Direct AV injection

[damien191]

nice, ill keep that in mind

[olkrwa]

Hi Damien.

My 16-inch Zenith porthole and 1948 teleking is running with direct input. When it works it works great. To make this work properly you need a video source of good quality. It is easy to get disturbance on the video if your media device has a cheap power supply and so on. My 16 Zenith using a media device with SD card and USB that just running in loop with old movies and commercials. To get a good result I had to add some ferrite core filters on media power supply and a galvanic isolator on the video AV connection. I leave you a link to a link to Antiqueradios for directions how to connect to the video amplifier tube and the audio connection. See also the link to my sets on youtube if you want to see my sets in use. Good luck

Best regards Kristian

https://antiqueradio.org/A-V_AdapterForVintageTVs.htm
https://www.youtube.com/channel/UCZm...yZtbykPkhUzCdg

[kf4rca]

A CATV modulator generally puts out about 60 db. Thats because some loss (12 db or so) occurs in the combining process with other channels that are also used. Generally the line level leaving the headend should be about 42 db so that the output from the first tap (say a 32 tap) is about 10 db.
A TV normally likes to see 0 to 10 db in to the tuner. Yes you can transmit from a modulator for a short distance. 78 db is 1 watt. 75 db is 1/2 watt.
Ideally you need a high gain antenna to put a decent signal around the neighborhood. But a yagi is directional. For a non directional antenna a super turnstile would be best.

[Findm-Keepm]

Originally Posted by kf4rca

78 db is 1 watt. 75 db is 1/2 watt.

dB (Decibels) express a ratio, not a value. Wattage is usually expressed in dBm or dBw, or in a 75 ohm system, dBmV.

30 dBm= 1 Watt
27 dBm= 1/2 Watt

The above are for a 50-ohm system.

For a 75 Ohm system, dBmV = dBm + 48.75 dB

Best calculator out there:

http://earmark.net/gesr/opamp/db_calc.htm

I graduated Channel Master's MATV/CATV course in the early 80s. They beat it into your head that 75ohm (TV) and 50 Ohm (everything else, at that time) had different calculations and that 78dBmV = 1 Watt = 30dBm in a 75 ohm system.

I went from that world into the military, where everything is pretty much based on 50 ohms, and you never forget that 0 dBm = 224mv(RMS) = 1mW and 30dBm was still one watt...

The pulsed power bench I worked in my first 6 years made it even harder, as duty cycle entered the picture, and peak power would be in the MegaWatts region, but RMS power was down in the Watts region.....

My Jerrold VHF-UHF Field Strength Meter is still the only instrument I own with a meter that will measure dBmV.

[damien191]

Originally Posted by olkrwa

Hi Damien.

My 16-inch Zenith porthole and 1948 teleking is running with direct input. When it works it works great. To make this work properly you need a video source of good quality. It is easy to get disturbance on the video if your media device has a cheap power supply and so on. My 16 Zenith using a media device with SD card and USB that just running in loop with old movies and commercials. To get a good result I had to add some ferrite core filters on media power supply and a galvanic isolator on the video AV connection. I leave you a link to a link to Antiqueradios for directions how to connect to the video amplifier tube and the audio connection. See also the link to my sets on youtube if you want to see my sets in use. Good luck

Best regards Kristian

https://antiqueradio.org/A-V_AdapterForVintageTVs.htm
https://www.youtube.com/channel/UCZm...yZtbykPkhUzCdg

thanks for the info - and definately going to take a look at your you-tube page

[msimendi]

Damien,

Is this what you are looking for?

https://antiqueradio.org/A-V_AdapterForVintageTVs.htm