Has anyone here have an AM transmitter and what is best one to buy?

[McDonalds]

I have seen this one

http://www.ebay.co.uk/itm/Spitfire-AM-M ... Swy4hUUlbT

Is this any good at all also how far on a clear dial as AM is pretty empty now days will 100mw go?
Are there any other transmitters to all ready built?
I all ready have powerful FM one so looking to mess around on MW as seems to be dying out now.
I hear hight does not make much a difference with AM as its ground wave?

[Gum]

No idea about that box but efficient antennas at these frequencies are B-I-G...

Audio quality will generally be much lower than with FM and subject to all sorts of interference from sources both close and distant as radio waves at these frequencies can travel a very long way, depending on the conditions.

If you hunt about on Google there is a ton of stuff from old MW pirates of the '60s / '70s that will give you an idea of what it takes to put out a decent signal.

[teckniqs]

If you want to mess around with AM you're best bet is to go for the SW band range. As Gum says the aerials are big and although SW aerials are considerably longer than FM aerials they are still a huge lot smaller than a MW antenna.
Also, unless your aerial is matched for your frequency you're gonna need an ATU (Antenna Tuning Unit)

[McDonalds]

On the other forums there is not much other than they want to keep there signal so it does not go far but I would like to broadcast as far as can.

[teckniqs]

I wouldn't expect too much from 100mW on MW, there is a few LPAM stations scattered around Manchester running about 1w up the top end of the MW band but they only do about 3 miles radius or so and are using very expensive vertical antennas. It's not worth the bother.

....With just 5-10w it's possible to be heard in most parts around the world on short wave and you can simply string a wire up between two trees as it's best to go horizonal so the signal bounces off the ground.
There's little HAM radio kits which send out 1w of morse code in CW mode which can be good enough to hear thousands of miles away.

[radio-berlin]

Im clueless with am, infact im cluesless with fm to ha ha

However ive seen these on ebay 321963039339, looks like a bit more power, Double the price though

[McDonalds]

I cannot see your link?

[teckniqs]

http://www.ebay.co.uk/itm/321963039339

[McDonalds]

Nice

[teckniqs]

If you want to run power there's so many HAM radio amplifiers built for HF which will cover most of the AM bands so all you'd need is enough power to drive it.

[Gigahertz]

In the US there a loop hole in the law where people can legally run a LPAM basically only 100mW.

There are people claiming upto 2miles range with these units. Also people have linked more than one together to extend there range.

Have a look.

http://www.am1000rangemaster.com

[shorty]

The sstran as good reviews for low power part15 am transmitting in states, the price is reasonable aswell,There are acouple good compact aerial design sites dedicated to getting the maximum out of the low power allowed licence free in the US.

http://sstran.com/

I remember reading about lower power am station somewhwere in the us that used four 100mw units to cover there town, they also posted some vids on youtube of how they did it, can't remember what the town was called i'm sure it had falls in it.

Never really done much with am gear i once built 2 watt unit with a crystal cut to 1602 top end of the band, used copper wire fastened between house and bottom garden fence and still needed another garden to have the wire fully stretched out, you need lots of ground for am.

[OgreVorbis]

When I first started experimenting with transmitting, AM was my focus, but I later moved to FM because of antenna efficiency problems. I was unable to have an efficient antenna other than a temporary balloon holding up a wire. On AM if you do the antenna correctly (full size vertical), you will have amazing range (maybe 3-5x more than eq power on FM) with very little power and you also have skywave at night which will get you out even farther. The only problem is getting the antenna tuned. It is very hard to make an efficient antenna for those low frequencies (0.5-1.8MHz). Don't waste your time looking at those short (few meter tall) antennas intended for microbroadcasting; they don't do shit under any circumstances no matter how well you tune them. I've tried everything. I learned that the only antenna designs worth while for AM broadcasting are the inverted L and the 1/4 wave vertical. Any other electrically short antennas aren't worth it. 1/4 wave at 1710khz (top of the AM band) is approx 145ft tall. So you need to cut a wire that long and hang it vertically (maybe from a window or something). Horizontal won't work very well and you won't be able to tune it. You may find a different length to be necessary due to surrounding objects, building wall, etc. The hard part is the ground plane. In addition to the antenna, you'll need as much metal on the ground surrounding the antenna as possible (water main, fence, guard rail, etc). You then attach the TX ground to the metal and the output to the antenna wire. If the antenna is only a few feet away from the transmitter, you don't even need coax; just use two wires. You'll need an SWR meter that works down to 1.8mhz. There are HAM antenna analyzers that would be even better. Unlike FM, you may be unable to get a low SWR even with a good antenna due to surrounding objects. I that case, you'll need a tuner on your antenna. The HAM ones that cover the 160 meter band (1.8mhz) will work on AM at 1.7mhz.

Don't even bother with those SSTRAN 100mW transmitters. That's not enough power to go more than a mile even with the best antenna. I really recommend the AM transmitters by Lesvos Electronics. He recently designed a DDS transmitter, but it's not in his store, so you might have to inquire.

http://www.ebay.co.uk/itm/AM-RADIO-BAND ... SwDN1USsXU

http://www.ebay.co.uk/itm/1kW-1-8-30MHz ... SwBLlVdx26

http://users.otenet.gr/~nsavvas/pll_en.html

They are reasonably priced and give you about 20 watt PEP if I remember correctly. AND REMEMBER: NEVER hook up your power/SWR analyzer and set it to 20W. You must not set it higher than 5W because when you modulate the AM signal varies between 5 and 20W to produce the audio transmission. The power you should set is always 1/4 the rated output power. If you want more power there are HAM pallet amplifiers that you can drive with this available on ebay that use those 1kW BLF transistors. With that you can output 250W. I once saw a really nice PWM 4kW PEP AM transmitter on ebay, but it's not available now.

Good Luck!!!

[Albert H]

If you want to have a go at AM, the transmitters aren't too difficult to build, components are cheap (you don't need expensive VHF transistors) and layout is much less critical.

As is mentioned in other postings, the aerial is the problem.

However, if you have a tall Tower Block that you have roof access to, you're in luck. Back in the early 80s, we invented the "Tower Block Sloper" - this was an aerial that used the lightning conductor (and the building earth) as one side and a long length of wire as the other side of a huge "inverted-V" aerial. The wire has to be insulated from the building structure - we used pieces of nylon rope - and the bottom end of the wire needs to be tied to something - we used nylon fishing line and tied it off to trees or high up to lampposts! If you get the "angle of dangle" right, you get a feed impedance very close to 50Ω. We used to use an antenna noise bridge to get the match correct before firing the rig into it.

You really don't want (or need) to run very much power into a well-matched sloper. We covered much of South-East England (in the daytime) with just 8 Watts carrier and ~35Watts peak.

The circuits for the transmitters are relatively simple: We used basic a CMOS synthesiser generating the carrier at a few volts, and drove that into the gate of a power switching FET (we favoured the BUZ11). The simplest (and least efficient but best sounding) modulator consisted of a power op-amp audio IC like a TDA2040 feeding the output FET through an RF choke. Without audio applied, the output of the audio IC would be ½Vcc. This would give enough voltage to the FET for ¼-power. As audio is applied, the voltage to the PA goes up and down, varying the carrier level - amplitude modulation!

The FET needed to be coupled through a hand-wound RF transformer (usually a couple of dozen turns on a big type-2 material ferrite toroid) into a lowpass filter. The filter coils were (usually) 40 -70 turns on a piece of white plastic plumbing pipe (coloured pipes are RF-lossy), and the filter capacitors to ground (usually of the order of 2 - 5nF) had to be 1kV rated (at least) to prevent fireworks!

Our MW rigs used to be about the size of a VHS video cassette box, with a large heatsink on top and a power supply box underneath. Supply voltages inside the box were usually 30V for the TDA2040 and 15V for the CMOS logic. I used to include a few extras in my rigs - envelope feedback for better quality audio and a basic compressor to equalise the varying levels of the tapes that got fed into them!

If anyone's interested, I've got all the circuits in my old notebooks.

Remember - at the kind of power levels you'll be able to run, daytime operation is the only choice. However, DF and I used to do a programme on P* AM from South-East London at dawn on a Sunday through the summer, called "P*" and we used to get reception reports from all parts of northern Europe even though the station was only running a few Watts! The coverage at dawn and dusk can be astonishing!

[stretchyman]

That's an easy question to answer!

MINE!

I sell one on eBay; 131595757554

Altho' aimed primarily at U.S. 6925KHz activity it will work on ANY frequency up to 10MHz.

Forget 100mW FFS that wont get you anywhere!

This TX will produce a 20W carrier, that's 100W pep ! @ freqs below 4MHz.

OK, Better introduce myself, Stretchy here!

I've been building radio circuits as long as I can remember and now have a full lab, spec ani, net ani etc etc and contract out my RF related skills around the globe, well the UK!

I got fed up seeing all the over complicated, out of date, junk box parts (no one has those, only the author!) designs and decided to find the simplest, most easily reproduced design out there and design a PCB for it. So a year or so on I've sold close to a 100.

I sell a kit CHEAP but also sell a built and tested system too, however I DONT have any MW Xtals, you will have to get your own, easily obtained from 'Quartslab' or wherever.

Let me know what you need, any questions you have etc, No Probs.

ALL the Best.

Stretchy.

[Albert H]

If you want to run power there's so many HAM radio amplifiers built for HF which will cover most of the AM bands so all you'd need is enough power to drive it.

NOT a good way to do it. AM is not in any way like FM. In an FM power amplifier linearity doesn't matter - most PAs are Class C (zero bias and no linearity at all). Conversely, AM conveys its information by varying the amount of carrier going to the aerial. This necessitates a VERY linear, low efficiency power amplifier. If you employ this approach (modulating at low level and amplifying), you'll generate much more heat than RF!

The traditional AM rig still isn't hugely efficient, but uses a Class C PA.... Generate the carrier frequency, amplify it with Class C amplifiers running at half the maximum supply voltage. Match to your antenna and connect to a good earth. Your modulator is an amplifier that (effectively) turns the PA supply voltage up and down with the audio. This will vary the output power, giving AM.

There are more elegant ways of generating AM - look up Cheirix or Ampliphase modulation - but these are quite tricky to get working.

[stretchyman]

Class E PA and a PWM mod both 90%+ eff, very easy, that's the current 'Trend'!

[Albert H]

In the US there a loop hole in the law where people can legally run a LPAM basically only 100mW.

It's not a "loophole" - it's deliberate. "Part 15" is the section of the FCC regulations that covers this. It was to allow things like toy walkie-talkies for kids and baby alarms and cordless phones to be used without licensing. It also allowed colleges to run low power campus stations without the expense of a licence. These things are also used by "Realtors" for "talking house" advertisements at properties for sale.

There are limitations to the size of the antenna and to the field strength that's permitted. The stories of "2 miles from 100 mW into a 10ft aerial" on medium wave are just that - they're stories (or wishful thinking). The reality of it is that a couple of hundred yards is good going!

[Albert H]

Class E PA and a PWM mod both 90%+ eff, very easy, that's the current 'Trend'!

Been there - done that! I built a couple of 2.5kW carrier 12.5kW peak boxes for Eastern Europe last year (125% positive-going mod - it sounds really LOUD!). These used buckets of switching FETs for the carrier and for the modulation. I always use envelope feedback too, to define the modulation bandwidth and reduce the distortion inherently generated by PWM.

Some of the commercial manufacturers (Nautel for one) use "pre-distortion" to try to achieve the same thing, but envelope feedback is far superior! I also use the phase rotation trick to increase the modulation density and make certain that the applied audio has a very carefully defined response, and has the right amount of feed-forward compression and limiting.

The boxes have been in alternate-day operation for over a year, without the slightest hitch. I was really pleased with the results from what were really prototypes!

[Mike Volume]

I also use the phase rotation trick to increase the modulation density and make certain that the applied audio has a very carefully defined response, and has the right amount of feed-forward compression and limiting.

Wonder if that's this? -

http://www.w3am.com/8poleapf.html