60 -75 mhz fm transmitter  - Page 1
Forum section: electronics / rf-microwave

author: Dom13c
author_rank: Regular Contributor
timestamp: October 11, 2018, 06:03:38 pm
content: I've got a radio receiver that can receive 60-75 mhz fm. I'm planning to build a transmitter that uses fm on the frequency between 60-70 mhz to transmit voice. Reason behind using this awkward frequency is that I wanna stay away from the commercial fm channels and don't want others to pick my transmission up. I haven't got time to design a transmitter now. Had searched online but found nothing. Anyone got a circuit diagram for this frequency range?

author: vk6zgo
author_rank: Super Contributor
timestamp: October 12, 2018, 02:13:56 am
content: Quote from: Dom13c on October 11, 2018, 06:03:38 pmApart from the fact that you will not be a legal user of any frequency in this range, your hope that "others" won't pick up your transmissions are forlorn.Anybody with an RF scanner will be able to hear you, as will people with cheap FM broadcast receivers.With modern ones, it will probably be plain old "image interference", but some older Japanese "home market" receivers which were maybe, picked up on overseas trips will directly tune to, at least the top of that range, as their FM band is different.

author: Beamin
author_rank: Super Contributor
timestamp: October 13, 2018, 07:22:37 pm
content: Quote from: Dom13c on October 13, 2018, 06:40:46 pmCould you find a FM transmitter for novelty use that does the FM band and then just adjust values to make it at lower frequencies, and also add another gain stage or more power to the transmitter amp? Those off the shelf ones have a range of less then shouting or talking loud. I wanted to do something like this myself. I might build it along with you I should have electronics lab here soon I hope.OR you can get these posts: That's illegal. Do you even have a ham license? The FBI will raid your house and you will go jail. What kind of person does this? What if the ambulance uses that frequency and some one dies? Oh the humanity of illegal out of allocated band transmitting, the horror the horror.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 14, 2018, 01:37:37 am
content: Quote from: Dom13c on October 13, 2018, 06:40:46 pmThe receivers which could pick you up would be 40 year old Japanese FM radios, which could well be lying around in many houses.This doesn't address the possibility of image interference in normal FM receivers.Old scanners would not be very expensive, so there may quite a few more around than you imagine.What do you intend to do with the thing, talk to yourself?I do hope you don't envisage using it as a clandestine "bug".That opens a whole other "can of worms", as you could get arrested under city or state laws, as well as possibly being sued."What was I thinking of?"-----of course, you wouldn't do that.If you were in Oz, that band would be the old CH2 TV Band.As far as I know, it is used by "land mobile" here.I'm not sure about the allocation in your country, but don't be surprised if you are crunched into the noise by a big, beastly FM comms signal.

author: Beamin
author_rank: Super Contributor
timestamp: October 14, 2018, 10:43:05 am
content: Quote from: vk6zgo on October 14, 2018, 01:37:37 amWhile its good you guys are looking out for him, it kind of comes off as overly protective naging mother. I have never seen an old japanese reciver or anything besides my scanner that picks up that range. Plus why would you monitor that band theres nothing on it? I think the people like me who play with their SDRs all day instead of getting a job are few and far between like less then 1/1,000,000 if that. That puts him out of range. Who cares what hes using it for maybe hes selling drugs who cares if some one you don't know has the FCC come to his house. All they will do is politwely tell him to stop. Its a fun project one that I want to try as the frequency has a smaller antenna and good range; going through walls and buildings. It would be fun to test propagation.So anyways, would a start to be to find a low power FM broadcast tx and then change the crystal or what ever makes it 88-108 and then either beef up the power transistor from a to92 and add more bias or even a second stage with a heat sink package to220 or to 3 if you can find it?Lets work on this part and leave the legality up to his lawyer.Maybe he just like his old radio and wants to listen to MP3s on it in his house without hacking wires into it? That's probably what he's doing.