Like when you connect BNC as the input signal soure to VGA montor, then you need connect VGA OUT interface,doesn't connect the VGA IN interface. The bnc to vga converter : Input: 1x BNC, 1x S-Video, 1x VGA;Output: 1x VGA.
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Newest 1Pcs 1.3M Computer Monitor VGA to VGA Cable with HDB15 Male to Male HDB15 Male Connector For PC TV Adapter Converter
Aliexpress UK
This BNC to VGA video converter can support high resolution (up to 1920 x 1080) video picture. The video converter can provide high quality picture and give stable image output to VGA output device.
eBay
1080P AV RCA to VGA Converter VGA to AV RCA Support PAL NTSC Video Adapter With 3.5mm Audio Output for TV Set-Top Box Monitor PC
Aliexpress UK
This BNC to VGA video converter can support high resolution (up to 1920 x 1080) video picture. The video converter can provide high quality picture and give stable image output to VGA output device.
eBay
1.8M USB Type C 3.1 to VGA Adapter Cable 1080P Type-C Male to VGA Male Video Converter Cable For HDTV Projector Laptop Monitor
Aliexpress UK
This BNC to VGA video converter can support high resolution (up to 1920 x 1080) video picture. The video converter can provide high quality picture and give stable image output to VGA output device.
eBay
VGA To HDMI-compatible Converter with 3.5mm Audio Cable for PS4 PC Laptop TV Monitor Projector 1080P VGA Female To HD Male Adapt
Aliexpress UK
CGA signal output(15K). Output Signal CGA: 640 480 P7 VGA: By Pass P4 Video: 480p NTSC and PAL P5 S-Video: 480p NTSC and PAL P6. Supports VGA output by pass. 1x Video Output Converter Board. Video/S-Video output.
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NEW VGA to HDMI-compatible Audio Video Converter 1080P HDMI-compatible To VGA Adapter Cable For PC Laptop to HDTV Projector
Aliexpress UK
CGA signal output(15K). Output Signal CGA: 640 480 P7 VGA: By Pass P4 Video: 480p NTSC and PAL P5 S-Video: 480p NTSC and PAL P6. Supports VGA output by pass. 1x Video Output Converter Board. Video/S-Video output.
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USBC to VGA Cable 1080P USB Type C Adapter HD TV Cable Converter for Phone MacBook VGA Monitor Projector Connecter
Aliexpress UK
This BNC to VGA video converter can support high resolution (up to 1920 x 1080) video picture. The video converter can provide high quality picture and give stable image output to VGA output device.
eBay
Mini DP to VGA Cable Adapter Mini Thunderbolt to VGA Converter 1080p Mini DisplayPort Display Port For HDTV For MacBook Air Pro
Aliexpress UK
This BNC to VGA video converter can support high resolution (up to 1920 x 1080) video picture. The video converter can provide high quality picture and give stable image output to VGA output device.
eBay
VGA to HDMI-Compatible Converter Adapter with 3.5mm Audio Video Cable VGA Input HDMI Output for Computer Laptop TV Projector
Aliexpress UK