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Vintage Radio The Sailor 66T Navigation Radio This radio was very popular in the 1960s, 1970s and 1980s. Primarily, it was deployed for radio navigation in the North Sea between Norway and Scotland, as well as being used in the North Atlantic prior to modern GPS navigation systems. It was made by Danish company SP Radio Aalborg. By Dr Hugo Holden T his article is more about the radio itself than its radio direction finding (RDF) applications. However, numerous radio navigation and radio direction finding systems existed in the past that no longer do because satellite navigation (eg, GPS) has taken over. The RDF system briefly discussed here was called Consol. The navigator takes a direction reading by rotating their radio’s direction finding (DF) antenna to receive and null signals emanating from a specific fixed radio beacon on land. By taking bearings from only two known radio beacons, then plotting those on a chart, the navigator can determine the vessel’s position. The DF antenna typically consisted of a ferrite rod and tuned coil that could be rotated manually. Loops can 88 Silicon Chip also be used. When the long axis of the ferrite rod is aligned with the axis of the beam from the beacon, there is a signal null. This is called a ‘relative bearing’. However, the rod could be pointed either towards or away from the beacon due to its figure-8 sensitivity pattern. To get around this 180° ambiguity and make a ‘relative determination’, there is a “Sense Switch” on the radio’s front panel. When deployed, the switch combines some of the received signal from the main antenna, which is omni-directional. This creates a cardioid sensitivity pattern. Therefore, when the ferrite rod is rotated 90° to a signal maximum, the combined result is more sensitive in one direction than the other. The navigator can combine the information with compass readings too. Australia's electronics magazine For North Sea navigation, one radio navigation beacon was on 266kHz in Bushmills on the north coast of Northern Ireland, and another on 319kHz at Stavanger, on the coast of Norway – see Fig.1. They had a typical transmission range in the order of 1000 nautical miles (about 1850km). The beacons transmitted their carrier waves as dots in one sector (sector A) and dashes in another (sector B) during the direction-finding transmission period. The transmission period for direction finding is 60s with a one-second pause, then the station call sign is transmitted for six seconds. Most of the remainder is a long dash (heard as a long tone due to the radio’s BFO) for 50 seconds, followed by a three-­ second pause. The DF information repeats again, siliconchip.com.au Photo 1: the connection panel for the radio is utilitarian, but it provides everything you need. Photo 2: when the optional speaker box is mounted, the connection panel is inside it. Photo 3: the loudspeaker is a quality unit. so the entire cycle takes 120 seconds. The speed of the rotation is one sector width per 120 seconds. For example, if you were in the position marked × in Fig.1, you would hear 48 dots of the remaining A sector and 12 dashes from the B sector from the Stavanger Beacon in Norway as the beam passes by your location. On the other hand, you would hear 28 dashes and then 32 dots when the beam from the Bushmills beacon passes. Aside from the internal battery pack, three more DC power options can be selected using an internal rotary switch for 12V, 24V or 32V operation – see Photo 4 overleaf. The radio sports a nice audio amplifier with two good-sized Philips transformers, each with a 10 × 10mm cross-sectional core area, visible below the switch. Just beside the upper (output) transformer on each side are the two AC128 output transistors mounted to heat-conducting fins. The audio output is rated at 1.8W. Also in Photo 4, at the bottom, is a large power stud-type 9.1V zener diode (BZZ19) mounted on a 4mm-thick, 6 × 8cm black-painted aluminium heatsink. This is because the voltage regulator design for the external power Features of the 66T receiver Apart from its RDF capabilities, it is a highly sensitive and capable superheterodyne radio receiver. It can be powered from an internal battery pack of six D cells in a battery box on the right side of the radio housing. When the attached speaker box option is not used, the radio’s power input panel, shown in Photo 1, is simply screwed onto the left-hand side of the radio. However, when the accessory speaker box is used, this panel sits on standoffs that attach the speaker housing to the radio’s housing and is attached with thumb nuts, as shown in Photo 2. To remove these, the speaker and the front panel retaining it must be removed. The speaker box has a hole in its rear to allow the main antenna connection to pass through. The speaker is a high-quality four-inch (102mm) unit – see Photo 3. Interestingly, it is mounted on a timber baffle, which likely improves the damping in the cabinet a little. siliconchip.com.au × Fig.1: the locations of the two main radio beacons for the North Sea area. The radial sectors provided a way to determine the ship’s location based on the signals received from both stations. Australia's electronics magazine June 2026  89 Photo 4: from top to bottom, you can see the power selector switches, output transformer flanked by the output transistors, phase splitter transformer and power regulator zener diode. Photo 5: the dial is large and clear. Note the index mark and calibration marks. option for this radio is a shunt regulator design. The excess input voltage is dropped across a substantial ceramic wire-wound power resistor. While that might seem inefficient to some, the beauty of it is that it makes the power supply and radio highly resistant to electrical abuse such as high voltage transients on the DC supply, because the zener diode snubs them off. It also prevents accidental reverse polarity accidents because it conducts in the forward direction in that case. More complex series pass voltage regulator circuits are more easily damaged, often requiring TVS protection devices or other protective parts. The radio can operate on four bands: • Long-wave (LW): 150-285kHz • Navigation band (NW): 255425kHz using the DF antenna input • Medium-wave (MW): 5251600kHz • Short-wave (SW): 1.6-4.2MHz The 66T has a very attractive glass dial with a well-calibrated scale for each band (see Photo 5). The dial contains some additional markings that are very helpful in performing an alignment (calibration) of the radio. While the calibration frequencies were mentioned in the manual, I could not find any mention of the critical index mark in the text. Having said that, I did not have a fully translated manual. The index mark controls the mechanical relationship of the dial pointer to the three-gang variable capacitor. That relationship in my radio was badly off, making calibration 90 Silicon Chip and tracking impossible until it was corrected. Photo 6 shows the general architecture of the radio. The rear section of the 3-gang variable capacitor is the one that tunes the set’s local oscillator and its associated inductances for each band. The middle section tunes the inductances associated with the RF stage, and the front section tunes the inductances associated with the antenna circuit. Notice the bends in the outer adjustment wings of the rear (oscillator) section of the variable capacitor; these are discussed later. Another notable feature of this radio is the 470kHz intermediate frequency (IF) amplifier board. This uses double-­ tuned IF transformers. On some versions of this IF board, the first IF transformer had an additional small coil added to its primary. It was a signal injection point labelled H. This was so that a low output resistance sweep generator could easily be connected without damping the tuning on the first IF coil. However, in later versions, such as my radio, that coil was dispensed with, and instead, two test points, corresponding to “Test point H”, were provided across the first IF transformer primary. This is a very high-­ impedance zone. I had to make a special adaptor to drive it, as will be discussed briefly in the alignment section. There was a note in the manual: “Never touch the intermediate frequency alignment unless proper Australia's electronics magazine measuring equipment is available” (by this they mean a sweep generator and scope). In this radio, if the IF tuning slugs are simply peaked at 470kHz, the overall bandwidth is far too low and the recovered audio modulation is therefore very muffled and lacking in high-frequency components. General specifications The radio weighs in at 8kg. The sensitivity of this radio is very good on the SW band, giving 50mW output for only 3μV RF input, specified with 30% audio modulation. The IF bandwidth is specified as 6.5kHz. This can only come about with correct tuning of the double-tuned IF transformers, as will be outlined in the alignment section. The image suppression was specified as an excellent 50dB or better at 2.2MHz. The audio frequency response is stated as 100-3000Hz (without the filter switched in). I found this a little restrictive. I reduced the value of a filter capacitor to widen the frequency response in the audio section, which made music listening better. In keeping with many transistor radios like this, the current consumption is amazingly low at around 40-150mA depending on the volume setting. The six D cells in the battery carrier have a very long life. On external power, due to the nature of the shunt zener voltage regulator, the current consumption is 400mA. The radio’s signal-to-noise ratio was specified in the manual. To measure siliconchip.com.au this requires an output signal from a low-impedance source (25W) and the use of a dummy antenna. This will be described in a later section. The radio also contains five quartz crystals for fixed-frequency reception. In my radio, the crystals fitted were for 2182kHz, 1792kHz, 1834kHz, 1841kHz and 1848kHz. The crystals are housed in a row on the lower rear chassis (see Photo 7). Circuit details and factory modifications There were a number of revisions of the circuit by the manufacturer. The first 66T set was series A, then going all the way to series K with small changes. After series A, most of the schematics are very similar except that after series A, an extra switch gang was added to switch the two local oscillator signals (crystal versus the four tuned bands) as separate signals into the mixer circuit. After series B, the RF amplifier was modified. It turned out that either electrostatic discharges (lightning) or RF output power from the ship’s transmitter via the antenna could fry the BF115 RF amplifier transistor. The general approach to this sort of problem is to use diodes to protect the transistor. Interestingly, in some of their earlier versions, they had a diode in series with the base of the RF amplifier transistor, likely to augment the AGC rather than to protect the transistor. Although a large positive signal impulse would tend to reverse-bias the diode, the diode’s reverse breakdown voltage is not enough to protect the transistor from very high voltages. No such diode was used in series B. Then they added a diode across the base-emitter junction of the BF115, as explained in the manual (translated from the original Norwegian): “Since we have received complaints that the RF transistor in some receivers burns out due to static electricity on the antenna or RF voltage from the transmitter, we have introduced protection for the transistor in future production runs. The protection consists of a silicon diode mounted across the base-emitter junction of the RF transistor.” The RF sections of the series C circuit are shown in Fig.2. This one corresponds to my radio. I have highlighted important sections with boxes. siliconchip.com.au Photo 6: the chassis layout is neat. You can clearly see the three-gang variable capacitor on the left; I bent some of the plates on the lower gang to improve the tracking. Photo 7: the five plug-in crystals for fixed-frequency tuning. They have matching coils and capacitors. Photo 8: the capacitors that match the crystals shown in Photo 7. Potentiometer R2 is the “Sense– Balance” preset, which is accessible through a hole in the front panel, just beside the Sense Switch. In my radio, a green LED power light had been placed in that hole. Its appearance and that of the wiring to it suggest it was done by the manufacturer, but it was only operational on external power. Australia's electronics magazine June 2026  91 RF amplifier Diode mixer RF ▲ Sense preset potentiometer (R2) ▲ OSC Channel selector switch* 92 Silicon Chip Crystal oscillator Oscillator for SW, MW, NW & LW bands Band selector switch* I switched the LED over so that it runs whenever the radio is powered from any source. It is good to have, because when the radio is powered by batteries, it is all too easy to leave it accidentally switched on. As noted previously, the Sense system creates a mix between the signal received by the DF antenna and the main antenna to create an asymmetry in the reception sensitivity so it can be used for unambiguous direction-­ finding. The Test H inputs are used to couple in the sweep signal for aligning the IF amplifier. This arrangement is not as ideal as the earlier version with the small coupling coil. Fig.2 shows the whole circuit for the 66T. The left-hand of the circuit shows the coil sets and the top end tuning capacitor for the SW- band. The other coil sets and tuning capacitors for the other bands (three for each band: the antenna coil, RF coil and oscillator coil) are connected to the empty positions on the rotary switches. For the fixed crystal reception frequencies, there are five crystals with an antenna coil and RF coil associated with each crystal channel. In this case, fixed polystyrene tuning capacitors are used for the antenna and RF 470kHz double-tuned IF amplifier and AM detector stages. The arrangement here accounts for 10 coils in total and 10 fixed tuning capacitors associated with them. These capacitors, two for each of the crystal channels, are mounted vertically on the side of the chassis, as shown in Photo 8. BF115 silicon transistors are used in both of the oscillators and the RF amplifier. AF127 germanium transistors are used for the IF amplifier. The specifications of both parts are excellent. The BF115 is a spectacularly good silicon planar epitaxial transistor. Its transition frequency is in the order of 230MHz, and it has a low noise figure of 1.2dB at 1MHz. The AF127 belongs to a family of parts that replaced the AF11x series of transistors, which are now prone to failure from tin whiskers. Fortunately, the AF12x series of parts does not suffer from these problems. The AF127 is a diffused-alloy transistor, with a transition frequency of 75MHz. It is a very capable part for RF and radio work, with a low noise figure of 1.5dB. One of its very useful features in IF amplifier applications is that it has a very low feedback capacitance, only in the order of 1.5pF. This means it can work as a stable IF amplifier Australia's electronics magazine without requiring neutralisation. On the other hand, older-generation germanium RF parts, such as the OC45, had feedback capacitances in the order of 10pF and always required neutralisation feedback components added to be stable in an IF amplifier application. One would therefore expect the performance (especially noise and sensitivity figures) of a radio such as the 66T to be very good on account of the very capable RF, IF and oscillator transistors. Certainly, the sensitivity figure specified for the SW band being less than 3μV input for 50mW output is very good. The signal-to-noise (S/N) ratio is specified at 10dB below 1MHz with a 10μV signal and a dummy antenna. The AGC system is shown on the right of Fig.2. It feeds a separate line to the RF amplifier and the first IF amplifier. A separate preset is used to adjust the AGC for the RF amplifier. The front-panel RF gain control affects both the AGC to the IF and the RF amplifier. The specified performance is that an increase in RF input voltage from 31μV to 100mV will increase the output by less than 10dB. The radio’s metal chassis is independent of the actual positive and negative siliconchip.com.au AGC amplifier and signal meter driver Audio preamp and audio output see text ★ ★ Front panel RF PCB preset gain (R46) (R49) ◀ ★ ◀ nfb AGC RF Signal meter BFO Shunt zener regulator (D7) Dial lamp * Crystal array, select switches and 10 associated coils and five crystal – two coils (L15 & L16) and one crystal E shown * three-gang 500pF variable capacitor, nine coils and nine top-end tuning capacitors: coils L1-L3 and capacitors C1-C3 shown – SW band supply power system, only bypassed to those with capacitances. So the radio could be mounted in a vessel that had either a positive or negative ground power supply system. In my radio, I made some modifications to three capacitor values in the audio system, shown with purple stars in Fig.2. One problem I encountered was a noisy volume control, which persisted even after substituting in a new control and renewing the coupling capacitors. I changed both the capacitors around the volume control to low-­ leakage 1μF axial tantalum capacitors. I could have used film capacitors, but I had no axial types of that value that fit the PCB well. Reducing the 10μF capacitor, leading away from the control, to 1μF substantially reduced low-frequency noise with control rotation. It did not degrade the audio low-frequency response. In this circuit, the resistances are such that the frequency response, even with a 1μF capacitor (rather than the 10μF value), does not reach -3dB until it is below about 20Hz. The 22nF capacitor in the base circuit of T9 resulted in fairly heavy audio high-frequency roll-off, muffling siliconchip.com.au Input power conditioning Fig.2: the radio’s circuit. It uses a 470kHz IF and has five sets of crystals/coils/capacitors for quick fixed-frequency tuning. The audio stages, AGC system, BFO and power supply regulator sections of the 66T radio are shown on the right-hand side of the circuit. the sound somewhat. That may well have been OK for voices but not so much for music. For a better tone balance, I reduced that value to 1.5nF. I could not find anything else that required changing. In terms of faulty parts, the only capacitor that I had to replace was C100, a 400μF electrolytic that I replaced with two parallel axial 220μF parts. The original had gone high in ESR, resulting in a motorboating effect with low-frequency oscillations in the audio. The audio amplifier in the radio is quite capable and gives a good sound with the speaker in the speaker box. The amplifier has negative feedback to reduce distortion, and audio transformers with good-sized iron cores. Conveniently, SP Radio provided the results of injecting signal voltages at different test points in the radio, under the condition that 50mW is being produced with a 30% modulation at 400Hz. This is helpful in verifying that the radio is working to specifications. Dial miscalibration When I checked the radio initially, I found that none of the received station frequencies were close to their Australia's electronics magazine Photos 9 & 10: after resleeving the knobs, they are close to the original but not identical. I made the sleeves by boring out a plastic donor knob. June 2026  93 Scope 1: if all the IF adjustments are tuned for 470kHz, the result is a response that’s too narrow and peaked. Scope 2: how the IF response should look like with correct alignment, with each element tuned to a slightly different centre frequency. Mechanical repairs One curio is that this model of radio has a peculiar failure rate of the black phenolic sleeves that were placed over the chromed knobs. They have a habit of splitting, falling off and getting lost. They were all missing on this radio, except one. This required some donor phenolic knobs. I machined them out with an internal taper to create a sleeve or shell so they would slip over the original chrome metal knobs to act as a reasonable replacement. As can be seen in Photos 9 & 10, these have finer finger-grip grooves than the original sleeve, but they were as close as I could find. Another mechanical problem that cropped up related to the signal meter; it was sticking. Investigation revealed that some rust crystals had projected out of the side wall of the laminated iron pole pieces and were catching on the meter’s coil form. I removed these by slipping in strips of sticky tape to extract them. Some people have attempted to blow debris out of meter movements with compressed air. This is better avoided, as it normally destroys the hairsprings and movement. Photo 11: I use this RF signal generator and this frequency counter for aligning radios. 94 Silicon Chip dial markings. Sailor went to the trouble of making a very precise-looking dial, suggesting the unit should have good calibration. This is unlike some domestic radios with poor dial markings, without graduations between them, and somewhat loosely spaced dial legends. On the SW band, it was not possible to receive the frequencies at all above about 3.6MHz. The radio was significantly out of alignment. One of the true arts of radio restoration is in the radio’s alignment. It might not be so important in some radios, such as pocket transistor radios, with single tuned IF transformers and limited dial markings. Still, in commercial types such as communications receivers, calibration is very important. It is often clear from inspecting a radio’s tuning dial whether the manufacturer thought of it as more of a domestic product, or more of a scientific instrument, where the dial information was expected to be reasonably accurate and meaningful. Australia's electronics magazine Alignment tools I have several useful tools to help siliconchip.com.au with radio alignment. One is the Philips PM5326 RF Generator, which includes an accurate frequency counter. It puts out exactly 50mV RMS into a 75W load on 0dB attenuation. It has an excellent shielded RF attenuator that goes beyond -80dB. A -80dB output corresponds to 5μV RMS into a 75W load. In most radios, the local oscillator (LO) runs at the intermediate frequency above the received station frequency. To examine the LO, I have a frequency counter with a programmable offset value, in this case set to subtract 470kHz, the set’s IF. As Photo 11 shows, with no signal input applied to the counter, its display reads 99.5300MHz. It has an input sensitivity in the range of 10mV to 40mV and its maximum counting frequency is about 48MHz. The input impedance is too low (in common with many counters) and its input capacitance is too high to directly connect to a radio’s oscillator circuitry without loading it and causing a large frequency shift. To solve that, I designed a buffer circuit that is described in Circuit Notebook on page 79. IF alignment It is the gain and bandwidth of the IF stages in a superhet radio that confer much of the radio’s selectivity and sensitivity. There is less selectivity in the RF and antenna circuits, as these need wide enough bandwidth to accommodate tracking errors. One basic principle of superhet radio alignment is to make sure the IF stages are correctly set up with the correct centre frequency and bandwidth (if the latter is adjustable). With the IF amplifier in the 66T, if all the IF slugs are peaked to the same frequency, the bandpass response is far too narrow. The result is a muddy sound with a loss of treble. The sweep result shown in Scope 1 occurs when all the IF transformers are peaked at 470kHz. The resulting narrow bandwidth response has an asymmetrical skirt. The manufacturer specified a bandwidth of 6.5kHz, meaning that the response should be 3dB down at ±3.25kHz around the 470kHz centre frequency. This is easily achieved by adjusting the IF slugs while using a sweep generator, with the result shown in Scope 2. siliconchip.com.au Indexing Prior to any other alignment processes, as well as the IF being correctly adjusted, it is important that when the dial pointer is pointing to a specific legend at the low-frequency end of the dial, the variable capacitor is in the correct position. This is so that over the tuning range, capacitance varies over the correct range to suit the coil set. The question is, where is that position? It may not be explicitly stated, or for that matter even present on some dials. It was once a custom for a manufacturer to put an index mark on the dial. In most cases, the pointer should be aligned with this mark with the variable capacitor fully meshed, or close to that. I found no mention of this mark in the Sailor 66T manual, although one was evident on the dial. This setting for my radio was so far off that the variable capacitor had completely unmeshed by about 3.6MHz on the shortwave band! It was therefore impossible to tune in to any frequencies above that. The dummy antenna The Sailor 66T manual says to use an IEC dummy antenna to interface the RF generator with the radio. It says to use it with a generator with a 25W output resistance (eg, a 50W output with a 50W terminator applied to bring the output impedance down to 25W). This is to be used for the LW, NW and MW bands but not the SW band, where they suggested using the 25W signal source directly. A typical dummy antenna is meant to be driven by a low source resistance of 25W or less, but there is little practical difference in using a 37.5W source, ie, a terminated 75W source. Fig.3 shows the American IRE dummy antenna circuit. Its performance is shown graphically in Fig.4. Unfortunately, the IRE version of the dummy antenna does not suit the Sailor radio, especially on the LW band, Fig.3: a standard IRE dummy antenna circuit. It will work for the MW & SW bands but is no good on the LW range. 150-280kHz. The IRE circuit mainly suits radios with MW and SW bands. Unfortunately, the circuit for the recommended IEC (not IRE) dummy antenna is not readily available. If attempting to align this radio with the IRE dummy antenna, the LW antenna coil would not come into range on its tuning slug because, at 17kHz, the IRE dummy antenna does not apply enough load to the primary circuit of the antenna coil. Its load is in the order of nearly 5kW capacitive reactance at 170kHz, on account of the 220pF capacitor. As a result of this, and the mutual coupling, the tuned secondary resonant frequency of the LW antenna coil was too low. Even with the ferrite slug removed from the former, it still only came up to a maximum of around 160kHz. As a solution, I made an adaptor to emulate the capacitance of the realistic antenna system shown in Fig.5(a). This capacitance is present regardless of what band on the radio is being used, so it is suitable to adapt the generator to the radio for alignment purposes on all bands. Since the length of the wire antenna is relatively short compared to the Fig.4: an impedance chart for the IRE dummy antenna shown in Fig.3. Australia's electronics magazine June 2026  95 Obtaining The Best Possible Dial Calibration Textbook alignment Once the IF and dial alignments are correct, the oscillator coil’s tuning slug (or its adjustable padder capacitor, if there is one) is set to receive the tone modulated test frequency for maximum signal out of the IF’s detector or the audio amplifier stages. The dial pointer is then moved to an instructed position near the high end of the band, and the generator set to that frequency. The oscillator’s trimmer capacitor, which is in parallel with the oscillator’s variable capacitor gang, is moved to tune that in for a peak signal. These two steps are then repeated a few times because they interact. After that, the antenna and RF coil slugs can be peaked at the low end of the band at the same dial locations, and the trimmer capacitors associated with those coils are peaked at the recommended high-end frequency. With this common alignment method, the tracking of the oscillator’s frequency is exactly correct at the upper and lower points and at some intermediate point. These three frequencies are called ‘crossover frequencies’. Photos 12 & 13: the oscillator tuning gang in the radio as I received it (top). The oscillator tuning gang in the radio after I minimised the tracking errors (bottom). 96 Silicon Chip In the tracking zones around the crossover frequencies, the local oscillator runs a little faster or slower than ideal. These errors, shown in Fig.a, are called ‘tracking errors’. They are intrinsic to a superhet radio where the variable capacitor’s gangs have the same capacity and the oscillator gang has a required padder capacitor in series to reduce its overall capacitance. When the padder capacitor is the correct value, the magnitudes of the + and – tracking errors, at their worst, are about equal. If significant enough, they can result in a reduction in the sensitivity of the radio and/or a reduction in the image rejection in those zones. Tracking alignment There is an alternative method to adjust a radio to ensure that the dial markings match the received frequencies as closely as possible and that the tracking errors are minimised. No modulation is required on the carrier from the RF generator in this process. This method does not rely on the IF amplifier, and it can also be used to measure the magnitude of the tracking errors. However, the IF amplifier must be properly set up for a final result. Once the IF has been set up correctly with the sweep generator and marker generator, and the mechanical relationship of the variable capacitor angle and dial pointer are set, the oscillator transistor stage is disabled. I do this by shorting the base to the emitter with a 100W resistor in the case of a separate oscillator transistor. For designs with mixer/oscillator stages, shorting out the oscillator’s resonant coil also works. Then, for each band, the cores in the RF and antenna coils are peaked on the manufacturer’s recommended low frequency, and the capacitor trimmers at the upper band end in the usual way, but in this case by monitoring the output of the antenna/RF tuned circuit (if present) where it feeds into the mixer, or on the RF amplifier’s variable capacitor gang. You need a low-capacitance (<1pF) probe to monitor the RF output; I have Australia's electronics magazine designed one that is presented in Circuit Notebook this month, on page 79. This allows the tuned carrier to be seen on a scope with negligible detuning effects on the RF stage’s resonant circuit. In essence, this part of the radio is being treated as a TRF circuit. Once the upper and lower frequency points are set for the antenna & RF stages, the positions of all other dial markings with respect to the dial pointer (representing the variable capacitor’s angle) can be checked to see how closely the dial markings and pointer match the applied carrier frequencies. This is why an RF generator with a built-in frequency counter is very helpful. In the Sailor radio, it turned out that the antenna and tuned RF stages were closely correlated with the variable capacitor’s pointer and the dial markings. In this case, there is no requirement to adjust the wings on the variable capacitor gangs associated with those two radio frequency stages. The glass dial’s markings had clearly been created from a law defining the tuned frequencies when a straight-line wavelength (SLW) variable capacitor was used. Rather than calibrating the dial in wavelength, which would have more evenly spread the values, it was calibrated in frequency. This is very convenient because any adjustments to the oscillator’s fine tuning can be targeted to match the dial markings as closely as possible too. This way, both tracking errors and dial marking/pointer errors for tuned stations can be simultaneously minimised. In the case that the dial markings closely follow the oscillator’s tuning, the wings of the oscillator’s variable capacitor should never be altered from standard. Only the wings of the RF and antenna sections should be adjusted (with the oscillator disabled) if required, to better match the dial/ pointer relationship. Setting up the oscillator After re-enabling the oscillator, adjust it at the low and high recommended frequency points on the dial siliconchip.com.au with the tuning slug and trimmer capacitor, respectively. It pays to do it a few times because they interact. Then the points on the dial in the tracking error zones can be checked by disabling the oscillator and tuning the antenna and RF system for a peak, then re-enabling the oscillator. If required, the adjustment vanes on the oscillator gang of the variable capacitor can be altered to improve the tracking. Due to the fact that the capacitance of the variable capacitor gang can only be reduced by bending the wing outwards, to gain full control, all the vanes will have to be bent outward initially. After that, you can bend one in to increase the capacitance or bend it out to decrease it further (see Photos 12 & 13). But this does not always need to be done. Every time the wings are adjusted, both the oscillator’s tuning slug and the trimmer capacitor have to be reset at the upper and lower frequency points to correct the upper and lower set frequencies. Ideally, before starting, you create a tracking error map. This is done by disabling the oscillator, as noted above, tuning the RF signal for a peak at each major dial frequency step, then re-starting the oscillator and inspecting its deviation. This is much easier if you have a counter that subtracts the intermediate frequency for you. As one might expect, the ideal adjustment of the wings would be an S curve, reminiscent of the tracking error curve itself. However, it is compressed due to the nature of the SLW variable capacitor’s vane profile. To get an actual curve, the vanes would require twisting as well as bending outward. Another approach, as shown in Fig.b, is to bend them directly outwards. There are not enough adjustment wings to acquire a super accurate result; 10 wings would be better. With the wings untouched and matching those of the antenna and RF stage gangs, in the zone between 1.8MHz and 2.7MHz, the oscillator is running a little more slowly than ideal and requires a little less capacitance; this is why the wings in that zone are better bent outwards. In the siliconchip.com.au Fig.a: typical tracking errors across the dial of a correctly adjusted superhet. Fig.b: by correctly bending the ‘wings’ on the variable capacitor, it is possible to minimise the tracking errors. Fig.c: the configuration of the tuning capacitor wings in this set. zone between 2.7MHz and 36MHz, the oscillator is running a little faster and requires more capacitance. With this radio, after adjusting the wings on the SW band, tracking was as ideal as possible on the other three bands. The SW band was the most convenient one to use for the tracking adjustment because the outer dial scale and pointer have a larger range of relative motion for a small change in angle of the variable capacitor, and the dial marking details are very helpful. The maximum mechanical error in the position of the pointer with respect to a dial marking in the tracking zones in SW mode, when all is set in proper alignment, is in the order Australia's electronics magazine of about 1-1.5 times the width of the pointer. Fortunately, in the scheme of things, the effects of tracking errors in single-conversion superhet radios are generally small. This is because of the relatively wide bandwidth of the tuned RF and antenna stages, being significantly broader than the oscillator’s tracking errors, so there is no significant loss of sensitivity or image rejection. It is the IF stage in the radio that confers the selectivity to the receiver as a whole. Still, it is good to have the radio in good alignment, as well as the dial pointer giving a good representation of the received station’s frequency. June 2026  97 Silicon Chip PDFs on USB with its own case The USB also comes ¯ A treasure trove of Silicon Chip magazines on a 32GB custom-made USB. ¯ Each USB is filled with a set of issues as PDFs – fully searchable and with a separate index – you just need a PDF viewer. ¯ Ordering the USB also provides you with download access for the relevant PDFs, once your order has been processed ¯ 10% off your order (not including postage cost) if you are currently subscribed to the magazine. wavelengths involved, there is no requirement to model the antenna’s inductance or the transmission line properties of the coax. The antenna system is essentially a capacitive load. The relatively low load of 37.5W (the terminated generator), placed in series with the load capacitance, has negligible effects on the total load, but it allows signal injection in series with the 680pF load capacitance. With this arrangement, shown in Fig.5(b), the antenna coil’s tuning slug positions closely matched the manufacturer’s slug positions (locked with red paint) on all bands. At 170kHz, the reactance of the 680pF capacitor is in the order of 1.4kW. At 4MHz on SW, it is quite low, around 58W. This low load is as recommended on the SW band by Sailor. Summary The Sailor 66T is a remarkably wellmade radio. It lives up to its sensitivity specifications on testing and sports a very attractive, well-calibrated dial. Its direction-finding capabilities are quite remarkable. In the days prior to satellite navigation, it probably saved a number of sailors’ livelihoods, and lives too, in the treacherous North Sea. It has a very satisfactory speaker and audio system, and with only a very small change to a capacitor value, makes a very pleasant sounding radio to listen to music stations on the MW SC band. Receive an extra discount If you already own digital copies of the magazine (in the block you are ordering). THE FIRST SIX BLOCKS COST $100 OR PAY $650 FOR ALL SEVEN (+ POST) NOVEMBER 1987 – DECEMBER 1994 JANUARY 2005 – DECEMBER 2009 JANUARY 1995 – DECEMBER 1999 JANUARY 2010 – DECEMBER 2014 JANUARY 2000 – DECEMBER 2004 JANUARY 2015 – DECEMBER 2019 OUR NEWEST BLOCK COSTS $150 → JANUARY 2020 – DECEMBER 2024 WWW.SILICONCHIP.COM.AU/SHOP/DIGITAL_PDFS 98 Silicon Chip Australia's electronics magazine Fig.5: (a) the recommended antenna for using the 66T radio on a ship; (b) a dummy antenna circuit that provides similar operating conditions for aligning the set. siliconchip.com.au