Ham Radio design basics

[demetal]

Hi,

Please help to understand design principles of ham radio.. How it differs from ordinary radio...?

Thanks

 

[BradtheRad]

Ham equipment works on the same principles as all radio transmission and reception.

The name 'Ham' has to do with amateur radio. The name had its origin decades ago and there is more than one story about what the letters h-a-m stand for. See link:

https://www.qsl.net/vu2msy/MEANING.htm

A ham operator transmits and receives on the bands which are allocated for amateur use. A license is required to transmit.

He can use store-bought equipment. Or often he designs and makes his own equipment.

The term 'amateur' does not mean one's knowledge and construction cannot be up to professional standards (or better).

Hams have a tradition of service to the community. They often are invaluable during blackouts and emergencies.

Some build and maintain 'repeater' stations which benefit other hams by extending the range of radio communications.

 

[demetal]

Ok... Thanks for replying.. sorry but I would like to know the design principles of ham radio... as it is operating in higher frequency than the ordinary radio what all parameters are needed to be consider while designing... Can anyone please provide me the main essential blocks of a basic ham radio with its operation and design considerations...

 

[BradtheRad]

An easy area to explore is the shortwave band from 1.7 MHz to 30 MHz. It's AM like the commercial AM band, except at a higher frequency.

Just a simple crystal radio is able to bring in AM. It needs no power if you can get a strong enough signal from the broadcast. A strong signal depends on a long antenna.

You can produce morse code with a sinewave oscillator. There's more equipment needed if you're going to transmit, however. And you need a license.

Your transmitter must broadcast a clean sinewave. If it contains harmonics then your signal might splatter over to other regions of the spectrum, and be audible in other people's radios/tv's/etc. You could have the FCC contacting you with complaints.

You'll have to check websites of radio enthusiasts to get the rundown about the equipment they use.

 

[demetal]

Can you suggest me effective methods to measure the harmonics rate in the transmission... I am waiting for the ham license which will take time due to Government process and forwarding's... meanwhile i need to know some basics in practical case.... I prefer homebrewing and for that i need help from experts like you... i googled many ham pages, most of them consist of circuits but no full explanation...

 

[BradtheRad]

Can you suggest me effective methods to measure the harmonics rate in the transmission

Sorry, I do not have much experience with transmitting equipment.

I believe a spectrum analyzer will tell you about harmonics in your transmissions. These are expensive but there is a project called the 'poor man's spectrum analyzer.' An internet search will turn up many articles about it.

It is important to have the right kind of antenna, and to match its impedance to your transmitter.

Your power supply needs good regulation. If its volt level drops whenever you draw power to transmit, it might change the frequency of your transmitter oscillator unexpectedly.

 

[chuckey]

A spectrum analyser is still a bit of a luxury for amateurs. If you follow a good design and operate it correctly it will be OK. If for some reason you are still worried about your transmitted harmonics, follow the transmitter with a bandpass filter. Or you can use your all-wave receiver to check for, and measure the harmonics.
Try to get hold of an AARL (American Amateur Radio League) or a RSGB (Radio Society of Great Britain) handbook. They will take you from basics to devices that professionals would like to use!.
Frank

 

[keith1200rs]

When I started with ham radio there was only one person I knew of with a spectrum analyser - everyone else used a wavemeter https://en.wikipedia.org/wiki/Absorption_wavemeter . I made my own wavemeter which seemed to satisfy the authorities when I was inspected. It consisted of a loop antenna, variable capacitor and diode to which I connected my multimeter.

Keith

 

[demetal]

When I started with ham radio there was only one person I knew of with a spectrum analyser - everyone else used a wavemeter https://en.wikipedia.org/wiki/Absorption_wavemeter . I made my own wavemeter which seemed to satisfy the authorities when I was inspected. It consisted of a loop antenna, variable capacitor and diode to which I connected my multimeter.

Keith

I think Wavemeter is more economic for me...Thanks for the link.. I have used those UHF type in microwave lab experiments... But still have doubt about it...

1. how to calibrate it.. like how should i calculate the area of the inductor, inductance, gauge of wire etc. for a particular frequency... ?
2. Also how can i measure the harmonics rate using this equipment...?

Thank you.

 

[BradtheRad]

1. how to calibrate it.. like how should i calculate the area of the inductor, inductance, gauge of wire etc. for a particular frequency... ?

The Henry value should be selected so that it matches (roughly) the resistance it will see.

The formula for inductive reactance:
X = 2 * Pi * f * L

Example: To calculate a coil for use at 3 MHz, where neighboring resistance is 200 ohms.

Rearrange:
L = R / ( 2 * Pi * f )

= 200 / 18849556

= 10.6 uH

A capacitor can be calculated likewise.

 

[demetal]

I would like to know how can i measure the harmonics rate using this equipment...?

Thank you

 

[betwixt]

A wavemeter isn't as accurate at measuring frequency as a digital counter and it isn't as accurate at measuring signal amplitude as a dedicated RF voltmeter, however, it should be OK for non-professional use. By far the easiest way to calibrate is with a known signal. If you can borrow an oscillator you can loosely couple it's output to the wavemeter and tune until you see a peak in output. The peak occurs at the frequency being produced by the oscillator so you can mark the scale at that point.

To measure harmonics, you simply tune to a multiple of the frequency you are transmitting on. For example, if you are transmitting on 7MHz, you would tune around 14MHz, 21MHz, 28MHz and so on to see if there was any signal at those frequencies as well.

Brian.