Beacon kit ...

[QRP]

What do you think about this kit? http://www.wa0itp.com/ns40.html
With some modification, it should be possible to use as a beacon.
There are only 14 electronic components, and no toroid or coils of any kind to wind.
Any comments about it?

//QRP

[beaconman]

The society runs milliwatt beacons only... this is over kill...
we totally home brew the beacons from scratch...


 

[QRP]

Is this OK? Only 200mw ...



This experimental 1/2 watt CW transmitter uses a 74HC240 high-speed CMOS octal buffer, one section which serves as a crystal oscillator, four sections of which amplify this signal, and three sections of which are unused. Because the 74HC240 dissipates 1/2 watt on 20M and 0.9 watts on 10M, it must be heat-sunk. Epoxying the IC to the ground plane in dead-bug of ugly construction provides adequate cooling. L1, a low-inductance coil, is sensitive to lead length, so if you build this transmitter with plug-in filters (Lew Smith uses phono plugs and jacks for this purpose), you may need to remove one or two turns from L1 to compensate for the extra lead length involved in wiring the coil plugs and socket. The newer 74HC240's available today show little power drop-off on 10M, while older ones exhibited a 20% power drop-off. The older 74HC240's can handle power up to 10V, the newer ones latch up at 9V. It is therefore important to operate the rig at a supply voltage of 7.8 to 8 volts, which is a compromise between maximum power and safety. The logic chips have built-in input and output buffers. The extra gain provided by the extra stage make it harder to get rid of key clicks. The rig's key-click filter therefore uses an unusually large time constant (33 ms.) The output stages in 74HCxxx devices are designed to have equal pull-up and pull-down transistors. This minimizes even-order harmonics, simplifying the rig's output filtering. The 74HC240 can directly drive a power MOSFET amplifier.

//QRP

[beaconman]

Thats a pretty niffty circuit and the power levels are right

e mail me at
hiferbeacon@yahoo.com

[syfr]

Challenge will be PS voltage, but some forward biased diodes in a series string (like 6 ) will do! Nice circuit.

[weaksigs]

Hello All!
That is a very impressive 40 meter kit!
The class "E" circuit is impressive and would greatly
minimize components for a beacon. Is it possible
to reduce the power while still staying in class E or
is a whole new set of parameters necessary for
"milliwatt" operation? 5+ watts is not normally called qrp!

Has anyone asked what the operational band width
actually is assuming reasonable harmonic suppression?

Not many beaconeers will use a strictly 40 meter circuit
as the choice of operational frequencies will not be in
the ham bands I suppose.

Another question, is there software available to move
the tuned circuits for operation on 30 meters or twenty
or any frequency??

weaksigs

[QRP]

Some variations on the 74HC240 transmitters can be found at:

http://py2ohh.w2c.com.br/trx.htm

http://py2ohh.w2c.com.br/trx/digital/rfdigital.htm

http://www.madisoncounty.net/~kj5tf/n7ksb.html

http://www.seboldt.net/k0jd/hcbuffer.html

Copy and reassemble this one:

http://www.radiohc.org/Distributions/Dxers/ultra-simple-transmitter.html

http://www.qsl.net/qrp/tx/logi-tx.htm

http://www.qsl.net/lu8eha/lab_ref2.html

//QRP

[cmradio]

http://www.qsl.net/lu8eha/lab_ref2.html

Caution to newbies: technique and layout is critical to get that one parasitic free and operating at peak efficiency.
(dead-bug it... the best chance of getting it right)


Peace!

[syfr]

...or Manhattan ... either way you're right , nothing beats building over a good ground plane. Those proto board solderless breadboard thingies are fine for some stuff, but they're lousy for RF as they lack a good ground .

I could never get over building dead bug mode that the pin assignments are reversed when looking from the bottom, but the rest of you are probably smarter then I am. :-)

The thing about that class E kit is that the inductor is already done in etch on the board, so if you're going to stray much from 7Mhz, the cap values you end up with might be odd at best.

One other considerations might be supply voltage.... (If you have to have multiple PS voltages it's a complexity).

[QRP]

OK guys, now I have heard much criticism of the options I have presented.
Now it's time for you to present the ultimate beacon drawing.

//QRP

[syfr]

The universal CW transmitter that's here in the files is a proven design.

There's nothing wrong with the sources you have, as long as you consider some of the constructive criticism...(PS voltage, design frequency,etc...).  The cmos design you posted is a neat one, but not going to be happy with a 12v supply for longer than a few milliseconds... :-)

[QRP]

The funny thing is that "4096 kHz in the Mojave Desert" using exactly my suggestion.
See the drawing at the bottom of this link: http://www.auroralchorus.com/4096khz.htm



//QRP

[syfr]

Actually there's one quite major, fundamental difference, which is exactly why I pointed out what I did, but suit yourself!

[QRP]

That was a very constructive response and now it's time for you to present your proposal to the beacon drawing. What equipment do you use?
//QRP

[cmradio]

That's adorable!

I like it

Peace!