where the person with the handheld can talk to your airship base, where the person with the better gear can't, just depends on where they are relative to each other.