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Providing only two primary windings in the S-40B as opposed to 4 such
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windings in the S-40A may have saved money, but it might also have made the receiver more useful to at least some owners. Whatever the input impedance of each of the four transformers is in the S-40A, they seem to be intended to match a relatively low impedance transmission line of a few hundred ohms or less. For frequencies above around 5 MHz, that would mean cutting a doublet to one half wave in length and using open wire line or coax to bring the signal to the S-40A. For frequencies lower than 5 MHz, though, many folks will not have room for a halfwave antenna and they may elect to use a shorter wire with the unbalanced input option. In the S-40A, though, the unbalanced option, a feed to terminal A1 with terminal A2 connected using the link to terminal G, will still expect a low impedance "source," the transmission line or short antenna which may actually have a relatively high impedance. There is no provision for feeding the line to a higher impedance point in the receiver. In the S-40B, the two higher frequency bands operate as in the S-40A but the two lower frequency bands have no primary windings and antenna terminal A1 is connected directly to the tuned circuit in each case, a higher impedance point that would have been the secondary of the transformer in the S-40A. In addition, a 1000 ohm resistor is added in series for Band 1. This will, maybe, better serve folks who will be using shorter antennas at the lower frequencies. This may not matter as matching impedances in receivers like this is probably not of much importance, but I wish that the S-40B manual had pointed out that terminal A2 is open when the two lower frequency bands are used. 73, Maynard W6PAP On 2/10/25 14:34, don Root wrote:
Richard, how do you define ¡°performed¡±? More than anything, the front |
