Hi Ward and all,
> The standard for spurious products used for ham equipment type
> acceptance is something like "all IMD products must be -40 dB with
> respect to the signal at 20 kHz from the signal frequency." (I'm
> grossly oversimplifying...) What we are looking for in this case is a
> similar statement - "All transient products may have a peak amplitude
> no greater than -x dB with respect to a CW signal's peak amplitude
> over a bandwidth of +/-y kHz centered on the CW signal."
There is no standard in dB for modulation products.
Radios do not require type-acceptance, only external power
The number everyone thinks of is for harmonics and problems not
generally related to modulation of the signal, and it is also used in
type-acceptance of power amps. HF rigs are supposed to meet
that number, but generally not for modulation products. That
number is for spurious signals, like harmonics. It is a basic number
of -40 dB, and 50 mW maximum power.
97.307 covers emission standards.
Modulation related rules state ALL modulation products have to fall
within the authorized frequency band for that operator and mode
segment (operating 7152 LSB is clearly illegal in the USA, or a
general class on 75 meters LSB two kHz away from the General
band edge would be illegal), and that modulation products can not
cause interference to stations on adjacent frequencies. You can
not occupy more bandwidth than necessary for the mode you are
If you click, and it is bothering someone and it is your problem, it is
This is much different than the 40 dB or 50 mW max rule.
BTW, if you have a harmonic or spur and it meets the -40 dB / 50
mW max rule...it is still illegal if it bothers someone. Many novices
received "pink tickets" by virtue of the fact their harmonics could be
heard! Not by how many dB down they were!
> So, there is a standard, but it is focused on non-linearities
> generating IMD products in the transmitter output. It is not written
> with respect to transient spurs generated by keying edges. Since
> there is no standard, there are no measurements taken.
The FCC only requires testing under carrier conditions. I can build
the trashiest PA in the world for IMD, and it will pass FCC TA with
Virtually every radio in use today fails the -40dB / 50 mW rule for
SSB IMD. The ARRL uses a different standard than the FCC,
which makes everything 6 dB better than a commercial test. So
when you see a lab report that says SSB 3rd order IMD -46...it
means the radio just squeaks by if you never use anything bigger
than a 500 watt PA on it. Even so, that -46 dB is technically illegal
if it causes interference or any of it hangs outside the authorized
area for that mode.
Technically, virtually every radio made since the 70's fails FCC
standards if you apply the -40dB / 50 mW to the modulation
We let it happen.
73, Tom W8JI
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