Hi Robert,
Well, at a fixed AM broadcast frequency a few poles of filter can
conjure up the required 10-20 uS delay. That won't suffice at 10X the
frequency.
Speaking of delays, I have a design which has almost a millisecond
of delay in the DSP RF path and therefore have to delay the audio
chain to match!
73 & Good morning,
Marv WC6W
-- Robert Meuser <Robertm@broadcast.net> wrote:
The group delay problem is almost always in the modulator path and not
the RF path. The bandwidth is relatively small in that chain. Am
stereo
stations dealt with this issue out to 15 kHz audio. Digital AM
stations
also use the technique across 30 kilohertz. Usually a compensating
delay
is put in the RF path. The bigger issue is the affect the antenna
would
have on this matching. A digital pre-correction scheme could handle
that. If you wanted an amp that worked perfectly from 160 M to 10M, it
would be a complicated design unless one was to settle for some manual
re-tuning.
R
wc6w@juno.com wrote:
><snip>
>
>
>
>>Then it came to my mind that joining the two articles seems almost
>>ideal: A class AB/F amp with ARF1500 MOSFETs would be free of
>>hotspotting, because in the AB class it would run at very low
>>voltage (20 or 30V at most) and above that it would be running class
>>F. At the same time, the reduced dissipation goes a long way in
>>helping with the cooling problem.
>>
>>
>
>
>
>>The added complexity of the modulated switching power
>>supply would be rewarded by the high efficiency. And the whole thing
>>would still be small, lightweight and reasonably cheap. Any takers,
>>out there?
>>
>>
>
>
>
>>I would be really interested in knowing what you think of this. Am I
>>a crazy dreamer (from reading too much 73) and just loosing my time,
>>or do you see merits to this approach? Or do I come late, and
>>someone has already done it?
>>
>>
>
>
>
>>Manfred, XQ2FOD.
>>
>>
>
>
>Hi Manfred,
> There is a small problem, often overlooked, in the envelope
>restored Class D/E/F "linear" scheme. The group delay through the
>modulating path must be equal to the RF path delay for the system to
>exhibit low distortion. This can be realized over a narrowband but,
>when a wideband system is considered it may prove to be easier to
>build an entire envelope restored transmitter than to construct a
>standalone linear.
>
>73 & Welcome to the group!
> Marv WC6W
>
>http://wc6w.50webs.com/
>
>
>
>
>*
>
>
>______________________________________________________________________
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