Building a Variable Frequency Transmitter - HELP! 1

[chakanafir7]

Hello to everyone! I'm new to Eng-tips.com, and I need some advice on how to construct a transmitter that will be adjustable preferably to any frequency that I would like to select, but I really only need a range from about 500 Kilohertz to about 40 Mhz. I would preferably like a PLL, so that my frequency doesn't drift. I am thinking about using an NTE 989, and if any of you are familiar with this particular IC, I would appreciate it if you could just point me in the correct direction. I would also like a digital selector/readout. As well as the Transmitter, I also need a reciever circuit, using the same IC, with the same range and everything.

I have a slight to fair knowledge of electronics, so PLEASE assume that I DON'T KNOW ANYTHING when explaining or helping.

It is totally possible (and highly probable) that some circuit of this nature already exists. If you know of anything that I can use like this CHEAPLY, then please point me in that direction. However, any and all help is appreciated.

Thanks guys, for helping a newbie to circuit design.

 

[BrianR]

You'll face some fairly serious licensing issues with a transmitter with that bandwidth. However digital function generators with at least that range are readily available and so are broad band linear amplifiers.
This doesn't answer your question but the fact you asked it suggests you might have some other issues to resolve with broad band RF, EMI/EMC, stability and so on.

 

[chakanafir7]

Everything that I could find on the FCC's website said that pretty much anything 1 watt or under would not be a problem. However, I may wish to use more wattage than that, because I won't be using the circuit to send any sort of signal, I just want to experiment with different frequency response over very short range, but I need a stable frequency with as pure a sine wave as I can get, for as cheaply as I can get.

Like I said from my previous post, assume that I don't know anything. I said that to ask this:
1. What is a Digital Function Generator? Is that a Sine Wave Generator?

2. Also, what is a broad band linear amplifier?

I am new to circuits and electronic components, and I don't understand all that I know about them, much less actually knowing what different electronic components are named and what they do. Basically, some things I know, and some things I don't.

I guess I should have said in my first post that I was defining what I need, and that I was looking for some suggestions as to how to accomplish what it is that I want to do.

Thanks again for all of your help.

 

[VEBill]

Unlicensed transmitters are strictly limited to certain frequency ranges and limited power or EIRP. One watt is not low power - you can communicate half-way around the world with one watt on the HF bands (not easily, but Ham radio operators using QRP [low power] do it every day). One watt is absolutely NOT automatically license-free.

Building a transceiver with 0.5 to 40 MHz range (most people are satisfied with 30 MHz as the upper limit) is a huge undertaking.

I recommend that you Google the terms 'QRP' & 'kit'.

Even these are not likely to cover the entire 0.5 to 30 MHz band end-to-end.

To use them to transmit in the Ham bands, you'll need a Ham license.

 

[melone]

What is the end goal of all of this? It sounds like you will be dabbling in very murky water with respect to the FCC.

 

[chakanafir7]

Thanks guys, for all of your pointers so far. However, let me reiterate that I do not intend to send any sort of voice or data or anything over these particular frequencies.

Also, my shop is a total metal enclosure... Namely, Tin. Not the stuff that they have been manufacturing for the last 20 years or so, but VERY old, very THICK tin. You can barely bend it with your hand, it is so thick. Inside this building, I cannot pick up cell phone freqencies at all, and I can barely recieve 104.1 Mhz, a Local Country station that is approximately 1 mile from my house. So I don't expect that I will have any trouble with the FCC, since I won't actually be transmitting anything with these freqencies, and I will be inside with all of my experiments.

As I said, I am experimenting with frequency response over short distances (like 10 feet), just because I want to. Most of the frequencies that I will be using are below 1800 Mhz anyway, but I would like to have the capability to go higher if I choose. 30 Mhz would be fine for a top end. I just picked 40 arbitrarily.

Thanks again, guys. I appreciate y'all.

 

[sreid]

Analog Devices make IC's called Direct Digital Synthesizers (DDS). The output sine wave from the DDS could be fed to, say, a CATV amplifier.

http://www.analog.com/