How Do Radio Signals Travel Underground?
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- Опубликовано: 6 окт 2024
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In this instalment we look at the leaky feeder, an ingenious antenna system that's used in mines, tunnels and other confined spaces where radio waves don't travel well.
This is the Manchester Airport tunnel system that's used by the emergency services to pass radio signals down the length of the tunnel to maintain coverage.
I have never once driven through the tunnels at Manchester Airport and have no desire to do so.
Thanks for letting us all know, we’ll sleep well tonight now.
Wow, really missed the point.
hahahaha good@@RingwayManchester
I hate tunnels. And Manchester. And airports too. You'll never catch me hanging around any of them 😬😂
I wonder if this is the system used for DAB in the long tunnels (up to 25 km) we have here in Norway.
I used to work on leaky feeder systems. One point that few know is that the coverage in an area covered by a leaky feeder is almost perfect with no nulls caused by reflections. The radiation from thousands of tiny "antennas" along the cables fills all signal nulls.
Very interesting thank you for sharing your inf
@@garrysekelli6776 lol
Here in Norway we use leaky feeders to distribute Emergency Radio and DAB+ coverage in nearly all tunnels.
There are repeaters at even intervals and the repeaters are fed with fiberoptic cabling from a central controller at one of the ends of the tunnel which has the uplink antenna outside.
I was involved in replacing the repeaters in one tunnel, and the repeaters were very sensitive about signal delay, so all the fiber cables had to be balanced to be at equal lengths. That meant having coils of up to 4km of fiber inside patch panels placed near the controller to make the nearest repeater get the signal at the same time as the one farthest away. Newer systems don't need physical cable lengths but correct the signal electronically.
I don't work with that equipment anymore, but I'm currently looking at using leaky feeders to get WiFi coverage inside parking garages of apartment buildings.
Why not just use WiFi access points ?
@jasbindersingh2441 We have been having some issues with getting good coverage for EV chargers, so my thought is that a leaky feeder will get us a more uniform coverage throughout the whole garage. The one I'm looking at now is around 200-300m in length. But I'm waiting for a quote from our suppliers, it might be too expensive, I don't know yet.
Seems like a few POE repeaters would work much better. Otherwise use 5ghz for backhaul and 2ghz for the guests. WiFi is so underpowered anyway I just can't imagine it working with a leaky feeder.
@@fungo6631 Yes, he did say that. But you do get leaky feeders made for 2,4 and 5ghz.
If you try and connect an external antenna (and/or a booster amplifier) to a WiFi router, you won't believe the amount of interferences you're going to bring it in. WiFi works well as long as you operate a specific network name.
My suggestion is to use a single WiFi router with a mesh access point every 50 metres. Mesh networks use the same SSID, MIMO and the same channel. Note that the 5 GHz channels are meant for indoor use only.
I worked on the design and procurement of the 5th mobile network in the Netherlands in 1998. A key business objective back then was capturing roaming traffic from people arriving at Schiphol Airport in Amsterdam - once signed on to a network they were unlikely to change so we’d keep all their highly lucrative traffic! But we were the new boys and couldn’t install base stations in the airport or in the tunnel used by all the taxis heading in to town - the existing operators had leaky feeders etc. and didn’t want more competition. So we found a supplier of GSM 900 MHz parabolic antennas (this was in the 2G days) and fired a high powered base station via the parabolic positioned by the exit of the tunnel. It worked very well, propagating down the tunnel and around the bend by reflection and/or refraction - and we got out traffic!
Student radio used to require the use of restrictive antenna systems to limit the range achieved, these were very often inductive loops but leeky feeder was used as well. I remember working on the instalation of leeky feeder at Salford University when we moved from one system to the other. 963KHz medium wave by the way.
SOP for ambo is to park one vehicle at the entrance and switch its Airwave radio system to repeater mode, enabling coverage in the shorter tunnels to the hand held radios and any units that have driven in underground.
Here in the states under Part 15 FCC Rules AM/FM/SW and LW can be broadcast over leaky feeder however there is still a limitation on field strength measured by mV/per meter from the radiating leaky feeder, I took advantage of this rule and broadcast on AM/FM to a mobile home park i was living in, hiding the cables was no easy feat
I have heard of this, it seems interesting. Can you give some more details on how you did it?
Starlite Stabrite. First power to my emitter tonight.
Can some explain this what any of this means ??
Vaðlaheiðargöng is a 7.5km tunnel through the mountains here in Akureyri, Iceland. Radio reception and cellular quality is perfect through the entire tunnel. I'll have a look next time I drive through and see if the same method of feeder is used inside
Much of the UK research work into radiating cables was conducted by British Rail Research and the National Coal board back in the late '60s / 1970's.
Cable construction and choice is critical and depends on the frequency band being used and the distance to be covered - lower frequencies being superior to higher frequencies. As I remember the optimum determined then was around 50-60 Mhz - but obviously not usable for PMR.
There are many cable constructions developed by differing manufacturers for differing frequencies. Andrews basically grind the top off the helax screen for example. Another type uses a UR67 type construction with a number of screening wires removed, others use punched holes in the copper foil screen others slots.
A significant design issue is loss per unit length which determines the size of the cable and/or the need for repeaters. Other design considerations have to address the distance between the cable and the mobile unit. On a railway for example this is pretty well fixed so a cable in the roof of a tunnel will cover two tracks with probably only 3 metres between the cable and a trains antenna, with no significant obstructions. Whereas a cable in a road tunnel has to consider not only the height and distance of vehicles but also any blocking across lanes by high vans and trucks.
To extend coverage on a long cable repeater systems can be bidirectional or unidirectional the later having a base TX at one end of the cable and a base RX at the other. Some smart systems use RF over fibre to get signals to the radiating cable end from a parent Base Station, maybe on top of a tunnel in railway world. The fibre to RF units being able to serve multiple cable lengths negating the need for repeaters in long sections. In theses cases, because the RF signals are all coherent, there are no drop offs / standing waves as mobile units move between cable sections and the outside world.
The brand name is RADIAX. In some places, it is required to be installed in the elevator shaft (most accessible part of building that covers every floor) of high rise buildings so emergency services can communicate.
I bet that's expensive stuff and I wonder how it compares to a roll of cheap rg58
There's another type called GAINIAX which increases the signal. Marvellous stuff. A friend of mine used to swear by it, but apparently it's no longer made 😂
Decades ago the biggest AM radio stations in my city got together and funded an antenna that runs the length of the longest tunnel here to allow people to listen to their stations without drop outs. It had an antenna and a wide band amplifier at one end so every AM station in town (even the ones who paid nothing) would be transmitted through the tunnel.
The system failed several years ago and remains dead because no one cares about AM radio anymore.
We used leaky feeder to install dvb-t coverage inside a UN policed zone inside of an accommodation building, gave access to our encrypted channels normally fed from satellite in a building that we couldn’t fit drops to each room, worked very well
Good video Lewis when I worked on London Underground repairing the CCTV cameras the platform cameras used a leaky feeder under the platform edge to feed pictures to the Tube driver to show that doors were closed and no one was trapped.
But that spoils all the fun for the driver!
😅@@ProdigalPorcupine
Leaky feeders been used for cellular for long time in tunnels but also corporate areas in early days. Before London underground finally got round to allowing cell coverage, we at orange were talking with the other operators to get a leaky feeder solution there. Probs 15-20 yrs it took in end
Just about any infrastructure project or major purchase of equipment takes 10-20 years to even get started because the politicians are useless leeches who care more about their own careers than actually doing anything. By the time we got around to deciding on a new military helicopter, the original ones being considered were already outdated, so we had to go through the process twice.
London Underground has used leaky feeders for a long time for their own radio systems. They are also used mainline railways, but less common since tunnels are usually shorter and straighter so directional antennas at each end can work.
The "new" Denver airport built in the late 90's did something that may have been leaky feeder, but it was described as cables embedded into the concrete with passive antennas on the ends. I read about it before i was a ham, and ive since wondered exactly what they did. while unshieleded stubs could have received signals, I shudder to think of the loss involved passing down the wire to radiate from a similar not tuned stub from the other end.
Leaky feeder cables buried into a concrete slab is pretty common in industrial settings.
You never fail to enlighten me Lewis. Thanks. 👍
The Tyne Tunnels use this system to provide lots of FM radio stations, even Sun FM from a neighbouring city and isn't even meant to cover the area where the Tyne Tunnels are. For some bizarre reason though, someone has decided that BBC Radio 3, BBC Radio 4 and Classic FM are not needed in the Tyne Tunnels. Those are the only stations that don't work and someone seems to have consciously made the decision to not include them.
Follow the money there!
@@chrissewell1608 No, I don't think it's necessarily that reason. BBC Radio 4 is the second most listened to Radio station in the UK and Classic FM is the sixth most listened. I think it might have more to do with perceived tastes which are not the same as actual tastes. That's only my guess. Whomever installed the system has effectively shunned or snubbed those three particular stations based on either their own personal tastes or those of a relatively small sample size.
Thanks for explaining.
I appreciate you didn't go into 45 min history lesson before the essentials.
We use a similar system on the London Underground for carrying Station CCTV Camera feeds to a monitor in the drivers cab within a certain length either side of the station. This system is used both below and above ground, but only on the Central, Northern and Jubilee lines. The Victoria and Sub Surface lines use a much newer system, with the Piccadilly and Bakerloo lines still utilising old style monitors on the end of the platforms.
Great video. My father in-law led the development of the same system some years later to allow the roll-out of Tetra underground, a brilliant engineer. I remember him having parts of the London tube network closed when the authorities were signing it off.
I've seen Yagi's at the entrances of tunnels before, as well as regularly spaced omnidirectional dipoles, but never would i have suspected a plain looking cable being used as an antenna.
I love the drum and bass outro!
I designed a built a broadband leaky feeder system in use 50 feet below ground at the Stanford Linear Accelerator Center. The systemI built is 11,000 feet long with 14 amplifiers distributed around a ring tunnel. You're right about intentionally porous shielding being the key to its operation. And yes, 1 GHz is about the upper limit of a leaky feeder system
I'd never thought about leaky feeders before, but it makes so much sense. I love just having the antenna run along the wall like that
Been through both the pedestrian tunnels and the main one many times and never noticed noticed them or indeed knew that. Incidentally the white doors above the pedestrian tunnels I do not remember seeing previously. Great info as always Lewis.
Why did you say 'notice' 2 times? What are you hiding? :*/
Er...
Speaking of radio signals traveling underground, have you heard of the Jim Creek Naval Radio Station in Washington state?
We have a similar concept in the US for our railroads where the Distributed Power trains run through tunnels and the locomotives on the rear of train are radio controlled from the front.
When I was around eleven years old I started a superior technical certificate (equivalent to a HND or associates degree) in hydraulic civil engineering with a specialisation in drainage systems engineering. The early months were practical heavy before they became heavy on theory, and I had to descend underground into culverts, storm sewers, etc to train for inspection, maintenance and modification and in a section of one specific culvert, the rebar in the reinforced concrete acted as a faraday cage which caused a temporary loss of signal in that section underground.
I worked in the Washington, DC subway in the early 2000’s. They used the same thing. The problem was outside agencies entering the system for emergencies. We had setups for that in command vehicles.
I once read that back in the days before FM, the tunnels in places like New York City just had a long wire to conduct MW signals.
Vancouver’s downtown Skytrain expo line has had a leaky coax system in there since the early 90s for cell, but as with Manchester, I am not sure if it was ever adapted for the newer digital signals. Also Skytrain also uses leaky coax for train control and communication. Two parallel limes crossing at fixed intervals for the LIM based Bombardier system, and one for the newer but less sophisticated Canada line to Richmond and the airport.
Fascinating!! I'd never guessed how that was being done. Great content!
There is a non-powered version of these. I know it as "passive repeater", two antennas separated by resonate length of balanced feeder.
I've also seen the "leaky feeder" used without being powered.
It's all about resonance and impedance.
Another great video, Lewis. I guess the slot sizes and spaces have to be such that there is resonance at half-wave and their spacing will affect the radiation pattern - important particularly if there is no line-of-sight from one end of the tunnel to the other. Great stuff. 73
Here in Berlin leaky feeders are used in all subway tunnels for cellular service for many many years. You can see mostly two cables along the wall if you pay attention.
I've driven in the Lincoln and Holland tunnels under the Hudson River and the radio worked perfect down there.
The first time I ever heard of leaky feeders was when I read about the one in the Lincoln Tunnel. SiriusXM has repeaters in tunnels, too.
Always been puzzled by how when taking the tunnels under the airport signal is maintained.... similar in the Mersey tunnel too 😁 Had no idea how it functioned though! Thanks mate 👌🏻
"Leaky feeder" haha i love that term, sounds like a CB handle :)
Or an interesting porn fetish.
Sounds like a dog I once had!
Or a pub for radio engineers/ enthusiasts
Cool to learn about this, I will now be on the lookout for this every time I am in a tunnel somewhere. I often wonder how things like this work, like how do they feed WiFi to passengers on Amtrak trains running through the countryside.
It could be in service, or there could be a new, concealed, leaky feeder in the tunnel (they tend to go that route in Stockholm Subway and the commuter rail tunnels when renovating). As far as I've seen, they route it in plastic conduits that look like part of the ceiling panels, or, in some cases, hidden behind the ceiling panels.
What an impressive antenna system. I thought that relays where in use but this is better
Here in the US, our tunnels in my city had these leaky feeders for some time. However, after tunnel rehab projects, all the straight tunnels have a microwave system, clearly visible at both ends. Not sure about the tunnel locally that has a curve to it.
Very interesting! Thanks Lewis, appreciate all the research you do.
I use the leaky cable in the tunnels of grain elevators all the time. I have even used a 3 way splitter/combiner on 3 tunnels each running 100 meters without any issues. Business band repeater (150 & 450 MHz) up on ground floor. What I suggest you do is look into a company called Luxul. They have a controller that can handle up to 32 Access Points of their's. And not have the huge losses of WiFi. That way things are more handled like a cell tower. You could do the amplifiers, but you also have to have power at each location. Then you need to make sure the amplifiers do not cause you interference. Also will they pass the other frequencies. Been in RF since 1988 so seen many issues.
I remember they had some sort of leaky feeder at my old uni where the student radio station broadcast on really low power throughout the halls of residence. It's so mean-spirited of the powers that be not to grant a licence for the whole town as the airwaves weren't exactly full to the brim back then in the early 90s.
(But for a leaky feeder of course you didn't need any licence at all, because the power was too low.)
I remember being outraged last time my friend was in hospital. I looked everywhere for the headphones piping in the BBC and hospital radio but there was nothing! Just rent a Freeview TV for well over £5 a day! What an uproar! No more amateur DJs (except on the BBC 🤪‼️) I'm sure hospital radio didn't use leaky feeders. Surely that was more like cable radio...?
I heard that the first BBC broadcasts to Mayfair, Belgravia and similar places were actually delivered by cable. I can't remember if this was TV, radio or both. Is that right...?
Most college radio back in the 70's and 80's transmitted through the power lines. Each dorm building had their own small transmitter.
@@brucekives2194 someone told me it was a copper wire but it's not like I actually saw the wire! I'm pretty sure it was MW, if that makes any difference. I remember electric lights interfering with AM radio badly especially kitchen lights. I tried to get longwave radio recently and it is still going, but only one station: BBC Radio 4 on 198 LW. The signal was totally covered in interference until I got at least 20ft from any building and then it came through.
@@ZadenZane
In the US, it was more often carrier current over the power for MW. For FM and TV, they had coax in every room. Things might have been different in the UK.
en.wikipedia.org/wiki/Carrier_current
I was a volunteer in hospital radio (broadcasting) for about 15 years. It was 100v mono though a number of amplifiers at the hospital, and carried over BT analogue leased line to the remote hospitals and their amplifiers. At the bedside was a selector, 4 channels, one dedicated to the "tv on legs", a BBC national (usually) either a local station or another national, and the channel for the hospital radio. Quality was poor to say the least. Those bedside TVs were adapted to take the hospital radio feed, still in mono, and provide additional radio services, and TV, and yes you have to pay for the TV services but the audio was free. The station I was at now streams on the internet and expect listeners to 'tune' in that way. With many having a mobile phone that is probably quite easy but at the time I left, personal electronic devices were taking over as a patient's choice of entertainment. (I now stream on twitch from a home studio, who needs transmitters when the mobile networks have provided a global mesh?)
I've got some crappy RG58 that appears to also be a leaky feeder! 🤣 I'll have to give it a try!
@04:30 Was that Andy zipping by in his 'Twizzy'? 😂👍
That's really interesting stuff Lewis that I would never have thought about. Good one mate. Keep 'em coming..
Something relatively local and maybe worth a look is the road tunnels under the river mersey. I suspect they just retransmit FM radio frequencies from above ground to below, as the likes of DAB doesn't work, but FM does. Both tunnels appear to have a similar system in place
Norway scrapped the FM system in favor of DAB. I stopped listening to radio because the system was so shit. I don't regret it though, the programming also became shit, or maybe I just awoke from the brainwashing.
What an interesting topic. I never knew this was a thing. But from the comments, it is used world wide, in many applications! And I can tell you have done a lot in researching this subject.
I could use a leaky feeder antenna, in the basement of my house, to combine with my crossband repeater. To help get the signal out, when using an HT.
This is really interesting. I always wondered how this stuff worked, even more so since my local commuter trains apparently implemented this feeder type for vehicle wi-fi^^
You know. I was just thinking about this the other day. Glad there's an explanation now to scratch that itch
Copy that 🙂. I will have to look out for the cable when i next drive through the Hatfield tunnel on the A1M. Interesting stuff.
Here in Germany radio coverage in tunnels is a big problem, you usually lost everything on the first meters in. I never used more than UHF radio for myself, but I can tell you that the only thing you got is white noise. Also a lot of emergency helpers I know reported that there is litterally no coverage of radio communication inside of a tunnel, that can be a real problem.
But as this country is known for doing the absolutly possible minumum for technological advantage, I have to say I'm not surprised :D
Interesting! I don't live near any tunnels, so the thought never crossed my mind, honestly, but it's cool to see! I wonder why they don't just have "regular" antennas set every few hundred feet or so instead of the length of coax? (perhaps ease of maintenance or less likely to be damaged by a vehicle?) Either way I'd never heard of it & I love all things radio :) Thanks for the vid!
Some road tunnels do have this for mobile coverage. If you look at the ends of the Hindhead tunnel, for example, you can see a small square white box above the matrix displays. These boxes provides phone coverage throughout the tunnel.
On others, such as the Limehouse Link, leaky feeders are used.
I'm now interested in designing leaky feeders. Is there a design calculation on how it's made?
I was once consulted by a friend on how can they increase wifi coverage for the entire property without spending tens of thousands (pesos) on mesh wifi or repeater devices.
I never thought of using a seemingly "bad" coax as an intentionally designed transceiver.
Belgian coax manufacturer Eupencable once had a calculator available, don't know if it's still there for grabs. 73 de ON4WIX
I was expecting a lecture on very long wave transmissions!
I know for sure that the channel tunnel uses a leaky feeder from my time working on the construction, but I have no idea what frequencies they used.
Our radios were all preprogrammed Motorola jobbies, with selective calling facility.
I've wondered about these things and then forgotten when I'm not in a tunnel!
Very interesting information thanks, it's a great phrase in general..:::
Could you make a video about the 198khz transmitter that is in the thames tunnel. I couldn't find information about this on the internet. Greetings from Poland. I like your radio themed videos. best regards, Tomek SP6TK
wow , going to be looking for these now
I bet there are really cool leaky feeder systems in the tunnels of Switzerland and the nordic countries.
I'm sure I read of one of the local RAYNET groups doing a tunnel exercise back in the 80s with Greater Manchester Fire Service. I believe they had success in using the 70Mhz band to communicate from one end of the tunnel to the other.
That was the Standedge Tunnel exercise, and they used the 1.2 GHz band, 433 MHz was tried but only went about 300 Mtrs.
The tunnels are 3 miles long and solid comms were achieved the full length of the tunnel using a handheld radio at the tunnel entrance, and a mobile radio with a magmount antenna on a vehicle driving through the tunnel.
That’s what we do in Hong Kong and Japan to rebroadcast FM and MW radio, but the tunnel operator sometimes will interrupt the program and insert their traffic report
might also be what is used in singapore too... especially the KPE-MCE underground sections...
There are leaky feeders in my area too, and a couple of car tunnels where they feed FM broadcasts over them.
Worked with Radios connected to a leaky Feeder in conjunction with repeaters. The Main System for a Train Station fits in A Rack the Size of a Fridge, with the Feeder being one Drawer or Two. Systems Like this will likely not be dismantled for Years AS a Fallback. Might still be in use nowadays.
That great . some systems like this in the US in use today. was wondering on 4G cell signals getting in to subways and underground . I have been threw some tunnels in the US and my cell phone 4G works just fine. a few do not at all. FM radio and SAT radio goes out as well as GPS . but some AM broadcast can go underground a bit. There is a pedestrian tunnel in my area underground . everything goes out but a few AM stations. also longwave can be herds but so few now. our subway has cell service underground . no FM and AM so much noise can't make anything out. 73's
Love that DnB outro! Let’s goo 🎉
Interesting!
There must be systems like this for satellite or gps, also?
I have a GPS unit in one of my cars with no vehicle speed sensor input, and i was surprised to see it continue working and keeping progress under certain long tunnels.
When I had xm satellite radio it also kept working under that same tunnel, when it would normally die under any form of heavy cover.
GPS does not work indoors, likely your car will be using multi-axis accelerometers to approximate your position during loss of GPS signal.
@@SuperSpecies it's one of those cheap android radios (quite old now) so that's probably how it does it, if that's how phones keep their route bearings while underground.
Thanks
XM has their own terrestrial system for tunnel coverage. Some extremely old XM radios can’t receive it.
GPS on a phone inside a tunnel is often just AGPS ( Assisted ) using information provided to the phone inside the tunnel of approximate location inside based upon the usual AGPS cellular signals coming from the microcells inside the tunnel. It gives the illusion of GPS being received when the actual GPS receiver isn’t hearing anything.
You can play with this by taking a GPS only receiver in and comparing it with the phone in the tunnel.
Thanks for this, I knew about it but not actual coax construction.I did not know it was multi band❤
A few ways to tell if its still live is likely with A EMF meter / SDR Radio / Non contact Voltage detector pen up on a Telescopic Washing line pole / Radio Scanner with a Signal Strength meter
i do love the SDR Due a Simple Antenna in a Pringle's can can make for Quite directional and Hi gain pick up
As for the Non contact Voltage detector pen you may want a crazy mate in the car to do some 2am ~ 3am ~ 5am unsafe Slow Driving and tunnel walking (fake temp car problems)
just thought the new longer tunnel may have it Leaky cable more camouflaged or embeded it may even share the same ducts & cable Trunking as the ac lights or a vary high Close to surface pipe in the road even share a SW Drain pipe
I tried to encourage a local electricity company I worked for to use a leaky feeder system in a cable tunnel and I did all the reasearch for them on the subject but it was thrown out and was told it wouldn't work when the proof was in black and white in front of them paased history left the company shortly after that.
So thats how I hear FM radio going through both Mersey Tunnels.
Interesting stuff, You can receive Greatest Hits Radio (possibly other stations) when driving through the Mersey tunnel perhaps they use the same tyoe of antenna?
Yeahhhh rog!!!!
What a strange bit of coax, learn something new everyday they say!
So thats how they get data and comms working in metro tunnels in my area
Why run the cable (antenna) down both sides? Wouldn’t it be just as effective if you had on run down the center of the ceiling? The power level must be quite low to prevent resonance or multi path error.
That is brilliant.
1997 was also when RDS was still being tested
Cool videos
1:42 Looks like they need to replace the Denso tape, on the cable...
So even the emergency signals has upgraded throughout the years.
good vid
The UK Tetra system for the the Police (And other Agencies) uses similar technology to this
I said this in the video Mike 😂
@@RingwayManchester Very puzzled by this as you mention Airwave but not Tetra? can you explain please?
@@Mike_5 airwave IS Tetra
when i saw the title i thought you were going to explain radios for pot holing , . next time maybe.
Good evening,
How are you?,
Have you evere used Tyt-uv8200 Ht?
What can you says about that?,
Thank.
Can you make a video on how the tetra radio unit works and they operate it if you don't mind
I´m wondering what systems are used to "feed" such an antenna? Must be somekind of multiband transceiver which doesn´t care abou the dedicated frequencies or how does this work?
I installed the system at Manchester, it's a wide band RF amplifier for the particular frequency bands required.
We use them for mobile phone stuff.
4:30 that can’t be road legal!
I was just at the light rail station. Short answer is they don't haha
How would the coax be tuned or matched? It's not an actual tuned antenna.
It's 50ohm coax with a terminating resistor at the end.
@@Charles20112011 In the Manchester Metrolink tunnels, they terminate the feeders with a 3 element Yagi pointing along the line to fill in dead spots in cuttings.
@@Charles20112011 ok, that would make sense.
@@jonmac3995 so the coax leads to something and not just a dead end.
Repeaters probably
10*
vidya on 800 mhz xts ???????????? please
Andrew Radiax, expensive Hole-y Heliax……..
😊
I bet the physics of this are _"boring."_ 😉
YES, I realize posting puns like this are equivalent of _"Digging myself into a hole."_ 😊
*BA DUM TSS...🤭*
never heard of a leakyfeeder, but the physics of how it works is interesting, standing waves, and signal reflections and lots more was running through my head.
My wife says that I have a leaky feeder. It likes to go in a tunnel, but it's not 400m long.