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#27
October 15th 18, 01:17 PM
posted to uk.radio.amateur,rec.radio.amateur.antenna
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4NEC2?
On 14/10/2018 22:01, Ralph Mowery wrote:
In article , lid says... On Sun, 14 Oct 2018 12:04:52 -0700 (PDT) Jeefaw K Effkay wrote: On Sunday, October 14, 2018 at 7:33:10 PM UTC+1, Jeff Liebermann wrote: It might help to understand why some bands use LSB while others USB. In the early daze of sideband radio, the common IF frequency was 9MHz. The radios had only one sideband filter. With one filter, it was cheaper and easier to mix and up convert in the transmitter. So, to save the cost of adding a second filter, the bands below 9MHz were designated as LSB and the band above 9MHz became USB. Eventually, radios were built with two sideband filters, and this was no longer important. As usual, the legacy technology remained in place to haunt the survivors to this day. I've seen this explanation before, but it doesn't make sense. A 9MHz USB signal mixed with a 5.0 to 5.5MHz VFO will produce mixing products in the 80m and 20m bands - but both will be upper sideband. When the 9 MHz is mixed with the 5 mhz the 20 meter signal is upper sideband. The 80 meter signal is inverted and becomes the lower sideband NOT usb. Years ago when ssb was just starting out on the ham bands this made 80 meters and 20 meters easy and inexpensive compaired to other methods. So it was decided on by hams to use 40 metes and lower frequencies as LSB and 20 meters and above as USB. Then the government stepped in for the 5 and 10 MHz bands and dictated what to use. For other reasons most digital is in the USB mode for all bands except for RTTY. RTTY is usually used in the LSB mode for all ham bands, but can be used in the USB mode if the tones are inverted. The commercial RTTY was usually inverted from the normal ham RTTY. "Geoff" has long had a 'difficult' relationship with HF. -- Spike "Nearly all men can stand adversity, but if you want to test a man's character, give him an internet group to manage" |
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