74HC240

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Tests with the 74HC240

The IC 74HC240 was initially used in transmitters by the american ham N7KSB, who built versions for 10m (0.9W), 15m and 20m (0.5W) and with a vertical ground plane antenna worked more than 30 countries and all the continents. See the link to:

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

Other ham using them was K0JD, who uses the 74HC240 as a buffer for VFOs, he also mentions the use of the 74HC04 and the 74AC04.

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

The 74HC240 is an 8 bit inverter buffer in origin, so it has 8 inverter gates enabled by groups of 4 (2 enables). The nominal working voltage is 5 Volts, though most people makes it work at 8 Volts in order to increase the power.

Another example is the famous Christmas Cracker, a 40m 1/2W transceiver using the 74HC240 as VFO - buffer - PA and driver for the balanced diode receiver mixer, built by G3CWI. See in:

http://www.qsl.net/g3cwi/christma.html

Another implementation is in german in the site:

http://www.ardf.ch/Technik/Tx_80m.htm

A very good work can be seen in the NorCal 38 SPECIAL 30m transceiver, where the 74HC240 is the transmitter PA, see it in:

Schematic in http://www.norcalqrp.com/kits/38spcl/38sch.html

Specifications in http://www.norcalqrp.com/kits/38spcl/38spcl.htm

Parts list in http://www.norcalqrp.com/kits/38spcl/parts.html

Our friend Gomes PY2MG already drew a VFO-Buffer with the 74HC240 in an AM 10W TX in:

http://www.qsl.net/py2mg/Images/LU8EHA_TX.PDF

The LU8EHA original work is in:

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

We have another (cuban) version of the N7KSB work in:

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

Finally 4S7NR drew more informs about the 74HC240 application in:

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

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