| DIY FM antenna, can it be better than radioshack junk? - Click HERE for Original Thread |
| homer09 |
Im looking for a good DIY FM antenna for my Yamaha t-1 tuner. Right now im using a dipole and it pulls strong signals very well. But, i want to catch 99.9 here in montreal, which is a notoriously difficult one to pull.
Right now, i could catch it in mono/narrow slighlty off-tuning it intentionally. If i hold my dipole vertically, i get a flickering stereo light. So this is fringe reception, i need a little boost to get some nice stereo here.
What are you guys using for indoor FM antennas? A DIY solution interests me. here is what i absolutely need:
- better gain than a standard dipole
- the smaller the better, dont want to have to move furniture for this :dead:
- something that doesnt need constant adjustment for each station
shoot away :D |
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| dnsey |
It's perfectly possible and not difficult or expensive to build your own antennas - a member of the amateur radio fraternity would probably be happy to help you with it - but I think you'll have to compromise in order to balance your requirements.
To achieve more gain, your antenna must be more directional. In the case of a Yagi array (the usual type for domestic FM), this is achieved by adding directors and reflectors, which increases the overall size of the antenna. The extra directionality will make it necessary to rotate the array to receive different transmitters.
The only option I can think of is a switched pair of dipoles, one of which is dedicated to your DX station, perhaps with a VHF amplifier added.
All sorts of designs have been tried - some of which use materials such as aluminium foil and cardboard, so cost virtually nothing - you can have a lot of fun experimenting once you grasp the theory.
Whatever you settle on, make sure that it's properly impedence matched to your feeder and tuner - a great deal of signal loss can be due to a mismatch here.
Good luck! |
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| homer09 |
thanks for the ideas. can you give me more specific leads for me to get started on? my requirements were in order of importance, so i will sacrifice the last one. do you have a recommended antenna recipe?
impedence matching, can you explain further? |
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| TwoSpoons |
You'd better sacrifice #2 as well. Small antenna's won't get the performance as their aperture is smaller (=less power pickup).
The best result is going to be had by putting your antenna on the roof, and using low loss co-ax to feed your receiver. I'd assume your receiver input is 75 Ohm? So you need 75 ohm co-ax (RG-59 IIRC). If you use a folded dipole it will have a 300 ohm impedance, so you will want a 4:1 balun to connect to your coax. |
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| homer09 |
| quote: | Originally posted by TwoSpoons
You'd better sacrifice #2 as well. Small antenna's won't get the performance as their aperture is smaller (=less power pickup).
The best result is going to be had by putting your antenna on the roof, and using low loss co-ax to feed your receiver. I'd assume your receiver input is 75 Ohm? So you need 75 ohm co-ax (RG-59 IIRC). If you use a folded dipole it will have a 300 ohm impedance, so you will want a 4:1 balun to connect to your coax. |
it has to be an indoor solution, i dont have the liberty to pull coax into my room or mount things on the roof.
my tuner has boath 75 ohm and 300 ohm. which is best to use?
still looking for an indoor solution that beats a dipole... |
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| TwoSpoons |
A colinear dipole might help. Though it will need loading coils to get the size down.
Basically, though, you're stuffed if you want gain at 99MHz, and you want it inside. Any solution with gain at that frequency is going to be big - simple physics. After all, the wave length you're after is around 3 metres, so even a proper 1/2 wave dipole is going to be 1.5 metres long. |
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| homer09 |
| quote: | Originally posted by TwoSpoons
A colinear dipole might help. Though it will need loading coils to get the size down.
Basically, though, you're stuffed if you want gain at 99MHz, and you want it inside. Any solution with gain at that frequency is going to be big - simple physics. After all, the wave length you're after is around 3 metres, so even a proper 1/2 wave dipole is going to be 1.5 metres long. |
well if its big but concealable, i dont mind, i just dont want something that doesnt looks like those big roof top antennas in my room. i dont mind something the size of a standard dipole, only mine isnt performing for me.
do you have more info on colinear dipoles and how i would build one?
thanks for the help, appreaciate it |
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| TwoSpoons |
| Would you mind accurately describing (or photographing!) what you have currently? It would help knowing where you are starting from, in order to get improvements. |
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| mcs |
| quote: | Originally posted by homer09
well if its big but concealable, i dont mind, i just dont want something that doesnt looks like those big roof top antennas in my room. |
A good FM antenna will be big, and most likely look like one of the roof-top antennas...
But it could still be concealable if you make one yourself using thick copper wire instead of aluminium tubes - that way you could make it flat at least.
Best regards,
Mikkel C. Simonsen |
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| homer09 |
Thanks dnsey,
Here is my current setup: i have this tuner:
a write up for the t-1 is available here:
http://www.fmtunerinfo.com/yamaha.html
note: this tuner is much better already than a technics tuner i was using previously (techincs st-c03)
i took a pic of the back of the tuner, but it really isnt clear since my camera is very bad. It basically consists of a 75ohm input, a 300 ohm input and an AM antenna input. (the dipole is currently connected in the 300 ohm input)
Also is a picture of a standard dipole antenna you can buy at any electronics store for a few dollars.
my room is located on the second floor, close to a window. |
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| homer09 |
| the dipole i use (obviously i stretch it out and orient it as best i can) |
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| TwoSpoons |
Ah, I thought as much. I too have one of those nasty ribbon antenna's. And my one is **** .
So there's hope for you yet! :D
This site shows you how to build a similar antenna, but tuned closer to your weak station. I'd try that first as its quick, cheap and easy. |
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| homer09 |
| quote: | Originally posted by TwoSpoons
Ah, I thought as much. I too have one of those nasty ribbon antenna's. And my one is **** .
So there's hope for you yet! :D
This site shows you how to build a similar antenna, but tuned closer to your weak station. I'd try that first as its quick, cheap and easy. |
Thanks, i will try this!
will connecting the crossbar of the antenna with 75-ohm coax be better than using more 300 ohm twin lead? i noticed the apparently very good FM Reflect dipole from C. Crane
http://www.ccrane.com/fm-reflect-antenna.aspx
uses 75 ohm to terminate. any other insight between the differences between this FM Reflect and a standard dipole? |
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| jimbo1968 |
| quote: | Originally posted by TwoSpoons
Ah, I thought as much. I too have one of those nasty ribbon antenna's. And my one is **** .
So there's hope for you yet! :D
This site shows you how to build a similar antenna, but tuned closer to your weak station. I'd try that first as its quick, cheap and easy. |
What's the difference? Is the 300ohm wire much better than that used in the ribbon antenna? |
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| dnsey |
As Twospoons pointed out, a straight dipole is terminated at 75 Ohms, and a folded dipole at 300. (Actually it's a bit more complicated, especially if you start adding elements...).
What the DIY site describes is a folded dipole:
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so it needs a 300 Ohm cable.
The Drake looks like a straight dipole:
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and will therefore require 75 Ohm cable.
EDIT: The site doesn't like my diagrams, but I hope you understand what I mean! |
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| homer09 |
| quote: | Originally posted by jimbo1968
What's the difference? Is the 300ohm wire much better than that used in the ribbon antenna? |
i have read that some wire used in cheap dipoles doesnt even have 300ohm impedence, some have closer to 200. thats one improvement.
second, my dipole is almost 6' long, which is terrible considering that is optimized for 78 MHz, when FM is 88-108 MHz and my problem station is 99.9 MHz. this will be the second improvement.
Still wondering about that FM reflect antenna and if anyone has any insight on how it is built inside?
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| homer09 |
| quote: | Originally posted by dnsey
As Twospoons pointed out, a straight dipole is terminated at 75 Ohms, and a folded dipole at 300. (Actually it's a bit more complicated, especially if you start adding elements...).
What the DIY site describes is a folded dipole:
so it needs a 300 Ohm cable.
The Drake looks like a straight dipole:
and will therefore require 75 Ohm cable.
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Sorry what is the "Drake" is this the antenna i just posted a pic of? Because if it is, this one looks like a folded dipole to me, notice in the picture there are two runs of coax... how could it be using 75 ohm then? |
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| homer09 |
another pic of the FM Reflect
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| dnsey |
I have no idea where I got 'Drake' from!!:xeye:
I was referring to the FM Reflect, which looked to me like a straight dipole, but I see from the larger pic that it's not.
As I said, it's not really as straightforward as all that (what is?) - the impedence actually varies with the point of attachment of the feeder. It's also quite possible that the two runs of the Reflect are not electrically conected - one may well be acting as a parasitic element.
The best feeder for a simple ribbon folded dipole, however, is 300 Ohm.
I'd be a bit dubious about the reports of some feeders being 200 Ohm - it's possibly so, but not an easy thing to measure, and will vary according to various extrinsic factors, so I wouldn't worry too much.
Just for fun, I've read that a pair of 'Slinky' spring toys arranged as a dipole can be very efficient - might be worth a try: cheap copies are available here in 'Pound Stores'. |
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| homer09 |
| quote: | Originally posted by dnsey
The best feeder for a simple ribbon folded dipole, however, is 300 Ohm.
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what do you mean by feeder? the cable that connects from the antenna to the tuner?
you say a folded dipole is 300 ohm. isnt it the cable that determines what ohm it is? so to make a folded dipole with coax is inefficient? only a single dipole would be efficient with coax? |
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| DigitalJunkie |
I got curious and connected a J-pole to my Sansui TU-717.
*WHOA!*
The whole band came alive! I can easily get stations from 80+ miles away.. 104.7 (some 70+ miles south) sounds like it's in my backyard! :bigeyes:
I'm impressed,and it was easy to make with some copper pipe.
If you scroll down to the bottom of this page,there's some info.
It's also possible to make a J-pole from 300-ohm twinlead.
http://www.pcs-electronics.com/en/g...hp?sub=antennas |
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| dnsey |
Yes, feeder is the cable - it's usually thought of in terms of a transmitting antenna, hence the term.
The termination impedence of the antenna is fundamentally determined by the position of the standing waves on the element relative to the point of termination - don't worry about it unless you want to get heavily involved in antenna design ;)
The characteristic impedence of the feeder cable should match the antenna termination in order to avoid both losses and internal reflections in the cable, which can cause distortion of the signal.
Naturally, the tuner input should match the cable.
So yes, a single dipole would be a good match to 75 Ohm feeder. If you wanted to use this cable with other designs, various techniques (Pawsey stubs, baluns etc.) can be used to match it, but there's little point in your case, as you have both 75 and 300 Ohm inputs, and can cater for either case.
There's little to choose between the two for domestic use - balanced feeder is more susceptible to impulse interference in some cases, but if you don't have trouble from motor ignition systems, switching transients etc., then this isn't important. |
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| homer09 |
| quote: | Originally posted by DigitalJunkie
I got curious and connected a J-pole to my Sansui TU-717.
*WHOA!*
The whole band came alive! I can easily get stations from 80+ miles away.. 104.7 (some 70+ miles south) sounds like it's in my backyard! :bigeyes:
I'm impressed,and it was easy to make with some copper pipe.
If you scroll down to the bottom of this page,there's some info.
It's also possible to make a J-pole from 300-ohm twinlead.
http://www.pcs-electronics.com/en/g...hp?sub=antennas |
interesting, what design did you follow? |
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| dnsey |
| Note how the j-pole uses a variable stub to achieve correct matching to the feeder :) |
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| TwoSpoons |
Never really looked at the J-pole. Seems rather tasty! Think I might build one. Probably use 1/2" pipe to get the bandwidth up.
Googling for J-pole turns up lots of info. |
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| Rahul |
HI!
Now this is something from deep down my heart. First you need to decide wether you need a directional antenna or an omnidirectional one.
For a directional one its simply a matter of choice either go in for a yagi or a cubical quad. All would give a gain over normal pair of dipoles but then they are directional. The gain increases with each additional element. It is a simple way to achieve a gain this may not be of significance where reception is concrened but when you transmit a 3db gain on antenna would alone provide you with signal equivalent to twice the power. This is economical when you think in terms of putting a signal worth 2KW while using only 1Kw. Passive gain.
Most antennas are restricted in bandwidth to over come this shortcoming one can try a log periodic.
A normal dipole has a feedpoint impedence of75 ohms folding a dipole cause its impedence to increase as well as its bandwidth:
Z (imp)=sq *turns
Hence a folded dipole has 2sq impedence ie 4 times that equates to 300ohms for nominal impedence of 75ohms half wave dipole.
Secondly it is balanced sort of antenna hence a balanced ribbon feeder.
Now on to omni directional one, basic one is quarter wavelength ground plane, this results in good match to various TX and signal. Going one up we come to antennas in range of 5/8 lmbda ie wavelength, the J pole comes in this catiegory these provide some gain over the basic Ground plane or the quarter wavelength.
Many may have noticed a vertical dipole .Very popular with pager systems mostly many of them are stacked to achieve some omnidirectional gain a 4 element vertical dipole provides more than 6dbs of omnidirectional gain. Once again the folded vertical dipole provides a higher bandwidth.
However a multi element qubical QUAD with an antenna rotor still beats anything available worldwide.
Now for some interested in an RF preamp do a google on norton noiseless feedback preamp or a gasfet preamp. These are hard to beat where reception is concerned.
Regards
Rahul |
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| pinkmouse |
This is all fascinating!
I'm looking at building a DAB antenna in the near future, are there any good general design reference sites that you guys can recommend? |
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| dnsey |
I don't know of any good websites (I'm sure there are some!), but the RSGB publishes some excellent books on the subject.
Try
here |
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| Ron E |
The proper length for a folded dipole antenna is:
L=vf*c/f
Vf=velocity factor, c=speed of light, f=frequency
For the FM band, a folded dipole has a wide enough bandwidth that tuning it to 98MHz is good enough.
For some twinlead, vf=0.75, but it can vary greatly with construction, IIRC.
L=0.75*300000000/98000000=~2.3 meters
I highly doubt that a manufacturer would make a folded dipole the wrong length, so doubting them is not productive. IF the folded dipole doesn't work for you, you may just need to orient it properly. Dipoles have a null in their gain plot very much like a dipole speaker, highest gain is normal to the plane of the antenna's "arms" and lowest (zero) gain is looking down the cable of the arms.
J-poles are omnidirectional and may pick up a lot of multipath in big cities IIRC.
I experimented with a few antenna types over the years. I finally broke down and bought one of those amplified antennas and it doesa fairly good job in the metro area where I live.
One thing I noticed when playing around wiht antennas is that there is a pretty foolproof way to check the quality of the signal. If you connect a small speaker between the + connections of the left and right channels of your amp, the speaker plays a L-R, or difference signal. I believe FM is transmitted with a L+R and L-R signal and the L-R is susceptible to degradation. Regardless of the reason why, though, if the L-R signal sounds good (no static or dropouts) The FM station will sound good.
The best antennas by far are the old TV type that have an FM section - the type that mount on your roof and need to be rotated. |
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| homer09 |
| quote: | Originally posted by Ron E
The proper length for a folded dipole antenna is:
L=vf*c/f
Vf=velocity factor, c=speed of light, f=frequency
For the FM band, a folded dipole has a wide enough bandwidth that tuning it to 98MHz is good enough.
For some twinlead, vf=0.75, but it can vary greatly with construction, IIRC.
L=0.75*300000000/98000000=~2.3 meters
I highly doubt that a manufacturer would make a folded dipole the wrong length, so doubting them is not productive. |
i will disagree with this. i just cut my commercial cheapo dipole down to about 56". (i think there is an error in your calculations, 2.3m seems very wrong).
i didnt connect the ends, just cut a few good inches off each end, and the result: significant jump in signal strength!
then i twisted the ends together, making the loop: dissapointment, my signal strength actually decreased! (anyone venture an explanation?)
so my 56" 300ohm non-folded dipole with "parasitic" conductor is now my reference antenna.
more tests:
i took heavy guage solid copper wire (insulated). cut two equal lengths of 28", stabbed them into a cork, connected one to the shield of a coax cable and the other to the conductor. wounded a balun and hooked it to my 75 ohm input. result: its as good as my stock dipole. a dead end i think.
next test: the same design as the 300ohm dipole but using shielded coax. going to try different configurations (using shield, using inner conductor, both, parasitic, folded dipole, etc)
any thoughts? |
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| homer09 |
Tests with coax worked, but i couldnt get anything better than my reference dipole. there wasnt much difference when i tried different connections, i think this is as good as a simple dipole gets. which is still not good enough for me.
so i stumbled on this, and im trying the "Fulllband Loop" FM antenna. It seems to be the best one for my situation, and is of a reasonable and manageable size. it should give me about 3db gain over my dipole :)
anyone try this antenna?
EDIT: what does the author mean exactly by "#12 electric wire"? is this simply single conductor 12 AWG wire? |
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| Illusus |
It'll work ok, but you could try a J-pole(end-fed half -wave), these can be built to look very nice... or a polarized double loop...and if you're nuts you can give a helical antenna a go, they are about as good as you can get, but too big for most people...it needs it's own room unless you have a large hall and can tell people it's modern art.
ohh.. a vertical ground-plane antenna beats a dipole as well, and is pretty small, it can de made foldable.
Edit...I should read things through before I post..the J-pole has been mentioned.. in your situation it's what I'd choose, it has a small footprint, and, if you're crafty, you can make it look good. |
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| jackinnj |
in the U.S. there are a lot of restrictive building codes which limit a ham radio operator's ability to build a good antenna. naturally, a resulting phenomena is that hams have gotten very good at disguising their antennas.
since at the outset of the thread you stated that you couldn't pull coax or mount an antenna on the outside of your residence you might want to consider mounting a thin wire yagi on the ceiling of your living room. if you have a good idea of the location of the transmitter (you do know the frequency) it is a relatively simple matter of scaling the dimensions of the reflector and directors and their spacing to a given ham radio design -- instead of aluminum rods, use #22 wire. works if you have a plaster or sheet-rock ceiling.
I use an 6 element yagi that is sitting on the attic floor, pointed in the direction of my favorite station's transmitting tower -- in the NY Metro area this isn't difficult since most of them are now on the Empire State Building.
What's the impedance on your receiver btw -- 50R, 75R or300R -- if it's 50R don't use RG59/U, use RG58 -- 300 ohm twinlead used to have lower loss than all but the expensive coaxial cables -- I don't know the situation today since I just use RG8 ! |
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| homer09 |
| quote: | Originally posted by Illusus
It'll work ok, but you could try a J-pole(end-fed half -wave), these can be built to look very nice... or a polarized double loop...and if you're nuts you can give a helical antenna a go, they are about as good as you can get, but too big for most people...it needs it's own room unless you have a large hall and can tell people it's modern art.
ohh.. a vertical ground-plane antenna beats a dipole as well, and is pretty small, it can de made foldable.
Edit...I should read things through before I post..the J-pole has been mentioned.. in your situation it's what I'd choose, it has a small footprint, and, if you're crafty, you can make it look good. |
i am very confused when researching j-poles because they are mostly used for HAM and transmitting. i want to receive signal and have no idea where this all fits in.
Illusus, can you just give a quick description of what materials you used, and what length of rods for your j-pole?
i know how to make a polarized loop, but how do u make a double polarized loop, and is it better?
whats a vertical ground-plane antenna?
sorry if these are all newb questions :shy: |
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| jackinnj |
EDIT: this design is a log-periodic array -- has nice bandwidth although the gain is somewhat lumpy:
here's an EDIT implementation used by a ham radio operator on 432MHz which can be repurposed for FM -- this design will give around 8.5 dB of gain with a front-back ratio of 22 to 28dB:
they used copper tape for the elements and affixed them to a piece of foamcore.
for a 100MHz antenna (98Mhz to 102MHz) the element spacings are as follows:
D1 = 0.259m
D2 = 0.248
D3 = 0.238
D4 = 0.228
D5 = 0.218
D6 = 0.209
D7 = 0.200
the length of the elements are:
L1 = 1.561m
L2 = 1.495
L3 = 1.432
L4 = 1.371
L5 = 1.313
L6 = 1.258
L7 = 1.204
L8 = 1.154 |
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| Rahul |
Hi!
I feel a J pole is reasonable antenna in terms of gain, omnidirectional coverage, ease and cost. In amateur radio circuit a popular one goes by the name of Slim Jim.
A google on the term has brought up this simple to make design and plan:
http://www.irational.org/sic/radio/omni-aerial.html
Regards
Rahul |
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| Illusus |
| quote: |
Illusus, can you just give a quick description of what materials you used, and what length of rods for your j-pole |
I used EMT conduit and a junction box, all available at home depot or most hardware stores for that matter. I made a wooden box/base around the junction box to hide the ugly and match my other equipment, I also painted the conduit with 'Black Satin'* paint. The long tube is 7.5' long the short, 'hook' tube is 2.5'.
| quote: | | i know how to make a polarized loop, but how do u make a double polarized loop, and is it better? |
Yes a double loop is better, a single loop will have a horizontal or vertical polarization depending on it's orientation to the feedpoint...a double loop has both vertical and horizontal poles. It's easy enough to build but it has a funky impedance which can be corrected by using two equal lengths of 75Ohm coax and connecting their shields at either end, you'll have to tightly coil the phasing line to create a choke...the antenna is balanced and it's signal needs to be converted to unbalanced, coiling the T-line creates a choke and easier than making a balun, one to one transformer.
How to build one?...it's simple but the words escape me, I'll try, basically it's two 38.25" dia. loops with a slight overlap, both on the same plane, not perpendicular or anything...on one side where the loops overlap will be the feedpoint for both of them, it's actually diagonally polarized...ah heck...I couldn't make sense of this If I read it...I'll draw a pic.... |
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| Ron E |
| quote: | Originally posted by homer09
i will disagree with this. i just cut my commercial cheapo dipole down to about 56". (i think there is an error in your calculations, 2.3m seems very wrong).
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Yup, I forgot to divide by 2 to get a half-wave antenna. |
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| Illusus |
| quote: | | 'Black Satin'* paint |
Oh, I forgot about the asterix... OT story... near my home, some fools spray painted "SATIN RULES" on the side of a church. I'm sure they meant to write satan rules but satin is just so funny. Alas, the graff was gone by the time I came around with a camera.
Fools:
- "Dude, I just love satin...it's so smooth!"
- "F!'n A, man! Satin rules!! Praise satin!" |
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| TwoSpoons |
| quote: | | i am very confused when researching j-poles because they are mostly used for HAM and transmitting. i want to receive signal and have no idea where this all fits in. |
Antennas work equally well transmitting or receiving - i.e. a good transmitting antenna is also a good receiving antenna. Otherwise it would disobey one of the laws of thermodynamics!
From the sites I've seen
1. 300 ohm ribbon varies widely in velocity factor, its not a parameter controlled during manufacture. So calculating the right length is going to be tricky.
2. fatter conductors = wider bandwidth, which is want you want for receiving FM.
3. A j-pole is an end-fed half-wave dipole, with a quarter-wave matching stub. It can be built as an end-fed 5/8th wave, but tuning is supposedly more finicky. J-poles are nicely ground independent.
4. Velocity factor for 1/2" copper pipe is about 0.95, at 98MHz
Kind of random, but that summarises some of the stuff I've found. |
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| jackinnj |
| quote: | Originally posted by TwoSpoons
Antennas work equally well transmitting or receiving - i.e. a good transmitting antenna is also a good receiving antenna. Otherwise it would disobey one of the laws of thermodynamics! |
But a transmitting antenna is built to take anywhere from a few watts to two kilowatts for ham use -- so the materials might be different -- this becomes problematic for yagi's and LPDA's where you have to contend with wind and ice-loading.
Most university libraries (and county libraries in the U.S.) will have a copy of "The ARRL Antenna Handbook" -- this is a great source of theory and practice. The book costs around $39 and comes with a CD-ROM of programs which put the calculations into some easy programs (although many of these are java-scripted for the web nowadays.)
It surprises me that there have been relatively few articles on FM and AM antenna's -- a couple years back there was a nice article in EW describing how a.m. radio buffs in the UK built multiple loop antennas in order to hear bluegrass from the U.S. I think that AudioXpress and its predecessor have only had a half-dozen articles in the past 30 years or so. I have only been receiving Elektor for 4 or 5 years and would be interested to find out if they have any good FM antenna articles. |
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| Scott Stansbury |
The ARRL is definitely the source for all the info you need. The ARRL Antenna Book is the bible, and the site itself has good info. Check out:
http://www.arrl.org/tis/info/antproj.html
Any step in the direction of a real antenna will produce good results.
Best regards. |
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| gengis |
Has anyone tried those car antenna that extended automatically when the radio is turn on? Go down to the junk yard and pick out a late model cadillac, and take out the antenna.
That would be pretty cool. |
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| homer09 |
| hmmm. i guess it would be "cool" but what about performance? |
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| gengis |
| It should be fine. Just like any rabbit ear antenna. |
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| richie00boy |
| Just bookmarking this thread as I want to build an FM aerial soon. |
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| homer09 |
| quote: | Originally posted by richie00boy
Just bookmarking this thread as I want to build an FM aerial soon. |
be sure to report back with your experiences! |
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| richie00boy |
| I promise I will, but it will be a few months yet, too many other jobs to do... |
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| DigitalJunkie |
I don't recall the exact dimensions of my J-pole,but there's info all over the net on how to build one..
One trick I used,was to drill a hole in each of the copper pipe caps that go on top (to keep rain out,etc) and solder a nut on the inside of them,then I cut a couple short (3-inch?) pieces of "all-thread",and screwed then into the endcap+nut,and put a nut on the top to lock them inplace..
This way you can fine-tune the length of the J-pole..
(Mine was actually intended to be used with a small transmitter,but it works just as well on a reciever.)
I shot it with a coat of grey spray-primer,and it blends in with the grey house nicely,It's right outside my window,and you'd hardly notice. ;)
It's matched for 50 ohms,but works quite well on the 75ohm input of the reciever. Got a run of RG-8 going to it.. |
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| DragonMaster |
WBTZ is quite far from Montreal, the antenna is situated in Plattsburgh, 80KMs away. They use directional antennas, instead of non-directional like most others.
You might also want to know that the antenna is 550m higher than sea level.
More info:
http://www.fcc.gov/fcc-bin/fmq?list=0&facid=52807
I have one antenna able to receive that channel perfectly; A RadioShack Active Directional FM/VHF/UHF rabbit ear antenna. It's the only active antenna I have. All others have separated signal amps. There's a strange thing with 99.9 is that if your antenna is incorrectly placed is that you receive all the powerful channels between 90and 100MHz :94.3, 95.1, 96.9 and 99.5. Also, in my case, my CDP produces so much interference that I hear the line out of my CDP in the tuner.
The only thing is that if you listen TV with the same antenna, TVA reception will suck. Doesn't matter, it's a sensationalism channel with only poor content.
You might also want to mod your tuner's IF section:
http://www.amfmdx.net/fmdx/mods.html
and Google. the link I provided is not the best I found. |
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| Dick West |
Antenna design is mostly a matter of mathematics. You can't fool Mother Nature. Antenna elements must be able to resonate to certain frequencies. Any element (or 1/4 wave stubs placed end to end to be a 1/2 wave antenna) is only good for a limited frequency range (fatter element is better) so to get the entire FM band one needs 3-4 separate elements. Or, you could design an antenna just for the desired transmitter's frequency.
Then, consider if its signal is vertically or horizontally polarized or has some sort of a circular polarization. This would relate to how the elements are positioned.
Next shun amplified antennas. If there is no signal you can't amplify it and most modern FM tuners are extremely sensitive to the slightest hint of a signal.
Next, find the room's "hot spot" for the desired FM station. The elements should be placed at right angles to the station but moving the antenna fore and aft or left or right even a few inches can make a big difference and the directional position may not always follow logic. I currently am using TV rabbit ears with each 1/2 extended out 26" and the antenna is nested in a ceiling fixture lamp shade. That particular spot is the best spot in the entire room for some reason and I am getting quite regular good reception of an 89.9mhz station located 98 miles away up a river valley (no high hills in the way).
Also, be aware of tropospheric bending or ducting. Depending on atmospheric conditions you may get excellent reception with a coat hanger dangled from a window and at other times even the best of outdoor antennas may not provide a useable signal.
An indoor antenna is a vexsome thing and can consume a lot of time fiddling with it as the signal strength is so low in amplitude and it gets jumbled from object reflections. Multipath distortion will always be a big factor and can cause reception distortion. And, the room will definitely have a hot spot for each station.
BTW, Radio Shack antennas are not junk. If I were you I would buy their yagi FM antenna and try positioning it around the room to find the best spot and then figure out how to make it appear as a work of modern art or a mobile dangling from the ceiling. |
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