AM SWL using Stock 2.7 Filter
From Zerobeat
Have the KBPF3 and only have the stock 2.7 roofing filter?
You can listen to AM SWL using sideband, but then it sounds like sideband. Very good sideband, but very non AM like.
Or you can buy the AM filter. I am waiting for an FM filter, it seems resonable that it should be good for AM receive, and at bandwidths greater than 5 khz.
For now, here's a way to listen to real AM with your stock K3, and it sounds excellent as well.
1. Enter a frequency for example 5.883.95, then AM.
2. The K3 will go silent, not finding a filter for the AM mode.
3. Press CONFIG, dial VFO B to FL(n) BW.
4. Press XFIL until your 2.7 filter is selected.
5. Tap Menu.
6. Use the LO cut to reduce to .10 use hi CUT to MAX of 3.1
7. Find a strong AM broadcast, should be S9 or better.
With a 40 meter dipole at might most of the signals are S9 or better without the preamp.
Tune the signal carefully for fidelity and the filter is not a problem. It helps to set the RX EQ (main menu) where you have band 3 (the lows) can be set to maximum, also bands 5, 6, and 7 raised, suit to taste.
The K3 will not use the 2.7 filter for AM the next time you power up, but everything else can be saved in a memory, just perform step 3 to call in the filter.
Don't be confused by blow-by as in "conventional HF transceiver" where the crystal is used to determine final selectivity, in that case blow by is highly undesirable.
With K3 in normal setup, any blow by through the crystal then has to make it past the DSP filtering after that which is highly unlikely.
What's happening with this trick setup for AM SWL reception is you are centering the audio part of the powerful SWL broadcast into that 5 pole filter at it's center frequency and the blow by allows a little extra frequency fidelity, then the DSP has been opened up fully to accomodate and amplify (through RX EQ) what small amount of blow by there is.
This SWL AM setup is quite contrary to usual K3 setup and operation for amateur band signals - where that 2.7 filter is more than adequate, in fact the K3 may be the best available big signal transceiver available at any price.
