R F Modulator question

[k0ua]

How far is this coax?

 

[MikeInEburg]

The root of your trouble is loss over the length of coax. Channel 28 (RF 249MHz) has just about double the loss as compared to channel 3 on any given length of coax cable. While you don't mention the type of cable, if it's RG6, then you're losing 1.5dBmv per hundred feet of coax at channel 3, and 3.15dB per hundred at channel 28. For sake of discussion, say that you're launching at 40dBMV at the camera and your goal is 0dB at the monitor. So, 40dB at launch minus 4dB for combiner (backward splitter in your case) - now you're at 36dBMV leaving the barn. On channel 3, you'd arrive at house at 16.5dB, and on channel 28 you'd arrive the house at -4dB. This assumes you're really launching at 40dB. Check your modulator to see what they really output and update my math. My sense is that the channel 28 modulator is not 40dB, but rather 30dB output - which would account for the snowy picture. You'd be better off going back to channel 4 (or 5 would be better). If you can pad down the modulator signals (aka attenuate), then into an amplifier at the barn, you should be able to make this run work. Most amplifiers won't tolerate the input signal being in the 30dBmv range. Good luck!

 

[tallyho8]

The coax is 1200'. The camera on channel 4 has an excellent picture. The other modulator is a UHF monitor and starts at channel 13. Since we have over the air tv stations in the area that use all the channels between 13 and 26, I set this modulator to ch 28 to avoid interference.

 

[tallyho8]

Would I do better just purchasing this more expensive modulator that I could use to set my camera on channel 6?

Premium Agile RF Coax CATV UHF VHF Channel Modulator CH2-138 With 1dB Output | eBay

 

[k0ua]

It looks like it would do the job and the output signal is adjustable. BUT here is one problem I can see on the horizon, it only does air channels 14 thru 83, which is what you want to avoid as those are frequencies 471 MHZ thru 885 MHZ. Which you want to avoid as the losses in that very long cable you have are much much more than the lower VHF air channels where your other modulator is located on. Losses are much much lower at these low VHF air channels. It does do cable channels which will start at 48 mhz which would be ideal, BUT can you TV do both air channels and cable channels at the same time. This may have been the problem with the other modulator you sent back. Air channels and Cable channels are two different things. and usually you have to put your TV in air channel mode or cable channel mode. Remember Channels are just arbitrary numbers we put on frequencies. Frequencies are real and exist in the real world, Channels are arbitrary and just "labels" we put on certain frequency schemes. The cable and air channel schemes are different and arbitrary. So bottom line. Go buy two of these new devices and put one on channel 2 and one on channel 4 on the cable scheme, This will be the lowest frequency range starting at 48 mhz and will keep losses lower in your very long length of rg6 cable. You will have to adjust the levels to get things right. Get on the phone with someone on the TV end and make the level adjustment to overcome the loss in the cable.

Lets see what someone else has to say that deals with setting up CATV MATV devices has to say. But bottom line I say buy two of these, disconnect your current air scheme rf modulator on channel 3 air, and set your TV for cable and use two of the lower cable channels and set the levels correctly on your two new devices. Just what you wanted to hear isn't it.

This is why people set up multiple cameras as IP cameras and use wifi or ethernet as a backhaul to get it to their networks. I am certainly no expert in setting up CATV systems, I have a lot more experience in working with IP and IP devices, but if someone came to me and said I want multiple cameras in my barn the IP solution is the solution I would recommend.

 

[techman]

You could try putting an antenna amplifier, rated for UHF, at the end of the line to try to boost the signal. It might work and a cheap solution. Something like:

Amazon.com: Skywalker Signature Series SKY38323 25dB Amplifier VHF/UHF/FM w/variable gain (SKY38323): Home Audio & Theater

Paul

 

[k0ua]

Next thought that pops into my feeble mind is this:. If this proposed unit can do air channels 14 tru 83 and you have to avoid other air channels and use channel 28 like you attempted with your current UHF RF modulator, will this new unit with adjustable RF gain have enough power to drive that long run of cable and allow your TV on the other end to stay on "air" channels like it is now? Your current RF modulator is set to work on either air channel 3 or 4 which is down in the 60 to 70 mhz range and has enough "soup" to drive that length of cable down there on those low frequencies, but your new UHF modulator does not because the frequency is just to high and the coax losses really increase on those high frequencies. BUT maybe this new one would have enough power to drive it as is. MAYBE. I DON"T like the specification on the RF modulator saying it has 100 dB of gain. Gain relative to what? I am very suspicious when you don't specify gain in terms of a standard. Like dBm for instance or dBuv. I need a standard to measure gain. 100 dB relative to nothing could mean 100 dB relative to a horseapple for all I know.

Bottom line: I guess you could order one of these and see if it could work at the air "channel" 28 and if you could adjust the gain high enough to drive your cable. If not then order another one and set your TV up for CABLE and use the lower channels. Of course you may be using the TV to actually watch air TV channels too. you didn't say. See all the variables? This gets hairy in a hurry.

 

[k0ua]

You could try putting an antenna amplifier, rated for UHF, at the end of the line to try to boost the signal. It might work and a cheap solution. Something like:

Amazon.com: Skywalker Signature Series SKY38323 25dB Amplifier VHF/UHF/FM w/variable gain (SKY38323): Home Audio & Theater

Paul

yes, this is what I mentioned in my first reply to his current UHF modulator. Getting enough signal on channel 28 air to drive that 1200 foot of coax with that tremendous loss at these frequencies. "mo power".

that would have to go from the output of the UHF modulator BEFORE it hit his splitter/combiner so the VHF signal DOES NOT get boosted too as its level seems to be enough as is to drive his cable due to its low frequency and less loss in the cable.

 

[tallyho8]

I installed an amplifier between the UHF modulator and the splitter and my camera on Ch 28 got a decent picture. Not a good one but a decent one. BUT, then my camera on ch 3 has a bad picture. So that won't work for me.

 

[tallyho8]

I sent a message to the eBay seller of the modulator I mentioned previously and he responded with the following answer. I hope this means it would work.

New message from: weesolutions (17,332 )

Your previous message
I have 4 surveillance cameras. One is going to my tv on channel 4. With 3 of your modulators can I set them where the other 3 cameras will go over channels 6, 8 and 10?


Yes, you got this modulator figured out right. You can use 3 of these RF modulators to convert the video output from 3 of your cameras into 3 separate TV channels as desired, such as Ch6, Ch8 and Ch10 and then use a 4in 1 out coax RF combiner such as our ebay item 311466234667 to merge the RF outputs from 3 modulators and your 1st camera together into one coax cable and run into the TV so you can see each individual camera video by tuning into the corresponding TV channel.....

Regards,

Jason / Support

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