AM radio antenna questions - Page 1
Forum section: electronics / projects

author: Deactivated-1
author_rank: Frequent Contributor
timestamp: October 12, 2022, 06:36:14 am
content: I want to be able to receive AM radio signals as far as I can, would be great if I could receive them across the globe, what would be the best antenna type? I was wondering if a dish antenna would be great, but it seems I would need an antenna over 500meters in diameter to effectively receive a frequency of 1200khz, what if I use a dish a fraction of the size... let's say 2.5 metersmaybe a loop antenna would be more ideal in that case? I would prefer a directional antenna but I can live with it if it isnt.and also what do I do about lightning? some clamping diodes on the front end of my receiver seem one way to help with it not blowing up in a storm, but could I perhaps elevate the voltage of the antenna to a few hundred volts to keep lightning from striking it?also what about using multiple dish antennas in an array? would that possibly lower the effective frequency band of the antenna to be more ideal for AM radio?

author: Kleinstein
author_rank: Super Contributor
timestamp: October 12, 2022, 01:50:14 pm
content: AM radio usually means low frequency and thus not practical dish antennas. One could use a combination of 2 or more anrtennas to get some some additional directionality, but it would only really help much of the antennas are separates quite a bit. In europe some countries (e.g. Germany) have stopped / reduced AM radio (still short wave AFAIK). How far the radio signal can go depends on the wavelength.In some bands there is also quite some interference from computer uses. So an old radio may have been great in the 1960s but could be fail today with more interference.

author: mag_therm
author_rank: Frequent Contributor
timestamp: October 12, 2022, 02:30:24 pm
content: I suggest to look at the wspr mode. An amateur license is not required for participation as a short wave listener (swl)wspr can use conventional ssb receivers, and sends audio baseband to computer for decoding using Wsjt-x software.That allows you to experiment on analog side with your own receivers and antennae.You can build a complete receiver, of do as I did, modify a vintage tube receiver by increasing its performance so it can receive wspr and the other digital modes.Building or modifying tube receiver for digital use incorporates a lot of the issues you mention on your other thermionic threads:Stability, selectivity, hum and noise mitigation, distortion, gain measurement and control etc and adds in the interesting possibility to design better demodulators.

author: radiolistener
author_rank: Super Contributor
timestamp: October 12, 2022, 08:08:19 pm
content: Quote from: ELS122 on October 12, 2022, 07:56:13 pmAt this band you can use ferrite rod antenna, it is small and pretty effective. But the main issue on that frequency is to keep your antenna and radio far away from any device with SMPS, LED lamp or other digital electronics which produce a lot of noise. The safe distance at this frequency is about 545 meters. But in reality you can get pretty good radio reception when you staying at about 200-300 meters away from mains line or building with electric devices.Recently we have blackout, entire city was stayed with no electricity all local FM stations also was down, and I found that city noise also affects FM radio very significantly. When entire city has no electricity, it is possible to listen FM radio up to 60-100 km distance away (from another cities). And when electricity was enabled, they all are flooded with a high background noise...So, the noise from SMPS, from LED lamps and other electronics has a very significant influence on radio reception even on FM band...

author: Kokoriantz
author_rank: Frequent Contributor
timestamp: October 12, 2022, 11:54:46 pm
content: You can listen AM band long distance only in the evening. To get high sensitivity, you can parallel the ferrite antennas as many as you want if you respect the polarity of the two coils. I, son of TV repair, when I was a teenager, I doubled many times the ferrites to customers asking better reception .

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: October 13, 2022, 12:11:14 am
content: Directionality and height may help as AM is much more dependant onthe antenna than FM is.You will find many stations slightly step on each other, also day and nightpower levels varry per station.Jeff

author: Geoff-AU
author_rank: Frequent Contributor
timestamp: October 13, 2022, 12:38:40 am
content: https://en.wikipedia.org/wiki/Medium_wave#Propagation_characteristicsYou're looking at "many hundreds or even thousands of miles away" for night time sky-wave propagation. "Across the globe" won't happen but there are tons of shortwave stations around 7MHz or so that go quite a bit further.MW antennas you're probably better with a long wire, as long and as high as you can get it. For SW stations you're starting to get into the wavelengths that you can make a tuned antenna for (a tuned dipole as high as you can get it is best).Quote from: ELS122 on October 12, 2022, 06:36:14 amUnplug your antenna when storms are likely. If you can hear thunder you are in the danger area for a lightning strike.Elevating the voltage of the antenna to a few hundred volts as a discouragement to millions of volts is not effective... and definitely not worth the risk.

author: Terry Bites
author_rank: Super Contributor
timestamp: October 13, 2022, 04:44:28 pm
content: You might want to think about a loop antenna. They are directional but that isn't always a bad thing. Bigger loops enclose more magnetic flux. Long wires are the easiest antennae but you need to have the space for it.

author: TheMG
author_rank: Frequent Contributor
timestamp: October 13, 2022, 05:48:50 pm
content: Tuned magnetic loop antenna. Lots of plans and calculators how to build one can be found online.Not very difficult to build just a frame of non-conductive non-magnetic material (eg: wood, plastic) to support the wire loop, and a variable capacitor (preferably air dielectric type) in parallel for tuning. It can be either directly connected to the receiver (via a pick-up loop), or indirectly by simply placing the receiver's ferrite rod antenna within the loop antenna.They are surprisingly effective antennas for their size, and pick up less noise than a long wire. Disadvantage, needs to be re-tuned every time you want to listen to a different station.

author: radiolistener
author_rank: Super Contributor
timestamp: October 13, 2022, 05:50:41 pm
content: Quote from: Kokoriantz on October 12, 2022, 11:54:46 pmIt depends on the distance. In the evening you can listen stations which are 2000-6000 kilometers away. Several years ago there was a high power MW transmitter about 50-100 kilometers away and it was possible to listen it 24/7 with a very strong signal level and no noise. Unfortunately it was shut down several years ago, so now there is no MW transmitters in my region.

author: Kokoriantz
author_rank: Frequent Contributor
timestamp: October 14, 2022, 03:24:49 am
content: I do remember having seen in my childhood rhombic antennas, just a cross wooden frame and wire run around in spiral. To remind that old radios didn't had any antenna, a roof one was a must have.

author: Kokoriantz
author_rank: Frequent Contributor
timestamp: October 14, 2022, 04:31:10 am
content: Look in archives of old magazines.https://worldradiohistory.com/hd2/IDX-Site-Early-Radio/search.cgi?zoom_sort=1&zoom_xml=0&zoom_query=+antenna&zoom_cat%5B%5D=37&zoom_per_page=10