Preselectors, the ALEX button, and RX2

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w-u-2-o
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Preselectors, the ALEX button, and RX2

Postby w-u-2-o » Tue Mar 20, 2018 2:25 am

This post will try to address the mysterious ALEX button, and how to manage the receive preselector, i.e. band pass filter (BPF), array.

Once upon a time, before there was any Apache Labs radio hardware, there was a board called "Alexiares". This board was designed as a filter array for the early openHPSDR family of SDR hardware. For some reason this board was controlled by firmware in the SDR FPGA, not by the software, i.e. PowerSDR.

1. The ALEX button was born out of the this legacy of hardware that predates the ANAN-10 that requires the use of the "firmware" mode of operation.

2. When ALEX is ON, there is a hard-coded table in firmware that looks at the frequency of VFO-A and sets the preselection BPF in accordance with the frequency. If both RX1 and RX2 are being fed by ADC1 then this may often be in conflict with the frequency of VFO-B.

3. When ALEX is OFF, the software, PowerSDR, looks at the frequency of VFO-A and sets the preselection BPF in accordance with that frequency per the settings in Setup > General > Ant/Filters. Again, if both RX1 and RX2 are being fed by ADC1 then this may often be in conflict with the frequency of VFO-B.

4. Neither mode, ALEX on or off, is actually "manual". This is a confusing misnomer. They are both completely automatic unless one goes into Setup > General > Ant/Filters and manually takes control there.

5. To turn off preselection filtering completely, set ALEX to OFF and

- On the 100 and 200 series radios, check both the "ByPass/55 MHz HPF" and "6M/Bypass on RX" boxes
- On the 7000 and 8000 series radios, check the "ByPass/55MHz BPF" box (not 100% sure about this on the 7000)

6. It can be convenient to preset the settings in Setup > General > Ant/Filters as per (5) above and use the ALEX button to switch between firmware and software (aka "manual") modes of operation. In this way you get an easy way to bypass all preselection filtering from the main console user interface.

7. In all hardware the 55MHz LPF is not defeatable (nor should it be!)

Editorial note: IMHO the firmware modes of operation should be deprecated for Apache Labs radios, as philosophically all control should be from the software in a software defined radio.
ik7ytt
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Joined: Tue Mar 12, 2019 11:48 am

Re: Preselectors, the ALEX button, and RX2

Postby ik7ytt » Tue Mar 19, 2019 6:44 am

i have anan 7000 an i want understend the below questions
plus what is the LNA 15/12/10 button?



2. When ALEX is ON, there is a hard-coded table in firmware that looks at the frequency of VFO-A and sets the preselection BPF in accordance with the frequency. If both RX1 and RX2 are being fed by ADC1 then this may often be in conflict with the frequency of VFO-B.


where can find the hardware BPF bandwith? there is 1 BPF for each band or like in manual mode they are more wider?



3. When ALEX is OFF, the software, PowerSDR, looks at the frequency of VFO-A and sets the preselection BPF in accordance with that frequency per the settings in Setup > General > Ant/Filters. Again, if both RX1 and RX2 are being fed by ADC1 then this may often be in conflict with the frequency of VFO-B.


i see for example that the 2-/15/15 manula BF1 is set quite wide 11 to 22 mhz.
if i want only 14 to 14,35 bandwith and set t manually. will hare really the filter working for this freq? or will still keep the main hardware bandwith?




6. It can be convenient to preset the settings in Setup > General > Ant/Filters as per (5) above and use the ALEX button to switch between firmware and software (aka "manual") modes of operation. In this way you get an easy way to bypass all preselection filtering from the main console user interface.

bypass of each sigle band filter can be made in both frimware and manual mode?



thanks
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w-u-2-o
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Re: Preselectors, the ALEX button, and RX2

Postby w-u-2-o » Tue Mar 19, 2019 6:15 pm

where can find the hardware BPF bandwith? there is 1 BPF for each band or like in manual mode they are more wider?
The filter response curves for the filters have never been published by Apache so far as I know, and I've never seen any measurements of them. I can tell you they are not very sharp, being only third order filters.

i see for example that the 2-/15/15 manula BF1 is set quite wide 11 to 22 mhz.
if i want only 14 to 14,35 bandwith and set t manually. will hare really the filter working for this freq? or will still keep the main hardware bandwith?
The "manual" and "firmware" settings are, as described above, very poorly labeled. They should have been labeled "software" and "firmware". Whether it is under software control, or firmware control, the same hardware is utilized on the PA/filter board. The adjustable limits in the software control panel merely tell the hardware which filter to select when VFO A is within those limits, they do not allow you to change the properties of the filters in any way.

bypass of each sigle band filter can be made in both frimware and manual mode?
No. You can only bypass in "manual" (really "software") mode, just like it says above.
K9RX
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Re: Preselectors, the ALEX button, and RX2

Postby K9RX » Wed Mar 20, 2019 12:41 pm

Scott,

Forgive me if this is not posted in the right place ... I think it is correct.

So why is it when I tune outside a ham band the panadapter changes drastically? How do I continue to tune outside the ham band as if nothing changed? I SHOULD be able to do that ...

Gary
K9RX
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w-u-2-o
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Re: Preselectors, the ALEX button, and RX2

Postby w-u-2-o » Wed Mar 20, 2019 2:54 pm

Ha ha, not the right place, Gary, sorry! Because it is not an issue caused by the preselectors.

The issue is caused by the feature of PowerSDR (and Thetis) whereby panadapter high/low limits are maintained in the database on a band by band basis, and there is no option in the software to create a global default. So every time you change bands, even to an "out of band" band, much of which the software treats as SWL bands, you have to go into Setup > Display > RX1 (Spectrum Grid) and change the settings there.

You can even see in that section of the setup how it displays the name of the band ("Band for Max/Min Levels").

73,

Scott

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