im building a new transmitter with a 74hc240 ic chip, they reccomend a 50 ohm antenna. I have a uniden scanner antenna with a bnc connecter do you think this will suffice LOL? If not would a wire antenna work decient?
Yes, for receiving. If you want to transmit--and you will remember from the Ham Test that a 7.040 meter antenna is half that wavelength, all of that wavelength. You need some sort of SWR meter to know if you have a decent 50 ohm 'load' as they say. If it's not 50 ohms, you probably won't get much if anything in the way of signal out. Low power radio is all about the antenna. You want it to be perfectly resonant with an SWR of 1:1 for this transmitter.
I may have you confused or may just be confused myself whatever the case, I am building a transmitter called "radio habana cuba ultra simple transmitter" you can google it to view the diagram, I orderd all the parts. On the diagram it shows a "50 ohm antenna", for all I know thats some sort of ham antenna. I just want to know how I can brew one or get one easy and cheap. Thats why I ask.
It is any antenna with a feed point impedance of 50 ohms. As long as we are googling, google that. The RHCUST lists crystals in three frequencies--which one are you using? If we know that frequency you know the length of the antenna to make it 50 ohms. A wire antenna for 7.040Mhz is 66.48 feet long. Two pieces of wire 33.24 (10.1 meters) with the radio in the center--a simple dipole. This is a 50-ohm antenna. There are other designs, but this is one. What is your callsign? I'm Jonathan KC7FYS
50 ohm has nothing to do with resistance its the impedence of the antenna since most coax are 50ohm or 75ohm (for cable & satelite TV) so taking that to account its not realy the 50ohm part thats troubling its the wavelength thats important
as you want to get closest to either full length half or quarter length the closer you are to the full length the better the emission/reception for that frequency (hence wavelength )
Yes, I sure am, my first one. and I'm debugging it now, as something isn't right - it does the motorboat thing with a 9v. with 2 cr2032's it stops... however, i've also got something else wrong that i'm not catching, as it's putting out a constant carrier with those batteries...
It will put out a constant carrier. This transmitter is always oscillating by design. The frequency of the tone will shift when it's keyed, but it is 'always on' as it were. Some have complained that those nearby are annoyed by the carrier. Your rig works. Voltage should be 12V to get full power and get rid of that motorboating. You can also install a resistor mod to stop it--but getting the voltage above 9V is a good start.
Sounds like SSTV comming in there?
knikk77 2 years ago
sz42781 SAID:
im building a new transmitter with a 74hc240 ic chip, they reccomend a 50 ohm antenna. I have a uniden scanner antenna with a bnc connecter do you think this will suffice LOL? If not would a wire antenna work decient?
kc7fys 3 years ago
Yes, for receiving. If you want to transmit--and you will remember from the Ham Test that a 7.040 meter antenna is half that wavelength, all of that wavelength. You need some sort of SWR meter to know if you have a decent 50 ohm 'load' as they say. If it's not 50 ohms, you probably won't get much if anything in the way of signal out. Low power radio is all about the antenna. You want it to be perfectly resonant with an SWR of 1:1 for this transmitter.
kc7fys 3 years ago
I see do you think say a radioshack would sell a 50 ohm antenna?
sz42781 3 years ago
Do they sell wire? Yes. The 50-ohm part is you measuring it. For the Pixie, what is your frequency of interest?
kc7fys 3 years ago
I may have you confused or may just be confused myself whatever the case, I am building a transmitter called "radio habana cuba ultra simple transmitter" you can google it to view the diagram, I orderd all the parts. On the diagram it shows a "50 ohm antenna", for all I know thats some sort of ham antenna. I just want to know how I can brew one or get one easy and cheap. Thats why I ask.
sz42781 3 years ago
It is any antenna with a feed point impedance of 50 ohms. As long as we are googling, google that. The RHCUST lists crystals in three frequencies--which one are you using? If we know that frequency you know the length of the antenna to make it 50 ohms. A wire antenna for 7.040Mhz is 66.48 feet long. Two pieces of wire 33.24 (10.1 meters) with the radio in the center--a simple dipole. This is a 50-ohm antenna. There are other designs, but this is one. What is your callsign? I'm Jonathan KC7FYS
kc7fys 3 years ago
50 ohm has nothing to do with resistance its the impedence of the antenna since most coax are 50ohm or 75ohm (for cable & satelite TV) so taking that to account its not realy the 50ohm part thats troubling its the wavelength thats important
as you want to get closest to either full length half or quarter length the closer you are to the full length the better the emission/reception for that frequency (hence wavelength )
romeoneverdies 2 years ago
what did you do to correct the issue?
gibletcaptain 4 years ago
I increased the voltage to stop the self-oscillation of the op-amp. Are you building the Pixie?
kc7fys 4 years ago
Yes, I sure am, my first one. and I'm debugging it now, as something isn't right - it does the motorboat thing with a 9v. with 2 cr2032's it stops... however, i've also got something else wrong that i'm not catching, as it's putting out a constant carrier with those batteries...
gibletcaptain 4 years ago
It will put out a constant carrier. This transmitter is always oscillating by design. The frequency of the tone will shift when it's keyed, but it is 'always on' as it were. Some have complained that those nearby are annoyed by the carrier. Your rig works. Voltage should be 12V to get full power and get rid of that motorboating. You can also install a resistor mod to stop it--but getting the voltage above 9V is a good start.
kc7fys 4 years ago
where could I get a schematic, and couldent you power it on and off to everytime you key to stop the carrier? IDK, looks cool though
sz42781 3 years ago
how about adding a transistor instead of the switch ?
romeoneverdies 2 years ago