![\"prea144-2\"](\"https:\/\/pa3csg.nl\/wp-content\/uploads\/2009\/10\/prea144-2-300x200.jpg\")
\nThe result of the NF measurement. Something 0.25dB NF according to my home-brew DJ9BV noise figure meter.<\/p>\n
A modification \/ combination of the DJ9BV & I5TDJ
\n144 MHz preamp designs<\/p>\n
The original I5TDJ design used a rather long coaxial input design. This was rather awkward to
\nput in my preamp box at the feed of my dish. I decided to use the DJ9BV helical input design instead.<\/p>\n
Original designs were published in Dubus:
\nI5TDJ design: Dubus 3\/94
\nDJ9BV design: Dubus Technik IV book<\/p>\n
The preamp is shown here. Note that the number of windings of the input helical has been reduced with half a winding. Source inductance of about 2mm on each source leg of the MGF1801.<\/p>\n
Another view of the preamp. Output circuit is the original I5TDJ design. Bias circuit is adapted to the parts in my junk box.<\/p>\n
\nThe result of the NF measurement. Something 0.25dB NF according to my home-brew DJ9BV noise figure meter.<\/p>\n
![\"144prea-nf-meter\"](\"https:\/\/pa3csg.nl\/wp-content\/uploads\/2009\/10\/144prea-nf-meter-300x151.jpg\")
<\/p>\n
Gain plot of the 144 MHz preamp. The simple input circuit has a gain drop of 10dB at 175 MHz and of 22 dB at 98 MHz.
\nThis is better than many other designs. Thanks to Jack Smeets, PE1KXH for performing the measurements.<\/p>\n
Plot of the preamps gain.<\/p>\n
![\"plot\"](\"https:\/\/pa3csg.nl\/wp-content\/uploads\/2009\/10\/plot-300x214.jpg\")
<\/p>\n
The I5TDJ schematic<\/p>\n
![\"schema-i5tdj\"](\"https:\/\/pa3csg.nl\/wp-content\/uploads\/2009\/10\/schema-i5tdj-300x208.jpg\")
<\/p>\n
The parts list for the I5TDJ preamp<\/p>\n
![\"parts-i5tdj\"](\"https:\/\/pa3csg.nl\/wp-content\/uploads\/2009\/10\/parts-i5tdj-141x300.jpg\")
<\/p>\n
Mechanical design for the DJ9BV design.<\/p>\n
![\"mech-dj9bv\"](\"https:\/\/pa3csg.nl\/wp-content\/uploads\/2009\/10\/mech-dj9bv-300x213.jpg\")
<\/p>\n","protected":false},"excerpt":{"rendered":"