Supplying The Broadcaster and Hobbyist with The Ultimate FM Transmitter, Stereo Encoder, Limiter Kits from NRG
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FAQ (Frequently asked questions)


Question To Be Answered: I would be very grateful, if you could please give me a list of full setup's to be bought. This list should include everything I need to have to run a private radio station.

The Answer: In the UK, ALL FM Broadcast Radio Stations require a Radio Authority licence to operate within UK law.You need a Limiter/Compressor, FM Transmitter and an Aerial to get started. In addition you will require all the studio equipment. Please see our new PLL-PRO III transmitter line up and select the power level you require. 40 Watts is considered ample power for a small community radio station. A 13.8 Volt 7 amp power supply will also be required in most cases. If you are wanting to broadcast in stereo, then you will need a Pro III Stereo Coder.



Question To Be Answered: Why do I need a compressor when I've used a tx without a compressor before and it sounded fine.

The Answer: If you are broadcasting JUST pre-recorded music, then yes you will be able to set the volume (modulation) level on the transmitter to the correct level and it probably will be fine. That is provided that the pre-recorded music is all roughly at the same loudness level to start with. However, try broadcasting some live studio speech without a limiter compressor, and you will find major problems with both over and undermodulation. This is because live speech can vary by up to 20 times in level. The limiter compressor acts as an automatic volume control and will make sure the transmitted sound is as loud as it can be, but not overmodulated. For any serious broadcasting, a limiter compressor is mandatory, to prevent overmodulation. And remember, overmodulation will cause 'splatter' either side of your fm carrier which may cause interference to other radio broadcasters!



Question To Be Answered: My current xmitter (transmitter) splatters off of the assigned frequency, how can I avoid this with your xmitter (transmitter)?

The Answer: 'Splatter' is really a slang term for excessive transmitter RF bandwidth and is generally caused by overmodulation (too loud!). Which is usually caused because you are not using a limiter in front of the transmitter. Please make sure that you use a limiter and that you set the transmitter modulation control so that your signal is no louder than the other stations on the dial. The correct maximum transmitted RF bandwidth is plus/minus 100KHz, a total bandwidth of 200KHz. This means that a transmitter centred on 100 MHz, will actually transmit a whole range of 'sideband' frequencies between 99.9 and 100.1 MHz. At the listening end, the receiver will also have a receiving RF bandwidth of 280 KHz, or a 'window' of 280KHz space, is a good analogy. Now, if your receiver is tuned to exactly 100 MHz you should hear crystal clear sound. If you tune your radio to 99.9 or 100.1, you will still hear reasonable sound, with a little distortion. Tune your radio to 99.8 or 100.2 and you will hear distorted sound. This is normal. However, if you can still hear your signal at 100.4 or 99.6 then that is splatter and the transmitted sound level must be reduced. (note: FM receivers have the wide 280 KHz bandwidth to make sure that all the sidebands are recovered, for low distortion and good stereo separation, even if the receiver is lightly detuned.)



Question To Be Answered: I have one of your transmitters and a linear. I have 25-30W. I live on the first floor and i have installed my dipole on the 6th floor (roof). i have used 30m RG58 cable. Is it ok or i have to redoes the distance between the transmitter and the aerial? Would it be better to connect an RG8 cable?

The Answer: This is a very good question and you would be much better to use 30 metres of RG8, RG213 or UR67 coax cable instead of the relatively lossy RG58 cheap coax. With 30 watts of power going into 30 metres of RG58, you will have about 11 watts coming out at the aerial end. If you change the coax to the much better RG8 then you see about 25 watts at the far end, which is a loss of only 5 watts and quite negligible. As a general rule, for every 20 metres of RG58, you lose 50% of the power. So 100 watts into 40 metres of RG58 will get attenuated down to a mere 25 watts!



Question To Be Answered: I recently purchased a NRG 1 watt stereo transmitter from a builder here in USA. After several hours of operation the power drastically decreases. There is a small cooling fan built into case... however that may not be enough???

The Answer: I think the straightforward answer here is to replace the Motorola 2N4427 output transistor. At the same time, the latest parts update improvement should be fitted to enable the very best performance to be achievable with the 1 watt stereo transmitter. Make sure that the swr of your transmitting aerial is reasonable because a bad swr can cause operating temperatures to rocket..



Question To Be Answered: Can I use one of you 1/2 wave antennas from half way up a tower block. I would push the antenna out of the window with a pole. I know that it is not ideal but would the antenna still provide a gain?

The Answer: This should not be attempted with anything other than a directional beam aerial. If you use a vertical half wave omni directional aerial, or a tuned dipole, you will saturate the tower block with RF and probably ruin TV reception and cause blocking on FM receivers. There will be no gain from the half wave aerial, the radiation pattern will be badly distorted and the performance will be poor. The solution is to use a 3 element directional yagi beam aerial (59.95) although remember you will only cover the area in the direction away from the tower block. The real answer is to get the vertical half aerial onto the roof of the tower block. Remember that height and a clear view for the aerial to 'see' are the all important factors in getting good transmission range.



Question To Be Answered: Can you modulate an RDS encoder along with a Mono Fm transmitter or does it have to be stereo? And if you can, what is the max amount of characters (letters) contained on a RDS encoded display?

The Answer: Yes you can use RDS without broadcasting in stereo, although some car FM radio's don't seem to display RDS unless a stereo pilot tone is present and the RDS subcarrier is locked to the stereo pilot. The RDS system is digital and quite robust, so it does work well with even low power transmitters. The maximum amount of characters, in the station name for example, is eight and that includes spaces.



Question To Be Answered: I recently bought a PLL Pro III 4W exciter unit from you in Kit Form. Once assembled, the unit worked very well. Recently however my power supply failed and put 35v through it. This blew the fuse. On replacement of the fuse the unit now appears dead. It has obviously damaged one or more components on the board. Which are the most likely components to have been affected?

The Answer: The most likely components are TR8 and TR6, the output and driver transistors. However, the 4 transistors in the oscillator circuit should be replaced also. Your starting point then is a 2SC1947, 2N4427, 2 x BF199 and 2 x BF245C transistors. Also the 7.5 volt zener diode should be replaced, that is ZD4. The main thing is to get the left hand side of the pcb working, that is the RF section. Don't worry about the unit locking to frequency until you see 4 watts of RF coming out of the RF socket. Alternatively, NRG Kits will be more than happy to service the unit for you. Although the tx has had 35 volts put into it, the PLL-PRO III components are relatively low cost and a skilled rf engineer could perform an economical repair. At the very worst, you will have to replace all the semiconductors on the PCB. It is unlikely that the logic chips will be damaged though, because they are supplied from an on board 5 volt regulator IC which would have stayed at 5 volts despite the huge 35 volts input at power terminals. Don't give up on this as it can be fixed! Best regards from NRG Kits



Question To Be Answered: What is the set standard minimum distance for a cable run between the TX (Transmitter) and the aerial?

The Answer: There is no set standard minimum distance, but 10 metres is usually the minimum required to reach the roof mounted transmitting aerial. The best cable to use for low power fm is 50-ohm RG213 or RG8. You can use up to 40 metres of either with little loss of power. There is no point in trying to reduce the cable length to less than 10 metres by mounting the transmitter outside with the aerial, the gain will not be noticeable.



Question To Be Answered: I am looking for a transmitter that plugs into a computer sound card and allows the output from that card to be broadcast to a radio receiver. I would prefer it to be FM stereo although that is not absolutely necessary. I would like enough range to cover my whole house (approx 200 feet).

The Answer: The NRG Kits 50 mW low power stereo transmitter has been used by many people for this purpose and the signal will easily cover your whole house. There is also a very low cost mono version available. The transmitter has RCA/phono type input connectors so you would have to obtain the appropriate lead to connect your sound card output to the transmitter input. This would have the small stereo jack to plug into the card and twin phono plugs to connect to the transmitter.



Question To Be Answered: I just wanted to know how you would set up a radio station that could link all around Dublin (Ireland).

The Answer: With VHF FM transmission equipment, the only way would be to install the transmitter on a very high hill or mountain outside Dublin and use a directional aerial array to beam the signal in. You would need at least 200 watts of transmitter power and probably more unless the channel frequency was absolutely clear. You could use a high frequency link to the transmitter which would enable you to put the studio down in the city.



Question To Be Answered: I have a 75ohm dipole, and use a 50ohm cable RG58 and 50ohm transmitter. So i need to make a balun (balanced to unbalanced). But i dunno how to do. On the web site of nrgkits, there is a small draw..but it seems it makes shorts cuts.. is it normal ? and the coax used as BALUN should it be twisted around the feeder cable or just parallel? u can find the draw here : Then i need a swr meter.. all i can find here is stuff for CB so no more than 50Mhz.. any tips to make it works a 100Mhz?

The Answer: Please take a look at the revised dipole section in the Workshop pages. On the picture, look at the top where the main feeder connects to the aerial rods. The balun outer shield connects directly to the inner conductor of the main feeder right inside the aerial terminal box. Then look down to the other end of the balun and here the balun outer shield is soldered to the outer shield of the main coax feeder. You have to be careful not to melt the main feeder inner conductor! It looks like a short circuit, but it is not so at the frequency in use. Remember also that the inner core of the balun is connected to absolutely nothing. Finally, the balun must run parallel with the main feeder, NOT twisted round. Use adhesive tape to hold it parallel to the feeder. If you want a very good quality VHF SWR/Power meter, then please take a look at the Diamond SX range of instruments at the following website:



Question To Be Answered: Hello I have a 5 watt VCO transmitter connected up to a 40 watt amp, the amp dosent seem to be working. It is 4 watt in and I cant see any signal increase. Iam working a dipole could you help.

The Answer: The first thing to check is your power supply. It needs to be able to supply a constant 5 amps to the amplifier. If you are using a 3-5 amp power unit then change it for a 5-7 amp type. The next thing you need to do is to connect an SWR/Power meter between the 5 watt transmitter and the aerial. Check the power out and the Aerial swr. If the power is 5 watts and the aerial swr is 1.5:1 or better, connect the 40 watt amplifier input to the 5 watt transmitter output. Connect the Power/SWR meter between the amplifier output and the aerial. Again, check the power out and the aerial swr. If the power output is less than 40 watts, you should return the amplifier to us for checking. Another point, if the amplifier is delivering full power and the aerial is ok, the green led (rf power out) on the amplifier will be lit. If it isn't, you have a problem with the equipment. If it lit, then you had better get the aerial higher above the building because the extra signal power isn't going where it should! Make sure that all patch leads and coax cable connectors are fitted correctly and are a good tight connection.



Question To Be Answered: I have 2 limiters feeding a stereo encoder board, then off onto the 2 GHz link. I recently brought a RDS unit from broadcast warehouse & have a problem using this inline. As the 19k from the encoder is phasing with the 57k tone from the RDS unit, i think. I would guess the way to reslove the problem would be to use the crystal osc from either unit & multiply up / down for the other unit. Do you have any thoughts, suggestions or each a external osc kit with 19k & 57K outputs? P.S. intending to buy a 40w amp once I resolve this problem. Will the price of 109 remain for a while?

The Answer: First, you must ensure that the RDS coder is fitted either between the stereo coder and the 2GHz link tx, or between the link receiver and the main band 2 transmitter. Try both options if you can, to see if the problem remains. You do not actually say what the symptoms are, whether it is background clicking and whining sounds, or the RDS doesn't work at all. If the background noise is the problem then make sure the RDS level isn't excessive, it should be adjusted to be just 2-3 % of the total multiplex transmitter input. In voltage terms, if the total MPX level is 2 volts peak to peak then the RDS level is usually around just 40mV peak to peak. I would try feeding the main broadcast transmitter directly, no link, as a start. Also check the results on at least a couple of different radio tuners. I prefer the 57 KHz RDS subcarrier to be locked in quadrature to the 19 KHz pilot tone. If you contact Broadcast Warehouse, they will be able to advise and possibly do an exchange for their more advanced RDS unit that has RDS to Stereo Pilot tone lock. One final point is that I have tested the standard BW RDS coder and our own low cost switching type stereo coder, and the results have been fine on most car radios. In theory, the RDS does not have to be locked to the 19KHz pilot tone.



Question To Be Answered: If you have 10W of RF going into RG-58, which is 15 meters long, and the operating frequency is 100.8MHz, what losses are likely in the coax, and how many of the 10W are you likely to see at the antenna end of the coax. Assume that the antenna is correctly matched.

The Answer: RG58 coax cable is quite lossy at 88 - 108 MHz and on average the loss is 3dB per 20 metres. This means that for every 20 metres used, you lose half the power. For 10 watts in to a length of 20 metres of RG58, you would have 5 watts at the aerial end. For a 15 metre run you will see just under two thirds of the input power at the far end of the coax, about 6.3 watts and you lose 3.7 watts as heat in the cable. Note that the cable loss is greatest at 108 MHz and is somewhat less at 88 MHz. In any event, you should use RG213 coax if the length is more than 20 metres as this will greatly reduce lower loss. But it's also three times the price of RG58!



Question To Be Answered: What's the difference between a BLW60 and a BLW60C.? Which one is used in your PLL PRO 3 40 Watt tx.?

The Answer: The BLW60 is electrically the same as the BLW60C. The package and stud are different though, meaning that the two are not physically interchangeable. We use the BLW60, as we have hundreds in stock. We have plenty of the BLW60 also. The other difference is the price, the BLW60 is half the price of the BLW60C. We have found these devices to be very rugged and reliable, although they need considerable driving power. But with the PLL-PRO III four watts output, that is not a problem.



Question To Be Answered: How do you connect the outer shield of the coax to the tx box? I asked this question last year and got an answer but had not written it down. I know I should use a resistor or capacitor of some sort (i think) but need more details. Can you box the tx for me on order?

The Answer: If it's the RF output cable at the transmitter aerial socket, the outer shield is connected directly to the tx box, via the body of the aerial socket. Screwed solder tags are use as you can't solder directly to aluminium box material.If you mean the audio input screened cable going from the tx board to the socket on the box, then you normally use a 1000pF and a 10,000pF (in parallel) capacitor from the outer braid to the metal box. You would also fit a 100pF capacitor across the phono socket terminals.



Question To Be Answered: Howdy from Texas in the USA! I am going start my own private radio station and I want to know how many radios a 35 watt transmitter will reach?

The Answer: Two, yours and the one in the FCC monitor van!



Question To Be Answered: I recently bought a 5 watt VFO (non-pll) stereo transmitter kit, and I'm pleased with the results. The only trouble is, on some recievers, the carrier is quite strong but there is faint modulation. It is there, but very suppressed. The 19kHz stereo pilot must also be suppressed, because it isn't being detected by the reciever. If I back the voltage down to slightly under 9 volts, the modulation returns in full stereo. I checked the MPX signal at the input stages of the transmitter section, and it appears normal. In most recievers, this is not a problem, as it works just fine. In others it won't. Help?

The Answer: It sounds as though your transmitter is very slightly off tune. You can fine tune the frequency by opening or compressing one of the coils that form L1. You see, some receivers automatically mute when the transmitter signal is not exactly on frequency. The muting window is wider on some receivers than others. If the muting window is narrow, then the transmitter frequency has to be exact or you wont hear any sound. Hope that helps, I can't think of anything else that would cause the problem.



Question To Be Answered: I wanted to setup a small London Radio station, What do I need? I have Technics 1210 and a Vestax mixer.

The Answer: You need a Limiter Compressor, an FM transmitter and a transmitting aerial. The transmitter should be at least 5 watts output but no more than 40 watts output. A heavy duty 7 amp 13.8 volt power supply will also be required to power the equipment if it includes a 40 watt tarnsmitter. It is very important that the transmitting aerial is mounted as high as possible outdoors. The transmission range will be basically line of sight from the transmitting aerial. You will need the maximum power transmitter for Stereo Broadcasting and mono transmissions are preferable for low power FM stations. In the UK, all FM Radio Stations require a licence from the Radio Authority.



Question To Be Answered: I have an unboxed 40W (1W drive) amplifier which I bought from you last year. I was wondering if it is possible to adjust the output power down to around 10W but still maintaining the 1W drive (variable power supply?).

The Answer: This is a tricky one and care will be needed. The 40W amplifier (1W drive) is a high gain 2 stage amplifier which is designed to work from an external 13.8 volt psu. You will certainly have to reduce the power supply voltage down to around 9 or 10 volts to get a substantial power reduction. If the power output is still excessive at 9 volts, you will have to reduce the drive power slightly by using either a resistive attenuator pad or a 10 metre length (maybe 20 metre) length of RG 58 (lossy) coax cable between the transmitter and the amplifier input. After doing all this you should monitor the cold end of the BLW60 dc feed choke (4 turn silver coil), with an oscilloscope, for any low frequency oscillations (500KHz to 5MHz). This should be done with a 50 ohm dummy load connected. Low frequency instability is unlikely but it still must be checked at low voltage, low drive operation as such malfunction will put spurs either side of the main VHF carrier.



Question To Be Answered: Why does my CD player make a hum and buzz sound when the transmitter is plugged in. It sometimes skips or stops playing too!

The Answer: You have a problem with RF! When you switch on your transmitter, your transmitting aerial creates a very strong RF Electromagnetic field (radio waves) in the immediate surrounding vicinity. The audio and mains cable to your CD player are picking up this RF and injecting it directly into the internal electronic circuits of your CD player. This causes the circuits to malfunction! Please do the following:

1. Make sure you are using a correctly tuned aerial, mounted outdoors at least 10 feet above the roof. If the aerial is not matched, your coax feeder will radiate, which will 'swamp' the house with RF. Never, Ever, use an indoor transmitting aerial if the tx power is more than a couple of watts.

2. Suppress your CD player against the RF by fitting ferrite chokes on the power cord and RF bypass capacitors on the CD's phono outputs. It should be pointed out that CD players will usually tolerate a large amount of RF interference without a problem. This would indicate that your studio is full of RF and sadly so will be your next door neighbour's house! If your aerial is correctly tuned, and high up, you will have to reduce your transmitter power in order to lower this local RF interference.



Question To Be Answered: If I want to broadcast for about 2 miles radius or below, what kit shall I buy? Can you give me the product weblink, and the prices, could you also tell me what else I need to buy??

The Answer: A range of under 2 miles should only require low power. The PLL-PRO III One Watt transmitter kit ready assembled costs 99.95 and is ideal to use with a tuned dipole aerial at 23.95. You will need a 13.8 volt 3 amp dc power supply to power the transmitter. It is very strongly recommended that ALL broadcasters use a Limiter Compressor with the transmitter to make sure the transmitted sound (modulation) is correct. The new NRG Kits Stereo Limiter Compressor comes ready to use at 89.95. To view these products, please click on their names highlighted in blue above in this document



Question To Be Answered: What is the optimum position to clamp the boom of a vertically polarised dipole antenna on a tall pole?? I say this because in some professional installations that I have seen, the boom is actually a quarter of a wavelength from the top of the pole. Shouldn't the aerial boom be clamped to the very top of of the long pole, for maximum height?

The Answer: In a professional installation where the required height can be achieved, regardless of cost, the perfect mounting position for a Vertically polarised Dipole (open or folded type) is indeed a quarter wave length from the top of the mast. This avoids any imbalance on the two halves of the balanced dipole, and everything is equal. However, a long boom is still needed, because even though the mast presence is equal to both sides of the dipole, the effect of the mast is to alter the impedance of the aerial and create some directivity, which you don't want with a dipole. In many instances, where the mast isn't high enough to start with and the dipole has no balun fitted, the general rule is to just get the dipole as high as possible with 'earth side' downwards! This is wrong of course, but acceptable results can sometimes be obtained. Remember, Folded dipoles and standard open Half Wave Dipoles are balanced aerials and you should not just connect unbalanced coax cable straight to the terminals, with no balun. If you do, the coax will radiate too!



Question To Be Answered: Do you intend to produce microwave link systems; utilsing microwave horns, modulated power supplies, lnbs and satellite receiver front ends or do you know where I can obtain bits from particularily the first two from?

The Answer: This sort of equipment is traditionally used by London and Birmingham "private" stations and currently the microwave 10GHz sender horns are said to be in short supply. The old Amstrad satellite receiver front end cans are just about gone too. You have to appreciate that the surplus parts market is always a temporary one, the stuff is very hard to get now and costs a lot more than it did 12 months ago.



Question To Be Answered: Do I need any expensive equipment to assemble your 1 Watt PLL PRO 3 transmitter or is a soldering iron the only thing I need?

The Answer: No, you do not need any expensive equipment, but you will need the following tools for assembing the kit:
Side Cutters
Long Nose Pliers
Soldering Iron
Solder (22 SWG)
A solder desoldering pump is very handy when you do something wrong. Next, you need to ask yourself is your soldering of a reasonable standard and have you got a soldering iron with a tip size of 2.5 mm or smaller. Only attempt to build a transmitter kit if you are ok with the above requirements. No expensive test equipment is required either, but anyone constructing and using radio transmitters should possess an SWR meter. This instrument is cheap to buy and is a real Godsend when checking transmitters and aerials for correct working status. Please take a look in our workshop section at the kit building advice page and you will see an example of a kit that has been correctly put together. You will also see how it should not be done. To see this document Click Here



Question To Be Answered: What does SWR mean? How is it measured? Why must a dipole antenna be tuned to frequency? Isn't a standard receiving antenna adequete for low power??

The Answer: Whole books have been written on the subject and people are still not fully agreed as to the exact goings on. SWR stands for Standing Wave Ratio.
1. A bad swr will not usually damage a 1 watt low power transmitter.
2. The dipole aerial must be tuned to the frequency range in use.
3. A standard receiving antenna (unless it's expensive) should not be used.
4. SWR is measured with an SWR meter, e.g. Diamond SX200.
5. The transmitter output is called the Forward Power. WANTED
6. Reflected power comes back from an unmatched aerial. NOT WANTED
7. A Standing Wave is the resultant addition and subtraction of forward and reflected power/voltages within a length of coaxial cable.

SWR stands for standing wave ratio, it refers to a so called standing wave that can exist within the coax feeder cable. Standing waves are created by reflected power from the load (aerial) combining with the forward power from the transmitter, within the coax feeder cable. The perfect SWR figure would be 1:1, which means that there is NO standing wave at all on the cable. This because a perfect 50 ohm aerial would not reflect any power. If the aerial was not correct, it would reflect a lot of the power back down the coax, to the transmitter. And then it gets reflected back again from the transmitter to the aerial. And back and forth it goes. Just like water going to and fro, standing waves are developed from the interaction.

The main problem is that a high SWR on the cable, caused by an untuned aerial, presents the transmitter with a termination that is nothing like the 50 ohm impedance. This can destroy the transmitter output transistor sometimes. This is unlikely with a very low powered transmitter, but the transmitter can deliver a 'dirty' signal under these conditions and cause interference. Remember too, that the transmitter can only deliver it's rated power output into a 50 ohm termination.

The term SWR should actually be VSWR, standing for voltage standing wave ratio. If the VSWR is 2:1, then there are voltage peaks every half wavelength along the cable that are double compared to what is at the transmitter socket. In very high powered installations, the VSWR has to be kept low or the coax cable will flash over at these voltage 'maxima'. Imagine a 20:1 vswr in a 20 kilowatt system!



Question To Be Answered: What is the difference regarding range between using just 1 watt & using 10 watts of power into a dipole aerial? Assuming a height of around 40feet.

The Answer: In my experience, a ten fold power increase from 1 watt to 10 watts, will just about double the actual transmission range. So if it was 1 mile at 1 watt, then 10 watts should easily do 2 or 3 miles. However, the important point is that all the previous dead spots in the reception area will be served a lot better. This will increase the population coverage by up to 4 times. In theory, the range of any FM VHF transmission extends to the horizon that you can see from the transmitting aerial location. This is regardless of the transmitter power used. It is called line of sight reception and the transmission range you get is decided mainly by the aerial height. Increasing the power will not usually significantly increase the range, but will give much clearer reception at the "fringe" of the reception area. Stereo transmissions in particular, benefit from high power. This is because most of today's 'plastic' stereo radio receivers requires a very strong signal to deliver good stereo without an annoying hiss.



Question To Be Answered: I am using a veronica (paul hollings company) stereo coder, nrg pll pro II, and a ramsey limiter/filter for the audio. Now, here's the problem, when I modulate in mono, the audio sounds fine. When I try to modulate stereo at the same level, I hear a "swishy" sound in any car radio that I listen to the broadcast on. The pots are on the stereo coder set all way the up, the pot on the transmitter is adjusted so that the audio is a good level, just below that of commerical stations, and the ramsey limiter is set just below limiting. Is the stereo coder dead or what's the problem?

The Answer: The first thing is to make sure that the PLL-PRO 2 is locked on frequency and that the pre-emphasis jumper is definitely removed, to disable the transmitter pre-emphasis. It's next to VR1. Next, adjust the input pot (VR1) on the transmitter to mid position or just slightly more (20 degrees max) towards the louder end. Remove the Ramsey limiter and connect audio directly into the stereo coder. Adjust the input pots on the stereo coder for a balanced and correct level output when listening on a good quality receiver. The output should sound crystal clear and if it does not then either the frequency has some interference on it or the stereo coder has a fault. Please note that low cost stereo coders are not fitted with 15 KHz low pass filters, so make sure that the limiter you use has the filters fitted. Without the filters, a side effect called 'aliasing' is produced when using CD material. I do not think aliasing is your problem though because you have to really listen carefully to hear the symptoms of aliasing, on average CD music.



Question To Be Answered: I have ordered a 5 watt stereo transmitter from NRG and I have just realised I will need an Aerial. I already have a Starduster CB aerial and I was thinking of using that as it already fixed on the chimney. Is this ok or do I have to buy a new aerial too?

The Answer: You must NOT under any circumstances use a CB (Citizen's Band) aerial with a 88 - 108 FM transmitter. You could easily damage a transmitter by doing this because the SWR (standing wave ratio) of a CB aerial at VHF frequencies will be extremely poor. The aerial will be a complete mismatch and could even cause interference to other frequencies. You must make or buy a purpose built VHF transmitting aerial. One of the best all round aerials is the Tuned Dipole. Remember, the Aerial is just as important as the transmitter, the performance and transmission range depends greatly on using a correctly matched aerial and getting it as high as possible. Using a CB aerial on an FM broadcast transmitter would be like putting square wheels on a Ferrari--it wont go very far!



Question To Be Answered: Can I upgrade the PLL-PRO III 4-watt transmitter by replacing the output transistor with a BLW 60 transistor that you say gives 45 watts and costs 9.95. What modification would be involved to make it work with a BLW60?

The Answer: Please don't even think about trying this! The output transistor in the PLL-PRO III is a 4 watt 2SC1947 and this is the ONLY device that can be used. Your idea of a huge power upgrade will not work! You see, the BLW 60 needs 4 watts to drive it and it also has to get rid of a fair amount of heat. If you want more power using the BLW 60, then you must make a separate power amplifier which could then be driven by the PLL-PRO III. Generally speaking, never try to upgrade the power on high quality exciters, go for a separate amplifier instead. The BLW 60 is a very rugged transistor and is the ideal transistor to use for linear amplifier service



Question to be Answered: I have built a NRG transmitter (1 watt stereo) and I am going to put it in a box. I have plenty of old ABS (plastic) boxes and I could easily fit it in one of those. Someone said though that I should only use a metal box, is this right?

The Answer: It is always a good idea to put any built electronic kit into some kind of enclosure. It makes for better handling and prevents damage from accidental knocks etc. Plastic boxes are ok for many non-transmitter projects. Transmitters though, should always be enclosed in a metal box, then the box acts as a screen and prevents unwanted harmonic signals being radiated from the transmitter circuit board. To fasten the transmitter circuit board into the box, you should use plastic spacers, not metal posts. Take a look at the metal enclosures at out components page. You can also see a home constructor's efforts at boxing a kit, to see what's involved.



Question To Be Answered: Ok, there's one more thing I need to know before I send you the cash for one of your kits. Does the wattage rating (E.g" 1 WATT- PLL Transmitter") mean the power going into the TX from the power supply, or the power going to the aerial from the TX? Just wasn't quite sure how you measured the power rating. Kind regards,Chris

The Answer: Chris, that is a good question. The power quoted is the RF power available at the Transmitter RF socket. The power quoted is the minimum achieved and typical outputs are usually slightly higher. In amateur radio circles, transmitter power used to be often quoted as the dc power (in watts) drawn by the transmitting final amplifier, not the RF power output, which would always be less than the DC power input!
A 1000 watt Broadcasting RF Power Amplifier will provide 1000 watts (RMS) of Radio Frequency Power for delivery to the load, usually an aerial. The power consumed from the DC power supply will probably be around 1500 watts.
On the other hand, a 1000 watt 2 metre (144 MHz) RF Power Amplifier for amateur radio use may well deliver only 700 watts of RF power, but draw 1000 watts of DC power.
In summary, Broadcasting Equipment power output is always measured as the RF power available at the Aerial socket!



Question To Be Answered: What is the performance differences between the PLL pro II and PLL pro III ? I realise the pro III has out of lock power down, as well as the final being no-tune - but I'm interested in the actual performance (i.e. how good is the filtering on the pro II compared with the pro III ?) Have I outlined the main differences, or is there something I'm missing, performance wise?

The Answer: Specifically, this question relates directly to the NRG flagship transmitter kit, the Phase Locked Loop Professional Transmitter kit version 3. The PLL-PRO 3 is more powerful than the PRO 2 if you get the 4-watt version. The output filtering in conjunction with revised transistor matching circuitry produces a better quality signal with regard to harmonics. The second harmonic on the PRO 3 is generally better than -60dB compared to -50dB on the earlier model. The requirement in the UK for licenced RSL use is -40dB for power output levels up to 25 watts. So you can be confident that the PLL-PRO 3 is more than adequate as a high performance transmitter/driver. We guarantee that all spurious frequencies will be at least -50 dB down on the carrier and that in-band spurious will be at least -70 dB down. There is no 'power slump' with temperature, every unit will mange at least 4 watts. Groundplane area is large and the whole thing is rock solid stable. It will drive high power amplifiers in the enclosure, without 'howlround', and is not prone to loud hum at the slightest provocation.



Question To Be Answered: If I am going to get a Stereo Encoder, is the fancier more expensive Pro IV Encoder really worth the price?? I like the idea of it but the cheaper Pro III is just that. Cheaper.

The Answer: The Pro 4 Stereo Coder will sound noticeably superior in a controlled listening test. It simply is a superb product. On the other hand, some people may not be able to detect a great deal of difference in stereo separation and clarity, but it is worth the extra money and one big plus point is that the Pro 4 version has 15 KHz low pass filters on the input circuits. The Pro 3 does not. These filters are important to prevent ultrasonic audio frequencies from CD's spoiling the stereo separation. An unpleasant 'aliasing' effect is therefore completely avoided. But the main merit of the Pro IV Stereo Encoder is that it uses Digital Oversampling as the method to generate the composite MPX signal. The Pro III Stereo Coder, as good as it, uses a much simpler switching technique which cannot possibly match the Advanced Pro IV series.
One final point, to realise the full performance of a top quality Stereo Coder, your transmitter must also be good quality! A linear modulator audio response from 30Hz right up to 60KHz is essential.



Question To Be Answered: I received my Pro III Stereo Limiter kit this morning and I've made a start on it, thanks for the speedy delivery !! I have a couple of quick questions just to clear up a few things I'm uncertain of. Firstly, as I will be putting the stereo limiter into an enclosure, I would like to fit some 'panel mount' LED's to the front of my box. I was just wondering what voltage LED's I would need to buy. I am a little confused from the schematic as it is a complex circuit so I would appreciate it if you could clarify this for me. Secondly, I will be running the output from the limiter into a Band 1 link transmitter which is only Mono at the moment. But the Limiter is Stereo! What is the best way of turning a stereo output into a Mono output. Would it be acceptable to run the Left and Rights outputs from my mixer into the Left and Right inputs of the limiter and then to use a resistive combiner on the Left and Right outputs of the limiter to sum them into one channel before feeding the signal into the mono link transmitter. Another approach I considered was to simply only connect one output channel from the limiter into the link (say for example the left channel) and not connect the right channel to anything. I would be very grateful if you could advise me on these matters.

The Answer: The first thing is that you are advised not to put any limiter circuit board in the same box as a transmitter board. Limiters have some sensitive circuits which could be adversely affected by strong transmitter RF fields in a combined enclosure. The led's are just standard hi-bright 5mm leds and other than colour, you don't need any other parameter such as voltage. As far as I know most leds require the same voltage although current consumption varies. Your suggestion about the resistive combiner for converting a stereo line to a mono line was spot on and that is what you should normally do to make a stereo signal into a mono signal. However, with the NRG stereo limiter, all you have to do is connect the Left and Right outputs directly together (yes, hardwired together!). This is because the output op-amps on the limiter feed the output phono sockets via a resistor network and this will allow you to join the left and right limiter outputs directly together without any further resistors. It's easy! Good luck.



Question To Be Answered: I have a veronica 'easytune' 1-watt pll transmitter and have just blown up the main output transistor - this is the PT8860 - it seems to be very difficult to source these in New Zealand - is it possible to swap it with the 2n3553 that is in the NRG 1-watt PLL-PRO III transmitter? I know this question should be going to veronica but they are a little hard to get information out of sometimes - and with your knowledge and past experience I thought you may be able to help.

The Answer: I would say there would only be a 25% chance of success here without you modifying the input matching to the different device. I could be wrong and I have never used the PT8860, it's just that the 2N3553 is a slightly different (lower) input impedance than most low power transistors. My advice if you are really stuck is to go ahead and try the 2N3553. This device certainly has the power and the gain, you just might have to tweak the circuitry a little. We have a huge stock of the 2N3553. Another option of course is the Motorola 2N4427, these can do 1 watt with ease and we use to use them on the pll-pro 2. Once you have the replacement device working and delivering 1 watt of power (or near!) you should make sure the transistor temperature does not get anywhere 100 degrees centigrade (boiling point). High temperatures up to 70 degrees can be tolerated provided excessive RF 'power slump' does not accompany the high temperature.
When 'tweaking' circuits, we mean altering inductor-coil and capacitor values. For speed, have a ferrite slug and a brass rod available to artificially increase or decrease the inductance of inductors. Small capacitors can be 'dabbed' onto the circuit board to check for improvement. Remember that you need to get roughly 1 watt of output power right across the band, from 87.5 to 108 MHz, so check the power output performance at different frequencies!
Finally, make certain that the transmitter output remains stable, that it transmits on one frequency only. If you get lots of 'side frequencies' spreading over a large part of the band, then it is highly probable that the transmitter output stage has gone into low frequency oscillation. This must be avoided!



Question To Be Answered: I have an NRG Kitz low power 50 mW transmitter and I use it to transmit my CD music all round my house. If I use it on a 9 volt battery, the results are perfect. If I use a rather huge CB power supply, the results are also perfect. However, when I run it from a compact little wall adapter, there is a buzz on the sound and it can be annoying. I've had this problem before with other transmitters. I can reduce the buzz by moving the power cord from the wall adapter about but it can still usually be heard in the background. What causes this buzzing noise when powering a small transmitter from a wall mains adapter? I want to power it from the mains to save buying batteries but I don't want to use a great big CB power supply!

The Answer: The problem you have is called Modulation Hum. It is caused entirely by the inadequate design of low cost wall type plug in mains dc adapters. The problem arises because the internal rectifier diodes in these cheap 'Wall-Warts' are not bypassed with capacitors. The diodes switch on and off at 50Hz, causing a varactor effect which effectively modulates the groundplane area on low power single stage transmitters. You can pull the wall adapter apart and fit 1000pF capacitors across the rectifiers, this should cure the problem. Take great care as the voltages inside can be dangerous when plugged in.
A much better solution these days is to stop using these inadequate wall adapters. They are not designed for powering transmitters anyway. You will find the new generation of lightweight and compact Switch Mode Power units are worlds apart from inferior wall adapters. They are more expensive, but are so good in every other respect that they are worth that bit extra. If you start using a switch mode supply, your buzz problem will be cured instantly! And you still have all the benefits of small size and lightweight.




Thank you for looking at these subjects. There are more topics to come, so please visit this section again. If you want to ask a question, please email me directly at the following address: