HF RADIO NOISE SOURCES
6/8/07
1.2 & 2.4GHz VIDEO SENDERS
HF RADIO NOISE SOURCES
Monday 6th August 07
This is a new section that we hope to add to that will include various information on noise sources to HF Radio reception & how they can possibly be fixed.
INVERTER AIRCONDITIONERS
HOME APPLIANCES SOON
POWERLINE NOISEThe Inverter Air conditioner is a wonderful domestic appliance that will gain popularity due to the much lower cost to run compared to conventional air conditioners. Unfortunately it can be a very bad source of high frequency interference from the Inverter unit. Many do not have adequate filtering & can cause interference up to many hundreds of metres to HF Radio reception. The most common symptoms are wide band noise on the 40M band which just sounds like an increase in the noise floor up to S9, & noise spikes every 30 to 100kHz on the 20M bands & higher. Noise blanker's will not work at all as the noise is high frequency noise like atmospheric & corona noise. If you have one then you will definitely want to fix the noise as it is extremely annoying & impossible to operate HF. If your neighbor has one then you have an even bigger problem. Recently I purchased one as can be seen in the picture below. Its just brilliant in cooling the home & very cheap to run but it completely wiped out HF to 6 M operation. Initially I fitted a large number of clip on ferrites 15 in total, ( Jaycar Part # LF-1290 ) with some success, & earthed the air conditioner to the copper water pipe with a short length of braided cable. It cut the noise from about S9 to S7 on 40 Metres & around 3 S units on 20M. It was still however very annoying tuning around on 20M & 40M was useless when the unit was running. I recently found a mains filter MB1236 sold by Amtex in Australia for around $200 that seemed like it might do the job. It is a very high quality unit made by Lambda & rated at 35 Amps @ 50 degrees C. The filter has an attenuation of 40 to 60dB between 1 & 20MHz in Asymmetric mode. The unit was fitted inline with the single phase 240 Volt input for testing. The noise has basically disappeared & is now very difficult to hear through the noise floor at all. So it all looks quite successful & the filter can now be mounted inside a sealed box from the weather.
PICURE ABOVE SHOWS THE JAYCAR CLIP ON FERRITES THAT WERE USED FOR SOME TIME, & THE NEW MB1236 FILTER THAT WAS TEMPORARILLY INSTALLED FOR TESTING.
POWERLINE NOISE
Power line Noise can greatly affect operation on the HF & even up into the UHF spectrum depending on how close the noise source is. Below is a list of potential problems that can exist not only to Radio Amateurs but the general public.
Noise source around 300M or further away
1/ Bad or slight dot pattern on VHF TV mainly low band VHF.
2/ Interference on the HF Radio bands up to Low VHF which can normally be fixed with the Noise blanker
Noise source very close & up to 300M away
1/ Same as above but worse, may also affect VHF high band TV
2/ Interference to VHF FM Radio especially weaker community stations.
3/ Interference on HF & VHF Radio that overloads the Radio & pumps the AGC & cannot be eliminated with the noise blanker.
4/ Interference all the way to at least 1.2GHz even causing noise on strong FM radio transmissions.
5/ Interference to cordless telephones making them unreliable.
6/ Intermittent dropout of the mobile phone or not being able to make or receive calls.
7/ Sometimes not being able to open or close 433MHz garage doors. Also interference to other 433MHz devices.
8/ Possible interference to wireless 304 & 433MHz devices & security systems.
9/ Intermittent dropout of Digital TV
In the US power line noise is considered a quality of life issue & is dealt with promptly. The stress can be immense if it starts to affect the things that many of us take for granted in life. The constant reminder when using consumer products around the house like sitting down to watch your favourite TV show & the screen being covered in large white dots, or wondering why the remote won't open the garage door. In Australia its often very time consuming & very stressful just to get anything done & can take years. We have set standards for all things but rarely any are policed. We live in a world of self policing where very few are ever fined or at least told to abide by the standards. We have a Frequency Spectrum regulator that no longer wants to deal with interference issues, & little knowlege now exists in power utilitys or the TV repair industry to resolve problems. We allow the import of electronic products that are not up to Australian standards, or not legal for use to be sold in Australia.
Power line noise is a big problem in South Australia due to poor matinence & engineering practices. Many noise problems are from 11KV lines due to the use of horizontal insulators taking up the slack in the cable. Common problems are crook brushes in the horizontal insulators & bad & loose hardware. Other problems include cracks in the vertical insulators & broken or corroded earth straps on the pole. Transformers rarely cause noise problems, buts its these poles that normally generate noise due to the insulator & cable setup like the picture below. Below is a typical installation 20 metres from my house that has caused considerable problems in the past number of years. The picture clearly shows a number of poor engineering practices. Static build up on the insulators rely on the hook & eye connections for a return to earth connection which can freely move in wind. The picture clearly shows the centre hook relying on a rusty bolt for the connection. Better practice would be to have bonding straps across the hook & eye connections.
The picture below shows the extensive replacement of Insulators, & all cables including the main spans. Unfortunately the rusty bolt still remains on the bracket connecting the centre insulators hook. This is particularly troublesome after rain for a number of weeks probably due to new surface rust, & taking time to wear through to clean metal.
Below is a rather old commercial ultrasonic detector still used by the South Australian power utility. The idea is that you use it like a boar sight by look at the poles hardware through the hole in the centre of the back of the dish & line up the hole in the end where the 3 black arms house the ultrasonic receiver. These detect high frequency audio noise from the source but need line of site to hear the noise. They will not work if the noise source cannot be seen & may be on the opposite side of an insulator, or if the distance is too far to the noise source.
What can you do to fix your own problems
1/ Don't complain to your power utility until you have some facts to give them. Take notes on the times the problem occurs, & attempt to find the noise source. A Yaesu FT817 on AM mode with a suitable 430MHz yagi works extremely well to find the actual pole. You probably won't be able to find the cause on the pole as it will not be directional enough, but this should be enough information for the power utility.
2/ Ring the power utility & ask the quality control section to log the call as an interference problem & get a customer complaint number. Soon after you may get a call from the interference section or someone may knock on the door to investigate. Explain the problems you are having, & if the problem is present at the time, demonstrate the problem & possibly help the utility by showing the pole using your FT817 on 430MHz. This helps to reduce time for them to investigate with their own equipment. Try to get on well with the people that are investigating.
3/ Keep ringing at least every month as a reminder that you are serious, & quote your number & ask when it will be fixed. Keep an eye on the pole as quite often work may have been done already but they don't tell you. If the problem remains after repair ring them again.
4/ Be aware that there can be multiplie noise sources on a short distance of power line & poles that may show up after the initial problem was fixed. In fact it can take so long to eventually fix one problem when another has deteriorated & now causes noise.
5/ Buy a Digital free to air set top box this will greatly increase your TV watching pleasure.
6/ For HF radio operators try the MFJ1025 / 1026 noise canceller. I have one & its amazing at eliminating the noise at my location. You will need a good noise antenna closer to the noise source compared to your main antenna. I use two G5RV antennas at right angles with one along the road fence line around 20M from the power pole used as the noise antenna. S9 plus noise is completely eliminated. Some tuning of the controls when tuning across a band or changing bands is needed but is worth the effort. It even works on the radar interference from the asia area.
7/ Make sure that you tell the power utility. I hear many Amateurs, ( Hams ) complaining on HF but they never do anything about it. If you get on well with your neighbors ask them if they have any dot interference on their TV sets. Ask then if they would call the power utility & make a complaint about the interference. The more neighbours complaining may get quicker action. It could however cause other questions from the neighbor about other interference they may be getting.
1.2 & 2.4GHz VIDEO SENDERS This information is supplied to hopefully answer some of the questions asked about 1.2 & 2.4GHz video senders & using them for video links & ATV. Some time back I was able to evaluate a few of the 2.4GHz video senders & security links that are available in Australia & Overseas. Recently I have also been able to look at some of the 1.2GHz Video Senders. They are reasonable value for money when used for the purpose that they were designed for. However most were not suitable for ATV without major modification, as they have quite a few deficiencies. I have listed the problems below. A large number of senders are using SP5055 or TA1322 PLL ICs in the tuner modules, & a SMD version of the PIC or similar microprocessor to control the PLL. If you are looking at using sender RX or TX units for ATV, then be very careful what you buy. Make sure that they can be reprogrammed for the ATV frequencies & ask others what they are using. The manual tuned receivers have very little frequency drift & would be a good choice.
900MHz ( 0.9G )
All systems use 4 Channels. The common frequencies used are 910, 980, 1010, 1040MHz, ( 5.5MHz or 6.0MHz Subcarrier available ). These are not legal in Australia & many other countries.A Message from Marcel VK4TMH has allerted me to a possible threat to the IARU Protected worldwide Airtraffic Radar frequencies of 1.030 / 1.090GHz. The 3dB points of the receivers are 10MHz wide so frequency channels of 1040 & 1080MHz should not be used. Marcel reports of an interference problem to an overseas Airport radar by a video sender on 1080MHz operating from an Hotel that greatly reduced the radars range.
Many 900MHz Cameras that have inbuilt transmitters are not PLL & have free running oscillators that may drift with use.
1200MHz ( 1.2G )
All systems use 4 Channels. ( Recently lower cost manual tuning versions have
appeared ). The common frequencies used are 1080, 1120, 1160, 1200MHz, ( 5.5MHz & 6.0MHz Subcarrier available ). The standard 4 Channel fixed frequency versions are not legal in Australia & many other countries. The manual tuned version will go from around 800 to 1300MHz which could be used for ATV. Most PLL & manual RX versions use a standard 900 to 2150MHz tuner module. Reprogramming a PLL RX for 1250 or 1283MHz reception in Australia will depend on whether you can identify the microprocessor & PLL chips that have been used. Some manufacturers remove the markings on the chips in the factory to make it difficult to identify the chips.Many 1200MHz Cameras that have inbuilt transmitters are not PLL & have free running oscillators that may drift with use.
12 Channel ( 0.9-1.2G )
A new channel system has just been released. The receiver has 3 sets, ( Low Medium, High ) of 4 channels, making a total of 12 channels. The common frequencies used are 910, 980, 1010, 1040, 1.080, 1.120, 1.160, 1.200, 1.240, 1.280, 1.320, 1.360MHz,
( 5.5MHz or 6.0MHz Subcarrier available ). These are not legal in Australia & many other countries. Transmitters currently available using the 12 channel system range from 100mW to 30Watts.2400MHz ( 2.4G )
All systems use 4 Channels. ( Recently lower cost manual tuning versions have
appeared ). There seems to be various 4 channel frequencies that are used. The first lot is 2410, 2430, 2450, 2470MHz, ( 6.5MHz Subcarrier ), The second set is, 2413, 2431, 2449, & 2467MHz, & 3rd set is 2413, 2432, 2451, & 2470MHz, ( 5.5MHz Subcarrier ). Only the two lower frequencies are legal in Australia for low powered 10mW maximum. The two lower frequencies however do not line up with the 2415 & 2439MHz frequencies allocated in the WIA band plan for ATV. As was explained above with 1200MHz units, it may be difficult or impossible to reprogram the microprocessors in the PLL versions.12 Channel ( 2.2-2.5G )
Products with a new 12 channel system have just appeared on the Internet, January 08 The common frequencies used are 2.290, 2.310, 2.330, 2.350, 2.370, 2.390, 2.410, 2.430, 2.450, 2.470, 2.490, 2.510GHz. These are not legal in Australia & many other countries. Many are offered with high power transmitters up to 5 Watts.Be Ware that some companies many be selling sets of RX & TX that have slightly different frequencies. e.g. the Receiver May be 2410, 2430, 2450, 2470MHz, & the Transmitter might be 2413, 2432, 2451, & 2470MHz, or 2413, 2431, 2449, & 2467MHz. This may give less range on some frequencies.
Many 2400MHz Cameras that have inbuilt transmitters are not PLL & have free running oscillators that may drift with use.
New 4 Channel ( 5.8G )
A new channel system has just been released. The receiver has 4 channels in the 5.7 to 5.8Ghz ISM band. The common frequencies used are 5.7375, 5.7625, 5.7875, 5.8125 GHz, The retailer reports that these are not legal in Australia but the ACMA regulations don't specificaly mention video transmitters but they can be grouped under spread spectrum devices. A power of 10mW maximum is allowed. Initial tests are that the range is very poor through buildings & there is very high video noise indicating that no pre-emphasis or de-emphasis is used.
The information below is common with many 0900, 1200, 2400, 5800MHz units tested
1/ There is no such thing as a PAL or NTSC only video RX or TX. All are pseudo PAL/NTSC compatible& made to give reasonable results with any format. This means that the video response is flat & there is not Pre-emphasis or De-emphasis circuits in the RX & TX. A Pseudo TX generally is not compatible with anything other than a Pseudo RX. There is a large improvement with video quality if the RX & TX are modified to suit PAL or NTSC.
2/ Most systems did not have Video Pre emphasis in the transmitter, & De-emphasis in the receiver that is incompatible with our ATV systems, & produces more noise in the picture. Receivers that had some form of De-emphasis used a form of low pass filter in the video amplifier, & did not have a real PAL de-emphasis curve. I was not able to test the Audio Pre & de-emphasis.
3/ On the PLL versions a replacement microprocessor is needed for ATV. A reprogrammed micro for TX & RX units can be difficult to do unless you can identify the microprocessor & PLL ICs that have been used.
4/ The deviation used with some brands is rather low compared with the higher deviation that most of us are using, which requires readjustment of the transmitters deviation, & receivers video gain. The video level on one popular brand RX sold in the UK for ATV was not able to be turned down for higher deviation causing white crushing on the pictures. It also seemed to have a very narrow bandwidth SAW filter in the tuner module that was not able to fully pass a wider deviation ATV signal. It was however extremely good at seeing very weak signals which other receivers with wider BW could not see. The video quality however was extremely poor as the RX with the add on De-emphasis board had little or no colour or high frequency response. All other receivers tested were able to be used when adjusted ok.
5/ Two Security transmitter modules that were specified as 10mW were measured to be 100mW with +12volts supplied. These did not have an internal voltage regulator, & relied on zener diodes on the PLL & PIC microprocessor chips, & were specified for a voltage of between 9 to 12 volts.
6/ Some senders & receivers that have a PLL Synthesizer system, were slightly off frequency for the channel selected, so would not work over a long range when the signal became weaker. Some were found to be a few MHz off frequency, & the cause seems to be the programming of the microprocessor. It is possible that the frequency has been trimmed in the factory by adjusting the software in the micro to suit pairs of sender units. AFC ( automatic frequency control ) was not a feature used in any of the RX units tested.
Be Ware that some companies many be selling sets of RX & TX that have slightly different frequencies. e.g. the Receiver May be 2410, 2430, 2450, 2470MHz, & the Transmitter might be 2413, 2432, 2451, & 2470MHz, or 2413, 2431, 2449, & 2467MHz. This may give less range & generally poor results on some frequencies.
7/ Two receivers were reprogrammed to suit 2415 & 2439MHz. When tested they were not able to resolve the transmissions from the two ATV repeaters in Adelaide. They seemed to lack selectivity to reject other signals in the 2.4GHz band. This was compared to a EME91 2.4GHz downconverter connected to a standard analogue satellite receiver which produced perfect pictures.
8/ Most units with stereo sound use 6.0 & 6.5MHz. Some of the more simpler single channel audio units use 5.5MHz. This can be a problem as the frequencies can only be changed by replacing the ceramic filters & retuning the FM demodulator. In South Australia we have recommended audio frequencies for each ATV band from 1200MHz to 10GHz.
If you are looking for a very good 2.4GHz link system to use with your radio controlled aircraft etc, then I would recommend one of the readily available compact video transmitters used for security, along with a 4 channel compact receiver. For antennas use a 1.4 wave ground plane antenna on the aircraft pointing downwards, & receive, a high gain antenna like the gridpacks used for Pay TV pointing at the aircraft. A small PLL 2.4GHz transmitter & matching receiver is available from Mini-Kits.
Licensed Amateurs might consider using the 1250MHz band as it is a much lower cost alternative compared with 2.4GHz, & has very little interference. An EME154 1250MHz video TX Kit, & an Analogue satellite receiver with a EME103 KITS preamplifier is a good system.
TO BE CONTINUED
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