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TheMG
Premium Member
join:2007-09-04
Canada
MikroTik RB450G
Cisco DPC3008
Cisco SPA112

1 edit

TheMG to Karride

Premium Member

to Karride

Re: Cheaper source for this or something similar

Cheapest would probably be to make them.

For a basic DC over coax, a couple of capacitors and an inductor is really all that is needed. One of the capacitors will block DC from reaching the RF port of the devices, while the inductor and another capacitor form a filter to prevent RF from reaching the DC source.

Here's some good old ASCII art:

DEVICE RF-----||-----*------COAX
                     |
              C1     (
                     ( L1
                     (
                     |
                     *----
                     |    |
                     |    - C2
                     |    -
                     |    |
                     |   ___
                     |
                DC IN/OUT
 

Commercial units may have additional components for protection, voltage regulation, etc. But you can get away without those, especially for a shorter run.
lutful
... of ideas
Premium Member
join:2005-06-16
Ottawa, ON

lutful

Premium Member

said by TheMG:

Cheapest would probably be to make them.

Bias Tees with F connectors are widely available from local satellite installers. Maybe $15 new but surplus ones are even cheaper.

Minicircuits also sell just the guts (your ascii schematic) as a tiny module which can be soldered to any type RF and DC connectors. Less than $10 but involves shipping.
public
join:2002-01-19
Santa Clara, CA

public

Member

said by lutful:

said by TheMG:

Cheapest would probably be to make them.

Bias Tees with F connectors are widely available from local satellite installers. Maybe $15 new but surplus ones are even cheaper.

The camera is likely baseband video, not rf.
TheMG
Premium Member
join:2007-09-04
Canada
MikroTik RB450G
Cisco DPC3008
Cisco SPA112

TheMG

Premium Member

said by public:

The camera is likely baseband video, not rf.

Same difference. NTSC composite baseband video has content up to about 4.2MHz.

The same principles of transmission lines, impedance, filters, etc apply.
public
join:2002-01-19
Santa Clara, CA

public

Member

said by TheMG:

said by public:

The camera is likely baseband video, not rf.

Same difference. NTSC composite baseband video has content up to about 4.2MHz.

The same principles of transmission lines, impedance, filters, etc apply.

Yes but at the low end your inductors will not be feasible.
54067323 (banned)
join:2012-09-25
Tuscaloosa, AL

54067323 (banned) to public

Member

to public
said by public:

The camera is likely baseband video, not rf.

Which is why satellite coax should not be used to carry such a signal.

Baseband video requires a coax with a solid copper core, not copper plated steel which is what is found in satellite and CATV coax.
lutful
... of ideas
Premium Member
join:2005-06-16
Ottawa, ON

1 edit

lutful to public

Premium Member

to public
said by public:

The camera is likely baseband video, not rf.

I am curious how that commercial power injector device (linked in original post) is working.

The fluctuating "dc" power waveform will be superimposed on the lower end of the baseband video waveform.
54067323 (banned)
join:2012-09-25
Tuscaloosa, AL

54067323 (banned)

Member

?
54067323

54067323 (banned) to lutful

Member

to lutful
said by lutful:

since fluctuating "dc" power waveform will be superimposed quite far into the baseband video waveform?

Thats an incorrect assumption.
lutful
... of ideas
Premium Member
join:2005-06-16
Ottawa, ON

lutful

Premium Member

said by 54067323:

said by lutful:

since fluctuating "dc" power waveform will be superimposed quite far into the baseband video waveform?

Thats an incorrect assumption.

OK genius, what do YOU think will the DC waveform look like as the camera is operating? Please draw a sketch showing 0 Hz to ??? Hz spectrum content.

Of course, you also have to draw what you think the baseband video spectrum will look like from 0 Hz to ??? MHz.
54067323 (banned)
join:2012-09-25
Tuscaloosa, AL

54067323 (banned)

Member

said by lutful:

OK genius, what do YOU think will the DC waveform look like as the camera is operating?

First you can knock off the condensending comments, then you need to realize without knowing the cable length, gauge and makeup and the power drawn by the camera, coming up with anything would be a pure assumption.

But assume on if you wish.

BTW what do you think happens if you cut off 2 meg of the videos bandwidth?

lutful
... of ideas
Premium Member
join:2005-06-16
Ottawa, ON

lutful

Premium Member

said by 54067323:

... you need to realize without knowing the cable length, gauge and makeup and the power drawn by the camera, coming up with anything would be a pure assumption.

If you search my old posts in DSLR, you will probably find hundred entries on every technical aspect of supplying power over ethernet and coax cable to WISP nodes. FYI some nodes require 100W.
said by 54067323:

BTW what do you think happens if you cut off 2 meg of the videos bandwidth?

There will be no video at all if you cut off DC-2Mhz of NTSC spectrum.

However ... the devices used for satellite/antennas cut off just the DC-20Khz portion of the "baseband" spectrum to supply power and pass at least upto 650Mhz.
54067323 (banned)
join:2012-09-25
Tuscaloosa, AL

54067323 (banned)

Member

said by lutful:

However ... the devices used for satellite/antennas cut off just the DC-20Khz portion of the "baseband" spectrum to supply power and pass at least upto 650Mhz.

Really now...

»www.solidsignal.com/pvie ··· atellite Splitters&sku=874409002404

Last time I checked 2MHz was slightly different than 20KHz.
54067323

54067323 (banned) to lutful

Member

to lutful
said by lutful:

However ... the devices used for satellite/antennas cut off just the DC-20Khz portion of the "baseband" spectrum to supply power and pass at least upto 650Mhz.

Um, BTW satellite LNB's output on "L band" which is 950-1450, as such "up to 650Mhz" ain't gonna make it.

Just thought you would want to know.
lutful
... of ideas
Premium Member
join:2005-06-16
Ottawa, ON

3 edits

lutful

Premium Member

Click for full size
said by 54067323:

said by lutful:

However ... the devices used for satellite/antennas cut off just the DC-20Khz portion of the "baseband" spectrum to supply power and pass at least upto 650Mhz.

Um, BTW satellite LNB's output on "L band" which is 950-1450, as such "up to 650Mhz" ain't gonna make it.

a) The phrase "pass at least upto 650Mhz" implies that there are other devices which pass even higher frequency.

I personally use a custom bias tee design which passes upto 6Ghz and we do need that for TV whitespace, 900Mhz, 2.4Ghz, 3.6Ghz and finally 5.8Ghz radios.

b) However ... there are many satellite down converters which convert C/Ku band RF directly to (70Mhz or 140Mhz) intermediate frequency. These devices need a lot more power than a LNB. There are also bias tees for HF antenna amplifiers which need not go that high in frequency.

P.S. I helped to bring satellite-based internet to my country way back in 1996 ( »Re: low on budget middle of nowhere ) and founded a WISP equipment company back in 2002. I hope you will not continue the argument just to educate me.

*** Perhaps you, public See Profile, and TheMG See Profile will together come up with L and C specs for the generic bias tee schematic. A design which passes 10Hz-10Mhz should be perfect for the baseband cameras. Keep the power supply spectrum below 10Hz and don't forget to match 75 ohm coax.
54067323 (banned)
join:2012-09-25
Tuscaloosa, AL

3 edits

54067323 (banned)

Member

said by lutful:

a) The phrase "pass at least upto 650Mhz" implies that there are other devices which pass even higher frequency.

Funny way to imply that and it leads me to believe you didn’t even know the specs of what you where recommending until you read the link I posted and then realized it would not work as recommended.

However ... there are many satellite down converters which convert C/Ku band RF directly to (70Mhz or 140Mhz) intermediate frequency.

Which has nothing to do with what you recomended.
said by lutful:

I had already suggested the common power adders/inserters used for satellite LNBs which are designed for 75 ohm "dish cable" and later mentioned that 75 ohm BNC-F adapters are quite common and very cheap.

Which by your own admission, will not work.
said by lutful:

There will be no video at all if you cut off DC-2Mhz of NTSC spectrum.

But nice try at covering that error up by changing the subject, which you do so often it's predictable...
lutful
... of ideas
Premium Member
join:2005-06-16
Ottawa, ON

lutful

Premium Member

said by 54067323:

said by lutful:

a) The phrase "pass at least upto 650Mhz" implies that there are other devices which pass even higher frequency.

Funny way to imply that and it leads me to believe you didn’t even know the specs of what you where recommending until you read the link I posted and then realized it would not work as recommended.

FYI a power inserter that passes (x Khz to 650Mhz) range will definitely work with any analog CCTV camera.

I could design converters to support even 72 NTSC cameras on a single coax using that device.
said by 54067323:

said by lutful:

However ... there are many satellite down converters which convert C/Ku band RF directly to (70Mhz or 140Mhz) intermediate frequency.

Which has nothing to do with what you recomended.

FYI any bias tees that passes Khz to 70MHz would work with any analog CCTV camera out there and could even support 8 NTSC cameras on single coax.
said by 54067323:

said by lutful:

I had already suggested the common power adders/inserters used for satellite LNBs which are designed for 75 ohm "dish cable" and later mentioned that 75 ohm BNC-F adapters are quite common and very cheap.

Which by your own admission, will not work.

Not at all ... see comments above. FYI it was YOUR knee-jerk assertion that such devices would not work which prompted this debate. Go back and read all your comments.
said by 54067323:

said by lutful:

There will be no video at all if you cut off DC-2Mhz of NTSC spectrum.

But nice try at covering that error up by changing the subject, which you do so often it's predictable...

Actually YOU brought up the 2Mhz cut-off into the discussion after failing to understand how/why power spectrum will extend beyond DC/0Hz.

*** Once again, you guys all together can come up with values for L and C on that ascii schematic that will pass X Hz to 10Mhz and match approx 75 ohm. Explain what X should be to power a typical NTSC CCTV camera over 100m RG59 coax. No, X can't be 1Hz or even 10Hz.
54067323 (banned)
join:2012-09-25
Tuscaloosa, AL

54067323 (banned)

Member

said by lutful:

Actually YOU brought up the 2Mhz cut-off into the discussion after failing to understand how/why power spectrum will extend beyond DC/0Hz.

Na, I have actually known about that since Pelco prior to being acquired released this bulletin back in the late 80's.

»www.pelco.com/sites/glob ··· ble.page

FWIW I have been doing CCTV since RCA was selling B&W cameras with vidicons in them.