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
BY CHARLES R. COX, W5SQW, 11002 Montverde Lane, Houston, Texas 77099
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 Houston group decided to put a repeater on ten meters I was sold on the idea. What transceiver should I select?
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.