Covers 50 KHz - 30 MHz. Receives strong, clear signals from all over the world. L MHz. Mechanical zero. SO unnectors. They feature mounting holes and automatic grounding of unused terminals. One year unconditional guarantee. SO connectors. Insertion loss below. Center ground. N connectors. SWR less than 1. Full legal power L MHz. Mounting tabs. Animate weather maps. Display 10 global pictures simultaneously. Zoom any part of picture or map. Manager lists over FAX stations.
Automatic picture capture and save. For all electronic CW keyers.
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Iambic keying, speed wpm , weight, tone, volume controls. Huge 5A8 inch LCD digits are easy-to -see. Brushed aluminum frame. Daylight saving time feature. Earphone jack for private practice, tone and volume controls for a wide range of sound. Adjustable key. Can be hooked to transmitter.
Write orcaU The com- parator can be either a scope, which is used to observe the Lissajous patterns showing the drift of the local standard, or a digital comparator, which shows Ihe drift rate on a meter or chart recorder. The second part of this article will show the details of a digital comparator.
The Antenna System This is an active antenna using cascaded followers for a high input impedance and a low output impedance. The unit should be at least 25 feet away from the receiver and is connected to the main unit with coaxial ca- ble.
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Any common coax can be used since impedance matching is not a critical issue here. Power is supplied from 12 volts via a scries ohm resistor in the receiver and the signal is superimposed on this same con- ductor. The board should be mounted in a waterproof housing if it is to be mounted outdoors. See Photos A and B. Two types of antenna can be used, a wire or a ferrile rod. For the wire version, a 3- to foot an- tenna is connected to J2; the length depends on the signal strength at your location. To adjust, connect the circuit as shown in Figure 3A and adjust L3 for maxi- mum signal at GO kHz, A wire antenna can gather a lot of signal but may also pick up a lot of noise.
Also, a longwire antenna may pick up enough HF energy from a nearby ham transmitter to damage the preamp. Therefore, I recom- mend pulling in ihe extra effort to build the rod antenna. R You will also need about 50 feet of 28 gauge enameled wire, also available from Ami- don. Se- cure the ends of the windings with tape. The rod antenna is adjusted by first pow- ering up the board as shown in Figure 3 A and checking for regeneration. Rotate R3 throughout its range.
If it does not oscillate, swap the two tickler lead connections on the board. Then connect the generator to points A and B and tune to resonance by adjusting the number of turns of LI and choosing the correct value of C2, making it resonate at 60 kHz with CI at mid-capacity. After tuning, cover the entire winding with electrical tape. Final tuning should be done with CI after the rod is installed in its PVC housing and its attachment to the preamp enclosure.
I successfully used an 8-inch rod that was used as an AM antenna on an old stereo receiver. On this rod I wound 6 inches of wire 0. No spaces sold at gate. A maximum of 3 spaces per person non-transferable. Please send a separate check for Flea Market space s and admission ticket s. Spaces will be allocated by the Hamvention committee from alf orders received by February 1.
Please use 1st class mail only. Notification of Flea Market space assignment will be mailed by March 15, 1 Checks will not be deposited until after the selection process is complete. Trotwood, OH Free bus service Free bus service will be provided between Hamvention and our satellite parking areas, In addition, some motels may offer transportation to Hamvention.
J Send admission tickets regardless of flea market space assignment. Because the entire receiver operates on a single fre- quency, it must be well-shielded and is therefore built in two separate minibox mod- ules to prevent self-oscillation. RF connec- tions between modules are via coaxial con- nectors and cables and other connections are provided by barrier-strip screw connections.
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The receiver design is the result of many months of trying many different circuits and the discreet component version shown here proved to be the most stable and reliable of many that were tried. The jacks and barrier strips are mounted on the ends and tops of the boxes.
The covers may then be mounted to a rack panel or lo a cabinet base, as desired, In my final unit, I also included a multi -position switch so 1 can monitor other functions with the 50 p A meter Figure 4 shows the RF amplifier portion Ant. Ii consists of three siages of tuned amplifiers with cmiuer followers The followers and low collector current in the tuned stages help preserve the high Q of the coils to maintain selectivity. AGC is applied lo two stages.
This voltage is applied to diodes Dl and D2. The higher the current thai passes through these diodes, the more the signal voltage is shunted lo ground. During normal operation the output of this section of the re- ceiver is about a 1 volt P-P sine wave. Figure 5 shows the remaining amplifier stages and the AGC detector.
The high- er AGC voliage is reduced in this way, rather than with a voliage divider, to main- tain a greater dynamic range. The slow-re- sponding circuit sels the AGC level relative to ihe average sienal level, rather than a I- lowing it to follow the 10 dB carrier reduc- tion that occurs each second.
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The slow AGC voltage is available at board point J while the fast AGC voltage is at point H, These two voltaees can be used to drive a detector to decode the lime-of-day pulse information. Stages Q3 through Q5 amplify the main received signal and provide a 5 voli TTL compatible output, This signal is used to drive the 60 kHz input of the comparator unit or to connect to the scope. Connect the test equip- ment to the RF amplifier module alone using the scheme shown in Figure 3B. This is equivalent to a 30 microvolt signal at the ac- tual receiver input.
Observe the output sig- nal at J2 with the scope. Carefully adjust the three coils for maximum signal using a non- metallic tool The level should end up being about 1 volt P-P.
Temporarily ground the AGC line "F. If all is well, changing the generator output from mV up to LS volts a change of 20 dB should show no more than about a 6 dB change al TPL With the 50 tiA S- meter con- nected, it should read around mid-scale with the mV input and around 45 uA with the L5 volt input. The receiver will operate with an actual input level of only 3 microvolts with RI5 and R22 at maximum level counterclock- wise rotation 1 With nothing connected to the receiver input, there will be a 5 volt square wave at output J2.
This will be close to 60 kHz and is not an oscillation but just the amplification of internal noise, Any use- ful signal will override ihis so it is noi of concern, Finally, disconnect the generator and turn it off or change its frequency so the receiver won't pick it up. Connect the cable from the antenna unit and observe the TPl signal. You should see the 60 kHz signal, around 6 volts P-P or so, dropping in level every second. The signal should be a fairly clean sine wave.
The AGC will then compensate for lower signal levels at other times of day. Maximum signal should peak no higher than 45 u A on the S-meter.
During use, if' the meter shows erratic fluctuations other than the normal 1 pps time code drops, it indicates atmospheric distur- bances that may affect the signals useful- ness. If the meter is steady, the unit may be oscil- lating because the antenna is too close to the receiver. Phase Comparisons The simple form of phase comparison be- tween WWVB and your local standard is done with the setup shown in Figure 1, using a scope. The receiver output is fed to the vertical scope input and the local standard is fed to the horizontal input. The 60 kHz sig- nal and your local standard arc compared by observing the rotation of the Lissajous pattern.
Alternatively, connect the local sig- nal to ihc external sync input to synchronize the scope's horizontal oscillator.