From: chuck@eng.umd.edu (Chuck Harris - WA3UQV)
Newsgroups: rec.radio.amateur.misc
Subject: Re: Plans to build transceivers. (Review of Oak Hills 20m QRP xcvr)
Date: 10 Oct 92 17:59:30 GMT
Distribution: usa
Organization: University of Maryland, Department of Electrical Engineering

In article <1992Oct8.233658.20119@cbnewsm.cb.att.com> jeffj@cbnewsm.cb.att.com (jeffrey.n.jones) writes:
>In article <1992Oct8.155140.16974@odin.corp.sgi.com> adams@chuck.dallas.sgi.com (Charles Adams) writes:
>>In article <1992Oct8.023159.24448@ke4zv.uucp>, gary@ke4zv.uucp (Gary Coffman) writes:
>>
>>BTW I did finish the A&A, Oakhills Research, Tejas RF Technology,

Hi,
	I will give you my short review of the Oakhills Research 20m QRP
tranceiver....

	I built Oakhills 20m qrp transceiver.  I ordered the unit by telephone.
The proprietor answered the phone, was very nice and informative, and I got
my unit by UPS about 1 week later.  The unit arrived complete, the chassis
was made by TenTec, and was nicely painted, and labeled.  All of the holes
lined up properly.  There was a little difficulty in mounting the VFO tuning
capacitor.

	The printed circuit was a bit of a challenge to build.  It was a 
single sided G-10 fiberglass board which was solder plated and reflowed, but
had no soldermask, or component location silkscreen.  The assembly
technique was basically: "place all of the resistors, capacitors, transistors
and coils, solder carefully, use the partslist, and the pc board drawing
as a guide..."  There were 13 jumpers on the board.  All were on the component
side of the board, and all are fairly long, so as to clear the tops of the
components.  The jumpers were used to route the +12v to the various parts of
the circuit.  The instructions for the jumpers were something like: "cut the
jumpers to the lengths in the table, and connect jumpers to the holes marked
with the same letters (g. A->A, B->B...). Route the wires clear of the tops of
the components.

	The receiver is a fairly simple single conversion superhet design
with a 9MHz IF, and a 5-5.1MHz VFO.  The antenna is fed thru a band pass
filter into a NE602 Mixer chip.  This in turn feeds a crystal ladder type
filter using 4 selected 9MHz crystals.  The IF uses a MC1350 IF chip,
and the product detector is another NE602 Mixer chip.  The BFO uses
a 9MHz crystal controlled oscillator.  The detector is then selectably passed
thru a 2-stage narrow band audio filter, or directly into a constant gain
LM386 which also doubles as an audio derived AGC circuit.  Volume control
is done by a 1K pot from the LM386 output to gnd with the 8 ohm phones
connected between the wiper and ground.  This method of volume control works
terribly!

	The transmitter is also very simple. It is done by mixing the VFO
with a 9MHz xtal oscillator using a MC1496, and feeding a selected 2n2222A
that drives a 2SC1909 final transistor.  This arrangement gives about
3 watts of output when powered by 13.6 volts.  The transmitter sidetone
is generated by a multivibrator, and is rather harsh and is adjustible by
an internal trimmer, and the volume control.  It is hard to reach a compromise
in these settings, as a sidetone that is ok for loud signals is too loud
for weak signals.  The transmit relay is controlled by a retriggerable oneshot
circuit and responds quickly to the first key closure, and has a fixed hang
time of about 1/2 second.  This provides a semi-full QSK type of operation.

	The VFO uses a toroid as its main tuned circuit, and the lower end
frequency of the VFO is set by compressing the turns of this coil.  This
is very difficult, and it was impossible for me to make the dial markings
match up with reality.  The VFO drifts intolerably for the first 30 minutes of
operation, then settles down to an acceptable amount of drift.

	The lab tests that I did on the unit were somewhat problematic.  The
receiver easily met its .25uv MDS (with audio filter in), and its selectivity
was about 1KHz without the audio filter, and about 200Hz with the audio
filter.  When running without the filter, the signal was generally rather deep
into the receiver's internally generated hiss.  With the filter, tuning was
fast, but the hiss was virtually nonexistant.  I only run with the filter on.
The transmitter was where I had some difficulties.

	In testing the transmitter, I found two fairly strong spurs, one was
about 1MHz above the carrier, the other was about 1MHz below.  These spurs were
at -35dBc, and weren't affected by alignment.  The third harmonic was at -40dbc
The FCC requires ham transmitters in this power level to have all spurious
emissions less than -35dbc I am not confident enough about the accuracy of my
spectrum analyzer to swear that this transmitter meets these specs. (this is
because my Ailtec 707 is rated at +/- 1db)

	Operation is fairly comfortable.  If the signal is very loud in the
receiver, the other side might be just able to hear you.  The volume control
is the worst feature.  The difference between acceptable loudness, and ear
shattering loud is about 1 degree of rotation!  The AGC works pretty well, but
the threshold should probably be set lower then specified (you can set it
with a trimmer) If you are planning on running this thing on batteries, pay
close attention to its need for a long warmup.  If you are going to use it in
your home, just leave it on all the time.  I guess you will have to make your
own decision as to whether this beast is legal to transmit with.  I decided it
was ok for me, because its spurs are really in the flea power range
(~10E-3 watts) and probably won't travel too far (gee, wasn't that the point
of playing with QRP?).


73,

Chuck Harris - WA3UQV
chuck@eng.umd.edu