[Patrick Turner]

I have a few things to say about AM radio, and generation of AM waves etc.....

http://www.turneraudio.com.au/Kitche...adio-2015.html

http://www.turneraudio.com.au/AM-mod...state-2015.htm

http://www.turneraudio.com.au/AM-mod...tubed-2015.htm

Should you wish to fuel up the flame thrower, be my guest, gas should be at rock bottom prices because the Ay Rabs can afford to sell oil at much lower prices......

Patrick Turner.

[Peter Wieck]

On Thursday, February 18, 2016 at 3:17:00 AM UTC-5, Patrick Turner wrote:


Should you wish to fuel up the flame thrower, be my guest, gas should be at rock bottom prices because the Ay Rabs can afford to sell oil at much lower prices......

Far from it - AM radio once upon a time was a world standard and pretty good. I have a Zenith console from the 1930s that is capable of producing excellent sound - if fed a decent signal.

Sadly, AM today is a hodge-podge of compressed, limited bandwidth garbage shilling religion and the likes of Rush Limbaugh with little redeeming social value in very much most cases. I solve that problem for myself by using a small, full-range (20-20K uncompressed) transmitter from a CD changer. Most older AM receivers are much better than the signal fed to them.

Peter Wieck
Melrose Park, PA

[Patrick Turner]

I said....
Should you wish to fuel up the flame thrower, be my guest, gas should be at rock bottom prices because the Ay Rabs can afford to sell oil at much lower prices......

Peter Wieck replied.....
Far from it - AM radio once upon a time was a world standard and pretty good. I have a Zenith console from the 1930s that is capable of producing excellent sound - if fed a decent signal.

Sadly, AM today is a hodge-podge of compressed, limited bandwidth garbage shilling religion and the likes of Rush Limbaugh with little redeeming social value in very much most cases. I solve that problem for myself by using a small, full-range (20-20K uncompressed) transmitter from a CD changer. Most older AM receivers are much better than the signal fed to them.

Peter Wieck
Melrose Park, PA

There is much BS on AM stations here which have talk-back with crazies with nobody to talk to, with mix of endless adds and pop music.
Some have HF emphasis to compensate for poor receivers so a tone control is essential.
Govt owned ABC Radio National and a couple of local ABC have high quality content without adds. Print Handicapped has good AF signal. The same hourly news program goes to Govt ABC Classic FM stations and to AM stations, fed from same source and AM from tubed tuner sounds better than FM from bunch of generic 1980 ICs.

Many old radios I re-engineered has loudspeakers with stuffed voice coils and cones after previous 70 to 40 years. Sound was dreadful, and when I changed speakers to something modern and with decent AF amp with triode and GNFB, and treatment of box to lessen colorations, THEN there was always better sound than when someone bought the radio. A trioded 6L6 is better than 6F6/6V6 tetrode, EL34 triode better than EL84 pentode.

But nearly all the old radios made by so called leading brand-names only gave 100Hz to 3.5kHz AF bandwidth with usual THD 5% at all low levels and much higher when AF level was increased. Trio and later Kenwood made AM sections of AM-FM receivers with switch for tertiary of IFT1 to extend IF BW, thus extend AF BW.
But the old tubed Quad AM Tuner WAS GOOD, IMHO, nicely made and MUCH better performance than local stuff made in Oz.

I know the majority of old radios were crap, easily seen when you do have a good signal source with ability for 95% mod with envelope shape THD 1%. HP606A could manage a fairly good AM wave, but the one I just built for 380kHz to 1,750khz is much better.

Better still might just be an IC for AM production; I don't know which chip.. But Topward Instruments made a function gene with FM and AM and I recall it had a pretty decent AM signal. Only trouble was the horrid potentiometer for Vdc to control the Fo. The output amp had no protection, and even when I fitted some diodes to limit accidental contact of Vo to +/- rails of gear I was testing, I still managed to fry the output bjts. One day, I accidentally let output RCA lead touch 240Vac Mains. I got crackling sound and smoke as every single chip which could fry - did. :-) Into the bin it went.
Patrick Turner.

[Peter Wieck]

On Monday, February 22, 2016 at 11:50:36 PM UTC-5, Patrick Turner wrote:
I said....

But nearly all the old radios made by so called leading brand-names only gave 100Hz to 3.5kHz AF bandwidth with usual THD 5% at all low levels and much higher when AF level was increased. Trio and later Kenwood made AM sections of AM-FM receivers with switch for tertiary of IFT1 to extend IF BW, thus extend AF BW.
But the old tubed Quad AM Tuner WAS GOOD, IMHO, nicely made and MUCH better performance than local stuff made in Oz.

Well... my oldest radio is a home-brew from 1919, my newest (AM) a Grundig Satellit 700 purchased in the souks of Al Khobar, Saudi Arabia. The former drives a carbon-pancake horn, the latter has a reasonably decent on-board speaker. But the radios that I have that sound the best have massive (typically around 14" OD) field-coil speakers that have surprisingly good range. I have made sure that the VCs are good, that the paper is good, and that the surrounds are still supple.

But, I suggest you look into the AMT3000 or 5000 transmitter (made by a neighbor of mine, Phil Bolyn) that even shipped down under is reasonably priced and with excellent performance. They are Part-15 compliant in the US, so likely might be legal down under as well. They can certainly be throttled as needed to cover either just your dwelling - or several handfuls of hundreds of meter/yards/cubits with the proper antenna and a bit of elevation.

http://www.sstran.com/pages/AMT5000/..._overview.html

Peter Wieck
Melrose Park, PA

[Big Bad Bob]

On 02/18/16 00:16, Patrick Turner so wittily quipped:

I have a few things to say about AM radio, and generation of AM waves etc.....

AM is still the best for voice, particularly SSB with no carrier, for
long distance communication in the long and medium wave bands. For
short wave it may or may not be depending on skip and whatnot.

I don't know if AU has a lot of news/talk broadcast AM stations but
news/talk format keeps AM stations viable. they aren't good for music,
even though there were some stereo experiments, but it's great for
news/talk and late-night stuff.

/me used to listen to Art Bell back in the day... and keep daylight
hours so I can hear the Limbaugh show, even if I don't hear a lot of
what's going on when I'm workin' [becomes background noise].

With good quality quadrature detectors, AM has pretty good noise
rejection, but of course FM will always be better.

Older AM receivers [when music broadcast was common] often had 10khz
'peakers' in the circuit to make them sound better for music, compensate
for typical LPF at 10khz on the broadcast equipment. It was 'almost hi
fi' that way, maybe just a peaker coil on the plate circuit of an
amplifier tube [I saw something that did that, a heathkit AM hi fi
receiver from the 50's - wish I still had it].

modern AM receivers tend to sound kinda 'muddy' because they don't
bother to do things like that any more.

I built several AM radios, simple ones, back in the day. it's a great
kid project when learning electronics. Simple diode detector, tuned
circuit, wound antenna coil, tube or transistor amplifier south of the
detector. careful biasing of the diode will make them pretty sensitive,
or maybe use an op amp with a peak detector as the LPF. whatever. lots
of possibilities.

[Big Bad Bob]

On 02/18/16 00:16, Patrick Turner so wittily quipped:

I have a few things to say about AM radio, and generation of AM waves etc.....

http://www.turneraudio.com.au/Kitche...adio-2015.html

since you're using SS diode (1N914) you might as well use schottkey
diode instead since the forward bias is lower and more of a 'shelf' -
should improve low signal detection.

or you can bias the diode a bit... or use a tube with high Z which
should have ~0V forward bias at very very low currents (and no reverse
current at all).

[Big Bad Bob]

On 02/23/16 06:29, Peter Wieck so wittily quipped:
But, I suggest you look into the AMT3000 or 5000 transmitter (made by a neighbor of mine, Phil Bolyn) that even shipped down under is reasonably priced and with excellent performance. They are Part-15 compliant in the US, so likely might be legal down under as well. They can certainly be throttled as needed to cover either just your dwelling - or several handfuls of hundreds of meter/yards/cubits with the proper antenna and a bit of elevation.

http://www.sstran.com/pages/AMT5000/..._overview.html

looks like a nice transmitter. it'd probably work well for an amateur
AM radio station, driving a licensed power amplifier and antenna, so
long as freq instability doesn't cause it to cross into anyone else's bands.

I was thinking you could build one with some kind of balanced modulator,
with a detector on the output creating negative feedback to limit
distortion. you'd bias the modulator at 50% for zero signal level, and
then it should give you up to 100% with minimal THD. But that
transmitter also has a 5:1 compressor and other things you really need
for an AM transmitter. So yeah, probably can't build one cheap enough
(and have it be 'legal').


open-ended balanced modulators would stink for THD, but using negative
FB would make it work well, I bet. So yeah, just have a detector off of
the output, then use for NFB.

100mw into 50 ohms is ~2.2VRMS so NFB would be practical. 300 ohms
would be ~5.5VRMS (appropriate calculation for 100% modulation would
also give you 'that value' as the detected audio RMS voltage).

I suppose you could design an output transformer (air core even,
tunable) that would give you both impedences, then adjust RF gain
accordingly. A sharp cutoff pentode with an AGC-like circuit would do
nicely, such that the '50% modulation' output level on the appropriate
tap gives you 100mw.

[Big Bad Bob]

On 02/24/16 15:20, Big Bad Bob so wittily quipped:
I was thinking you could build one with some kind of balanced modulator,
with a detector on the output creating negative feedback to limit
distortion. you'd bias the modulator at 50% for zero signal level, and
then it should give you up to 100% with minimal THD. But that
transmitter also has a 5:1 compressor and other things you really need
for an AM transmitter. So yeah, probably can't build one cheap enough
(and have it be 'legal').

etc.

https://richmondradio.wordpress.com/...m-transmitter/


"The modulation is accomplished an older but quite capable (and still
available) MC 1496 Balanced Modulator/Demodulator IC. For AM operation
we don’t want a balanced condition so the chip is biased such that the
carrier is not nulled out."

a cheap method of carrier injection would be to DC bias the balanced
modulator such that the zero-AC-signal output power is the 'rated' power
(in this case, 100mW for FCC legal). Looks like this guy is doing "that".

I recall balanced modulators (and carrier injectors) being used in U.S.
Navy comms gear designed in the 1950's (with freq. synth, crystal ovens,
and lots and lots of tubes). It gave you SSB, supressed carrier AM, and
regular AM with the same unit.