开云体育

In some ways its futile focussing only on the 3rd order IMD since it
falls close to the transmitter frequency.
Whats more important is the higher order products, 5th 7th and 11 th
order products.
A Rockwell HF8022 TX and amplifier has its high order products
surpressed 100 db at 20KHZ, the typical ham radio is about 50 db.
The Ten Tec Orion is an example of a Transceiver with excellent 3rd
order figures but its higher order products at 20khz which causes all
the splatter is only down 50db. The Elecraft k2 is another example,
good 3rd order figure however its 20khz imd products are class C
like. The Icom 756 PRO series of radios is another radio thats close
to a CB radio because its IMD products beyond 3rd order is constant
out to 20khz. The FT1000D is one of the cleanest at about 70 db down
at 20khz. There seems to be no correlation between excellent 3rd order
IMD products and good IMD suppression at 20 khz. The designer has to
design the whole TX chain to achieve this.
The professional measurements of adjacent channel power and total
occupied bandwidth is more meaningful measurement. This is how ham
radio transmitters should be tested. The commercial spec for IMD is 36
below PEP but has a requirement for very good suppression of
adjacent IMD at least 80 db down at 20 khz. Now if you can find a modern ham radio like this it would be a miracle. Most commercial SSB
equipment can meet this spec. However i doubt people like the ARRL
would add another controversial number that will be compared their
advertisers would hate that. The league has never called a filthy
transmitter what it should be called, cheap, nasty and filthy that
interferes with other peoples enjoyment of the ham radio spectrum.
They promote and whine to the FCC about bandwidth and more space, but
yet they refuses to adopt policies and standards that is bandwidth
friendly in their reviews of ham equipment. Its time for all ham radio authorities to adopt a commercial standard
for transmitter IMD. Since hardly a ham homebrews a transmitter. Some
seem to think this will be a cost impost, this argument is rubbish.
In most cases all it would take is 2 dollars worth of parts and more
bias current. If a standard were to be adopted splatter would be a
thing of the past, unless you get the hifi audio lids who stick
screwdrivers in radios and profess they dont splatter because they see
what they putting out on a scope!
Greg