Tue 18th Apr 2017, 09:03
30 Mhz signal
I need to send a 30 Mhz signal to a distance of 500miles, and receive it at this distance.
Any one knows how it could be done? what equipment to use? sdr?
Also, I can display on an oscilloscope a carrying wave (400 Mhz) that I transmit from a short distance since the scope's probe get the signal. But how can I do it from a 100 miles distance?
Tue 18th Apr 2017, 11:08
We tried to sort out your last idea, but this one is even more stranger. Firstly, your 500 mile hop on 30MHz won't be licensable, and if it were, that frequency is unsuitable for that distance if you want reliability. You have some studying to do. I'll provide the key features that will start your quest. Firstly it's the Critical Frequency - HF radio bounces off the ionosphere, but at some point, instead of bouncing off, it goes through - lost into space. This is the Critical Frequency. The state of the ionosphere is constantly in flux, so this frequency changes hourly! Your 30MHz is right at the top, so most of the time, it doesn't skip back downwards at all. The upshot is that there is no way to get a reliable bounce off the ionosphere. The CB folk usually find their range very limited at 27MHz, then a bit of luck with the atmosphere and the 10 or so year sunspot cycle sometimes make talking to the US a possibility. No amount of squirting power will make the ionosphere reflect when it doesn't wish to. If you send out your 30MHz signal, you have the problem of sending somebody to the other end, to just the right place, to put up an antenna to receive it and send it back.
Your scope question also reveals a few problems - Radio waves, like other electromagnetic waves follow the inverse square law. They decay in a very predictable way.
Let's say you have a signal generator that puts out 1V peak-to-peak , and you stick a small aerial on it. A metre away you connect the scope, and you measure it at .016V - (I'm making these figures up, by the way). If you increase the distance to 2m, instead of the receive signal being .008V as common sense says, it actually goes down to .004V. Double that distance again, to 4m, and it's gone to .001V. It works in reverse too, but you cannot simply hire in a MegaWatt transmitter - because that won't work either because the earth is curved. Your local TV transmitter has MegaWatts, yet frequently has trouble getting TV just a few miles!
We tried to explain the physics in your other topic, but you refused to listen. 400MHz and a 100 mile trip is just impractical without atmospheric conditions and luck.
When we were in the Cold War era, the Government needed to communicate with the important places all over the country without using the telephone cables. They spent millions on hundreds of radio towers to do the hops between A and B, then B and C, then C and D. They called this 'backbone' - you can research this too if you like. You might also like to look at the old Russian Duga over the horizon radio transmitter that made a mess of the HF bands in the 70s - nicknamed the woodpecker. The idea was that it sent huge amounts of energy out to bounce back of incoming missiles, and the reflections were then received at a different location. Pretty much like your 30MHz idea, but frequency range of 7 to 19 MHz was pretty well the limit to where the thing actually worked reliably. Note - not 30MHz.
Tue 18th Apr 2017, 11:15
this is not a Yaesu question.
Wed 19th Apr 2017, 00:02
I am not sure what was so difficult to understand in my previous idea. You sending a pulsed signal which is received by 2 receivers that are connected to 2 channels of a scope. you may view the arrival time of each signal on the scope, and if you move one of the receivers toward or away from the transmitter, you would get a difference in the arrival time equals to 1ns for each foot you move the scope. see:
Originally Posted by paulears
Re the new question, the signal frequency can be lower than 30Mhz and the distance shorter than 500 miles (I thought of a satellite repeater), but you better have a direct eye contact between receiver and transmitter.
The best way is to have the experiment described in the attached youtube video, but for as large distance as possible. I don't even need to use a transmitter, If there is another similar signal from a different transmitter (Beacon? Wwv?) it may work, as long as I know its location and can display the signal on a scope.
Re the carrying wave on a scope, If I can display the modulated signal (audio for example) on a scope, Why can't I display the carrying wave in some sort?
Its all come to the bottom line: Toa in a nanosecond accuracy.
Thu 20th Apr 2017, 20:00
Originally Posted by snuz2001
Hey guys, while paulears sorting my idea, any one has an idea how to repeat the experiment in the youtube but for a much larger distance? what equipment should I use?
Thu 20th Apr 2017, 20:45
I need to point out that this is a ham radio forum, and this question has nothing to do with ham radio. You are also quoting frequencies outside of the (UK) ham radio bands.
As Paul has, quite politely and tolerantly put it, we have already tried to help with this matter.
Sadly, it is not the members here that do not understand.
This thread is now closed and moved to a more appropriate location.
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