one must also discover the
artful use of the RF Gain control as well
Adjustment of the RF gain control is not mentioned in Wayne's note on
using APF.
When I tried it here, the RF gain might have made some small
difference but it still did not allow un-copyable signals to be
copied. When testing APF I have made all adjustments the I thought
might affect signal quality. IIRC correctly I also tinkered with the
AGC parameters. But the APF never produced results any better than
simply narrowing the filters. Usually the regular narrow filters
worked better. I know I had not switched APF on for months. I did
switch it on to recheck before sending my note. But the noise is not
currently high enough to give it a good test.
I have found, in general, that careful adjustment of the RF gain
control can be useful. This applies to all receivers I have tried it on.
I'm wondering if the difference is in the type of noise. I have mostly
tried APF at times of high lightning activity. I think we in the SE
get more of that than other parts of the country. The higher noise
level means more weak signals. You need all the help you can get. But
that noise differs from the usual band noise.
And it may depend on each individual's hearing.
I have always puzzled over why some rave about how great APF is while
for myself, and obviously others, it is of no help at all.
73 de dave
ab9ca/4
On 2/5/16 10:13 AM, Bob McGraw K4TAX wrote:
While I find the APF works really nice, one must also discover the
artful use of the RF Gain control as well. Most hams seem to use
excessive RF Gain which will force noise through the filter and all of
those undesirable artifacts will be heard. If in doubt, reduce the RF
Gain.
Using this technique, I can tune the band with the APF engaged,
adjusting the RF Gain a bit, and actually hear signals with this
configuration which without the APC no signal could be heard. I view
this gives one the ability to actually "dig signals out of the noise".
73
Bob, K4TAX
On 2/5/2016 9:56 AM, dave wrote:
I'd agree. My experience with APF is that it will indeed pop a
signal that is already copyable, if a bit weak, out of the noise.
Makes for easier copy. However the ringing is so bad on a really
weak signal that it is of no help. I guess it depends on what you
view as 'weak' and your noise level. I was hoping it would make
previously un-copyable signals copyable, but that does not happen.
Instead it improves the copyability of weak but already copyable
signals.
I find that simply narrowing the filters to 50, 100, or 150 Hz will
give essentially identical results as using the APF and is much
easier to do.
As for the super critical tuning, I do not find it to be all that
critical. The signal can be improved somewhat by going to the 'fine'
tuning, but it makes only a small difference. 10 Hz steps are OK and
much quicker. The APF has a BW of about 30 Hz so tuning cannot be
all that critical. +/- 5 Hz out of 30 is not that big of a deal.
This has been one of my biggest disappointments with the K3. After
reading all the hype about APF I was hoping for a real improvement.
But does not happen. OTOH, the narrow filters of the K3 are
outstanding.
73 de dave
ab9ca/4
On 2/5/16 8:53 AM, David Kuechenmeister wrote:
I tried this the other day with no success. That is, the weak
signal that was barely detectable, became so buried in ringing that
I couldn't detect it at all. I think I followed the procedure
outlined in Wayne's email below... Noise was around S5 on 40m and
the K3 was configured with APF active. I had my 500 Hz filter
selected and varied the DSP WIDTH from 500 to 300 without
substantial improvement. FINE tuning selected. What am I
forgetting? vy 73,Dave N4KD
On Tuesday, February 2, 2016 9:36 AM, Wayne Burdick
<[email protected]> wrote:
Hi all,
This morning I was hearing lots of very weak signals in the
40-meter CW band, right at today's noise floor of about S-5. (Among
others, I copied BG4GOV in Shanghai.)
Many of the signals were not copyable until I turned on APF (audio
peaking filter). This filter's center peak is very narrow (around
30 Hz), but the response broadens out quickly below the 3-dB points
in the curve. This brings up the desired signal without allowing
noise to cause ringing--something often heard with narrow filters
of the "brick-wall" variety. On a noisy band, the effect is just
short of magic.
APF is very narrow, so you'll need to tune in 1-Hz increments when
it is turned on. Also, APF works best when used with a DSP/crystal
filter WIDTH setting of 300-500 Hz.
Use of APF differs for the three transceivers.
KX3: 1-Hz tuning is selected automatically on the when the APF
switch is pressed.
K3/K3S: APF is accessed via a hold of the XFIL switch. This
function is labeled "APF" on a K3S, or "DUAL PB" on the K3). Use
CONFIG:DUAL PB to make sure the selected filter function is APF.
See the K3/K3S owner's manual for a description of the alternate
setting. 1-Hz tuning can be selected by tapping FINE.
You might want to give APF a try if you haven't already.
73, Wayne N6KR
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