Connected to a Repeater over 75 miles Away! How?

[3cRadio]

greetings all!

new to gmrs radio and had a repeater question.  anyone now how its possible for my base station (20w) radio to make contact (receive & transmit) to a repeater that's over 75 miles away?  i'm using a amazon special gmrs fiberglass antenna that's only mounted 10 ft off the ground.  i have a local repeater approx. 6 miles away that uses .575 frequency with a tone of 162.2 in and out.  i can't connect with it due to a mountain in between it and my location.  as stated, the other evening i was able to communicate with the repeater that's further away which does have a .575 frequency with a tone of 162.2 in but 198.8 out.  i'm not sure how this is possible; am i some how connecting to the repeater local to me and it relaying he signal to the further repeater even though it has a different output tone?

[SteveShannon]

6 minutes ago, 3cRadio said:

greetings all!

new to gmrs radio and had a repeater question.  anyone now how its possible for my base station (20w) radio to make contact (receive & transmit) to a repeater that's over 75 miles away?  i'm using a amazon special gmrs fiberglass antenna that's only mounted 10 ft off the ground.  i have a local repeater approx. 6 miles away that uses .575 frequency with a tone of 162.2 in and out.  i can't connect with it due to a mountain in between it and my location.  as stated, the other evening i was able to communicate with the repeater that's further away which does have a .575 frequency with a tone of 162.2 in but 198.8 out.  i'm not sure how this is possible; am i some how connecting to the repeater local to me and it relaying he signal to the further repeater even though it has a different output tone?

It’s possible that it is tropospheric ducting. It’s also possible that the farther repeater’s signal is getting to you because they have a very high antenna or because it is reflecting off something or refracting over a sharp edge. 
And it’s also possible that the distant repeater is linked with a nearby repeater. 
If your radio doesn’t have a receive tone set, it won’t matter what the repeater output tone is; your radio will allow the audio to be reproduced. 

[OffRoaderX]

Is there a mountain between you and the further away repeater like with the closer one?

I regularly and normally connect to a repeater 69 miles away on my handheld radios and using my base-station with a big antenna on the roof, i can connect to repeaters 80 or 90 miles away - yet there are other repeaters 10 miles away that I cant connect to because of hills/mountains.

[dosw]

29 minutes ago, 3cRadio said:

greetings all!

new to gmrs radio and had a repeater question.  anyone now how its possible for my base station (20w) radio to make contact (receive & transmit) to a repeater that's over 75 miles away?  i'm using a amazon special gmrs fiberglass antenna that's only mounted 10 ft off the ground.  i have a local repeater approx. 6 miles away that uses .575 frequency with a tone of 162.2 in and out.  i can't connect with it due to a mountain in between it and my location.  as stated, the other evening i was able to communicate with the repeater that's further away which does have a .575 frequency with a tone of 162.2 in but 198.8 out.  i'm not sure how this is possible; am i some how connecting to the repeater local to me and it relaying he signal to the further repeater even though it has a different output tone?

You think that's amazing, consider that with a handheld Yagi antenna an amateur can talk through the International Space Station's 2m/70cm (VHF/UHF) crossband repeater using a 5w handheld radio. Five watts, to reach a repeater hundreds, even a thousand miles away.

But what's different about the ISS? It's not that the repeater is a ham repeater. It's not that the repeater has some amazing antenna. It's not that it's got a million dollar radio. It's that there's nothing between you on the ground, and the repeater up in space. Line of sight.

So if you're able to reach a repeater 75 miles away reliably from an antenna that is 10 feet above the ground, that repeater's antenna must be at about 1050 feet above the ground between the two of you. Otherwise the curvature of the earth gets in the way. As an example, I can easily hit this repeater:

But I can hit it because I live at 1600m, the repeater is at 1700m, and everything between us is at 1200m. We have line of sight.

[3cRadio]

5 hours ago, SteveShannon said:

It’s possible that it is tropospheric ducting. It’s also possible that the farther repeater’s signal is getting to you because they have a very high antenna or because it is reflecting off something or refracting over a sharp edge. 
And it’s also possible that the distant repeater is linked with a nearby repeater. 
If your radio doesn’t have a receive tone set, it won’t matter what the repeater output tone is; your radio will allow the audio to be reproduced. 

thanks for the reply!  never hear of tropospheric ducting but after looking it up, it's very possible.  supposedly in area Aug & Sept have a higher probably of this happening.

i'm not familiar with the linking of repeaters but from my understanding this is considered illegal with gmrs repeater but the repeater is operated by a radio network that has a few repeater near each other; maybe they are linked somehow.

my radio tones are set to 162.2 in and out, so no sure how i could hear them on the receive side; that still puzzles me.

thanks again for the reply!

[WRXB215]

@OffRoaderX I'm no expert but your situation sounds like it may be what's called "knife edge diffraction."

[3cRadio]

5 hours ago, OffRoaderX said:

Is there a mountain between you and the further away repeater like with the closer one?

I regularly and normally connect to a repeater 69 miles away on my handheld radios and using my base-station with a big antenna on the roof, i can connect to repeaters 80 or 90 miles away - yet there are other repeaters 10 miles away that I cant connect to because of hills/mountains.

thanks for the reply! there isn't a mountain as high as the closer repeater but i'm located in norcal (suburbs) and there are hills, trees and several buildings towards the further repeater; no real line of sight, open fields or deserts.

if i'm correct in thinking who you are; love your vids!

[OffRoaderX]

59 minutes ago, WRXB215 said:

@OffRoaderX I'm no expert but your situation sounds like it may be what's called "knife edge diffraction."

Don't try to overcomplicate everything.. It's just good line of sight..

[3cRadio]

6 hours ago, dosw said:

You think that's amazing, consider that with a handheld Yagi antenna an amateur can talk through the International Space Station's 2m/70cm (VHF/UHF) crossband repeater using a 5w handheld radio. Five watts, to reach a repeater hundreds, even a thousand miles away.

But what's different about the ISS? It's not that the repeater is a ham repeater. It's not that the repeater has some amazing antenna. It's not that it's got a million dollar radio. It's that there's nothing between you on the ground, and the repeater up in space. Line of sight.

So if you're able to reach a repeater 75 miles away reliably from an antenna that is 10 feet above the ground, that repeater's antenna must be at about 1050 feet above the ground between the two of you. Otherwise the curvature of the earth gets in the way. As an example, I can easily hit this repeater:

But I can hit it because I live at 1600m, the repeater is at 1700m, and everything between us is at 1200m. We have line of sight.

thanks for the reply!  pretty amazing that a 5w radio can make it up that far.  since earth has the whole coverture thing and obstructions, i can see why it might not go as far.

from what i can gather, the tower is probably approx. 2k ft elevation and i'm at 100 ft.  that image is pretty cool.  cant seem to find the site you were using but here's my google map image.  there are some hills but no huge mountains (from what i can tell).  

[WRXB215]

26 minutes ago, OffRoaderX said:

Don't try to overcomplicate everything.. It's just good line of sight..

Not only that, but I also misread your post.

[WRUU653]

Here is the line of sight tool. I know that area. That is a good reach for sure.

[WRTC928]

It's surprising how far you can communicate with a good line of sight. My personal best HT-to-HT is 22 miles, but we were both on elevated terrain features with apparently little or nothing between us. In Alaska, I had a cabin in a remote riverside location accessible (barely) with a 4WD vehicle. There was a lodge 12 miles away on a mountain that had phone service, and they monitored (as far as I could tell) every radio service known to man. When I got there, I'd flip on my repeater and check in with them. I couldn't directly communicate with an HT because of the trees, but by running an antenna into a tall tree, I could reach the repeater and thence the lodge from any reasonable distance with my HT. On the other side of the valley, some 60+ miles away, people on another mountaintop could talk to the lodge easily with an HT. I don't know how far a UHF signal has to go before it begins to degrade just due to distance, but it's a long way. Theoretically, it would be readable forever, but a radio wave isn't perfectly coherent. It will eventually begin to spread and scatter from things as minor as water vapor or dust in the air.

[WRYZ926]

UHF can go a very long ways as long as there is a clear line of site. 70cm is used all the time to communicate with satellites. Of course you don't have to fight the curvature of earth when talking to satellites.

A clear line of site is king when it comes to VHF and UHF.   

We have been having a lot of tropospheric ducting on GMRS over the last 2 weeks with the cooler than normal temperatures we have been having. I've been hearing a GMRS repeater located in Peoria, Illinois almost every day between 8:00 and 8:45 in the morning. Peoria is about 150 miles from me. I've also been hearing another repeater that is about 80-85 miles away.

[wayoverthere]

2 hours ago, WRYZ926 said:

A clear line of site is king when it comes to VHF and UHF.   

This sums it up well; i've talked into a GMRS repeater and a 70cm ham repeater on Joaquin Ridge on the west side of the San Joaqin Valley from a hill on the east side of the valley (75ish miles) with 5 watt HTs.  I've also talked into another 70cm repeater on Fremont Peak from a bit further east, around a 115 mile shot over the valley on the 50 watt mobile in my truck.  

In both cases, i had clear line of sight over the valley, as i was sitting around 4500-5000 ft elevation, and all of those repeaters sit around the 3000ft mark on hills/ridges.