Let's take another look at AM

[MiXiN]

You Have to look for them in greece, i think AM is unlicenced over there.
I found one: http://users.otenet.gr/~nsavvas/pll_en.html
20 Watts PEP 160 euro

Thanks for the link.

I can't find any way of buying anything from the website (using my phone, anyway) so will check from a PC when I get home.

There's some nice stuff on there.

[Albert H]

MiXiN - the frequencies involved in a medium wave transmitter are low enough that you don't have to take special precautions like you have to at VHF. You can even build transmitters on "Veroboard".

I'll put a basic medium wave design up here shortly. I'll also include all the design equations, and explain how to use them. These are important, because they'll allow you to scale the design for the range of frequencies that you're most interested in (probably at the higher frequency end of the band), and also scale for the power output that you want. For lower power, I'll include a "worked example" and a Veroboard layout.

The mathematics isn't difficult! You're calculating the number of turns of wire for a particular value of inductance, and you're calculating the output impedance of the PA and thus the turns ratio of the autotransformer that you'll use to transform that to 50Ω (or any other preferred match impedance). You're just substituting numbers into an equation and cranking out the answer - that basic algebra at school really was useful!

The modern power FETs that we use for the output stages on medium wave are usually rated for a few hundred Volts and several Amps, yet they still cost pennies! (I just built a 400W VHF PA, and the dual FET that I used - a Philips NXP one - cost almost £150!).

The logic ICs that we will use are just pennies each (unless you go to Maplin ) and the crystal is less than a pound too. The only (slightly) difficult bits to get will be the ferrite parts, but I'll suggest sources for those (though the manufacturer does small orders themselves). We'll need a few small toroids, and you're going to have to learn how to wind coils neatly on to them.

The modulator uses an audio power amplifier IC, which is (essentially) just a big op-amp. I'll also give the option of a few bells and whistles if you want to add them. These include a basic modulation compressor, a modulation depth indicator, frequency response shaping and the option for remote switching through your link.

I'm just finalising the notes, taking a couple of photos of a work in progress, and drawing up a neat 'n' tidy Veroboard layout. It won't be expensive to build and it won't be difficult, either.

You're going to need a multimeter, access to a frequency counter (for a one-time calibration), and access to a 'scope to set up the modulation depth indicator and to check the output waveshape and what the modulation looks like. I'll even mention "trapezoid tests" if anyone wants to get that precise!

You have to remember that a "5 Watt rig" might deliver 5 Watts into the load when unmodulated. On 100% modulation peaks, it will be delivering 20 Watts! Manufacturers call this the "Peak Envelope Power" and this is generally four times the unmodulated power. It's a more impressive figure than the blank carrier power! This means that we have to provide a well overrated PSU and plenty of smoothing capacitors, and we have to expect to get rid of plenty of heat because a basic AM transmitter is quite inefficient - it makes as much heat as it does make RF!

The power levels we're considering (at first) may seem very low compared to the hundreds of Watts on FM. However, medium wave isn't confined to the horizon, and with a good aerial and earth system and a clear frequency, you can cover a huge area just using modest power. Night time coverage can be reduced by the arrival of the skip signals from Europe, but if you've found a reasonably clear frequency (and there's quite a lot of them now that the French have gone), you'll get into Europe!

[sinus trouble]

The SAA1057 seems to support both FM and AM too?
Ive never tried? But ofcourse the I2C data would need modifying amongst other changes?

[yellowbeard]

Aye it's really for tuning consumer radios. It covers up to 0.5 - 32MHz on the AM input. Here's a page with hex codes for medium wave or general coverage with a PIC16F84:

Code: Select all

http://home.deds.nl/~radio102/freddos/s1057/s1057.html
And his homepage
http://home.deds.nl/~radio102/freddos/default.htm

[ronald001]

I'll put a basic medium wave design up here shortly. I'll also include all the design equations, and explain how to use them.

Albert, is it possible that you discuss shortwave ( 6200Mhz ) as well?

This is also very interesting band, the antenna is much shorter then MW and the range is much higher.


Thanks for sharing, really appreciated!

[ronald001]

Aye it's really for tuning consumer radios. It covers up to 0.5 - 32MHz on the AM input. Here's a page with hex codes for medium wave or general coverage with a PIC16F84:

Code: Select all

http://home.deds.nl/~radio102/freddos/s1057/s1057.html
And his homepage
http://home.deds.nl/~radio102/freddos/default.htm

Aah, Freddo's....nice find.

512-1800Khz TX and 6200-6400Khz TX on there as well

[radium98]

Albert H isnt my link that i provid for 25watts is ok i was planning to built one as i have no knowledge in AM MW transmitter and i front a problem with the aerial antenna do you suggest one let say for 1610 khz 1.61 mhz lol to low .i live in town dont have near me a sea and i exept some fun with it and experience as i my experience is n am is nill and what range mile could be expected for 25 watts .saying a clear frequency .

[Albert H]

25 Watts carrier or peak?

It mostly depends on the aerial and the earth. You should read up on aerials for 160m (1.8MHz) amateur band. The inverted-L or "Marconi" aerial can work very well. You need to get a good earth. My best-ever results came from using the water mains pipes beneath a village for the earth and a big vertical aerial - a disused electricity pylon!

I've also loaded up a bridge across a motorway, the central barrier along a motorway (for long wave) and even some disused railway track! You'd be amazed what you can make to radiate!

[radium98]

Albert H 25w carrier blank
please can you discuss breifley a simplest aerial for thatmw on 1610 khz thanks and am aerial isnt like dipole ?fm because someone said you only have to extend the radiator from coaxial cable i mean the inner center cuted on the frequency with C/F and the reflector from shield as long as i want is that true

[sinus trouble]

Hello Mr radium!
I think in theory a dipole would work? but it wouldnt be practical?
Going by the usual formulae for 1/2 wave dipoles (300/Freq x 0.935 x 0.5) it would need to be around 140 meters tall!!
Please feel free to correct me if i am wrong?

[yellowbeard]

At these frequencies your average pirate uses a 1/4 wave long wire with a good earth, there is tons of stuff on the internet for the amateur radio 160 Metre band - just scale up for medium wave. Albert's suggestion of a sloper is excellent if you have access to a 15 floor building, if not then you are going to need a large mast/tree or space to put the aerial in, or any combination of the two. Either way you are going to have to fit in 45 Metres or so of wire in order for the antenna to be resonant - it doesn't have to be that length to be resonant but thats a whole other topic.

[projuicer]

Had a go at Alberts recommended frequencies in the car Noerth of Birmingham on the M6 last night (I was bored).

846khz had Radio Star from Ireland with a slightly noisy but listenable signal.

I'm assuming the frequency between the TalkSports is 1071 - which is totally empty, and 954 and 1530 were pretty quiet too.

I'd be interested in seeing the £25 AM plans!

[MiXiN]

Anyone else get a warm tingly nostalgic feeling listening to stations on MW & LW?

I used to go to sleep listening to an Hospital Radio station on an old Pye Transistor Radio and found it relaxing.

[radium98]

Had a go at Alberts recommended frequencies in the car Noerth of Birmingham on the M6 last night (I was bored).

846khz had Radio Star from Ireland with a slightly noisy but listenable signal.

I'm assuming the frequency between the TalkSports is 1071 - which is totally empty, and 954 and 1530 were pretty quiet too.

I'd be interested in seeing the £25 AM plans!

look at page one of this thread i have posted a link of what you need but aerial not clear to me .If i built it i will post images.

[radionortheast]

Anyone else get a warm tingly nostalgic feeling listening to stations on MW & LW?

I used to go to sleep listening to an Hospital Radio station on an old Pye Transistor Radio and found it relaxing.

used to fall asleep to talk radio listening to someone named james! I checked the am band last night with my tiny radio, reception isn't so good on it but there wheren’t that many foreign stations there, seemed like lots of dead air or I mean crackingly you don't get the nice white noise you get with fm, suprized virgin is still there! brandson perhaps? possibly the last remaing popular music station, thought there was a station round 881 or something playing free from desire! anyway virgin reminds me of when radio 1 used to be on there...

[radionortheast]

Anyone else get a warm tingly nostalgic feeling listening to stations on MW & LW?

I used to go to sleep listening to an Hospital Radio station on an old Pye Transistor Radio and found it relaxing.

used to fall asleep to talk radio listening to someone named james! I checked the am band last night with my tiny radio, reception isn't so good on it but there wheren’t that many foreign stations there, seemed like lots of dead air or I mean crackingly you don't get the nice white noise you get with fm, suprized virgin is still there! brandson perhaps? possibly the last remaing popular music station, thought there was a station round 881 or something playing free from desire! anyway virgin reminds me of when radio 1 used to be on there...

actually it was absolute radio i was hearing course i don't keep up with names, it sounds the same to me and same channel 1215khz https://en.wikipedia.org/wiki/Absolute_Radio

[ronald001]

You can also use http://websdr.ewi.utwente.nl:8901/
Great for spotting pirates

If you tune in to 1648 now, you will hear one.
Also some activity on 6200+ 3200+

[Albert H]

I didn't know that "Star" in Ireland were on 846kHz these days.

It's worth looking at some of the frequencies recently vacated by the French stations. They frequently had no adjacents, so were very nice frequencies to use!

[WEBB-TECH]

Hey Albert
How's life treating you mate?

Sent from my SM-G920F using Tapatalk

[Albert H]

Hi Webb-Tech

Mustn't grumble! Getting old, but still enjoying life!

Cheers!