PK's Lab - FPV Video Series - ImmersionRC Rapidfire - Rapidfire modes demystified, "magic"explained

Here's a not so brief and kinda meandering video covering the ins and outs of what the ImmersionRC Rapidfire module is doing to fix up the received analog video signal in it's various modes of operation (Mode 1, Mode 2 and Legacy).

Hope you enjoy it!

~pk

PK's Lab - FPV Video Series - ImmersionRC Rapidfire - Internal video level calibration

This is an informal how-to on calibrating the internal video levels of the ImmersionRC Rapidfire video receiver.

NOTE: Doing this will probably void your warranty and isn't condoned by ImmersionRC... or myself for that matter.  I have no affiliation with ImmersionRC other than I own a few of their products.  You are solely responsible for your own actions and any damages you cause.

Required equipment:
- Oscilloscope with video triggering capability
- Insulated flat blade adjustment screwdriver
- 5.8 GHz vtx and camera

Enjoy :)

~pk

Dragonlink LNA review - Part 1

Here's a short look at the Dragonlink 1.2 - 1.3 GHz LNA.  We'll measure it's frequency response/gain in various configurations.

I ordered a single unit with my own $ from fpvpro.com.  Non-affiliate link to the item here: Video Signal Amplifier ( LNA ) 1.2 - 1.3 GHZ.

Filters used for testing (non affiliate links):
    TBS 1.2GHz VRX Notch Filter (868/915 MHz)

    Minicircuits ZX75BP-1260-S+

The test setup:

The device under test:

Power consumption at the minimum and maximum input voltages:

VNA sweep, device off:

VNA sweep, device on:

TBS/VAS 1.2GHZ VRX notch filter (868/915 MHZ) before the LNA:

TBS/VAS 1.2GHZ VRX notch filter (868/915 MHZ) after the LNA:

  

PK's Lab - Long Range FPV Video Series - Dragonlink 1.2 - 1.3 GHz LNA quick review - Part 1

It's time to start the morning off right, fire up the coffee maker and the VNA ;-)  Here's a quick video on the Dragonlink 1.2 - 1.3 GHz LNA.  We measure it's frequency response/gain and power consumption.

I ordered a single unit with my own $ from fpvpro.com.  Non-affiliate link to the item here: Video Signal Amplifier ( LNA ) 1.2 - 1.3 GHZ.

Video here:

Hope you enjoyed this.  And they say on youtube. stay tuned for part 2...  :-)

Part 1 - TBS/VAS 1.2GHZ VRX NOTCH FILTER (868/915 MHZ) - RF Sweeps

For the FPV RF nerds out there.  This one is for you ;-).  Here are some quick frequency response sweeps of the new PCB based 915 MHz notch filter.

I ordered 2 units with my own $ from heli-nation.  Non-affiliate link to the item here: TBS 1.2GHz VRX Notch Filter (868/915 MHz). 

For reference:
Marker 1; 900 MHz
Marker 2; 930 MHz

Marker 3; 1258 MHz

Marker 4; 1280 MHz

Trace 1 and 2 measure the thru response (S21, S12)

Trace 3 and 4 measure the SWR (S11, S22)

Ok, lets get on with the results :)

Filter #1:

Filter #2:

Both filters cascaded in series:

Results:

- The shape of the rejection notch is is very much centered around 915 MHz.

- There may be a different SKU for our European friends, but as it stands there's only about 17 dB of  rejection at 870.  This may or may not be enough depending on the filtering performance an blocking performance of your video receiver

- The part to part variation appears to be pretty low for the 2 samples I purchased (as expected since it's a pcb based design)

- Cascaded (2 devices in series) insertion loss of 1.2 dB @ 1280 MHz is impressive for the 50 dB + of rejection in the 900 MHz band.   

Thoughts:

The single stage: Reasonable rejection of  >= 25 dB in the US ISM band.  This may be enough for general rejection of crossfire signals at a flying field.  But might not be enough if you flying down to sensitivity doing long range flights.  Especially if you are only a few feet from your groundstation or using the fatshark goggle modules.  More on this in part 2.

The cascaded filter: I would hazard to say the it would def be worthwhile for Alex to spin a separate version of this with the two filters in series on one PCB. The insertion loss in the passband is very good for the amount of rejection it gets at 915. With a slight re-tune to shift the passband down just a touch for lower loss at 1258 and an LNA on the front end to help improve the overall noise figure of our receivers, you'd have a killer front end setup for both around the park and long range flying.

Coming in part #2:

Shootout with various receivers to measure actual


Hope you enjoyed this.  As they say on youtube. stay tuned for part 2... 

Foxeer Arrow Micro Pro Fix for AC coupled video output - 600TVL FPV Camera with OSD - HS1209

If you have one of the Foxeer Arrow Micro Pro cameras (HS1209) and have noticed incompatibility with certain OSDs, inability to maintain a sync lock with the ImmersionRC Rapidfire 5.8 Ghz video receiver (this is a known incompatibility documented here: rapidFIRE Camera/OSD/FC Compatibility) and other weirdness here's a quick mod to bypass the AC coupling cap and DC couple the video output from the camera. (Note: you will need to confirm that the video signal is going into circuitry that can handle the DC offset that will be present)

Here's what the video line looks like before the change:  (Note: The video line was terminated into 75 ohms as is standard)

All black video out:

Bright light on lense:

Mod:
Solder a thin wire across the cap pictured.

Video output after the mod:

All black video out:

Bright light on lense:

Hope this helps someone out there.

~pk

Thunder Chicken - Development Blog

... Codename: Thunder Chicken...

What's dis: The development/build log for (yet another ;-)) open source project.  The basics are an integrated ESP32 based flight controller with integrated 433 MHz LORA long range radio and dual band (1.3 / 3.5 GHz) video transmitter.

Mission statement: Learn, Fly and have fun

Current Status: (3/29/2018) WIP - Working on the schematic.

Development Files: Here on github

Latest Picture:

Quicklook - ELECTRIFYRC R33M 3.3 GHz Module for Fatshark Goggles

Here are a handful of microscope pictures of the 3.3 GHz Fatshark style receiver module.  Click the pictures to get the zooms ;)

Enjoy :)

~pk


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Notes:
- The SAW filter on the RTC6715 is a NDF4816B (Datasheet here).  The IF frequency is 479.5 MHz.
- The mixer is driven by a ADF4350 Synth
- Mixing is highside, thus when the RX channel is set to 3320 MHz, the ADF4350 is set to 2840.5, Giving it a 1st IF of 6160.5 MHz.  Consequently, the RTC6715 synth is programmed to (6160.5 - 479.5 = 5681 MHz)

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URL: http://hobbywireless.com/electrifyrc-products-c-281/r33m-33ghz-module-for-fatshark-goggles-p-4535.html

KINGKONG BLHeli USB Adaptor Unable to communicate with RacerStar RS40A V2 ESC

I ran into a problem recently where my KINGKONG BLHeli usb to ESC serial adaptor couldn't talk to my RacerStar RS40A V2 ESC.  Looking at the serial signal on the PPM pin, the voltage levels on the reply from the ESC wasn't swinging nicely down to 0V indicating the pullup resistor on the serial interface board might be a bit too strong.  

There is a 100 Ohm series resistor going to the SIG/PPM pin.

And a 3.3K pullup to +5V.  This is the resistor that needs to be changed.  I used a 6K 0402 resistor I had laying around and things worked like a champ.

Hope this was helpful to you out there.  Leave a comment if you have any questions or suggestions for future articles.

Thanks!

~pk