Ham radio is supposed to do both. One of my ham neighbors in LA checked into an 80 meter AM net almost every night with the same model rig that he used in the 1950's.
73, John KD6OZH ----- Original Message ----- From: W2XJ To: digitalradio@yahoogroups.com Sent: Monday, December 31, 2007 14:25 UTC Subject: Re: [digitalradio] Re: [illinoisdigitalham] Re: Power Mask for Bandwidth Rules - USA At one time the ARRL published plans for class B modulators with no filters. What they publish will stay with the times. There is no reason higher order analog filters can not be built if required. 25 or 30 db down at 3.5 K is not unreasonable since such analog filters are 1980s state of the art. Digital filters and digital modulators are no longer black art either. Then there are the popular SDR designs where almost anything is possible. I thought the hobby was supposed to advance the art not mimic commercial art of decades past. John B. Stephensen wrote: > The ARRL is publishing designs for simple phasing SSB exciters with 3-pole filters and filter-type exciters with 4-pole crystal filters so we can't count on DSP. Phasing transmitter kits have filters with at least 5-poles so they are somewhat better. These should be able to acheive 23 dB suppression 4 kHz from the carrier under any circumstances. There could be an exception for older AM transmitters or transmitters under 10W PEP. What is really needed is a rule that says 3rd order IMD must be at least 30 dB down. > > 73, > > John > KD6OZH > > ----- Original Message ----- > From: W2XJ > To: digitalradio@yahoogroups.com > Sent: Sunday, December 30, 2007 23:16 UTC > Subject: Re: [digitalradio] Re: [illinoisdigitalham] Re: Power Mask for Bandwidth Rules - USA > > > Modern filters that have been used in real equipment since the 80s can > be -1 db at 3100 and down 25 db at 3.5 k with negligible overshoot and > ripple in the 10ths of a DB. Chebyshev filters are not really the filter > of choice for this, elliptic tilers with some custom tweaks are a better > choice. They are in very common use in broadcasting. Today digital > filter, common in current rigs, can do much better. > > A lesson to be learned from AM broadcast is that when emission > standards were tightened, allowance in the standard was made for older > rigs. That so called mask was then later used as a means to add digital > carriers. There is a lot of interference created. A better approach > would exempt transmitter built before a certain date but only for the AM > mode. > > ohn B. Stephensen wrote: > > An emission mask must accomodate AM so I looked at the speech amplifier and modulator chapter in the 1955 Radio Amateur's Handbook. It advocates up to 25 dB of clipping and no circuit has more than a 3-pole filter. The best that can be done today is a Chebyshev filter with 1 dB ripple and a 2.5 kHz cutoff frequency providing 23 dB of attenuation at 5 kHz and 27dB of attenuation at 6.5 kHz. Filters would be worse in 1955 as modern filter design methologies hadn't been invented yet. > > > > Only the outer portions of the mask should be defined in the regulations so that old equipment can continue to be used but hams with more modern equipment can be more efficient and use a larger percentage of the channel. The ARRL proposal of 9 kHz at -23 dB might be the best than AM'ers can acheive now. > > > > 73, > > > > John > > KD6OZH > > > > > > > > > >
