All Things Amateur Radio
All Things Amateur Radio

QNZ – What It Means And How To Do It

QNZ is an ARRL NTS prosign that is used by net control stations on CW nets to instruct net members to zero-beat their transmit signal with net control’s transmit signal. If every station does this correctly, then all stations should hear each other with a pleasant audio pitch.

Most CW nets have an assigned net frequency. In normal circumstances, all net members set their frequency to the net frequency and all is well. However, sometimes the net control station calls the net up on a frequency that is different than the assigned net frequency. This is often due to having an ongoing communication on or very near the assigned net frequency and trying to avoid interfering with that ongoing communication. The net control moves up or down a few hundred Hertz and that’s where the problems come in. Some stations stay on the assigned frequency. Some pick a nice even frequency nearby. The result is that stations spread out all over the place to the point that they may not be heard by the net control. In nets, the correct net frequency is always the frequency that net control is transmitting on. Net control is never on the wrong frequency! It is the responsibility of all net members to transmit on the net frequency.

So how do we solve this problem? By doing what is commonly called “zero-beating” the net controls transmit frequency. When you successfully zero-beat the net control’s transmit frequency, you will also be transmitting on the same frequency (or very close to it) and all net members should hear you fine.

Back in the day of separate tube-type transmitters and receivers, think Drake Twins, the transmitter and receiver frequencies could be set anywhere in their range and were not tied together like they are in modern transceivers. In order to have a CW conversation, you had to make sure you could hear the other station and that the other station could also hear you. In separate transmitters and receivers, you had a SPOT switch that, when pushed, gave you a weak signal on your transmitters frequency that you could hear in your receiver along with the other stations transmit signal. You tuned in your receiver to the tone you liked, then adjusted your transmitter’s frequency until you heard your transmit tone go away. As you approached the other stations frequency, you would hear an audio beat note that was equal to the difference in the other station’s frequency and your own transmit frequency. This beat note would get lower and lower until you couldn’t hear it any more. When you were almost exactly on the other stations frequency, you could hear a very slow pumping of the AGC and even see it on your S meter. When it stopped, you were exactly on the other stations transmit frequency. You were “zero-beat”. This was normal, every-day, CW operating procedure.

With today’s modern transceivers, the transmitter and receiver VFOs are the same. You automatically transmit and receive on the same frequency. (Actually, this is only true for AM signals. SSB signals generally have a fixed offset similar to CW mode). This is great, and very convenient for voice operations but can lead to trouble for CW conversations. If your receive frequency and the other stations CW transmit frequency are exactly the same, you hear nothing! In order to hear another stations CW signal, you must offset your receiver’s frequency by some small amount. The amount you offset, that is, the difference between the transmit frequency and your receive frequency is the audio frequency that you hear in your speaker. If your receiver is tuned 440 Hz away from the transmitter, you hear a low ‘A’ tone. If your receiver is tuned 1200 Hz away you hear a high pitched tune. Most experienced CW ops choose a tone 600 Hz to 800 Hz away from the transmitter’s frequency.

In modern transceivers, most manufacturers offset the receiver frequency in CW mode by an adjustment to the CW sidetone frequency. The transmit frequency will be the frequency displayed on the dial. The receiver frequency will be the dial frequency plus or minus the displayed frequency. In CW normal mode, it will be plus (USB). In CW reverse mode, it will be minus (LSB). For example, in my Yaesu FT-450D, I set the CW sidetone to 700 Hertz. This is the tone I like to hear on CW. When I tune my radio display to the Ohio Slow Net net frequency of 3535.350 KHz, that is the frequency that I am transmitting on. Because my sidetone offset is 700 Hz and I am in CW normal mode, the transceiver automatically adjusts the receive frequency to 3535.350 Khz plus the 0.700 KHz offset. The receive frequency I am listening to is 3536.050 KHz. If the net members want me to hear them, they must set their transmit frequency to somewhere where the difference between the transmit frequency and the frequency I’m listening on is an audio note that I can hear. If they choose to transmit on 3535.350 KHz, I will hear a 700 Hz audio tone. If they choose 3535.500 KHz, I will hear the difference between my receive frequency, 3535.050 KHz, and their transmit frequency, 3535.5 KHz, which will be 450 Hz. This is readable but lower than I like to hear. On the other hand, if a net member transmits on 3535.000 KHz, I will hear them on 3536.050 KHz minus 3535.000 KHz which is 1.050 KHz, readable, but uncomfortably high for my taste.

All of the above assumes that all net members’ transceivers are transmitting with the same receive frequency shift. Not all transceivers act the same way, however. In my FT-450D, I can select the CW receive offset to always be above the transmit frequency, always below the transmit frequency, or in auto CW mode which sets the receive frequency below the transmit frequency on the 160m, 80m, and 40m bands and to above the transmit frequency on the 30m and higher bands. The ICOM IC-718 behaves like the FT-450D’s auto mode. It automatically sets the receive offset below the transmit frequency for the low bands and above for the high bands. If you want to be on frequency on a CW net, you must know whether your receive offset is above or below the transmit frequency and make sure it is set the same for all members of the net. Modern usage is to always use a receive offset above the transmit frequency.

Most modern transceivers put out their CW transmit signal on the dial frequency and shift the actual receive frequency by the frequency of the transmit sidetone. Most modern transceivers allow you to set the transmit sidetone to a frequency within a range, typically around 300 Hz to around 1000 Hz. Some rigs, particularly older rigs, have a fixed offset. Fixed sidetones are often 600 Hz, 700 Hz, or 800 Hz. Check your operating manual to be sure. If yours is adjustable, set it to the pitch you like to hear.

Most transceivers allow you to operate your key or keyer without transmitting a signal on the air. On the FT-450D, you can turn the break-in function off. When the net control station tells you “QNZ”, all you have to do is turn off break-in, key your sidetone, and tune your receiver until the net control’s received signal pitch is the same as your sidetone pitch. When you arrive at that point, your dial will show your transmit frequency and that frequency will be equal to or very near the net controls actual transmit frequency. If all net members follow this procedure, everyone will hear everyone else at their chosen (or fixed) sidetone pitch.

Note, if you are fortunate enough to own a high end transceiver, you may have several different ways to tune in the CW signal. The FTDX-3000 has an auto zero-beat function where you tune in the CW signal, push the right button and the radio automatically tunes the rig to the proper frequency. The Kenwood TS-2000 has a similar function.

Being exactly on another stations transmit frequency is not always an advantage. In CW contest operation, you may gain an advantage by deliberately tuning off the other stations frequency a bit. This will make your signal sound a little different than all the stations tuned exactly in and you may get noticed sooner.

In any case, having the knowledge of how your rig works in CW and the skill to zero-beat a signal will make you a better CW operator and, hopefully, increase your success and enjoyment of this oldest of communications modes.

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