I built the qrp wattmeter that was written up in Sprat 61 and Jan 92 QQ, page
10. I have mine calibrated for a 5 watt and a 1 watt scale. Used 50 trimpots to set the scale against my OHR WM-1. I used FT50-43 toroids. Neither article
specifies which toroids to use, but I got my idea that it was the 43 material
from building the OHR and from Mike Czahajewski's column in the latest issue of
QQ, April. Fun project and neat. Cul, 72, Doug KI6DS
From qrp-request@Think.COM Mon May 10 02:09:37 1993
There has been a fair amount of interest from my orginal posting on building
high performance, simple HF receivers, compact low cost receivers. Following
is additional information that has been requested.
The Micro 20M receiver was orginally published in Ham Radio Magazine, Feb. 1988.FAR Circuits made a PC board (1 1/2" X 3", ~$5). Contact info is FAR Circuits,
18N640 Field Court, Dundee, Ill 60118.
The author for the Micro 20 published two transceivers (using this receiver).
1. NE 602 Based 20M QRP Transmitter, Ham Radio Jan. 1989
2. QRP 15 Transceiver, CQ Sept. 1990
Note: The MFJ line of QRP transceivers are basically the above transceivers.
The Micro 20 also has audio derived agc (see below). Its good for SSB, but due
to loop response of audio signals, its attack time is slow and tends to pop on
attack. For CW rigs, I don't include it and just use a voltage divider circuit
with a potentiometer, the wiper through a 10K series resistor supplys 5V (max)
to 12V (min) to the MC 1350 agc pin (5).
For those who might want to SWL, the NE602 Product Det/BFO can be replaced with
a envelope detector (a diode).
Band Pass---NE602 Mix.---Cohn Xtal---MC1350---NE602 Prod.Det.---LM386 AF
Filter | Filter | | Amp.
VFO | BFO |
| |
|_________AGC Amp._________|
Following is a varation. The IF amp is elimited and replaced with a AF preamp.
The advantages are:
1. Better dynamic range due to less signal at the Prod. Det. stage. NE 602's
can get bashed and be careful when using them as a transmit mixer.
2. Circuit also shows a different AF power amp. The MC34119 was designed for
low voltage circuits. It has less audio distortion and you shape its band
pass with external R's & C's to be optimized for commucication audio. See
Motorola data sheet.
Band Pass---NE602 Mix---Cohn Xtal---NE602 Prod.Det.---NE5534---MC34119 AF
Filter | Filter | Pre Amp Amp.
VFO BFO
Should be able to build a portable receiver ( 6V battery,shirt pocket size)
with this design.
Either of the above circuits and easily be made into a simple switch selectable
multi-band unit by using another NE 602 to premix the VFO/Xtal oscillator to
generate a new stable VFO to feed the first mixer.
Band Pass---NE602 Mix--- Same as one of above
| _
Band Pass Fil. |
| | New
VFO-----NE602 Pre Mix. | Note: diode switch
| | xtal's for multband
Xtal Osc. _|
The NE602 is a double balanced mixer with on board oscillator and buffer in a
8 pin dip package and requires only a handful of external parts. Its made by
Signetics and cost about $2. Its built for low power use ( i.e. 6V @ 2.5 ma).
73's
Ed Pacyna W1AAZ
From qrp-request@Think.COM Tue May 11 17:09:36 1993
