Hi Roelof,
I compared the original miniwhip with the new eco version (single
SMT J310, 10Meg across the gate) and initially found it much noisier.
The problem was inadequate bypass capacitance for the cold end of
T1, the input xfmr for the SM6LKM converter, which I was using to
provide a bias current for the eco mw. Although the original mw
has perhaps 5-10 dB more gain, this can be offset by attaching a
30 cm wire to antenna of the eco mw. It was very gratifying to hear
DFC-39 while sitting in the living room with the eco whip in my hand.
It is an effective and simple design which draws less power than
the original mw. This means it will have less of a global warming
impact. Thanks for the design, Roelof.
Johan's VLF converter also works very well including VLF. The LO is 10
MHz and the primary of T1 is 5 mH. I have been testing it without
the diplexer and it seems fine -- leaving me to wonder if it is worth
the effort install a diplexer.
73
Joe VO1NA
On Tue, 3 Jul 2018, Roelof Bakker wrote:
Hello Joe,
The design is slightly different.
I use now 2 J310's parallel and Rs = 560 ohm.
Supply voltage can be anything between 4 and 20 V, whilst the current draw is 7
mA.
The output transformer is wound bifilar on a FT-37-43 with 20 turns, but a high
mu toroid will
work equally well. A BN-73-202 binocular core with 10 bifilar turns can also be
used.
VLF performance can be enhanced by increasing the 1M gate resistor to 10M or
higher.
73,
Roelof, pa0rdt
|
