Pirate radio. ;)
- Thread starter rigidigital
- Start date
It sounds like it was a very professional criminal enterprise you set up there, Grogster. Well done. 
I can well understand the desire of a student to operate a small radio station.
45 years ago I set up in my dorm room my own AM broadcast station at the small rural college I attended, as the official student radio station could seldom be heard outside the broadcast booth, whereas mine blanketed our small campus. When I was called into the office of the dean of students I was expecting to be expelled. Instead, the dean asked me to make some public service announcements. It seemed the school's station just didn't work very well.
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As a suggestion, you might consider using a few low power (legal) transmitters that are fed by audio from your son's PC and program sources, linked to other student's PC's on the school's network. In addition to the on-line audio, there are any number of reasons to actually broadcast analog FM signals around a university. This method would be both legal and functional, spreading a signal over as wide an area as desired.
I can well understand the desire of a student to operate a small radio station.
45 years ago I set up in my dorm room my own AM broadcast station at the small rural college I attended, as the official student radio station could seldom be heard outside the broadcast booth, whereas mine blanketed our small campus. When I was called into the office of the dean of students I was expecting to be expelled. Instead, the dean asked me to make some public service announcements. It seemed the school's station just didn't work very well.
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As a suggestion, you might consider using a few low power (legal) transmitters that are fed by audio from your son's PC and program sources, linked to other student's PC's on the school's network. In addition to the on-line audio, there are any number of reasons to actually broadcast analog FM signals around a university. This method would be both legal and functional, spreading a signal over as wide an area as desired.
In response to John West's 45 years ago: In 1967 portable electronic devices of any kind were exceptional- most were instead tube/valve mains powered, & many cars did not even have an AM radio! A pocket transistor radio was then a serious purchase ($$$ in today's money ~equiv. to a netbook PC/smart phone now), & cassette tapes had yet to be invented.
Almost all canned music then came from LP/45s "records", with even mains powered reel to reel tape recorders a big ticket item. Folks keen to a hear a top song would often listen for HOURS to a station on the off chance that it'd be played! The likes of the CDs/DVDs,PCs, internet, GPS, WiFi, smart phones,USB memory sticks, digital cameras, MP3 players,video games, calculators & touch screen tablets did not then exist. LEDs were mega exotic, & astronauts on the hi-tech Apollo moon program would have been dumbfounded with even mono LCDs.
In stark contrast to then, the average human now may be near overwhelmed - make that totally overwhelmed- with cheap/free on the go AV information sources & portable entertainment devices.
Over recent years I've helped special interest groups (religious,community,short term events etc) with FM transmitter setups. The costs of quality & legal off the shelf legal FM gear is often near incidental to program content. Dead boring aspects like power supplies/consumption, antenna type/location(& possible safety, structural & regulatory issues arising),copyright, legal aspects of broadcast material,announcers who go beserk, studio facilities, phone/internet lines & dedicated "staffing" are the real concern. With such overheads it may be better to instead broadcast on line to a potentially global audience.
THE crunch factor for a pirate FM wireless station now is usually ongoing operator dedication, that's attuned to the nearby target audience. Things may otherwise soon fold when when "no one listens"...
Almost all canned music then came from LP/45s "records", with even mains powered reel to reel tape recorders a big ticket item. Folks keen to a hear a top song would often listen for HOURS to a station on the off chance that it'd be played! The likes of the CDs/DVDs,PCs, internet, GPS, WiFi, smart phones,USB memory sticks, digital cameras, MP3 players,video games, calculators & touch screen tablets did not then exist. LEDs were mega exotic, & astronauts on the hi-tech Apollo moon program would have been dumbfounded with even mono LCDs.
In stark contrast to then, the average human now may be near overwhelmed - make that totally overwhelmed- with cheap/free on the go AV information sources & portable entertainment devices.
Over recent years I've helped special interest groups (religious,community,short term events etc) with FM transmitter setups. The costs of quality & legal off the shelf legal FM gear is often near incidental to program content. Dead boring aspects like power supplies/consumption, antenna type/location(& possible safety, structural & regulatory issues arising),copyright, legal aspects of broadcast material,announcers who go beserk, studio facilities, phone/internet lines & dedicated "staffing" are the real concern. With such overheads it may be better to instead broadcast on line to a potentially global audience.
THE crunch factor for a pirate FM wireless station now is usually ongoing operator dedication, that's attuned to the nearby target audience. Things may otherwise soon fold when when "no one listens"...
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Well indeed, manuka.
I in fact have not run my LPFM station in more then a year and a half now.
My primary reason for doing it in the first place, was to teach myself something about RF, and to escape from the annoying DJ's on commercial stations.
When I was running my station LEGALLY again(heh! heh!) after the fine, I was even licenced with the copyrighters at that stage, paying a yearly fee to APRA and ppnz for the right to transmit music, so it was all VERY kosher by the end of my running things - not wanting another fine, you see!!!
However, I tend now to listen to net-radio more then anything else, which is also why I never really bothered to put my station back on-air after a couple of very heavy hail-storms resulted in corona discharges into my GP aerial, which killed the final of the transmitter - killed two transmitters inside a month like that, and the idea of having to build a J-pole or Slim-JIM to get around this problem put me off - I had other things to get on with.
Anyway, with net-radio, and the THOUSANDS of stations you can choose from on the net, I can just pick a station that plays the genre of music I like, and listen to that.
I have been listening to .977's network and Absolute 80's quite a bit.
I in fact have not run my LPFM station in more then a year and a half now.
My primary reason for doing it in the first place, was to teach myself something about RF, and to escape from the annoying DJ's on commercial stations.
When I was running my station LEGALLY again(heh! heh!) after the fine, I was even licenced with the copyrighters at that stage, paying a yearly fee to APRA and ppnz for the right to transmit music, so it was all VERY kosher by the end of my running things - not wanting another fine, you see!!!
However, I tend now to listen to net-radio more then anything else, which is also why I never really bothered to put my station back on-air after a couple of very heavy hail-storms resulted in corona discharges into my GP aerial, which killed the final of the transmitter - killed two transmitters inside a month like that, and the idea of having to build a J-pole or Slim-JIM to get around this problem put me off - I had other things to get on with.
Anyway, with net-radio, and the THOUSANDS of stations you can choose from on the net, I can just pick a station that plays the genre of music I like, and listen to that.
I have been listening to .977's network and Absolute 80's quite a bit.
Eek indeed.
Anything that cheap probably would not have very nice RF output - I would also love to put it on the spectrum analyzer and see what it's harmonics and spurious emmisions were like.
But as a VERY GOOD highlight to how cheap these things have become these days....
A good-quality 1W stereo exciter used to cost upwards of $500 a few years ago, and that was just for 1W, had no fancy frequency display or anything like that either.
EDIT: Auction says harmonics and spurious are 30dB down, but I wonder if they are at that price! I think you can do better then -30dB anyway with proper filtering etc. More is usually better or at least desirable with respect to harmonics and spurs. You don't want harmonics getting anywhere near commercial TV bands or ATC(air-traffic control) frequencies - that won't make you any friends.
Anything that cheap probably would not have very nice RF output - I would also love to put it on the spectrum analyzer and see what it's harmonics and spurious emmisions were like.
But as a VERY GOOD highlight to how cheap these things have become these days....
A good-quality 1W stereo exciter used to cost upwards of $500 a few years ago, and that was just for 1W, had no fancy frequency display or anything like that either.
EDIT: Auction says harmonics and spurious are 30dB down, but I wonder if they are at that price!
I think you can do better then -30dB anyway with proper filtering etc. More is usually better or at least desirable with respect to harmonics and spurs. You don't want harmonics getting anywhere near commercial TV bands or ATC(air-traffic control) frequencies - that won't make you any friends. Grogster: Well said sir-my points exactly! Naturally I encourage "learning about wireless",for which even discrete breadboarded 88-108 MHz setups may do. Some years back (& pre Bluetooth!), Andrew Hornblow rustled up a short range PICAXE driven FM tone transmitter to good effect. See here - scroll ~½ way down.
At 433MHz a benefit is that devices "just work" & antenna can be compact & simple - see => here.
FWIW a very low power AM transmitter on the increasingly quiet 500-1600kHz MW band may be a good bet too,although AM band receivers are getting a tad elusive! I gained insights galore on LC circuits,superhets. etc down at this "DC band" back about 1966 when designing & making a 455kHz BFO (Beat Freq. Oscillator). My then costly (~2 weeks teen earnings) short wave radio lacked the ability to handle SSB (Single Side Band) or CW (Morse).
Although VERY educational (Wheeler's Formula etc),this was tough going pre Internet (& pre calculator- I used a slide rule!),with transistors (tediously ordered from the UK) costing ~$20 each in todays money. This BFO however helped get my ham ticket- in fact I've still both the very radio & inbuilt BFO at hand!
Stan. (ZL2APS since 1967)
At 433MHz a benefit is that devices "just work" & antenna can be compact & simple - see => here.
FWIW a very low power AM transmitter on the increasingly quiet 500-1600kHz MW band may be a good bet too,although AM band receivers are getting a tad elusive! I gained insights galore on LC circuits,superhets. etc down at this "DC band" back about 1966 when designing & making a 455kHz BFO (Beat Freq. Oscillator). My then costly (~2 weeks teen earnings) short wave radio lacked the ability to handle SSB (Single Side Band) or CW (Morse).
Although VERY educational (Wheeler's Formula etc),this was tough going pre Internet (& pre calculator- I used a slide rule!),with transistors (tediously ordered from the UK) costing ~$20 each in todays money. This BFO however helped get my ham ticket- in fact I've still both the very radio & inbuilt BFO at hand!
Stan. (ZL2APS since 1967)
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rigidigital
Senior Member
This became a very interesting thread, people stating their trials and experiences doing the same thing , except much larger range/power. The project will be worth it to learn about rf. However I can see the audience will dwindle (if it did pecome popular for awhile) just because they all seem to have phones and communicate with each other using facebook and twitter. That might be a couple of reasons he could latch onto.., to not even try ! Which would be a mistake by nearning little of elecromics. Sure you could do pod casts and similar. Over ten years ago i was doing something similar over the web.
I think the Amoeba suggested by SAborn is as good as anyway to begin. There are plenty of plug and play FM broadcatsing units that plug into your PC. Some cheap, others five to 6ix hundred and even a little more.
I think the Amoeba suggested by SAborn is as good as anyway to begin. There are plenty of plug and play FM broadcatsing units that plug into your PC. Some cheap, others five to 6ix hundred and even a little more.
Any RF project really needs a mentor. That was my experience anyway. I have no doubt you could teach it all to yourself with enough time and book reading, but in my case, the idea of trying to comprehend the Phase-Locked-Loop(PLL) equations down at mathematical level was just too daunting. This was back when I was thinking I could build my own PLL transmitter from component level. That was really a silly idea of mine, as RF design is a very demanding mistriss, in that you must know lots about RF, to design anything RF - kinda a catch 22!!!
What I mean by that, is simply laying out the PCB pattern wrong, can vastly affect the stability and reliability of your rig, to say nothing of the fact that incorrect RF layout will also cause all other kinds of mary hell, like spurious emissions, and if you are REALLY unlucky(as I was during one of my experiments!) a thing called "Parasitic oscillation" - which is to say major instability in the final(the RF power amplifier), the amp starts to self-oscillate, begins running-away with no frequency control, emits crud all over the band in the process, and pretty soon blows itself to bits - literally. In the one that I BUILT(without proper procedures), the final transistor got hotter and hotter, which fed the parasitic oscillation as the change in temperature alters the frequency characteristics of the transistor, and it was kind-of like the RF equivalent of letting the handbrake off on a car on a hill - it runs away, getting faster and faster, until(if not stopped by something), it crashes and self-destructs.
Anyway - that was some of my early RF lessons, and then I met and started working for a fella who luckily for me, knew lots about RF, and had spent about 20 years in the trade including working and repairing AM anf FM transmitters in the kilowatt range of output power, so he was a goldmine of information and PRACTICAL help, which you can't really get by justing studying books and equations.
It was him in fact, who when he found out about my aforementioned 15W of RF juice, said to me: "You'll get busted if you run that much juice." As I was not after about six months or so, I thought I was untouchable, until that knock on the door by the well dressed man from RSM(Radio Spectrum Management).
What I mean by that, is simply laying out the PCB pattern wrong, can vastly affect the stability and reliability of your rig, to say nothing of the fact that incorrect RF layout will also cause all other kinds of mary hell, like spurious emissions, and if you are REALLY unlucky(as I was during one of my experiments!) a thing called "Parasitic oscillation" - which is to say major instability in the final(the RF power amplifier), the amp starts to self-oscillate, begins running-away with no frequency control, emits crud all over the band in the process, and pretty soon blows itself to bits - literally.
In the one that I BUILT(without proper procedures), the final transistor got hotter and hotter, which fed the parasitic oscillation as the change in temperature alters the frequency characteristics of the transistor, and it was kind-of like the RF equivalent of letting the handbrake off on a car on a hill - it runs away, getting faster and faster, until(if not stopped by something), it crashes and self-destructs. Anyway - that was some of my early RF lessons, and then I met and started working for a fella who luckily for me, knew lots about RF, and had spent about 20 years in the trade including working and repairing AM anf FM transmitters in the kilowatt range of output power, so he was a goldmine of information and PRACTICAL help, which you can't really get by justing studying books and equations.
It was him in fact, who when he found out about my aforementioned 15W of RF juice, said to me: "You'll get busted if you run that much juice." As I was not after about six months or so, I thought I was untouchable, until that knock on the door by the well dressed man from RSM(Radio Spectrum Management).
rigidigital
Senior Member
Hi Grogster,It was him in fact, who when he found out about my aforementioned 15W of RF juice, said to me: "You'll get busted if you run that much juice." As I was not after about six months or so, I thought I was untouchable, until that knock on the door by the well dressed man from RSM(Radio Spectrum Management).
What kind of things were you broadcASTING ? I had a girlfriend many years ago that when living and working in England, she liked to listen to pirate radio ! I think she said some are off shore in a little boat/ship. Have a look at some of these units, just a couple of ebay searches you get between 100mw and 25 Watt
http://www.ebay.com/sch/i.html?_trksid=p2047675.m570.l1313&_nkw=FM+Stereo+Radio+Station+Kit&_sacat=0&_from=R40Yes, you're right - there are A LOT of offerings on ebay.
The higher-power ones are the ones that can be really dirty in their output, as something has to give at those prices(the cheaper, high power ones), and normally, that cost is saved in the output stage with little or no filtering at all! This is not saying that the really cheap low-power ones(500mW or less) are clean - they too tend to be lacking in filters, but at the low power, GENERALLY they cause less of an issue, as they have limited range.
25W of output badly filtered will get you noticed VERY quickly by people you really don't want to notice you!!!
The only way to see if any specific unit is compliant in that respect, is to plop it on a spectrum analyzer. Harmonics and spurs(spurious emissions) are the "Nasty" ones that need proper filtering to correctly suppress.
Generally speaking, with FM transmitter, is is the 3rd harmonic which is the most dangerous. Harmonics are unwanted copies of your carrier frequency, at multiples of your carrier frequency, so if you were running on 100.0FM for example, you would have measurable harmonics at 200.0MHz, 300.0MHz and 400.0MHz. The 3rd harmonic is 400.0MHz, which is getting close to some ATC frequencies depending on where you live. You really need an analyzer to see these harmonics and weather they are correctly suppressed or not, and unfortunately, most people don't have access to an analyzer due to their cost...
Oh yeah - on the music - I was and still am a fan of Rock and 80's music, so most of my playlist was of that genre, and I ran NO ADS, as this was one thing that really annoyed me about commercial stations - still does. No music cut off either. Originally, I had no crossfading either, but did put a gentle crossfading in the mix later in the running of things. I would run about 5 songs, then play a little comedy skit - something funny from the net or other souce(crank-calls etc), then back in to the music.
The higher-power ones are the ones that can be really dirty in their output, as something has to give at those prices(the cheaper, high power ones), and normally, that cost is saved in the output stage with little or no filtering at all!
This is not saying that the really cheap low-power ones(500mW or less) are clean - they too tend to be lacking in filters, but at the low power, GENERALLY they cause less of an issue, as they have limited range.25W of output badly filtered will get you noticed VERY quickly by people you really don't want to notice you!!!
The only way to see if any specific unit is compliant in that respect, is to plop it on a spectrum analyzer. Harmonics and spurs(spurious emissions) are the "Nasty" ones that need proper filtering to correctly suppress.
Generally speaking, with FM transmitter, is is the 3rd harmonic which is the most dangerous. Harmonics are unwanted copies of your carrier frequency, at multiples of your carrier frequency, so if you were running on 100.0FM for example, you would have measurable harmonics at 200.0MHz, 300.0MHz and 400.0MHz. The 3rd harmonic is 400.0MHz, which is getting close to some ATC frequencies depending on where you live. You really need an analyzer to see these harmonics and weather they are correctly suppressed or not, and unfortunately, most people don't have access to an analyzer due to their cost...
Oh yeah - on the music - I was and still am a fan of Rock and 80's music, so most of my playlist was of that genre, and I ran NO ADS, as this was one thing that really annoyed me about commercial stations - still does. No music cut off either. Originally, I had no crossfading either, but did put a gentle crossfading in the mix later in the running of things. I would run about 5 songs, then play a little comedy skit - something funny from the net or other souce(crank-calls etc), then back in to the music.
Another wee thing that comes to mind about my experiments is that I could not get away with any more then about 20W at the most, as I was transmitting from my house, and more then about 20W of power simply swamped the TV-aerial amp that every house around here has one of, causing MAJOR TVI(TV Interference), which would really have got the attention of the RSM. I had friendly neighbours at the time, so was able to run some tests, then ring them and ask if they noticed any interference on their TV sets. More then about 19 or 20 watts, and their TV screens would go mad - just so much RF in the area, that the masthead amps would overload and ruin their picture. This was still analog TV days.
Bear that in mind if you plan to run a juicy transmitter - although, it would not be advisable simply because you won't have a licence for that power, and you won't want to get fined like I was, would you?(rhetorical!)
Also, the more RF power you are running, the more important it is that your aerial is a correct match to the transmitter frequency - it DOES matter at higher output power(more then about 500mW or so), as a bad match will result in reflected power back to the output of the transmitter. This is normally dissipated at heat in the final, but reflected power is a bad thing...
Also with high output powers, you also need to pay attention to SWR(or VSWR depending on who you talk to), which is a measure of how well matched your aerial and coax are to the transmitter. A bad match will blow your transmitter output.
Starts to get complicated, doesn't it?
High power is a nice idea, but comes with it's own checklist of prerequisites including needing a license...
I had friendly neighbours at the time, so was able to run some tests, then ring them and ask if they noticed any interference on their TV sets. More then about 19 or 20 watts, and their TV screens would go mad - just so much RF in the area, that the masthead amps would overload and ruin their picture. This was still analog TV days.Bear that in mind if you plan to run a juicy transmitter - although, it would not be advisable simply because you won't have a licence for that power, and you won't want to get fined like I was, would you?(rhetorical!)
Also, the more RF power you are running, the more important it is that your aerial is a correct match to the transmitter frequency - it DOES matter at higher output power(more then about 500mW or so), as a bad match will result in reflected power back to the output of the transmitter. This is normally dissipated at heat in the final, but reflected power is a bad thing...
Also with high output powers, you also need to pay attention to SWR(or VSWR depending on who you talk to), which is a measure of how well matched your aerial and coax are to the transmitter. A bad match will blow your transmitter output.
Starts to get complicated, doesn't it?
High power is a nice idea, but comes with it's own checklist of prerequisites including needing a license...
Manuka is absolutely right about the difficulties of getting on the air at all back in the '60's. No plethora of kits or prefab transmitters flooding the market.
I spent my entire Christmas break stripping down an old 5 tube, (valve,) AM radio and completely rewiring the chassis as a 4 tube xmitter. I used parts from the TV repair shop I'd worked at as a youth, and even after a great deal of time and effort was able to get no more than 7 watts output on the AM broadcast band.
Fortunately, I'd picked up a used reel-to-reel tape deck over the summer, so I laboriously recorded long tapes off of vinyl records while I was constructing the xmitter so I would have something playing when I was at class, or meals, or when I was just too busy to play records.
Once back at school, I (surreptitiously) borrowed equipment from the college electronics lab to set up the xmitter and antenna. It all worked out well, even with some harmonic content I was unable to limit very well, probably due to the fact that there was only one other AM radio station on the entire radio dial with listenable reception back then.
But the entire project might not have worked out if the dean of students had had something other than a PSA in mind. Legal is good. Prefab legal modular xmitters are better, if less educational.
I spent my entire Christmas break stripping down an old 5 tube, (valve,) AM radio and completely rewiring the chassis as a 4 tube xmitter. I used parts from the TV repair shop I'd worked at as a youth, and even after a great deal of time and effort was able to get no more than 7 watts output on the AM broadcast band.
Fortunately, I'd picked up a used reel-to-reel tape deck over the summer, so I laboriously recorded long tapes off of vinyl records while I was constructing the xmitter so I would have something playing when I was at class, or meals, or when I was just too busy to play records.
Once back at school, I (surreptitiously) borrowed equipment from the college electronics lab to set up the xmitter and antenna. It all worked out well, even with some harmonic content I was unable to limit very well, probably due to the fact that there was only one other AM radio station on the entire radio dial with listenable reception back then.
But the entire project might not have worked out if the dean of students had had something other than a PSA in mind. Legal is good. Prefab legal modular xmitters are better, if less educational.
rigidigital
Senior Member
I took my time deciding to either order a transmitter from ebay or the Amobea and the CD. I just ordered the second suggestion. Amoeba and CD, be much more educational only drw back ws the 400meter broadcast. but for half the price of the ebay transmitters its a better way to start regardless of price.
Thanks everybody for your information and links,
regards, Rigidigital.
Thanks everybody for your information and links,
regards, Rigidigital.
rigidigital
Senior Member
With regard to broadcasting , if I manage to plug in to my TV ariel , would that be a suitable antenna ?
Als , unrelated, but what range can I get from an xbee sold on this site ? I believe One of the xbees can transmit a couple of kilometers, but im probably wrong ?
Als , unrelated, but what range can I get from an xbee sold on this site ? I believe One of the xbees can transmit a couple of kilometers, but im probably wrong ?
TV aerial would be an incorrect match - don't use it.
Transmitter aerials are 50-ohm impedance to the transmitter output 99% of the time, and a TV aerial is 75-ohm impedance, which represents a 50% mis-match to the transmitter - not a good thing.
I will have to look up the Amoeba from the previous posts - I think I missed that link, so I will look it up now...
Transmitter aerials are 50-ohm impedance to the transmitter output 99% of the time, and a TV aerial is 75-ohm impedance, which represents a 50% mis-match to the transmitter - not a good thing.
I will have to look up the Amoeba from the previous posts - I think I missed that link, so I will look it up now...
If 400m is not enough after the first project then there is also the ULTIMA bug with a 1km range.
http://www.talkingelectronics.com/projects/Ultima/Ultima.html
http://www.talkingelectronics.com/projects/Ultima/Ultima.html
OH YEAH!!!!
I remember those little TE bugs!!!!!
I had totally forgotten about them, until I found the link to the Aomeba thing.
On the aerial - just use the wire they will supply with the kit, or a length of wire as specified in the instructions.
These units cannot be connected to a base-loaded whip or other professional aerial easily(there is no output coupling capacitor for isolation - the output is directly connected to the output transistor), so just use the wire as supplied.
I remember those little TE bugs!!!!!
I had totally forgotten about them, until I found the link to the Aomeba thing.
On the aerial - just use the wire they will supply with the kit, or a length of wire as specified in the instructions.
These units cannot be connected to a base-loaded whip or other professional aerial easily(there is no output coupling capacitor for isolation - the output is directly connected to the output transistor), so just use the wire as supplied.
rigidigital
Senior Member
That TE bug sounds good but.... now he may not be going to boarding school, a last minute decision..... so podcasts are going to be the thing (possibly)
Still these bugs should still be fun to play and learn. Ive ordered them.
Still these bugs should still be fun to play and learn. Ive ordered them.
What TV aerial? A UHF one - no chance.
Even on ones without a balun?
I would think so. I MAY BE WRONG - Others feel free to correct me - I make no claim to being any kind of know-it-all with respect to RF, and in fact, am still learning new things!
As far as I know, the balun is a 300-ohm to 75-ohm unit, so the native at-elements impedance of any VHF TV aerial will be designed for around 300 ohms, which is even worse as far as a match for 50-ohms impedance is concerned. A balun or aerial such as the J-pole or SlimJIM are actually a DC short circuit by design, but NOT at RF frequencies.
Heres' a GREAT trick - get an aerial like a J-pole or SlimJIM.
Have the coax connections and loop of aerial that shorts them together visible, then connect a 21W 12v car light-bulb across the aerial. The bulb will light from the RF energy. Now show that to an electrician and point out the "DC short" - watch them try to explain or understand WHY the bulb is lit, when there is a short across the circuit which should prevent that from happening.
(you need a good 5W or more of juice before you can make the bulb light like this, and it has to be constant RF from the likes of an FM transmitter)
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You can make just about any balun you want with expert help, not just shop TV-ariel to VHF receiver.
Personally, I'd just get the bug out and pull your wire.
Aha, so sonny-boy isn't going to need a Tx but Dad is ..... Ummm.... people have used similar excuses (I'm buying it for a friend) down at the Pharmacy
Personally, I'd just get the bug out and pull your wire.
Aha, so sonny-boy isn't going to need a Tx but Dad is ..... Ummm.... people have used similar excuses (I'm buying it for a friend) down at the Pharmacy
Dont forget that tuning antennas is important.
The enclosed graph shows how the field strength (measured at 50M) from a RFM22B transmitter at 434Mhz varies as the wire antenna is trimmed down from 30cm.
Optimum length is 28cm and signal strength is -61dBm, versus -79dBm at the standard 1/4 length of 17cm.
So an 18dB difference.
The enclosed graph shows how the field strength (measured at 50M) from a RFM22B transmitter at 434Mhz varies as the wire antenna is trimmed down from 30cm.
Optimum length is 28cm and signal strength is -61dBm, versus -79dBm at the standard 1/4 length of 17cm.
So an 18dB difference.
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For that particular device, yes.
But the tuning will be different for different types of device, or indeed individual examples of the same type of device.
A good start would be a 1/2 wavelength dipole, mounted vertically. Connections are at the centre where the two sides (almost) meet and which is a low impedance point (high current/low voltage). Connect either directly or via 50 ohm coax (so not tv coax) with the grounded shield side at the bottom. Antenna design is a seriously black art, as so many things that you can't see affect the result. The thinner the wire that it is made of, the higher the 'Q' (sharpness of tuning) and the more sensitive it is to being the wrong length. So use thicker tube rather than thin wire and the match will be better, as well as being structurally easier to handle.
Power limits are often erp (effective radiated power) so having a high gain (=directional) aerial simply reduces the power you can apply.
This advice will self-destruct if you need but don't have a license for what you are doing.
Power limits are often erp (effective radiated power) so having a high gain (=directional) aerial simply reduces the power you can apply.
This advice will self-destruct if you need but don't have a license for what you are doing.
I was eagerly awaiting your comment, Prem.. What took so long?
BTW, I do have a 600W broadband amp from a piece of RF-excited medical gear. Now I just need to get it mounted on a suitable heatsink, as the one provided is only suitable for low duty-cycle pulses. But these comments are OT as far as broadcast gear goes, so I'll say no more.
BTW, I do have a 600W broadband amp from a piece of RF-excited medical gear. Now I just need to get it mounted on a suitable heatsink, as the one provided is only suitable for low duty-cycle pulses. But these comments are OT as far as broadcast gear goes, so I'll say no more.
WOW 1.5kW for $7.50?
HOW?!???!!!!
I think a 10W FM license here in NZ, provided you can get one was about $1,000 a year last time I inquired at RSM. The FM band is pretty busy here, which makes commercial licenses expensive. Admittedly, that was a few years ago, but the price is probably about the same or more by now. There were prerequisites for that too - you had to state the equipment you were planning to use including audio-chain and aerial specifications, and it ALL had to be backed up with laboratory certificates of compliance - yet more expense.
Certainly NOT a $7.50 exercise!!!!
What frequency was that 1500W license for?
...or are you pulling our legs with that $7.50 figure...
1.5kW for $7.50?HOW?!???!!!!
I think a 10W FM license here in NZ, provided you can get one was about $1,000 a year last time I inquired at RSM. The FM band is pretty busy here, which makes commercial licenses expensive. Admittedly, that was a few years ago, but the price is probably about the same or more by now. There were prerequisites for that too - you had to state the equipment you were planning to use including audio-chain and aerial specifications, and it ALL had to be backed up with laboratory certificates of compliance - yet more expense.
Certainly NOT a $7.50 exercise!!!!
What frequency was that 1500W license for?
...or are you pulling our legs with that $7.50 figure...
Don't know, but a possibility
http://en.wikipedia.org/wiki/Amateur_radio_licensing_in_the_United_States
I'll wait for John West...............
e
http://en.wikipedia.org/wiki/Amateur_radio_licensing_in_the_United_States
I'll wait for John West...............
e
I was right to say that you can't use a UHF TV antenna - I decided to do some tests and the results were that the UHF antennas (tried both the omni and contract aerial as transmitting antennas) were far worse than expected.
Due to not knowing where to connect an aerial to the little FM transmitter, I just used a VHF channel 3/4 RF modulator to transmit a TV signal (and that way it could be compared with use of the UHF modulator) and there was no picture when the receiving loop antenna was more than 5cm away from the dipole on the contract aerial. The picture shows the picture from when the distance was 4cm.
What was on TV was Channel 4 Racing and you can just about see the green of the racetrack (horse racing, not car racing!). The strange coloured patterning seems to be an issue with the compression done inside the computer by the tuner card as the problem is nonexistent with a good picture or on a CRT TV. However the white horizontal lines were on the CRT TV too so that must be due to the aerials being unsuitable. I can't imagine what could be interfering - all I could find through Google searching was that Band III is used for DAB and band II for FM but no use for band I (which includes VHF channel 3/4).
However working out that UHF antennas don't work for VHF isn't hard - Yagi FM aerials on houses are massive compared to the UHF ones which look small from the ground - but even the 10-element UHF one is 30 inches long so why would someone put up something that is at least this big both in width and in length if a UHF TV aerial worked fine?
Antennas work by being induced with a few microvolts of rf from 'the aether' and being made resonant at the desired frequency, to boost the required signal and reduce all others. A long-wire antenna is generally aided by an antenna tuning unit, whose job is to make it resonant and to match the impedance of the antenna into the rx. A yagi or any other intrinsically resonant design is cut to a specific frequency, and will also match the impedance of the rx/tx. The length of the main dipole element in a yagi is close to 1/2 wavelength, with longer reflectors behind and shorter directors in front. At other frequencies the whole director/reflector thing won't work and the impedance won't match, so they are effectively just a piece of untuned wire and may or may not pick up some signal.
Impedance matching is analogous to gearing. You can't start a car or ride a bike up a hill in top gear because there in an impedance mismatch. By matching the impedance you get maximum energy transfer. As the impedance of the car (speed and torque) changes so the gearing has to change. If the antenna impedance is not matched then the voltage standing wave ratio (vswr) which can be measured is not 1:1 meaning that power is reflected back into the source from the antenna. It is easy to fry a high power tx if the antenna goes faulty while on load, because the power that should be in the antenna is suddenly reflected back and dissipates in the tx.
The other issue is polarisation. If you transmit with a vertical dipole then your receive aerial should also be vertical. If it isn't but is say at 90 degrees then the effect is the same as crossing two polarised sunglass lenses i.e. nothing.
And then there are transmission lines .. but Nick is right, if you didn't need a big antenna then you wouldn't have one. Just as well that cellphones work on high frequencies (800-1800MHz). A cellphone on say 144MHz would need a 50cm antenna.
Impedance matching is analogous to gearing. You can't start a car or ride a bike up a hill in top gear because there in an impedance mismatch. By matching the impedance you get maximum energy transfer. As the impedance of the car (speed and torque) changes so the gearing has to change. If the antenna impedance is not matched then the voltage standing wave ratio (vswr) which can be measured is not 1:1 meaning that power is reflected back into the source from the antenna. It is easy to fry a high power tx if the antenna goes faulty while on load, because the power that should be in the antenna is suddenly reflected back and dissipates in the tx.
The other issue is polarisation. If you transmit with a vertical dipole then your receive aerial should also be vertical. If it isn't but is say at 90 degrees then the effect is the same as crossing two polarised sunglass lenses i.e. nothing.
And then there are transmission lines .. but Nick is right, if you didn't need a big antenna then you wouldn't have one. Just as well that cellphones work on high frequencies (800-1800MHz). A cellphone on say 144MHz would need a 50cm antenna.
LOVE the car gearbox analogy.
It's quite correct, and helps visualize the issue well - nice thinking.
...although I did bet a friend of mine when we were in high-school, that he could not do a stationary hill-start in top gear(5th, which is actually a slight overdrive in the car he had - 4th was the 1:1 ratio!), and he blew up the clutch...
People can be stupid when they are young, myself included for even suggesting that to him, but him too for making the attempt.
On aerials, that's why I like the quarter-wave ground-plane aerial, as they are easy to make, and work well, and are PROBABLY the smallest of the FM band aerials.
BUT they have caused me issues with static discharges in the atmosphere blowing finals. This WAS kinda my fault though, as the aerial mast was mounted on a large wooden fence-pole, and the pole was not earthed, which would have stopped that issue most likely.
J-poles and Slim-JIM's are quite easy to make too, but they are so much larger at the same frequency compared to the quarter-wave GP.
I have successfully made Slim-Jim's for 433MHz data use, and they are nice and small and can be sealed up inside a length of PVC pipe.
While you can get PVC drainpipe big enough for the width of a Slim-JIM at FM band, the pipe is that much wider and longer, that mounting almost requires involving the construction industry!
It's quite correct, and helps visualize the issue well - nice thinking.
...although I did bet a friend of mine when we were in high-school, that he could not do a stationary hill-start in top gear(5th, which is actually a slight overdrive in the car he had - 4th was the 1:1 ratio!), and he blew up the clutch...
People can be stupid when they are young, myself included for even suggesting that to him, but him too for making the attempt.
On aerials, that's why I like the quarter-wave ground-plane aerial, as they are easy to make, and work well, and are PROBABLY the smallest of the FM band aerials.
BUT they have caused me issues with static discharges in the atmosphere blowing finals. This WAS kinda my fault though, as the aerial mast was mounted on a large wooden fence-pole, and the pole was not earthed, which would have stopped that issue most likely.
J-poles and Slim-JIM's are quite easy to make too, but they are so much larger at the same frequency compared to the quarter-wave GP.
I have successfully made Slim-Jim's for 433MHz data use, and they are nice and small and can be sealed up inside a length of PVC pipe.
While you can get PVC drainpipe big enough for the width of a Slim-JIM at FM band, the pipe is that much wider and longer, that mounting almost requires involving the construction industry!