There are a number of different ways to measure video carrier frequencies some more accurate than others. This page won't explain how to record every signal precisely down to the Hz but it will allow you to display the frequency quickly and reasonably accurately to help other radio amateurs and DXers collect information on the unidentified TV signals in Africa.

The simplest way to measure the transmitter frequency is to use a communications receiver connected to some appropriate software, the radio is set to USB, tuned to a frequency that produces a tone from the transmitter and the resulting audio frequency is added to that displayed on the receiver. This combined total gives the transmitter frequency. This idea is fine in principle except it is rare for a radio to precisely on frequency, many will be a hundred or so Hz off and of course for most purposes this isn't a problem. Once again there are number of different solutions to this, most involve reference oscillators or external sources but the method I'm going to show although not as accurate will allow a reasonable degree of precision.

Firstly, the software I suggest using is Digipan from Skip Teller KH6TY, it's simple to set up and gives accurate results with the minimum of fuss. Digipan can be downloaded here. Connect the speaker or line out from your radio to the line in on the PC sound card, set the mixer to record from the line in and tune the radio till you hear a carrier. A bright yellow line will appear to scroll down the screen indicating the carrier frequency. While many of the features on Digipan are irrelevant for our use one handy tool is the marker than can be placed over the frequency in question, an AFC will lock it onto the exact spot to make it even easier and the result can be read in the bottom right hand corner of the programme.

This example is the BBC on 6.195Mhz with the radio set to USB and tuned to 6.194Mhz or 1Khz lower than the transmitter frequency, the result is a 1000Hz or 1Khz audio tone. Adding the tuner and audio frequencies gives the transmitter frequency of 6.195Mhz or 6195Khz.

The only problem with using this method for VHF television transmitters are they are rarely on the frequency they should be, either through design where the transmitter is offset from the nominal channel allocation to reduce interference with other stations or because it isn't using an accurate reference oscillator to lock it on frequency. Fortunately most of the high power 48 and 49MHz transmitters in Europe are regularly logged and their exact frequency recorded so if you are able to receive one of these a comparison can be made to calculate the error and an accurate reading taken of the signal being investigated. Knowing the exact frequency the TV transmitter is on allows accurate measurements to be made even with a radio that is slightly off frequency. Most transmitters will only drift a few tens of Hz so while you can't be sure you have the exact frequency the result will usually be good enough to identify it each time it appears. Amateurs in the UK have one more accurate reference, beacons GB3BUX use MSF derived oscillators and the carriers are precisely on 50.000 and 70.000Mhz, this is GB3BUX on 70Mhz taken with my IC-8500 tuned to 69.999Mhz USB.

So now armed with a known transmitter frequency you can tune the radio until you hear it's audio tone, add or subtract the difference between the listed frequency and the displayed frequency to calculate the receiver error and then use this difference when calculating other unknown transmitter frequencies. As an example, Spain is on 48.250.088 yet with your radio tuned to 48.249 you are receiving a tone on 1057Hz giving a result of 48.250.057Mhz, simply add 31Hz to this and any other carrier you discover. Alternatively, in Digipan simply add the error to the sample rate correction until the displayed frequency is accurate.

Some examples of E2 or 48Mhz carriers, with the radio set to 48.249.000 this shows two common carriers, the one on the left is Bantiger in Switzerland and the right signal is the Madrid transmitter of TVE. You can see from the grab that Bantiger is one of the few transmitters locked to a precise frequency, this one being 48.250.000Mhz.

Muro in Portugal is a useful marker as there are no other high power transmitters on a similar frequency so there is little chance of confusing it with anything else, this time the radio is set to 48.241.000 and the transmitter can be seen to be on 48.242.210Mhz.

The 49Mhz channel used in Eastern Europe and Russia also has some high power transmitters and a number of useful markers for frequency measurements. The first is Budapest Hungary on 49.739.531 and this example shows once again the radio tuned 1Khz lower on 49.738Mhz. Three carriers are present via ionoscatter and MS, a weak signal from Lviv in the Ukraine on 490, Budapest is marked on 531 and above that is Praque in the Czech Republic on 49.739.673

These examples rely on knowing what offsets some familiar transmitters are on, I will endeavour to keep the list here up to date but if you are stuck please email me and I'll reply with the most recent frequency I have listed for it. It isn't absolutely necessary to give frequencies to a single Hz and it could be argued that most will be inaccurate soon after measurement so even if you report it to tens or hundreds of Hz the information will be of benefit and greater use than a simple 48.250 video report.

My Cameroon page here shows just how useful measuring video carriers can be, without it I'd have missed the African opening completely.  Ian Roberts shows a number of different methods here and this is VK4CPs page on Digipan.

This method of carrier detection is also useful when watching for transatlantic signals on E3/A2 as the different mains frequency means any sidebands seen will be 60Hz apart instead of the normal 50Hz.

Finally, can I request that if you do receive a carrier you are unsure of, need help measuring or are able to ID as African please email me with the information so I can add it to the African round up page for the benefit of other radio amateurs and TVDXers.

48.250Mhz E2 transmitters.

48.242.210 IN51 RPT-1 Muro, Portugal.
48.250.100 LL75 EDTV Dubai, UAE.
48.250.088 IN70 TVE-1 Navacerada, Madrid Spain.
 

49.750Mhz R1 transmitters

49.739.531 JN97 MTV1 Budapest, Hungary.
49.744.792 JN86 MTV1 Nagykanisza, Hungary.
49.747.400 KO85 RTR Moscow, Russia.
49.757.620 KO46 RTR Glubokoye, Russia.
49.760.420 JN99 NOVA Ostrava, Czech Republic.