On Mon, 4 Mar 2019 at 12:21, jim via Groups.Io <ab7vf=[email protected]> wrote:
So, perhaps a dumb question or maybe two .., but "Why the continued instance on using low-pass filters ...Wouldn't some band-pass filters make more sense??
Jim
On Monday, March 4, 2019, 12:15:41 PM PST, Jerry Gaffke via Groups.Io <jgaffke=[email protected]> wrote:
As I said in post 66008: > Allisons extra filters would fix that, at the cost of considerable complication.
On Mon, Mar 4, 2019 at 12:03 PM, ajparent1/KB1GMX wrote:
o fix this more fully:
Switchable filters to replace? the 33mhz? existing one L1-4.
for the 3.5- 5mhz range a low pass filter with cutoff of 6mhz for the 7- 10mhz range a low pass filter with cutoff of 11mhz for the 11- 19mhz range a low pass filter with cutoff of 20mhz
for the 20- 29.9mhz range a High pass filter with cutoff of 20mhz ***Note for this range that helps but a band pass for 21mhz and a wide band pass for 24-29mhz would also be a better way (clean ssb). Either way 4 to 5 filters greatly clean up signals.
The 33mhz filter delete it.
Why would this work?? The RF source tends to be biased toward greater third harmonic for CW so putting effort into the second harmonic reduction for a filter is not required.? The result is a modest 15db reduction of third harmonic and spurs into the PA would clean up many if not all of the offending signals.? Good filters will with good switching can achieve more.
Since the work is being down at low power levels (sub 1 milliwatt) SMD inductors and capacitors will be adequate.? Switching can be done with diodes or relays.
The problem is space and simply doing it.? The board space is limited however the underside is totally unused.
