EMRFD Message Archive 1562

Message Date From Subject
1562 2008-04-20 07:33:00 Vincenzo Calandra DTC designing help
Hi all,

i'm in trouble with dtc designing.
I've built a simple 7Mhz ssb tx with two NE602, one for the dsb
generator and the other for the tx mixer.
The power chain is that in fig. 6.140 of page 6.80 of EMRFD.
To match the output of the NE602 with the 50 Ohm input of first 2N3904 i
designed (with DTC.exe) a dtc with 1k5 Ohm input and 50 Ohm output.
Next i have verified the response with GPLA.EXE. The simulation seems
very good. Only 2dB of loss.

But the real circuit after mounted never work as i hope.
The loss is very high. So at the end of the rf chain the power was very
I've simulated the same circuit with RFSim99 and found a loss of more of
30dB at 50Ohm output.

Where is my mistake?
Anyone can help me?

Many thanks in advance and... apologize me for my poor english:)

Ciao, Enzo. (IZ5GVP)


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1563 2008-04-20 12:21:31 Wes Hayward Re: DTC designing help
Hello Enzo,

It is hard to say where the problem is, but there are many places
where one can go wrong. We've all been there!

Be careful with mixing the terminations. It is all to easy to
design a filter to be driven with 1500 Ohms and loaded with 50 Ohms,
but then to put it in the circuit backwards. Also, be very careful
with the computer programs. I am not familiar with RFSim99. Some
other programs, such as LT SPICE, are very effective, but can mislead
us with regard to the way the term "dB" is used.

I just put a short document in the "files" secti