Car radios and portable radios are designed for high sensitivity, so can get away with a poor antenna. Proper audio FM receivers are designed for good sound quality, so may need a bit more signal.
If you understand antennas then you can make your own; other posters on here have told you enough to do this. Otherwise you will need to buy one. In any case the higher the better. FM uses VHF, which behaves quite differently from AM MW. On AM the longer the antenna the better (within reason); for VHF the antenna must be the right length - to get more signal you don't make it longer you put it higher. Forget everything you know about AM antennas.
I have no idea why you think that putting a 1k resistor in series with the wrong length antenna might work. It is surprising that you can receive anything at all with that.
If you understand antennas then you can make your own; other posters on here have told you enough to do this. Otherwise you will need to buy one. In any case the higher the better. FM uses VHF, which behaves quite differently from AM MW. On AM the longer the antenna the better (within reason); for VHF the antenna must be the right length - to get more signal you don't make it longer you put it higher. Forget everything you know about AM antennas.
I have no idea why you think that putting a 1k resistor in series with the wrong length antenna might work. It is surprising that you can receive anything at all with that.
I chose 90MHz as an example as its in the FM band (88 - 108MHz).
Obviously you don't need a different aerial for every station, but if you did it would work better. The transmitters have to have precise aerials - tuned to the exact frequency of transmission.
Horizontally and Vertically polarized. Most FM radio is horizontally polarized. Try having a look around the neighbourhood for FM radio aerials on the roofs of your neighbours, they are easily spotted as they are approximately 32" or 64" wide, unlike TV aerials. Have a look to see if they are flat (horizontal) or upright (vertical).
In urban areas its common to use an Omni-directional aerial which is circular in shape but still 32" in diameter (that allows the user to listen to stations from all directions).
Here's one such aerial .... http://www.ebay.co.uk/itm/Konig-Omnidirectional-VHF-FM-Aerial-Outside-Or-Loft-/190619609210?pt=UK_Sound_Vision_Other&hash=item2c61d0687a
I've just thought, some of Oz and NZ still use VHF TV, you'd need to find someone who has FM radio.
Obviously you don't need a different aerial for every station, but if you did it would work better. The transmitters have to have precise aerials - tuned to the exact frequency of transmission.
Horizontally and Vertically polarized. Most FM radio is horizontally polarized. Try having a look around the neighbourhood for FM radio aerials on the roofs of your neighbours, they are easily spotted as they are approximately 32" or 64" wide, unlike TV aerials. Have a look to see if they are flat (horizontal) or upright (vertical).
In urban areas its common to use an Omni-directional aerial which is circular in shape but still 32" in diameter (that allows the user to listen to stations from all directions).
Here's one such aerial .... http://www.ebay.co.uk/itm/Konig-Omnidirectional-VHF-FM-Aerial-Outside-Or-Loft-/190619609210?pt=UK_Sound_Vision_Other&hash=item2c61d0687a
I've just thought, some of Oz and NZ still use VHF TV, you'd need to find someone who has FM radio.
Last edited:
There was an awful lot of static so putting in the 1K reduced most of the static. I do have a bit of logic to things, I don't just randomly try things.
Your 1k series resistor buggers everything. - And the T antenna should be appx 5 ft and a few inches between the tips of the top T bar.
If you don't receive anything, there's a fair chance there's something wrong with the tuner part.....?
If you don't receive anything, there's a fair chance there's something wrong with the tuner part.....?
TheTubeAmper, There is an entire body of science devoted to "Transmission Line Theory" that you seem to be unaware of, as it changes everything about electricity than is commonly known. The problem arises when an alternating current within a single stretch of wire, say, 10ft long, reverses flow within said stretch of wire(10ft) when that happens.....all hell breaks loose.
I could tell you why but it would surely take up half the year or so & I don't fancy myself a teacher. Like I said, look up Wikipedia under "Transmission Line" and read the Overview. It is an extensive body of science, complete with lots of math. Have you ever seen a microwave conduit(Appx. 2-20 gigahertz)? As higher & higher frequencies try to travel down a wire even stranger & stranger things start to happen. Here's an "old-fashioned" "chart" attached that is used in the math that is applied. If you look carefully at that ribbon cable we talked about, you will see the two conductors are strangely spaced apart with a thin sheet of polypropylene between the two, a very special type of wire.
______________________________________________________Rick.......
I could tell you why but it would surely take up half the year or so & I don't fancy myself a teacher. Like I said, look up Wikipedia under "Transmission Line" and read the Overview. It is an extensive body of science, complete with lots of math. Have you ever seen a microwave conduit(Appx. 2-20 gigahertz)? As higher & higher frequencies try to travel down a wire even stranger & stranger things start to happen. Here's an "old-fashioned" "chart" attached that is used in the math that is applied. If you look carefully at that ribbon cable we talked about, you will see the two conductors are strangely spaced apart with a thin sheet of polypropylene between the two, a very special type of wire.
______________________________________________________Rick.......
Attachments
I don't think a Smith chart will be much help to the OP.
VHF does not suffer from static. It may suffer from local interference but severe attenuation (1K resistor) will reduce interference and signal by the same proportion. If the receiver is already low in sensitivity then this will guarantee failure. Logic is not much help unless it is informed by knowledge of RF.
VHF does not suffer from static. It may suffer from local interference but severe attenuation (1K resistor) will reduce interference and signal by the same proportion. If the receiver is already low in sensitivity then this will guarantee failure. Logic is not much help unless it is informed by knowledge of RF.
Well something must not be right because I've tried many of the designs I see online using some wire and a 75ohm coax to hook it up and I get terrible results.
Is it possible that you happen to be in a bad location for FM? Another possibility is that you are making the same mistake with each antenna you make (or the cable) - pictures might help us diagnose this.
At a minimum, get a set of rabbit ears from Radio Shack, use a balun to match it to some 75 ohm coax, and put the rabbit ears up high-in your attic if you can. Look in your attic first, though, to make sure you do not have radiant barrier insulation up there. Switch your tuner to mono for lowest noise and rotate your rabbit ears, listening to the reception quality as you do so.
Don't think i need a balun do I? This receiver has 300 and 75ohm connections on it.
I'd prefer not to run wires in the walls because its a pain, I'd prefer to have it in the same room if possible.
I don't think this receiver's tuner is bad but I guess it might be.
I also wouldn't say I'm at a bad location for FM considering a small antenna on a normal tuner does great for me.
Get a copy of the ARRL Handbook. Any year will do. There are many on Ebay. Cheap. Read and learn.
I'd rather not. I don't learn very well from books, and besides that's why I go on forums like this and make projects.
A balun is Ferrimagnetic material 'Ring' or other structure....I did a presentation (29yrs ago)on Ferrimagnetic materials..........I forgot, it had to do with Atomic orbital spins and all. Something about spin orientations become all aligned for magnetic polarity & when released the poles re-orient & transmit...or something like that.
____________________________________________________________________Rick..........
____________________________________________________________________Rick..........
You need a balun whenever you connect a balanced something to an unbalanced something. A dipole (two ends) is roughly balanced. Coaxial cable is unbalanced. To connect a dipole to coax you need a balun. Having said that, for FM broadcast reception many people don't bother with a balun and just accept a higher level of noise pickup on the coax.TheTubeAmper said:
The 75ohm connection will probably be unbalanced. The 300ohm one will probably be balanced. There is probably a balun inside the receiver to convert one to the other. In this case the balun does a 4:1 impedance transformation too, but a balun can also be 1:1 on impedance.
This forum is very good, but it cannot perform the same function as a book. You need both in order to acquire understanding. The alternative is to find a design and copy it exactly.
No. Some baluns use a ferromagnetic material; others do not. When present, it is not the ferromagnetic material which makes the balun but the material plus the copper windings on it.Richard Ellis said:
OP, do you appreciate that a Yagi Dipole will have gain in itself. The bigger the aerial generally the higher the gain.
Hi-End receivers are inherently insensitive in order to reduce noise, they often require a significantly higher input signal to function to spec.
In a strong signal aerial you can often get away with a single dipole, in outlying areas you might need a 3-4-5 or more element aerial.
Hi-End receivers are inherently insensitive in order to reduce noise, they often require a significantly higher input signal to function to spec.
In a strong signal aerial you can often get away with a single dipole, in outlying areas you might need a 3-4-5 or more element aerial.
A Yagi and a Dipole are two different antennas, although a simple Yagi may contain a dipole as the 'driven' element. A Yagi will not help the OP as he doesn't know which direction his favourite stations come from or what polarity they have.
High-end receivers are not inherently insensitive in order to reduce noise. Poor sensitivity increases noise. They may be slightly insensitive due to wide bandwidth in order to reduce distortion. Their AGC circuits may be designed to optimise low noise on strong signals rather than moderate noise on weak signals.
I suspect that he is doing something wrong, but remote diagnosis is not easy.
High-end receivers are not inherently insensitive in order to reduce noise. Poor sensitivity increases noise. They may be slightly insensitive due to wide bandwidth in order to reduce distortion. Their AGC circuits may be designed to optimise low noise on strong signals rather than moderate noise on weak signals.
I suspect that he is doing something wrong, but remote diagnosis is not easy.
I'm sorry it was so very long ago, I don't remember much about the theoretical...........I did do the math on a VERY large Log-periodic to cover the TV spectrum....it was downright huge.....just like the ones you see/saw in the stores....just 'bigger'.
I did set-up a multi-element Yagi-Uda (10?) outside my folks place when I was there. I just returned from U of O, bringing my Marantz 2220B, I wanted to pick up some stations from Eugene....From Portland it's about 100 miles. The antenna was rated for 110 miles. Fortunately my folks house was in the West Hills.....That Marantz sucked it in just like it was right next door...perfect reception.
___________________________________________________Rick..........
Last edited:
- Status
- Not open for further replies.