smg

Hopefully this helps

The displayed waterfall span at zoom level z is

BW = 30 MHz / 2^z.

Given a centre frequency cf (in kHz), the visible frequency limits are:

BW_kHz = 30000 / (2^zoom)
f_low  = max(0, cf - BW_kHz/2)
f_high = min(30000, cf + BW_kHz/2)

At zoom=0 the Kiwi always shows the full 0–30000 kHz waterfall, regardless of cf. For zoom >= 1, the span centres on cf (clamped so you never go below 0 or above 30000 kHz). (KiwiSDR)

Example with your numbers

• Command: SET zoom=0 cf=7550.000000
• Waterfall span: 0–30000 kHz (full band). (KiwiSDR)
• Command: SET zoom=1 cf=7550.000000
• BW_kHz = 30000 / 2 = 15000
• f_low = 7550 − 7500 = 50 kHz
• f_high = 7550 + 7500 = 15050 kHz
• So you’ll see 50–15050 kHz.

Why this matches what the Kiwi does

• Zoom levels are power-of-two subdivisions of 30 MHz (e.g., WF7 ≈ 234 kHz, WF8 ≈ 117 kHz), which is exactly 30 MHz / 2^z. (KiwiSDR)
• The waterfall data is 1024 bins wide; bin width is Δf = BW/1024. At zoom=0, that’s about 30 kHz/bin. At the max zoom (z=14), Δf ≈ 1.8 Hz/bin. (KiwiSDR)
• In the protocol/URLs the frequency values are in kHz (e.g., ?f=22500 for 22.5 MHz), same unit used by the cf you’re sending. (KiwiSDR)
• The Kiwi’s nominal coverage is 0–30 MHz (some installs set 32 MHz), hence the clamping in the formula above. (RTL-SDR, kiwisdr.com)

Mapping bins to frequency (handy for your Java code)

If you index bins i = 0..1023:

Δf = BW_kHz / 1024
bin i spans [ f_low + i*Δf , f_low + (i+1)*Δf )   (in kHz)

That should make your prototype line up perfectly with what the Kiwi sends.

John (Kiwi’s author) explicitly describes the zoom behaviour and bin counts here: https://forum.kiwisdr.com/index.php?p=%2Fdiscussion%2F1472%2Fsetting-dispalyed-bandwidth

John already has some documentation on antenna switches.

I started making my own code to work with a 3rd party switch

https://github.com/smegoff/RAAS-4-Scripts

Also, check out this thread

https://forum.kiwisdr.com/index.php?p=/discussion/3249/what-antenna-switch

I've been through a few iterations of Power Supplies, including what I thought was an adequate linear one, that ended up not firing up the Kiwi first time round (using the Kiwi supplied cable too!), and running hot, to settling on this:

https://www.aliexpress.com/item/1005006697287204.html

It runs cool, and seems to meet the demands of the Kiwi with no start up issues at all. I've had it open and its well-made and very clean and uses high quality components.

We run a WISP network here and use CGNAT - however if a customer wishes to run any services, we add $10/mth to their bill and give them a static IPv4 address

It wasnt Minecraft servers that was the issue - it was the warez servers we stood up ;-)

Found one in the public Kiwi list here