W5SQW
puts
a Heath HW1O1 and a Drake 2B
together
in an interesting combination. Several helpful mods to the HW1O1 are also offered to help make this a very
neat station.
Using
The Drake 2B
Receiver With The Heath
HWIOI
BY CHARLES
R. COX, W5SQW,
For several years now my rig has consisted of an
obsolete exciter with no ALC circuits, a Drake 2B receiver which I swear by and
never at, an SB220 Heath Linear, and a first class antenna tuner. I decided to
upgrade my station by replacing the exciter with a newer one having a first
class ALC circuit to work with the linear.
An investigation showed that most of
the transceivers on the market are smaller than my old exciter so why not use a
transceiver as an exciter? What would be the advantages? I certainly would like
to be able to transceive during contests. I am net
control for a Novice Technician Training Net and off frequency check-ins with
beginners is common. A transceiver with a simultaneous receiver would sure be
nice in this situation. When operating DX on 40 meter phone using my Phased
Verticals (CQ April 1972 page 30) I could monitor my frequency while
tuning the 7.100- 7.000 MHz band for DX phone stations. Armed Forces Day would
be a snap with simultaneous receivers. When a
We dug out the Drake 2B instruction
book and found that for the amateur bands, the 2B has crystal oscillators
running on 11 MHz, 40 meters; 18 MHz, 20 meters; 24.5 MHz, ten meter CW; 25
MHz, 15 meters; and 25.6 MHz, ten meters.
This is important because care must be
taken when running two simultaneous receivers so that the oscillators of one do
not fall in the IF bands of the other or so that one’s oscillators are not the
same as the others. Also harmonics of one should not fall in
the IF of the other if care is not taken here one receiver will
desensitize the other or a birdie will always be present in one or the other
receiver.
The VFO of the Drake 28 runs between
3.955 and 4.555 MHz. The first IF of the 2B is 3.5 to 4.1 MHz tunable and the
second IF is at 455 kHz. Another oscillator runs at 405 kHz and the third IF is
then 50 kHz.
Because I already
have the Heath SB220 and because of economics, I decided to check the Heath
HW1O1 specifications. The overall specs looked like a suitable rig. The
carrier oscillator runs on 3.395 MHz. The VFO runs between 5.0 and 5.5 MHz.
The Heterodyne oscillator frequencies
for the HW1O1 are 12.395 MHz for 80 meters, 15.895 for 40 meters, 22.895 MHz
for 20 meters, 29.895 MHz for 21.3 MHz, 36.895 MHz for ten meter CW, 37.395,
37.895, 38.395 MHz for the other ten meter ranges. The first IF pass band is
8.395 to 8.895 MHz and the second IF frequency is 3.395 MHz. It is obvious then
that no interaction should take place between a Drake 2B and a Heath HW1O1, and
so I got one.
Initial alignment was attempted and
drive was a little low on ten meters and on forty meters. I called a Novice
friend and he said he had the same problem plus he was replacing the crystal in
the 100 kHz calibrator oscillator for the second time.
The neutralization per the manual was
easy (as it is done on 80 meters) but proved very difficult thru ten meters
using Handbook methods. Preliminary TVI check showed bad TVI on Channel 2, but TVI on Channel 39
was utterly ridiculous.
The next
step was to read the Heath Manual (when all else fails
read the manual) including circuit descriptions. The Heath Manual
warns, Do not run the crystal calibrator in the transmit position as this can
cause transmitter outputs removed 100 kHz from the fundamental frequency. I
decided to take a hard look at the HW1O1 drive circuit and the HW101 crystal
calibrator circuit. A check showed them to be tied together with no isolation
in the transmit mode. The crystal in the calibrator is not protected or isolated from the driver RF power in
the transmit mode. Also the 8.5 MHz trap circuit, which is to protect the
receiver IF from an 8.5 mHz commercial signal, is
connected across the drive circuit in the transmit position, and due to its low
“Q” takes drive power at 7 MHz and in conjunction with stray capacitance from
the calibrator, takes power at some high frequencies. The diode in the
calibrator circuit causes TVI as any diode in an RF circuit produces harmonics.
By now you may have lost faith in
Heath but remembers the basic HW101 design is very good. The Heath ALC circuit
is very good; the SB220 never had any problems so the solutions proved very
simple.
The HW1O1 transmit receive relay has
two S.P.D.T. contacts which are not used (This is “RL1” located in
24 • Co • March, 1980
final RF section). It was decided to use these contacts to
(1) Isolate the crystal calibrator (in the transmit mode) from the drive
circuit. (2) Isolate the IF trap from the drive circuit in the transmit mode.
(3) Furnish an antenna input to the Drake 2B in the receive mode, also “RL1”
should mute the Drake 2B in the transmit mode, and grounding the Drake 2B
antenna input in the transmit position should protect its preselector
from high power burn out in transmit mode.
The relay was rewired as follows using
the extra coaxial cable supplied with the kit. All contacts are shown in the
shelf, deenergized, receive position. See fig. 1.
A radiation leak test of the HW101
showed it to leak slightly at the front and very severely at the rear. The top
and bottom of the HW1O1 are not fastened to the front in any way. There are six
screws thru the top shield at the rear but they go into nylon inserts making
nice little capacitors with no ground connection. The entire top and bottom
“shield” covers are only connected to the chassis thru the four feet. I called
Heath about this and they suggested I make an RF gasket out of coaxial cable
shield braid and they supplied me with metal inserts to replace the nylon.
Sanding away the paint and installing the RF gaskets stopped the leaks. The
technician told me that they were experimenting with various values of R202,
10k at the grid of the transmitter mixer but that some values as low as 100
ohms may cause the ALC circuit to be unable to limit on voice peaks. I found
that lower values of R202 drastically increase the drive especially on 10
meters making maximum output easy to obtain across the entire band. I am using
a 5000 ohm resistor for R202 now.
I wondered what would happen if both
receivers feed the same speaker. (If you try this be prepared to replace an
audio transformer as reverse power from one receiver will burn the primary out
of the other’s audio transformer.) The experiment was set up for CW reception
of a 40 meter signal. The HW1O1 receives CW in upper sideband mode; the Drake
2B, which has a tunable pass band and selectable sideband, was set up to
receive in lower sideband mode. The same station was tuned to the same pitch by
both receivers one in LSB, one in USB. Since each receiver delivers 1/2 the
power, the audio of both is turned down, the interference drops way down since
all interference is at only half power, but the wanted signal is at full power.
(Power functions follow the square law.)
Now one receiver is tuned so that a
slight tone difference exists in the wanted signal.
Mixing takes place at the speaker, the fundamental tones are present, also sum
and difference frequencies as well as secondary sum and difference frequencies,
and the results are startling. It sounds like MCW. Those of you who have heard
MCW know what I am discussing. It would be possible to add audio filters and
have single signal selectivity on CWI am now using two speakers to do the mixing
mechanically and to avoid reverse power audio burn out. It would be possible to
have this type detection in a single receiver by having heterodyne oscillators
to bring the other sideband pass to the audio stage.
The HW1O1 must be completely realigned after making these changes. The
neutralization changes because the 6146 grid circuit no longer runs all over
the transceiver, to the calibrator etc. The calibrator can be run in the
transmit mode since it is isolated in the transmit mode. The 40 meter drive improves
since the 8.5 MHz trap is no longer in the circuit on transmit.
After realignment is completed another TVI check is made. Channel 2 TVI is far
down but Channel 39 is bad. Time to examine shielding and
physical construction. The drive preselector
shaft runs the HW1O1. It sticks into the RF final shield cage in an insulated
bushing, drives the preselector capacitor thru rubber
pulleys and is not grounded. Its length is nearly resonant on Channel 39.
Soldering a shielded braid from a coax cable from this shaft to ground
completely eliminates UHF TVI and helps TVI in general.
The Drake 2B was connected at this
point and it was determined that neither receiver being on the line caused any
problems with the other receiver; the crystal calibrator of either can be heard
the same strength in the other. Both can be calibrated directly against WWV at
15 MHz by turning the Drake 2B band selector to 40 meters, preselector
to ten, and log dial to zero.
The Drake 2B works well with the HW1O1
and no desensitivity was noticed in either receiver
when the other was connected. There is not interaction between receivers even
though both are connected to the same antenna input. At this point I added a
Drake low pass filter at the exciter output, another Drake low pass filter at
the linear output and a good ground to antenna tuner, exciter, and linear.
Running 2000 watts PEP on 29.725 MHz with a portable TV tuned to Channel 2 sitting on top of the antenna tuner produces no TVI in
either audio or pictures. The portable has a pull up whip antenna with a Drake
300-HP-R high pass filter and a Radio Shack line filter where it is plugged
into the same outlet as the exciter. The picture does not dip and there is no
effect on any channel.
Anti-trip and Mute proved no problem
at all. “Spot” is easy by turning the mike CW level down and keying in CW or
pushing the mike switch in SSB. A check showed this does not cause a
“swish” on the air.
All in all it’s been a good
combination and fun to use. The experience provided an opportunity to tinker,
experiment and learn…one of the mainstays of amateur radio.
