SCU bandpass filter override

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  • Updated 4 years ago
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Is there a way to override the SCU bandpass filters, such as to force it off, or to force it to stay on a particular band regardless of how wide the panadapter is 

I often have trouble when operating down at the bottom of 160m where the bandpass filter clicks off unless my panadapter is  adjusted so my transmit slice is right at the edge of the panadapter., which is rather annoying.
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Greg Zenger [N2GZ]

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  • frustrated

Posted 4 years ago

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W5XZ - dan

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great idea, Greg. It would be cool to see the BPF freq response.   73, HNY, W5XZ, dan
(Edited)
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Ken - NM9P, Elmer

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I have this too... As the panadapter shifts, the relay clicks and the noise floor on 160 shifts by 3-5 dB, depending upon the panadapter zoom...
Perhaps they could have an option to shift the frequency at which the bandpass filter engages... perhaps 50-100 KHz lower?  That might do it.
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Tim - W4TME, Customer Experience Manager

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Official Response
Bandpass filtering or the preselectors are not dependent on the slice frequency.  The SmartSDR software dynamically enables the band specific preselector based on the bandpass filter (preselector) bandwidth and the panadapter viewable bandwidth; turning a bandpass filter on when it will properly reduce out of band signal energy (remember, the SCU is sampling all RF energy from 70 kHz up through the 6m band depending on radio model).

To disable the preselector, either open another panadapter in a different band or zoom out until the panadapter viewable area exceeds the bandwidth of the preselector.  These conditions will prevent the preselectors from becoming enabled.

Can you force on a band specific preselectors?  The answer is no; there is not a way to force on a preselector and circumvent the logic that dynamically enables it.  

SmartSDR has logic to dynamically enable or disable the preselectors depending on the viewable bandwidth of all panadapters associated with a particular SCU, and the actual bandwidth of the preselector (bandpass) filter.  Forcing a particular preselector on when it should not be would degrade the receive performance of the radio.  We have put a lot of time and effort in making the radio perform at an optimal level with minimal user interaction and configuration (the smart in SmartSDR).

"I often have trouble when operating down at the bottom of 160m where the bandpass filter clicks off unless my panadapter is  adjusted so my transmit slice is right at the edge of the panadapter., which is rather annoying."

This is because the preselector on 160m is very tight around the band edges due to the presence of strong BCB signals just below it.  The function of a preselector is to reduce the total spectral energy getting to the SCU (the wide band AD converter).

On 160m, if the viewable area displayed, is no less than ~1.790 MHz and the upper frequency does not exceed ~2.1 MHz, the 160m preselector is enabled.  I suspect that what is happening is as you tune towards the lower band edge, you end up pan edge tuning, meaning the panadapter is tuning to a lower frequency with the slice resulting in the lower frequency of the panadapter going below 1.790 MHz.  As you have noted, judicious zooming of the panadapter (adjusting the panadapter bandwidth) will allow you to tune a slice at the band edge without disabling the preselectors.  

Rather than using the stepped zoom controls, you can click and drag the frequency display of the panadapter to adjust the viewable bandwidth without centering the active slice in the middle of the panadapter viewable area.
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Greg Zenger [N2GZ]

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Ok. darn. I was hoping there was a hidden developers menu or something that I could use to give myself a little bit of added flexability.

Due to BCB signals at my QTH, 160m is almost unusable without the 160m preselector selected. Obviously some of my RX antennas are more susceptible than others. 

I fully understand how the radio works and the purpose of the preselectors. I understand that the radio has logic to set the radio up the way it thinks is best for me, and much of the time it does pretty well,. However sometimes it gets it wrong and that is why I am looking for a override setting so I can guide its logic to suit my needs.  When operating 160m, I find myself constantly having to tweak the panadapter to get the preselector to remain enabled. (Oh, and I never find myself using the zoom controls, I am 100% a click and dragger, but thanks anyway for the tip!)

Feature request:
It would be dandy to have the option to override the radio's logic to force a preselector to stay on, regardless of the current viewable panadapter bandwidth. I imagine that instead of saying "WIDE" at the top right of the panadapter it could say "OVERRIDE"  or "OVERRIDE:160" etc. instead.  In my little dream world there would be a "BPF" button down by TNF and CWX that would toggle between override mode and Auto (what we have now), right-clicking would bring up a menu to change the override setting.

I am perfectly content having a pan adapter open that shows heavily attenuated signals on a portion of the panadapter that falls outside of the selected preselector, especially if the pan-adapter is marked "override."
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Ken - NM9P, Elmer

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I like that.  "BPF OVERRIDE: 160" would be handy so we wouldn't need to keep dragging the panadapter every time we tuned too close to the edge of the band.
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Denley W3XY

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Better yet, how about an option to lock the panadapter so that it doesn't move when we tune near the band edges?
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Greg Zenger [N2GZ]

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Id like the ability to not only lock the panadapter, but to be able to enter Min and Max frequency, or center frequency and width like you would on a spectrum analyzer or other piece of frequency domain test equipment.