Receiving antenna range - good? - Page 1
Forum section: electronics / beginners

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 13, 2013, 12:43:56 am
content: So I set up a simple FM dipole antenna, about 1.5m long, ~5m from the ground on the roof of my house. Few trees in the immediate vicinity, and the terrain from me to this transmitter I picked up is relatively flat (<30m difference). The transmitter I picked up, CBHC-FM, is 82km away with a power of 1.17kW. How is this? I have nothing really to base this on, I am sure it is better than a regular car stereo could do. What do you guys think?

author: AG6QR
author_rank: Frequent Contributor
timestamp: August 13, 2013, 02:05:13 am
content: For FM radio reception, height above terrain and obstructions is the most important factor. They use so much transmitter power that, if there's a reasonable path from their antenna to yours, the signal will make it, almost (but not quite) regardless of the quality of the receiver or antenna. When you put the antenna higher up, you improve the chances that there's a good signal path to reach your antenna.Compared to ham radio, you're not doing anything to get too excited about - that transmitter is using a HUGE amount of power, and the transmitting antenna is likely to be very well engineered for efficiency and placed for maximum coverage. As a Ham, I've achieved greater than 80 km with a 5 watt handheld on 2 meters. That's roughly 146 MHz, a bit higher frequency than the FM broadcast, but roughly similar propagation characteristics. I was using a short 1/4 wave whip antenna mounted on a car. That kind of range on 5 watts isn't extraordinary, but it won't work without a fairly clear path between stations.I applaud anyone who builds, plays with, and/or experiments with their own antennas, though. If you enjoy it, consider getting a ham radio license, and/or playing with shortwave (HF) bands. On HF, you can talk around the world with 5 watts and a decent antenna when conditions are good.

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: August 13, 2013, 05:14:48 am
content: The theoretical distance between two radio stations, before the surface of the Earth blocks the signal path, is roughly:D(km) = 4 * (sqrt(H1) + sqrt(H2))where H1 and H2 are the transmitter and receiver antenna heights in meters above sea/minimum terrain level. This is under absolutely best conditions for radio waves, not optical line of sight, and assumes flat terrain between receiver and transmitter.So if your antenna height is 15m, and the transmitter is at 100m (high mast on a hill), the theoretical maximum distance is about 55 km. If either or both of you are at high elevations, the distance quickly increases. A transmitter on a 3.5km high mountain would cover about 230 km in radius, before you consider the height of the receiving antenna.Thus 82 km isn't unusual, if either you or the transmitter is at a high elevation above terrain.----Late edit: Added the missing closing parenthesis for great justice!

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 13, 2013, 12:42:50 pm
content: Thanks for the replies, that is disappointing, can't really make a huge tall antenna where I live, which would be fun. I was thinking of trying to mess around with a huge am antenna, like full, wave loop or something, any suggestions? That or shortwave, which I have a couple of older transistor radios to mess around with.

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: August 13, 2013, 01:02:45 pm
content: You should get better reception with the same polarization as the signal your trying to receive .Your broadcast station in question is vertical , not sure if you are horizontal with your antenna ?Then propagation [ weather conditions ] can get higher frequencies [ line of site ] to go hundreds of miles .Also a ham radio operator .

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 13, 2013, 02:30:27 pm
content: antenna is horizontal, vertical would improve reception for this station?

author: AG6QR
author_rank: Frequent Contributor
timestamp: August 13, 2013, 03:41:31 pm
content: Actually, most FM broadcasters use circular (or elliptical) polarization these days. Long ago, they mostly used horizontal polarization, like TV stations. But when people started putting FM radios in cars, with their vertical whip antennas, most FM stations went to circular polarization as a reasonable compromise so that they could be received by both horizontal antennas on buildings and verticals on cars.So do the experiment, but I suspect the antenna won't work much better when vertical. You might be able to find the polarization of the transmitting antenna listed on-line somewhere.Most communications stations (fire, police, ham, taxi dispatchers, etc.) use strictly vertical polarization, and will be received much better with a vertical than with a horizontal antenna.

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 13, 2013, 03:53:39 pm
content: ahhhhh thats cool, thanks for the info!

author: madires
author_rank: Super Contributor
timestamp: August 13, 2013, 04:18:08 pm
content: A mismatch between horizontal and vertical polarization of sender and receiver causes an attenuation about 20dB.

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 13, 2013, 05:06:18 pm
content: wow that is pretty significant!

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: August 14, 2013, 10:46:49 am
content: Quote from: sonnytiger on August 13, 2013, 12:42:50 pmTried a compact multiturn loop for AM? They are just about the most rewarding project you could make in radio and they're simple and cheap. They will work indoors but outside on a balcony or patio is best.A square loop 50cm a side will allow even a cheap AM radio to hear signals hundreds or thousands of km away. What's really cool is when you get two stations on the one frequency you can seperate them by turning the loop to null one out.On shortwave 10 - 20 metres of wire will work. But so will loops provided you're happy to retune them when you change stations. Loops may be lower noise and directional. This time loops are built from metal strip or tubing.Loops can be made for VHF / FM but you'd hardly bother as directional yagis are not too big, are cheap, simple and work better.More info and demonstrations of HF transmitting and AM receiving loops in the links below.To give a taste of their capability, even a few watts of HF transmitting power applied to a hand-carried 40 - 80cm loop can be heard hundreds if not thousands of kilometres away.

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 14, 2013, 03:09:14 pm
content: I actually made a loop just before I checked hahaha, unfortunately I couldn't find a single am station! The loop is about 30cm by 20cm and I have it set up a few feet above the ground. I have it connected to the stereo just by a couple wires, no coax or ladderline or anything. But the loop forms the large majority of the antenna, the loop is probably 40 or 5o feet of wire, with 10 feet of wire going to the stereo. The links you are talking about are the ones in your signature?

author: MatCat
author_rank: Frequent Contributor
timestamp: August 14, 2013, 03:40:16 pm
content: There are so many factors involved with antennas and RF that it's just crazy, one of my hobbies is FPV (A hobbyist form of UAV/Drones), I can get video transmissions to go about 20 to 30 miles (32km to 48km for you non-Americans)with my current setup, plane has a 700mw transmitter, uses a circularly polarized antenna, my RX antenna is a fairly directional crosshair circular polarized antenna (pretty much 2 dipoles in 90 degree phase with a reflector), I have seen others achieve as far as 110 miles (177km) with similar setups but different antennas (usually much more directional antennas at this point!). Even crazier is I saw one of the antenna gurus in my hobby actually attenuate a transmitter to something like 25mw and go 10 miles (16km!) with video!To pick up a radio station at 82km is really not that big of a deal.

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: August 14, 2013, 08:29:47 pm
content: Quote from: sonnytiger on August 14, 2013, 03:09:14 pmI can see a few problems here. The loop should really be larger (say 50 x 50 cm). You can wind it on a cardboard box or milk crate if you wish.The most important thing is it must be tuned, ie have a tuning capacitor in parallel with the main winding. The tuning capacitor can be salvaged from an old radio. You can switch in parallel capacitors to increase frequency range. This tuning capacitor is very sharp and must be adjusted each time the station is changed.If using a portable receiver you need no electrical connection - just put the radio inside the field of the loop. If using an external receiver eg stereo then you need a single turn loop for coupling.QuoteYes - both articles and videos.

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 14, 2013, 09:31:40 pm
content: Quote from: MatCat on August 14, 2013, 03:40:16 pmDarn haha. Hate the feeling of being wrong/being "humiliated" but its one of my character flaws that I need to get over.Thanks!

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 14, 2013, 09:33:36 pm
content: Quote from: vk3yedotcom on August 14, 2013, 08:29:47 pmRight I have a couple of radios I should be able to salvage one out of, this sounds fun, I will do, though I don't think I have any wire left ahha.

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 14, 2013, 09:36:14 pm
content: If I just use the existing small loop antenna I made and added the capacitor would that help?

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 14, 2013, 11:02:06 pm
content: nice site btw vk3yedotcom

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: August 15, 2013, 09:14:28 am
content: Quote from: sonnytiger on August 14, 2013, 09:36:14 pmI'd suggest making a new one.A loop that's very small has limited capture area so won't pick up as much signal.Also a small loop may not have enough wire to resonate with the tuning capacitor on AM band frequencies - resonance will increase the strengh of signals about 10 or 20 times.The one on my website with the wire wound on a cardboard box would be a good starter.

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 15, 2013, 02:20:46 pm
content: ok sounds good thanks!

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: August 15, 2013, 08:16:43 pm
content: Yep the crystal set one that can be used as a loop is the one I meant.The ones demonstrated here are even better:

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 16, 2013, 05:04:31 pm
content: First of all thanks for all the help!I actually made the crystal radio set where the antenna is detailed just for fun, made the antenna a bit under 1 meter square and took pictures of everything else just to make sure all is good. Unfortunately the nearest AM radio station to me is like 70-80km away so out of reach for the crystal radio set but I may try the antenna with my modern AM radio. If i do try the antenna with my stereo how should I connect it? just run some wires? the wires would have to be like 5 meters long.

author: G7PSK
author_rank: Super Contributor
timestamp: August 16, 2013, 05:42:45 pm
content: If that transformer is the RF coil its inductance will be far too big for RF, when I used to build crystal sets (as a kid back in late 60's) I made a former from a turned piece of wood one and a quarter inch dia and put 93 turns of fine wire onto it, worked a treat, I also found that an overhead phone line made a great antenna, coupled with a small capacitor of around 25 or 30 pf or just wind 3 or 4 turns of copper wire around the outside of the incoming telephone wire.

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 16, 2013, 05:56:33 pm
content: the transformer is for the audio portion, to up the impedance from the 8 ohms of the earphone. vk3ye suggested that even a power transformer would work

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: August 16, 2013, 09:20:52 pm
content: Quote from: sonnytiger on August 16, 2013, 05:04:31 pmUsing that antenna with the stereo will make the huge difference.If the stereo has one of those little plastic loop antennas put that inside the middle of the big loop.Or wind one extra turn around the big loop, and connect to some coax cable and then run that to the tuner (depending on the tuner's antenna connections). If the tuner has a swinging ferrite rod on the back you could wind a few turns for coupling on that as well.

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 17, 2013, 04:40:31 pm
content: no loop antenna, and no internal antenna as you cant hear a single thing on am band. I have a bunch of RG6 is this good enough? I imagine it would be, good enough for FM radio. would coax be screwy cause its not balanced though?