- October 1, 2005 at 11:25 am #6414pianoplayer88keyParticipant
Total posts : 5
questions about propogation/noise/etc at several frequencies
I have a few questions about several frequency bands. Basically I’d like to know how they behave, including…
What is the typical noise floor (in mV/m, uV/m, etc, or dBu or dBm)?
How do you convert dBm to mV/m (or dBu to uV/m)? (this I think would apply to ALL frequency bands)
What’s the typical rate of loss in relation to distance? (if I know my signal is a certain intensity at a certain distance, how do I figure out the intensity or distance at someplace else if I know one of those two values?) Also how would ground conductivity affect these calculations?
Basically, with the power/antenna/field levels specified, how far under normal conditions should I expect a signal to go that is one of several modes – CW, SSB AM 5kHz, mono DSB AM 10kHz, stereo AM 15kHz, narrowband FM 5kHz mono response, wideband (200kHz channel) FM, TV (6MHz)? (if you want to just specify for one mode, and tell me how to make necessary calculations to figure out for other modes, that’s ok) (for bands in which something won’t fit, don’t include it)
If I think of anything else, I will edit (or if it won’t let me, reply to) this message.
If power or field strength is not specified, what’s the typical rule of thumb for safe human exposure to high RF fields?
Ok, here are the bands, and proposed power/antenna/field strengths?
9kHz and below – unknown power. Antenna most likely to be very short relative to wavelength. (not sure if would run wire around a perimeter of a property or a room, or would erect a short vertical radiator).
160-190kHz – 1 watt, 15-meter antenna
9-490kHz – 2400/kHz uV/m @ 300m
490-1705kHz – 24000/kHz uV/m # 30m
510-1705kHz – 100 milliwatts, 3 meter antenna (also could be 15uV/m at 47715/kHz meters)
1705kHz-10MHz – 100uV/m @ 30m (or 15uV/m @ 30m, or bandwidth(kHz)/frequency(MHz) uV/m @ 30m)
13.553-13.567MHz – 15.848mV/m @ 30m
26.96-27.28MHz – 10mV/m @ 3m
40.66-40.7MHz – 1mV/m @ 3m
49.82-49.9MHz – 10mV/m @ 3m
88-108MHz – 250uV/m @ 3m
902-928MHz – 50mV/m @ 3m
2400-2483.5MHz – 50mV/m @ 3m
5725-5875MHz – 50mV/m @ 3m
24-24.25GHz – 250mV/m @ 3m
300 GHz and above (can separate infrared, visible light, ultraviolet, x-ray, gamma ray, cosmic ray, etc) – currently unknown. (note that signal would need to be able to pass through optically solid objects – would this range even with high power be unusable?)
EDIT #1: I just came across [url=http://www.srs.pp.se/phpBB2/viewtopic.php?t=22&sid=b53b4590da6952f9e5ce57e06b608434]this website[/url]. I noticed they give some specs for AM broadcast. I’d basically like to know what those specs are for these other bands, too, and/or how to figure them out.October 1, 2005 at 8:49 pm #12593techpuppyGuest
Total posts : 45366
Here’s a quick reply. Forget 9khz and under. The government uses some frequencies slightly above that. There are technical reasons and there are also some reports of people near those transmitters suffering from headaches and a variety of symptoms while the transmitters are operating. There is not sufficient bandwidth for anything other than code.
Forget the 300 Ghz and above frequencies (light), unless you are shooting it down some fiber optic cable.
I would recommend you get some copies of the ARRL Handbooks at a nearby library or ham operator. Even editions from previous years are worth looking through. They have a wealth of information on frequencies adjacent and in the bands you are talking about. You can read about propogation, antenna design, and other information. The ARRL (American Radio Relay League, an amateur radio organization) can be found at [url]http://arrl.org[/url]
The advantage in referring to the handbooks is that you will be reading actual experiences of users of various frequencies which may be more valuable than a mathmathical calculation.
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