Trying to build decent AM transmitter

[Mike Bates]

The am broadcast band isnt hardly used around here anyway, and i can only
pick up with 3 different recievers about 4 stations. thats it.

I have built the transmitter from the WRPDJ design, except I am using a big
modulation transformer, and an IRF510 mosfet with 19vdc driving it.

i dont have the parts to build a VFO, thats why I built the crystal
controlled CMOS divide by 4 circuit. it runs at approximatly 1610khz. (also
an empty freq).

I found a board from the WRPDJ clone, and modded, and used it insted since
it had a matcher/harmonics suppresor on it. so the system does go farther,
and stays on one frequency now.

Here is my problem. im only getting about a watt out of teh IRF510. The
mosfet is capable of putting out about 7 to 15watts.

How would I get my 1watt out to about 7 to 10 watts out?

Thanks!

 

[Joerg]

Hi Mike,

Not to spoil the broth here but this is most likely not legal. I believe
FCC part 15 transmitters are limited to 100mW input power of the final
amp and 3 meters antenna length, with some exceptions such as tunnel
radio etc. You can look it up:

http://www.access.gpo.gov/nara/cfr/waisidx_02/47cfr15_02.html

Regards, Joerg

http://www.analogconsultants.com

 

[Andrew Holme]

Mike Bates wrote:
[snip]

I have built the transmitter from the WRPDJ design, except I am using
a big modulation transformer, and an IRF510 mosfet with 19vdc driving
it.
[snip]
Here is my problem. im only getting about a watt out of teh IRF510.
The mosfet is capable of putting out about 7 to 15watts.

How would I get my 1watt out to about 7 to 10 watts out?

Some or all of these may work:

1. Increase drive level to MOSFET.
2. Change the output matching network so the drain "sees" a smaller load
resistance (Power = V^2/R).
3. Increase DC supply voltage.
4. Add a linear amplifier.

 

[Paul Burridge]

On Mon, 1 Nov 2004 20:15:06 -0000, "Andrew Holme" <andrew@nospam.com>
wrote:

Mike Bates wrote:
[snip]
I have built the transmitter from the WRPDJ design, except I am using
a big modulation transformer, and an IRF510 mosfet with 19vdc driving
it.
[snip]
Here is my problem. im only getting about a watt out of teh IRF510.
The mosfet is capable of putting out about 7 to 15watts.

How would I get my 1watt out to about 7 to 10 watts out?

Some or all of these may work:

1. Increase drive level to MOSFET.
2. Change the output matching network so the drain "sees" a smaller load
resistance (Power = V^2/R).
3. Increase DC supply voltage.
4. Add a linear amplifier.

And/or use a MOSFET driver in the gate circuit.

--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[Clarence]

"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:XAxhd.37526$QJ3.11673@newssvr21.news.prodigy.com...

Hi Joel,

snip

I believe digital AM is pretty much dead. Certainly if it weren't 100%
compatible. Heck, even HDTV doesn't want to catch on. Most if not all of
the lower priced TV sets we can buy here in California are analog only.
I don't know anybody who can receive the offered HDTV-on-air broadcasts
here in town. So, while there is programming the audience is lacking for
technical reasons. I don't think that was the FCC's plan.

Regards, Joerg

Might it be the `$4,700 cost of the HDTV?

I know someone who has one. He watches about once a week. I can't see the
cost.

 

[Mike Bates]

ive tried all of that.

ive tried a buffer stage in between, and i tried a mosfet driver for the
mosfet. it weakens the output, and becomes distorted.

ive also tried increasing the supply to 24 and even 30 volts. Range becomes
limited, and sound starts to phase out and distort.

i dunno.



"Paul Burridge" <pb@notthisbit.osiris1.co.uk> wrote in message
news:vsado09ia9qjjvjv3c7sp002v3bifq8tet@4ax.com...

On Mon, 1 Nov 2004 20:15:06 -0000, "Andrew Holme" <andrew@nospam.com
wrote:

Mike Bates wrote:
[snip]
I have built the transmitter from the WRPDJ design, except I am using
a big modulation transformer, and an IRF510 mosfet with 19vdc driving
it.
[snip]
Here is my problem. im only getting about a watt out of teh IRF510.
The mosfet is capable of putting out about 7 to 15watts.

How would I get my 1watt out to about 7 to 10 watts out?

Some or all of these may work:

1. Increase drive level to MOSFET.
2. Change the output matching network so the drain "sees" a smaller load
resistance (Power = V^2/R).
3. Increase DC supply voltage.
4. Add a linear amplifier.

And/or use a MOSFET driver in the gate circuit.

--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[Paul Burridge]

On Tue, 02 Nov 2004 00:00:29 GMT, "Mike Bates" <nospam@nospam.com>
wrote:

ive tried all of that.

ive tried a buffer stage in between, and i tried a mosfet driver for the
mosfet. it weakens the output, and becomes distorted.

ive also tried increasing the supply to 24 and even 30 volts. Range becomes
limited, and sound starts to phase out and distort.

Are you quite certain that you have matched the MOSFET's input and
output circuits properly? I mean, you have ensured that your matching
networks are appropriate at the required frequency for that particular
MOSFET's admittance/impedance parameters? Can you post a link to the
circuit diagram?
--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[Paul Burridge]

On Tue, 02 Nov 2004 17:43:28 GMT, "Mike Bates" <nospam@nospam.com>
wrote:

i have no idea what that means.

i just well, morphed it out of my head. kinda built it from scratch with
different ideas from different circuits. it works, and sounds damn good, but
power is very limited.

Well if that's how you built it, you're lucky it works at all!
--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[Paul Burridge]

On Tue, 02 Nov 2004 20:20:06 GMT, "Mike Bates" <nospam@nospam.com>
wrote:

well, if you want a better explanation:

I took a 7 watt transmitter design that had a VFO. well, I didnt have any
parts for a VFO, so i took a CMOS ocillator in place of a VFO. and have the
harmonics supressor on the end. Thats what I did.

I cant give you a schematic, unless i physically draw it out. i dont have a
scanner to scan a drawing.

Well we're not goiing to get very far with it, are we? Unless it's the
one I'm maybe thinking of in the RSGB's Radcom Handbook?
--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[Mike Bates]

if that doesnt help, ill try to draw one in photoshop.



"Mike Bates" <nospam@nospam.com> wrote in message
news:QD6id.98519$5v2.95627@fe2.columbus.rr.com...

ill better explain this:

I took this circuit: http://home.att.net/~weatheradio/wprdj_schematic.gif

and replaced the final and the modulator ONLY. Thats it. From this design
here:
http://www.usinternet.com/users/kyledrake/schematic/vfo-schematic.jpg

Thats all i did. I tried using the buffer stage in the above design, but
it
didnt work with the CMOS ocillator. no noticble difference.





"Mike Bates" <nospam@nospam.com> wrote in message
news:7z6id.98464$5v2.93147@fe2.columbus.rr.com...
no. its the WRPDJ schematic thats on the net right now, I just took out
the
npn final, and the 386 modulator, and replaced it with a FET and a
modulation transformer, along with a seperate B+ supply.
Thats all I did.



"Paul Burridge" <pb@notthisbit.osiris1.co.uk> wrote in message
news:h6cgo05ibebldf8fniqbvqlanl9bebsrej@4ax.com...
On Tue, 02 Nov 2004 20:20:06 GMT, "Mike Bates" <nospam@nospam.com
wrote:

well, if you want a better explanation:

I took a 7 watt transmitter design that had a VFO. well, I didnt have
any
parts for a VFO, so i took a CMOS ocillator in place of a VFO. and
have
the
harmonics supressor on the end. Thats what I did.

I cant give you a schematic, unless i physically draw it out. i dont
have
a
scanner to scan a drawing.

Well we're not goiing to get very far with it, are we? Unless it's the
one I'm maybe thinking of in the RSGB's Radcom Handbook?
--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[Paul Burridge]

On Wed, 03 Nov 2004 15:29:05 GMT, "Mike Bates" <nospam@nospam.com>
wrote:

The other main reason im using a CMOS ocillator, is because the frequency is
rock solid. It NEVER drifts, at least not noticble to me.

im thinking the problem lies in the carrier wave, because the CMOS is
supposed to put out a 5vp-p drive to the mosfet. Problem is, i think that
5vp-p isnt enough to drive the mostfet to its max output. i tried using a
buffer amplifier between the mostfet and the CMOS ocillator. it didnt change
anything. Tried using a fet buffer stage with another irf510, and that made
it worse. (probably not matched/tuned)

I've seen the two 'donor' diagrams you posted but would like to see a
diagram of the final, modified circuit you've come up with in its
entirety. How did you got about selecting the irf510? What makes you
think it a suitable mosfet for this application? There are TTL drive
level mosfets out there that would fully switch on from your 5v input
signal, but they might well be lacking in other necessary
characteristics. Just because you've breached V_threshold with your
CMOS input drive signal doesn't mean you're going to get a decent
output. You may well need more voltage *and* current drive. What's the
input capacitance of that FET? I thought you said you'd tried a
driver, anyway.
Forget about Paintshop; download a free copy of LTSpice from
www.lineaer.com and use it to assemble a circuit diagram (the symbols
are already created for you so you just choose the right ones and join
'em up. Then use the Tools menu to copy the diagram to bitmap in
Paintshop; convert to .gif and post the complete schematic to your
website. At least then there's a fighting chance of nailing the
problem!
--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[Joerg]

Hi Frithiof Andreas,

HDTV took so long to roll out that people got used to the Internet and those
people are now unhappy about the slow, liniear, push-format 'offered' by the
TV media; i.e. *why* should *I* adjust my schedule to when the *broadcaster*
deigns appropriate? *why* should I sit through a boooring news item?


In the US people use TiVo to get around that. It lets you hand-pick the

content and avoid much of the commercials. But AFAIK it is only possible
on a paid subscription basis. No free lunch here.

Not to mention that most of the programmes are crap anyway: a deluge of
quizz shows, advertising and movies - that were bad even a decade ago - the
kind of swill upon which better picture and sound quality is entirely
wasted.


That's why we went to the video store last week and rented "Once upon a

time in the West", to see it for the tenth time or so ;-)

HDTV is dead - some sort of Internet-based distribution will be the cable
TeeVee of the future.


I think you may be right about that. But it will require the roll-out of

fibers into the homes for enough bandwidth. Then you have your HDTV
again, just in a different delivery mode.

I remember when an analog form of HDTV was touted big time in Europe and
some Scandinavians bought these extremely expensive sets, only to
discover a short time afterwards that the programming started to vanish.

Regards, Joerg

http://www.analogconsultants.com

 

[Joel Kolstad]

"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:5Iwhd.37512$QJ3.36188@newssvr21.news.prodigy.com...

Not to spoil the broth here but this is most likely not legal.

He probably knows that and figure he's going to risk it anyway; the pirate
radio community is alive and well. I do think you can make a good case that
there's been a coordinated effort by commercial broadcasters to keep 'little
guys' (e.g., <=50W stations) off the air due more to concerns about
competition/loss of advertisements than any technical issues.

I do wonder where he is that the AM band is so dead. That used to be the
case in many locales, but talk radio created a huge revival some 5-10 years
ago.

What will be interesting to see is whether or not some form of 'AM digital'
catches on. Although there already are digital broadcasters on FM, AM has
the somewhat unique advantage that it's almost trivial to keep compatibility
with traditional AM transmitters and receivers while adding much higher
fidelity from a digital add-on.

---Joel

 

[Joe]

Joel,

In the middle of the country, where the population is sparse, so is the
radio coverage.

When I lived in the westernmost county of Oklahoma, there were very few
stations to receive. Without an external antenna, some FM stations from
Amarillo TX weren't heard. There was a local radio station at a town 45
miles away ... a class D station whose antenna field I suspect hasn't been
inspected in a looooonnnnngggg time and needed repair. Another couple of
stations were at a town 60 miles away.

The propagation path out there wasn't the best on the conductivity scale.
--
Joe
http://www.fcctests.com


"Joel Kolstad" <JKolstad71HatesSpam@Yahoo.Com> wrote in message
news:W7qdnWXn7s0wBxvcRVn-hg@comcast.com...

"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:5Iwhd.37512$QJ3.36188@newssvr21.news.prodigy.com...
Not to spoil the broth here but this is most likely not legal.

He probably knows that and figure he's going to risk it anyway; the pirate
radio community is alive and well. I do think you can make a good case
that
there's been a coordinated effort by commercial broadcasters to keep
'little
guys' (e.g., <=50W stations) off the air due more to concerns about
competition/loss of advertisements than any technical issues.

I do wonder where he is that the AM band is so dead. That used to be the
case in many locales, but talk radio created a huge revival some 5-10
years
ago.

What will be interesting to see is whether or not some form of 'AM
digital'
catches on. Although there already are digital broadcasters on FM, AM has
the somewhat unique advantage that it's almost trivial to keep
compatibility
with traditional AM transmitters and receivers while adding much higher
fidelity from a digital add-on.

---Joel

 

[SioL]

"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:ugbjd.5533$zx1.1069@newssvr13.news.prodigy.com...

Hi Frithiof,

Rumour has it that the 'vanilla' ADSL we have here in the DK can actually
run at 8 Mbit/s - the requirement presently being that one knows a techie
with the right access at the dominant telecoms provider. Who shall not be
named

Yesterday I talked with an engineer who is currently trying to squeeze a whole
more than that through twisted pair.

The other rumour is that they want/need 12 Mbit/s om ADSL before they commit
to providing TV on it - in reality it is probably the 'Brownshirts' from
RIAA that are preventing any operator from enabling the downloading of DVD's
legally on players with storage, which would alleviate the BW problems
somewhat.

Actually you need about 4-6Mbit/s for TV. Plus 1-2Mbit/s for Internet, usually.
I have it in my living room. I already had ADSL so upgrade to tv was logical and
cheaper step since my new apartment did not have cable.

Unfortunately my ADSL line is a bit far from the central so with some programs
I get a bit of "blocking" once in a while.

Another negative aspect is that you can only watch one channel at a time (only
one
TV) or it would indeed take 12Mbit/s + whatever internet needs.

SioL

 

[Mike Bates]

well, if you want a better explanation:

I took a 7 watt transmitter design that had a VFO. well, I didnt have any
parts for a VFO, so i took a CMOS ocillator in place of a VFO. and have the
harmonics supressor on the end. Thats what I did.

I cant give you a schematic, unless i physically draw it out. i dont have a
scanner to scan a drawing.



"Paul Burridge" <pb@notthisbit.osiris1.co.uk> wrote in message
news:2kifo09bq85ulv6ngoffden6c4kefr7lo7@4ax.com...

On Tue, 02 Nov 2004 17:43:28 GMT, "Mike Bates" <nospam@nospam.com
wrote:

i have no idea what that means.

i just well, morphed it out of my head. kinda built it from scratch with
different ideas from different circuits. it works, and sounds damn good,
but
power is very limited.

Well if that's how you built it, you're lucky it works at all!
--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[Mike Bates]

no. its the WRPDJ schematic thats on the net right now, I just took out the
npn final, and the 386 modulator, and replaced it with a FET and a
modulation transformer, along with a seperate B+ supply.
Thats all I did.



"Paul Burridge" <pb@notthisbit.osiris1.co.uk> wrote in message
news:h6cgo05ibebldf8fniqbvqlanl9bebsrej@4ax.com...

On Tue, 02 Nov 2004 20:20:06 GMT, "Mike Bates" <nospam@nospam.com
wrote:

well, if you want a better explanation:

I took a 7 watt transmitter design that had a VFO. well, I didnt have any
parts for a VFO, so i took a CMOS ocillator in place of a VFO. and have
the
harmonics supressor on the end. Thats what I did.

I cant give you a schematic, unless i physically draw it out. i dont have
a
scanner to scan a drawing.

Well we're not goiing to get very far with it, are we? Unless it's the
one I'm maybe thinking of in the RSGB's Radcom Handbook?
--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[Mike Bates]

ill better explain this:

I took this circuit: http://home.att.net/~weatheradio/wprdj_schematic.gif

and replaced the final and the modulator ONLY. Thats it. From this design
here: http://www.usinternet.com/users/kyledrake/schematic/vfo-schematic.jpg

Thats all i did. I tried using the buffer stage in the above design, but it
didnt work with the CMOS ocillator. no noticble difference.





"Mike Bates" <nospam@nospam.com> wrote in message
news:7z6id.98464$5v2.93147@fe2.columbus.rr.com...

no. its the WRPDJ schematic thats on the net right now, I just took out
the
npn final, and the 386 modulator, and replaced it with a FET and a
modulation transformer, along with a seperate B+ supply.
Thats all I did.



"Paul Burridge" <pb@notthisbit.osiris1.co.uk> wrote in message
news:h6cgo05ibebldf8fniqbvqlanl9bebsrej@4ax.com...
On Tue, 02 Nov 2004 20:20:06 GMT, "Mike Bates" <nospam@nospam.com
wrote:

well, if you want a better explanation:

I took a 7 watt transmitter design that had a VFO. well, I didnt have
any
parts for a VFO, so i took a CMOS ocillator in place of a VFO. and have
the
harmonics supressor on the end. Thats what I did.

I cant give you a schematic, unless i physically draw it out. i dont
have
a
scanner to scan a drawing.

Well we're not goiing to get very far with it, are we? Unless it's the
one I'm maybe thinking of in the RSGB's Radcom Handbook?
--

"What is now proved was once only imagin'd." - William Blake, 1793.

 

[Ken Smith]

In article <zKSjd.6373$zx1.321@newssvr13.news.prodigy.com>,
Joerg <notthisjoergsch@removethispacbell.net> wrote:
[...]

There is a company (Key Eye Communications) out here that attempts to
run more than an order of magnitude faster over CAT-5 and CAT-6. Short
runs only, like a 150ft or so to the street box but that would allow all
your visitors to watch a different channel if they wanted to. I believe
their goal is 10Gbit/sec over copper. On the local level that could blow
fiber out of the water.

You don't really need that much bandwidth if you assume some good
compression is used. Assuming we compress down to the information
contained in a network program we should be able to work out the average
number of bits needed. Then we can just divide by 3600 to get the data
rate. I'll make a start on the estimate for you:

There are a total of 4 basic plots which when combined with the various
subplots will take about 8 bits to transfer. So thats 1 byte per show.


--
--
kensmith@rahul.net forging knowledge

 

[Joerg]

Hi SioL,

Actually you need about 4-6Mbit/s for TV. Plus 1-2Mbit/s for Internet, usually.
I have it in my living room. I already had ADSL so upgrade to tv was logical and
cheaper step since my new apartment did not have cable.


Interesting. Where do you get the TV channels from? The fastest I have

seen were channels like Bloomberg at 250kbit/sec. Maybe a bit more
nowadays but not much.

Another negative aspect is that you can only watch one channel at a time (only
one
TV) or it would indeed take 12Mbit/s + whatever internet needs.


But watching more than one channel at a time usally fries a human brain

quite quickly, doesn't it. Unless you want to create a sports bar in
your basement.

Regards, Joerg

http://www.analogconsultants.com