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#41
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Indoor FM boost with no cables?
On 7/30/2014 1:22 AM, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:lr9ohj$33f$1@dont- email.me: But the amplifier you're trying to use is meant to feed a receiver directly, not another antenna. So output is going to be very low (on the order of microwatts) - much lower than any amplifier which feeds an antenna. Small point, but.... Microwatts. Those new legal microstransmitters are said to be in NANOwatt range output, but allegedly work on the distance scales I'm interested in. Microwatts should certainly have worked, but despite the crude test dipole being good (on standard wired reception test anyway), it didn't work for transmitting even a foot or two with the radio's whip parallel to the upper part of it. If nanowatts should have, the MAR-6 looks like driving picowatts, if I'm lucky. I would suggest you check again. Receivers aren't that sensitive. Most unlicensed transmitters are in the 100-500 mw range, and have a coverage of maybe 100 feet. And picowatts aren't even worth discussing. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
#42
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Indoor FM boost with no cables?
Jerry Stuckle wrote in news:lraskh$gup$1@dont-
email.me: Most unlicensed transmitters are in the 100-500 mw range, and have a coverage of maybe 100 feet. That sounds right. I thought nanowatts seemed a bit small a claim. I probably need about 10mW based on what you said there. (I think it was Wikipedia's article that stated the nanowatts, but as so often happens, there was no mention of the antenna and actual radiated power, no hint of what efficiency (or lack of) resulted. I won't retry for now. Messing around with a direct wired link to the external aerial is more fun for a while. ETM on a PL-390 is as fun as many people have said it is... And picowatts aren't even worth discussing. I should never have mentioned them. |
#43
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Indoor FM boost with no cables?
Jerry Stuckle wrote in news:lras98$ebf$1@dont-
email.me: As for determining whether it is oscillating or not - I wouldn't trust anything short of a good spectrum analyzer. The signal could be anywhere (and changing frequency). A spectrum analyzer will still show it; a receiver won't necessarily. No clues at all? I remember when I first set up that little MAR-6 based preamp, it had some nasty side effects on the sound till I added a springy ciopper alloy strip to each side on the underside of the board so it bit gently into the aluminium case when I slid it in to it, finally curing the local RF oscillations it had before I solved this. I was wondering if similar audible sounds might be heard as a guide to other, larger scales of local feedback and oscillation. |
#44
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Indoor FM boost with no cables?
On 7/30/2014 5:00 PM, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:lras98$ebf$1@dont- email.me: As for determining whether it is oscillating or not - I wouldn't trust anything short of a good spectrum analyzer. The signal could be anywhere (and changing frequency). A spectrum analyzer will still show it; a receiver won't necessarily. No clues at all? I remember when I first set up that little MAR-6 based preamp, it had some nasty side effects on the sound till I added a springy ciopper alloy strip to each side on the underside of the board so it bit gently into the aluminium case when I slid it in to it, finally curing the local RF oscillations it had before I solved this. I was wondering if similar audible sounds might be heard as a guide to other, larger scales of local feedback and oscillation. Not necessarily. Even if there were physical vibrations, they may be out of the audible range. But even vibrations are not common. You were lucky you could hear it. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
#45
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Indoor FM boost with no cables?
amdx wrote in :
Anyway, keep plugging away, as I listen to WABC in New York on my internet radio, driving my FM transmitter that I receive on a portable radio I carry around while doing my morning routine, part of which is writing a compound sentence while in Florida. :-) Sound a bit like the kind of fun I have with serial links (on smaller scales). I'll give it a rest for now but I will retry eventually, I like exploring this stuff. (And others, like coding, which is a rival for my time right now..) Soon to merge the two demands in a bit of code to make a Psion Organiser XP control the AR-3000. Lot of fun to be had there, I think. |
#46
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Indoor FM boost with no cables?
Jerry Stuckle wrote in news:lrbmkt$ohq$1@dont-
email.me: Not necessarily. Even if there were physical vibrations, they may be out of the audible range. But even vibrations are not common. You were lucky you could hear it. Well, it was like a flanger having a psychedilc fit. Hard to ignore! Fortunately easy to cure. I imagine that many other sources of wild RF oscillation might affect the sound like that. |
#47
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Indoor FM boost with no cables?
On 7/30/2014 5:08 PM, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:lrbmkt$ohq$1@dont- email.me: Not necessarily. Even if there were physical vibrations, they may be out of the audible range. But even vibrations are not common. You were lucky you could hear it. Well, it was like a flanger having a psychedilc fit. Hard to ignore! Fortunately easy to cure. I imagine that many other sources of wild RF oscillation might affect the sound like that. Not really. To affect the sound, you need something which will respond to the RF in a physical vibration manner (i.e. magnetic), and the signal must be in the audio spectrum. Neither is very likely. -- ================== Remove the "x" from my email address Jerry Stuckle ================== |
#48
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Indoor FM boost with no cables?
Jerry Stuckle wrote in news:lrcavl$dok$2@dont-
email.me: On 7/30/2014 5:08 PM, Lostgallifreyan wrote: Jerry Stuckle wrote in news:lrbmkt$ohq$1@dont- email.me: Not necessarily. Even if there were physical vibrations, they may be out of the audible range. But even vibrations are not common. You were lucky you could hear it. Well, it was like a flanger having a psychedilc fit. Hard to ignore! Fortunately easy to cure. I imagine that many other sources of wild RF oscillation might affect the sound like that. Not really. To affect the sound, you need something which will respond to the RF in a physical vibration manner (i.e. magnetic), and the signal must be in the audio spectrum. Neither is very likely. To produce audio from RF directly all that is needed is for the difference (a beat frequency) to fall within the audio pass band of the equipment. A wildly varying frequency of oscillation could make a sweep of audio pitch. Timbre or variability of effect might give plenty of clues as to cause. That's what led me to find and fix the original oscillations in the dodgy ground plane connection in the preamp casing. If it can happen this way on one (tiny) scale, I see no general reason why it could not happen on the larger scale with feedback between antennas a hundred feet apart. Whether I can use it diagnostically is questionable, but I think it can exist. Given the number of frequencies picked up by the antenna, I find it hard to beleive that NO stray feedback oscillation would differ from any one of them by a value that puts it in the audio band. I'm fairly sure I'd hear something, especially if choosing a clean audio signal over which it woudl easily show up. |
#49
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Indoor FM boost with no cables?
On 7/31/2014 3:36 AM, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:lrcavl$dok$2@dont- email.me: On 7/30/2014 5:08 PM, Lostgallifreyan wrote: Jerry Stuckle wrote in news:lrbmkt$ohq$1@dont- email.me: Not necessarily. Even if there were physical vibrations, they may be out of the audible range. But even vibrations are not common. You were lucky you could hear it. Well, it was like a flanger having a psychedilc fit. Hard to ignore! Fortunately easy to cure. I imagine that many other sources of wild RF oscillation might affect the sound like that. Not really. To affect the sound, you need something which will respond to the RF in a physical vibration manner (i.e. magnetic), and the signal must be in the audio spectrum. Neither is very likely. To produce audio from RF directly all that is needed is for the difference (a beat frequency) to fall within the audio pass band of the equipment. A wildly varying frequency of oscillation could make a sweep of audio pitch. Timbre or variability of effect might give plenty of clues as to cause. That's what led me to find and fix the original oscillations in the dodgy ground plane connection in the preamp casing. If it can happen this way on one (tiny) scale, I see no general reason why it could not happen on the larger scale with feedback between antennas a hundred feet apart. Whether I can use it diagnostically is questionable, but I think it can exist. Given the number of frequencies picked up by the antenna, I find it hard to beleive that NO stray feedback oscillation would differ from any one of them by a value that puts it in the audio band. I'm fairly sure I'd hear something, especially if choosing a clean audio signal over which it woudl easily show up. Yes, I know how it works - I've held both amateur and commercial licenses for well over 40 years and worked on almost everything from $40 CB sets to multimillion dollar mainframe computers. I've even done some design in my free time. I suggest you not try to teach those who know more than you your "facts". The facts a to have the beat frequency, you need two signals within 15kHz or so of each other. Those signals must be mixed, which means at least one must be non-linear. This will give you a beat frequency in the audio spectrum. Once you have this, you need something to generate a strong enough magnetic field in the audio frequency range to act as a driver, and something close enough and made of a magnetic material to vibrate. I've seen a fair number of spurious emissions over the years (mostly from VHF/UHF radios). Every one of them has been RF, and none of them have created audio oscillations. A few months ago we even had a case right here where a VHF radio in a county bus had a spur on the input to the local 2 meter ham repeater. Once again, no indication in the bus this was occurring. The county found out about it only after the hams contacted them. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
#50
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Indoor FM boost with no cables?
On 07/26/2014 09:24 PM, David Platt wrote:
A few years ago I helped chase down a noise source which was wandering randomly through the 2-meter repeater input sub-band, and causing prolonged noisy squelch tails on the ends of transmissions on several different repeaters in the Silicon Valley area.... Reminds me. Some years back I had the duty of fox-hunting a noise source inside Great Mall of the Bay Area that was throwing noise on Milpitas PD's receivers. I wandered around the back doors in the south core with a PD handheld and a scanner. Turns out a Muzak machine's power supply was doing it. They sent a replacement and the problem was gone. Once there was a laundromat in Redwood City whose TV was spewing junk around 154 MHz, out the antenna port, jamming Fire channels. I don't recall how that was resolved, whether an amp was installed isolating the antenna, or they just got the place a new TV. |
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