UHF/ RF Modulators For TV Systems Explained

March 15, 2023

What Is A RF Modulator & How Does It Work?


To learn more about RF modulators, what they do and how they work, read on for an in depth description including their uses with TV systems with tips and advice on how to do this for yourself. If you’re not familiar with the term’s modulator or modulation, worry not we will cover this too but the short of it is, if you wanted to convert a source of AV equipment into a TV channel that could be tuned into and received by a television receiver, you would use some form of modulator in order to achieve this. Lets begin!


What Is Modulation?


Before we rush off talking about this subject, it helps to understand what modulation means with regards to the transmission of radio-waves or TV signals. Modulation means the transmission of a signal over a carrier wave. This could be the over a wireless or wired medium. There are many types of modulation that most people are already familiar with. For instance, AM or FM radio which standards for Amplitude Modulation and Frequency Modulation respectively, but there are many other types that we are concerned with as aerial/ satellite/ AV installers.


Demodulation in this respect, is simply the method of extracting the modulated signal from the carrier wave, for digital TV this would be the method of converting the binary data (bits) into a TV picture.


What Is The Purpose Of An RF Modulator?


RF Modulators within TV systems are used to turn an AV source into a digital or analogue TV channel that can be tuned into TV’s or distributed via a TV system, examples include Sky Q box, DVD/ Bluray player, games console etc. It used to be common that many sources of Audio Visual equipment would have it’s own built-in modulator, like VCR’s where it could be tuned if a SCART or RCA connection wasn’t possible. Or Sky boxes where you could watch your Sky box in separate rooms via the RF2 connection.


These days, UHF TV modulators typically are an external device that will connects to a video output from your AV device and converts this to an RF channel. I have already written a couple of articles where the use of modulators is suggested which you may want to check out once finished here, this includes how to integrate CCTV into a TV system.


Types of TV Modulators

Although there are many types of modulators available, there are two main types that we use with the installation of TV systems that I have already mentioned.


Analogue RF Modulator

An analogue RF modulator would typically convert a RCA or SCART connection into an analogue TV channel. If you’re unsure what the RCA connection is it’s the red, white, and yellow phono leads that transmits stereo sound (red, white) and composite video (yellow). There are many types of analogue TV standards but within the UK we used PAL which stands for Phase Alternating Line, this is important to know when installing a modulator you need to ensure that the modulator you use is compatible with your demodulating equipment. Other countries outside the UK often used different standards, for example in France they use SECAM.


Digital TV Modulators

Digital TV modulators typically would convert an HDMI output signal into a digital multiplex to tune into a digital TV channel. Because of the process/ equipment required to do this, digital RF modulators are usually significantly more expensive than analogue versions and they’re usually a little bit more tricky to set up as a bit more technical knowledge is usually required. With digital TV modulators, there are two main types. These are ones that are compatible with the DVB-T standard and others that are compatible with the DVB-T2 standard, it’s very important that you make sure that your demodulation equipment is compatible, as TV’s branded as ‘Freeview’ but not ‘Freeview HD’ are not compatible with the DVB-T2 standard. This can be especially confusing as ‘HD Ready’ and ‘Full HD’ refer to separate things, meaning that you could have a Freeview compatible TV that is either Full HD compatible or HD Ready and it still not be compatible with Freeview HD. For your reference Freeview HD which is compatible DVB-T2 uses MPEG-4 compression for predominantly high definition TV services. Full HD and HD Ready applies to HD picture resolutions.


Analogue vs Digital RF Modulator

The advantages of the analogue option is that it’s that it’s considerably less expensive than the digital option. An analogue option will generally be 1/5th of the price of the digital equivalent, maybe even less still. It’s also less complicated to install an analogue modulator as less technical knowledge is required.


The main benefit of the digital option is that it offers a much greater picture quality. Since everything went digital and we can now stream 4K images, we have quickly become accustomed to very high quality video, so an analogue TV picture especially on larger TV screens may be acceptable for you anymore. Digital signals will also work best for when there is a busy UHF spectrum as digital services can be placed on adjacent UHF channels whereas you need a few channels buffer for analogue services. You will also likely futureproof yourself for longer as I’m sure one day in the not too distant future analogue tuners will no longer be built into TV’s.


Installing a UHF Modulator

The process of installing a modulator is relatively simple, first I will explain how you would install an analogue modulator and then explain how the set up for a digital modulator may differ. Most modulators would typically have a video input, RF input, and RF output. The RF input is not essential to be connected for the working of the modulator but is used for when you wish to combine with existing TV signals with the modulated signal from your AV source. The RF output would be both the TV signals and the modulated signal to feed to other TV’s.


1-     Connect the AV source to the modulator. (Usually RCA phono’s for analogue systems)

2-     Connect the RF output cable. This is usually a coax cable with F plug connection.

3-     Select frequency output of modulator, this will usually be a UHF channel number 21-69 which associates with a small frequency range.*

4-     Connect the RF input cable if required.

5-     Connect TV to RF output cable of modulator. This will almost certainly be a male coax IEC plug, commonly referred to as just a “coax plug”.

6-     Tune the TV in to receive the modulated signal. As you already know the frequency output you could manual tune the TV supports this or just run an auto-scan.


* If you’re also connecting a RF input signal, you need to make sure that this does not overlap existing frequencies being received by your TV aerial. You may need to do some research on what signals are being transmitted by local TV transmitters to you or try a few different frequencies to find one that works. It’s a good idea these days to avoid UHF channels 50 and above as these are now used for 4G and 5G mobile broadband services, would could interfere with the signal or if you have filters in place could filter out the modulated signal.


Installation of Digital TV Modulators

There are many types with slightly different facilities, but generally speaking follow the process below. When setting up a digital modulator the main difference is you will also need to set a Logical Channel Number (LCN). This is the number of the channel that the AV source will appear on your digital TV. You need to make sure when setting the LCN number and combining with an existing TV service that you pick a channel number that doesn’t correspond with an existing TV channel. For example you can’t choose 1, because that would be BBC 1 already in the UK, you can’t choose 2 because that would be BBC 2 etc. I’m sure you get the idea already, but I recommend picking a number within the 900 range to be on the safe side. If you’re not combining your modulated signal with an existing TV aerial signal, this is not important as there will be no clash with LCN numbers.


You will also typically have a signal gain option. The is the level that the modulated AV signal will be amplified to, usually given in dB before leaving the RF output of the modulator. You should try and set this to a similar strength to your existing TV signals if known. If not, some tips of advice would be: turn it up for longer cable runs and turn it down for shorter ones or where passing through another separate amplifier.


Finally, you may have a QAM adjustment option. QAM standards for Quadrature Amplitude Modulation as it’s a bit above this article but it regards to the amount of bits that will be transmitted per cycle. When setting the QAM it’s best to just check what digital TV services in your area use and copy that. 32 QAM would usually be a good option. To set the QAM too low or high with a TV that does not support it would mean that the TV will not be able to tune into it and it will not work.


What If I Need To Use The Video Signal For My First TV?

The obvious potential drawback with fitting a modulator to a video output of your AV device, is that what if you need to connect that video output to both a TV directly and to the modulator. This is especially true where more and more equipment like Sky Q boxes only have a HDMI video output now. You have a few options here:

1- Connect modulator and TV via different video outputs. If you’re AV device has both HDMI and RCA outputs, you could connect one to TV and one to modulator. Obviously the HDMI output would offer the superior picture quality in this instance so you may want to connect that to the TV that is used the most.

2- Install some form of splitting equipment. If you have one HDMI output signal you could install a 2 way HDMI splitter/ amplifier and connect both. HDMI distribution can get quite complicated with different TV’s supporting different resolutions, so it’s best to choose the same resolution all TV’s. If you need to run different you may need to individually upscale/ downscale the HDMI outputs to achieve this.

3- Purchase a modulator with a video loop signal, most don’t have this facility so you need to check. For HDMI modulators, this will mean that it has a HDMI input and output. The input connects to your AV source, the output connects to your TV.

4- Connect your first TV to your AV equipment with the modulated signal itself and tune it into your TV. This may mean having to install a splitter or amplifier after the RF output of the modulator itself to allow you do this.


Picking The Correct RF/ UHF Channel For Your Modulator

As briefly touched on above, picking the correct RF channel for your modulator can be a bit of trial and error as it will change from region to region. This is important when integrating with an existing TV system, but should you wish to apply a bit of method to the madness. You can try following:

1- Avoid channels 50 and above where possible to avoid potential 4G/5G interference.

2- Find all the frequencies that nearby transmitters broadcast on. Please read our previous blog 'Find TV Transmitter In My Area' for help and advice and avoid using these.

3- Avoid channels immediately beside frequencies that are being broadcast. If a transmitter broadcasts on channel 30, avoid channels 39, 41.*

4- Due to harmonic relationships, try to avoid frequencies 3,5, and 9 channels apart from those already being broadcast on. If the transmitter is again broadcasting on UHF 30, try to avoid channels 27, 33 for 3 channels apart, 25, 35 for 5 channels, and 21,39 for 9 channels. Please note that the potential detrimental harmonic effect decreases with distances away from the original frequency. This means that using a channel 9 channels apart is preferable to 3 channels apart.

*Please note that digital TV channels can be placed beside one and another, meaning there is no need to leave a buffer channel and it’s less important to avoid harmonics.


Modulators With IR Equipment Control Facility

If just being able to transmit your AV equipment through your TV system for you to watch isn’t enough, you also need to be able to control the equipment as you would with an old Sky RF2 playback system there are options for that too.


You could purchase a modulator that also has the capability of relaying infra-red commands across the system, this works with an IR receiver/remote eye being installed and connected to the coax cable that feeds your 2ndTV and an IR wand/ emitter that sits in front of your AV device. The modulator will supply the DC voltage required to power the remote eye and the IR emitter will replay these back to the AV equipment. Care needs to be taken when setting up the IR emitter to make sure it sits in the correct place in front of your AV device. This process can be extended to control several AV devices with separate emitters being sited in front of each piece of AV equipment.


If the modulator you purchase does not support, infra-red control you can install an external device like a TV-Link Plus that will be installed in situ which will allow this facility.


Modulator For Sky Q Playback System

If you formerly had a Sky playback system where you could watch and control your Sky box in another room or around your house, you’re probably already aware that Sky Q no longer supports this type of system as it only has a HDMI video output on the new Sky Q box. I have already written a blog on how to distribute Sky Q around the home, but the solution described in the above section would be a good work around. I recommend the Triax MOD103THDMI to COFDM Modulator as being the easiest way to do this, this particular modulator is perfect for the task as it has a HDMI loop connection and IR compatibility so you can continue to use your Sky remote eye.


Commercial/ Communal Modulators/ SMATV Systems

If you have a block of flats where you wish to relay multiple services through your system, you could install multiple modulators. Or you could install a modulator with multiple video inputs, which can then distribute each all these across you system within a single multiplex.

SMATV stands for Satellite Master Antenna Television system, which is a Master Antenna Television System with the added benefit of additional channels being transmit through the system with the addition of modulated satellite TV signals. This was typically done with individual Sky boxes set to single channels and then combined into the system with one of the RF outputs. This type of system has fallen out of favour somewhat with the increased number of services available with digital TV and generally superseded by Integrated Reception Systems (IRS), but are still fairly common in hotels, gyms, care homes and so on. In fact, then gym I go to currently has one of the Sky Sports channels supplied from this type of system not working on the treadmills and exercise equipment and it hasn't worked for a while. Frustrating when you know how to fix!

RF/ UHF TV Modulator Questions

If you have any comments or questions arising from this blog, I will try to help where we can and we welcome feedback. Please post them in the Blog Comments section below only, and please be patient when awaiting a response. I answer these personally and may not be able to respond as fast you like. Please also DO NOT CALL OUR PHONELINES, we do not offer free over the phone technical support and advise and can't help you this way. Please also do not privately e-mail or fill out the website contact forms, I do not have time to respond privately and individually over e-mail. If you do send a question this way, the most likely outcome is that you will not receive a response.

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