In message Wed, 22 Apr 1998 13:16:34 -0400, Bill_Ames@hysoft.com writes:
>> I think the FCC regs are written that way so that 5W (e.g. CB XCVR)
>> would be pretty well soaked up by the PA grid & not go anywhere.
> Does this imply that there is not a linear relationship to the signal into
> mic and the output from the amp? Such as you nothing out of an amp until
> you reach a level of 5 w into the amp so that any sound below the level
> needed to drive the rig to 5w out are essentially clipped?
>>They set the
>> limit at 50W to keep amplifiers from working with the 5W level (and
>> probably also to keep non-teckkie CBers from figuring out how to get
>> them to work with their rigs). For 50W, however, as an example, in
>> Ameritron's ad in a recent QST the AL-1500 says "... 65 watts drive
>> gives you the full legal output...." I think most amplifiers out there
>> would work -- just not quite at full rated output.
> Why doesn't someone make a small amp that would give me, say, 350 w out on
> SSB for 50w in?
Let me try to set you on the correct to understand the FCC's requirements on
amplifiers so that you can determine the answers to the above questions.
This thread ran on a list last year but there are some newcomers now.
The FCC in 1978 banned the manufacture and marketing of any external
radio-frequency power amplifier or amplifier kit that is capable of
operating on any frequency below 144 mhz UNLESS the FCC has issued a grant
of type acceptance for that model amplifier. In addition an amateur may not
construct or modify more than one unit of the same model in any calendar
For type acceptance the following is required. (See part 97.315 and.317)
(1) it must not be capable or operation between 24 Mhz and 35 Mhz or exibits
no more than 6 db gain between 24 & 26 Mhz and 28 & 35 Mhz and 0 db gain
between 26 & 28 Mhz.
(2) Not capable of designed output power when driven with less than 40W mean
RF input power.
(3) Not capable of amplifying the RF driving signal by more than 15db.
Now let's look at what this really means to a company desiring to build a
low power output amplifier (say 50 watts out) to be driven by a qrp rig of
(1) we must have an input power of at least 40 watts for full output of the
amplifier so a qrp rig couldn't be used to get the 50w output of this
amplifier and who would build an amp that put out 50w for 40W input.
(2) Now a linear amplifier is a linear amplifier at ALL power levels.
Therefore only the power required for full output and the max gain (15db)
needs to be considered. Lets assume an amplifier of 10db gain say something
like an Ameritron AL80. If we drive it with 100W we get 1000W output and we
satisfy the FCC's 50W minimum drive limit. Now it's linear so we can also
drive it with our qrp rig at 5W and get 50W output. So we can purchase a
linear for our qrp rigs but who would buy a 1000W amplifier just to get a
maximum of 50W.
This is it in a nutshell. It's either against FCC requlations to build a
small amplifier of 50 or 100W output that can be driven with 5W or it's
economically not feasible to build one (1000W) that IS legal.
72 Jim K4CGY
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