XPhase QRM Eliminator



In practical work on the air I often hear from other operators complaints about high noise level on low-frequency bands. Yes, what I hear ... I myself have been convinced of this many times and experienced the same problems! At 80 meters the noise level was never lower than S9 points. Does this mean that you can not accept a station that is below 9 points? No, it is possible if you suppress this interference.

          I. Introduction



Before talking about interference and methods of dealing with them, it is useful in a simplified form to consider their classification. Interference is divided according to the degree of source remoteness from your main receiving antenna to local and remote and by waveform, to impulse and harmonic (sinusoidal). If the source of interference is within the line of sight from your main receiving antenna, conditionally speaking, within a radius of 100 meters, then this interference is local. Any interference, the source of which is located outside the radius of 100 meters, will be considered remote. Pulse power supplies for televisions and a wide range of other home appliances generate interference in the form of pulses, and our radio amateur transceivers, signals and interference of a sinusoidal (harmonic) shape.
The XPhase device is designed to suppress ONLY local local disturbances in a mostly impulse form. It can also greatly weaken the harmonic interference, but only if it is a local local disturbance.
Here are 3 common situations:

1. Impulse noise from the panel TV behind the wall in the next room, computer monitor, your own laptop, etc., etc.
2. Interference from a neighbor neighbor working with a kilowatt-hour PA.
3. Interference from a powerful station located somewhere far (for 2000 km) from your QTH, but close in frequency, so that the flashes of its signal greatly prevent you from listening to correspondents.

So in the first and second cases, with proper use, the XPhase device will be very useful for you, eliminate and weaken this interference to a large extent, but in the third case, you should not expect a positive result from it.

For example, in my QTH at 50 meters there is a 5-storey apartment building with a lot of sources of impulse noise in the form of various household appliances, however I absolutely do not feel any influence of these jammers, 50 meters is still the distance! At the same time, my own TV, monitor and laptop together give impulse noise at the low bands of 9 +10 dB and the XPhase device reduces the level of these interference by 80%, given that the AUX auxiliary antenna is a piece of wire, just stretched out along the table in the immediate vicinity of the monitor and laptop.

There are a lot of sources of impulse noise around us. Any impulse devices - power supplies for computers, televisions, other household appliances, luminescent energy-saving lamps, Chinese neon street lighting ... that's far from a complete list of sources of local interference. Such devices include a switching power supply (SPS), where the AC voltage of 50 Hz is first rectified and a direct current source of 380 volts is obtained from which a sufficiently powerful square-wave generator with a switching frequency in the range from 30 to 300 kHz is fed, and this is already frequency of the long-wave range. Further voltage conversion occurs at the frequency of this generator, which is the source of broadband noise. It should be noted that switching power supplies have a number of undeniable advantages over conventional ones. Light weight and dimensions at high power. The main part that determines the weight and dimensions of the power transformer is a transformer. In SPS, the transformer core is ferrite and the windings contain significantly fewer turns than in conventional PSs at a conversion frequency of 50 Hz. This is due to the fact that with an increase in the conversion frequency, the efficiency of the transformer increases dramatically. Thus, the poor electromagnetic compatibility of SPS with amateur radio equipment is their only drawback. It should be noted that this disadvantage of SPS is not felt by anyone except us, radio amateurs. Therefore, it is up to us to find a way out of this situation and it was found.

          II. History


The scheme of this device, similarly known as QRM-eliminators or squelch, was first proposed in 1989 by G4WMX and improved in 1993 by GW3DIX. Then in 1998/99 Hanns DK9NL improved this scheme.
Among other things, he introduced the HF-Vox switching of RX / TX modes by supplying high-frequency voltage, and also created a printed circuit board. This device was called XPhase and was repeatedly implemented by many radio amateurs around the world.


When I got acquainted with the DK9NL scheme, I was very interested in this issue and decided to assemble such a device for myself. Later I found another, interesting publication from PA0NHC on the same topic.

Speaking about noise suppressors, it should be noted that there are also conceptually other solutions in this area, for example such as MJF-1026, the device for phasing the DK2KQ antennas, the Sevastopol variant, Vladimir R6KV and JA1DI. A distinctive feature of all these devices is that they are designed to deal with a wider range of interference than XPhase, while they are more complicated schematically, more expensive and less convenient to operate and configure.
Scheme XPhase QRM Eliminator one, - DK9NL! It is simple, reliable and meets the needs for interference suppression in most cases. An exception can only be in a situation of very severe electromagnetic environment with a large number of sources of interference.
Another great advantage of the device XPhase is its broadband. Look at the diagram, there is not a single node of frequency selection, oscillatory circuit, filter, etc. From the consumer point of view, this gives speed and convenience in use. You adjusted the device to suppress noise one time and no matter how you "walked" around the range, nothing else to twist is not necessary. Even if you switch to a different range, all adjustments will remain in the dune.
When you are confronted with a choice, what kind of squelch is needed for you, based on the gravity of the electromagnetic environment in the place of your QTH? We can say that XPhase is a typical, budgetary solution. Everything else is exclusive.

          III. Principle of operation and block diagram XPhase




We have two antennas. On the first, let's call it MAIN listen to the air polluted with noise, the second AUX should take ONLY broadband noise and this should be sought! For the correct operation of the device, the minimal penetration of the useful signals of amateur radio stations into the AUX noise channel is the most important, otherwise it will weaken these signals too! For this purpose, the device consists of a high-frequency transformer TR1 on a ferrite ring. It matches the AUX antenna to the input of the phase shifter and, because of the magnetic properties of the core, passes signals below 300 kHz and attenuates signals above this frequency to form a low-pass filter.
Antenna AUX is a piece of wire length of 2 - 3 meters stretched inside the shack. When placing this antenna, it is necessary to analyze the dislocation of noise sources with the most intense level and arrange it in such a way that the noise level induced in this antenna is maximally possible. You can experiment with this antenna by manipulating its length and positioning in various configurations with respect to the sources of the noise signal, achieving the necessary noise level for the effective operation of the XPhase device in the AUX channel.
So we have two MAIN and AUX signals. If we rotate the AUX signal by means of a phase shifter 180° and apply to the input of a phase discriminator to the other input of which we give the signal MAIN, then if the amplitudes of the interference components are equal at the inputs of the phase discriminator, at its output we get a signal MAIN cleared of interference, Since the interference components are compensated in the phase discriminator. To ensure the condition of equality of the amplitudes of the interference components, two attenuators with smooth level control (potentiometers Gain1 and Gain2) are provided at the inputs of the phase discriminator. To fine-tune the phase rotation in the phase shifter, the Phase potentiometer is used.
Consider the process of suppressing impulse noise in a phase discriminator on a graph:



The graph "a" shows the impulse noise, the graph "b" illustrates the useful signal affected by the impulse noise, the gray band, this is a high-frequency harmonic sinusoidal signal. The "c" plot of the interference is rotated by 180° and the "d" graph is a useful signal at the output of the phase discriminator cleared of the interference. Of course, that the graph is an idealized model of the interference cancellation process, in practice everything is much more complicated. Firstly, there will always be some penetration into the AUX channel of a useful signal and this will somewhat reduce the level of the useful signal at the output of the phase discriminator. Secondly, only one interfering signal is shown here, in practice there is always a superposition of several interferences on each other and a useful signal.
Some radio amateurs claim that MAIN and AUX antennas should be the same. Perhaps this is true for squelchers working on the principle of phasing antennas, but for the device XPhase this is not so. If the MAIN and AUX antennas are the same, then it assumes the identity of the signals in the MAIN and AUX channels, as a result, at the output of the phase discriminator we get 0 (zero)... complete silence, because these signals mutually cancel in the phase discriminator. Look at the graphs: b + c = d
Antenna, an expensive and complex component of the radio station equipment, especially in urban conditions, since its placement requires an area. Especially, if your squelch requires two identical full antennas, moreover, and spaced at a certain distance! ... How to fulfill these requirements in urban conditions? Look at this question from the economic point of view, what will be the share of the cost of the squelch itself and the cost of the two antennas in the total cost of the system, taking into account the area for their placement?
The main advantage of the noise reducer XPhase, in comparison with the phasing of antennas, is that it does not require a second full antenna, but rather the other way round.

          IV. Circuit diagram




After analyzing the circuit DK9NL, I introduced some minor modifications: In the DK9NL scheme, relays RL1 and RL2 in RX mode are under current, and in TX mode they are de-energized. From my point of view, this is illogical, since when working on air most of the time the equipment is in RX mode, and the TX mode is switched on for a short time, so in my scheme this is the other way around. To do this, one more stage on the transistor Q3 is introduced into the circuit of the commutator. In addition, I do not do HF-Vox switching of RX / TX modes. Although the printed circuit boards (v1.0 & v2.0) have been developed taking into account the details for this switching, but I do not install them in the assembly. Why is this so? The fact is that applying RF voltage to the XPhase device in RX mode is not safe for phase-discriminator field effect transistors, although the diode protection of these transistors is available in the device circuit, but if you operate 100 watts per "bare transceiver" without PA, them.

In addition, according to PA0NHC in the article I referred to above, "The only correct way to switch the XPhase device between RX/TX modes is to use an external PTT signal that should provide the correct time delays. RF power only after a short time after switching the relay from position RX to TX position. Immediately you can just go back to RX mode from TX mode. "

I assume that DK9NL was forced to turn on the relay in this way because of the implementation of HF-Vox switching. The whole question is in the difference in the time of operation and release of the relay. According to Dataseet for the Tianbo HJR1-2C L-12V relay used in my design their response time is t (triggering) = 6 ms, release time t (return) = 4 ms. Obviously, the difference in 2 ms is not so significant, however, only if we use the PTT signal to control XPhase. Thus, all time delays when switching RX / TX are determined in the transceiver itself.

The switching unit RX/TX is assembled on transistors Q3 and Q4, is a current follower (direct current amplifier without inversion). This node is required so that in the transmit (TX) mode, the current of two RLA and RLB relays connected in series does not load the PTT line. It works as follows: As can be seen from the circuit diagram, the base of the transistor Q3, through the series-connected resistors R7 and R8 is connected to a +12 volt power supply. In receive mode (RX), this causes the current to flow through the base-emitter transition of transistor Q3 and it is open. The resistance of the collector-emitter junction Q3 is small and the lower circuit of the resistor R9 turns out to be connected to ground. Therefore, the resistor R9 shunts the base-emitter transition of transistor Q4 and it is closed. Thus, the resistance of the collector-emitter junction Q4 at this moment is large and the current through the windings of the relays RLA and RLB does not flow.
When the transceiver transitions to transmit mode (TX), it closes the PTT input to the ground and, accordingly, the base of transistor Q3 through the protective diode D5 is connected to ground. This causes the disappearance of the base current of the transistor Q3, its closing and, accordingly, the opening of the transistor Q4, the current flowing through the relay coils and their operation.
Thus, the PTT line controls the base current of the transistor Q3 and this current is an order of magnitude smaller than the total current flowing through the RLA and RLB relays and the collector-emitter transition of the transistor Q4 in the transmit mode.

          V. Adjustment of the device


Despite the simplicity of the circuit diagram of the device, I can not say that it does not require adjustment at all. The device is an analog device and contains a sufficiently critical and moody node as a phase discriminator. For the proper operation of this node and the whole XPhase device as a whole, the identity of the current-voltage characteristics of the transistors Q1 and Q2, as well as their mode of operation with direct current, are of great importance. At the assembly stage, I select a pair of resistors R2 and R3 with the same resistance as possible. Resistance of these resistors can be in the range of 10 to 30 ohm, but the difference in resistances R2 and R3 should be 0.1%. A pair of transistors of the phase discriminator Q1 and Q2 are selected with the same volt-ampere characteristics during the adjustment process. Approximately 10 of them manage to find a pair that satisfies the conditions of the problem. Only after that, I'm sealing up these transistors.

          VI. PCB and parts.




The device board was developed by me in a complex with the entire device design, wiring under a certain type of parts. The configuration and dimensions for this enclosure. Printed circuit boards are made on firm equipment under the order, two-sided with silkscreen and protective coating. The device does not contain SMD components. The device contains an RF transformer TR1 on the ferrite ring Amidon FT50-77, and These rings are really American branded rings from Amidon, thanks to Lee WA8QFE low bow and thank him for it. The rest of the details are made in China.



          VII. Housing


The case of the device is made of aluminum, consists of four parts: base, front and back panels, as well as a cover. The base of the case is made of a section of an aluminum channel 50x100x50x5 mm. 110 mm long. Rest the body parts are made of aluminum sheet 2 mm thick. The case is painted black with a matte paint. The dimensions of the case are 110x100x50 mm. Knobs of potentiometers are aluminum, can be of three colors: White, yellow or black. The weight of the device is 485 grams.


          Front Panel


          Back panel


          Knobs for potentiometers


          Internal view

          VIII. Connection.



          Rear view

XPhase is located in a shack in the vicinity of your TRX and is included in the gap of the antenna feeder. In case you are using PA, between TRX and PA. Thus, the "Main" jack must be connected main operating antenna or PA input. Connect the "TRX" jack to the antenna socket of the transceiver. To the "Noice" jack, connect the AUX antenna, 2 to 3 meters Any wire stretched along the shelf of your shack. The XPhase includes an RX/TX switch that is controlled by a signal PTT from the ACC output of your transceiver.
To power the device you need an adapter for 12 volts DC. You can take any smallest adapter with a standard plug (+ in the center). It is possible to feed the device from the same source as the transceiver.

Be careful and very neat! RF signal for transmission through The XPhase device can ONLY after execute ALL of the above connection and turning on the power on the device itself, at the same time it should glow corresponding indicator "PWR" on the front panel of the device.
As can be seen from the circuit diagram, the XPhase device in transmission mode forms through high-frequency channel between the connectors "TRX" and "MAIN". Maximum The power of the high-frequency signal transmitted through this channel should not be exceed 100 watts! Do not connect the instrument to the PA output under any circumstances!

          IX. Setup and operation.



          Front panel view

The instrument is adjusted by three potentiometers "Gain1", "Gain2" and "Phase" on the front panel of the device and is reduced to level balancing noise components at the inputs of the phase discriminator and fine adjustment phase rotation in the AUX channel. The criterion for evaluation is the indication S-meter, Spectrum Analyzer (if it is in your TRX) or by ear for a minimum noise levels in headphones or speakers when set to free frequency TRX. First set all the potentiometers to the middle position and Set the transceiver to a frequency that is free from the stations. Then rotating potentiometer "Phase" left or right to achieve a minimum of noise. After this, perform the same actions with the potentiometer "Gain2", and then "Gain1". Repeat this 3 to 4 times. Balancing of the device can be considered successful if a minimum of noise is achieved provided that none of the Potentiometers are not in the extreme position. An exception may be be the potentiometer "Gain1", which has very little effect on the noise level, But in certain, small limits it affects the level of the useful signal. When changing to another range, you may need to re-enter balancing.

          X. In what cases can XPhase be useful?


In all cases when working with traditional types of modulation on low-frequency bands.
This is the correct answer, however, consider this key question uncover and in detail.

1. When working in the air (CW and SSB) on the low-frequency bands 160, 80 and 40 meters in urban conditions, especially if you live in a block of flats, is very effective.

2. In the event that your antenna field is located near the power line - an irreplaceable thing.

3. In the event that your neighbor is also a radio amateur and it's difficult for you to share an ether with him. A special case, simultaneous operation of several operators on one collective station, for example in competitions.

Summing up what was said above:
XPhase extends the receiver's dynamic range by clogging up to incredible wide limits, which other traditional methods will not allow and means. Presence of manual adjustments and availability of antenna AUX allow It is very selective and flexible to approach the issue of suppressing local interference radio reception in the most difficult situations. This is the universality and usefulness of this device.

The most important questions:
In order not to get frustrated by the time and/or money spent for the XPhase device to acquire and receive from this device the maximum of its capabilities during operation, it is NECESSARY:

1. Clearly imagine the principle of his work.

2. Perform an analysis and have a detailed understanding of the electromagnetic environment in and around your shack. On this basis, make and place the antenna AUX based on the conditions of maximizing the noise level induced in it and minimizing the level of useful signals of amateur radio stations. This requirement, in a sense, may seem contradictory, but it is indispensable to strive for this. Therefore, do not make the AUX antenna too large. This antenna should be designed to provide in the AUX channel noise level comparable to the noise level in the MAIN channel, so that it would be possible to adjust these levels by the attenuators Gain1 and Gain2 to achieve equal noise components at the inputs of the phase discriminator, and only. The number and dislocation of noise sources is of decisive importance. If basically they are inside your shack or apartment, then this is a simple situation. But if these sources are very large and they are located outside your apartment or premises, then you will have to conduct certain experiments with the AUX antenna, which would achieve acceptable results.

3. Accurately and correctly perform all connections and settings of the device.

4. In the event that you have something that turns out not how you wanted or how you imagined it, do not rush to make premature hasty conclusions, carefully read the instructions, analyze the situation and do not hesitate to ask questions through the feedback form on the "Contacts". Try to describe in as much detail as possible what exactly you can not and what it expresses.

Unfortunately, in the absence of necessary instruments, I do not have the opportunity produce and publish here the results of measurements of the dynamic range my hardware without an XPhase device and with it, however, I can share His personal impressions of the use of this device.

Without the XPhase device:
At my disposal is the Icom IC-756 transceiver, an analog device, although there is DSP, but at the existing noise level it does not cope and causes distortion. Also in the transceiver is Noice Blancker, whose work without XPhase is extremely unsatisfactory. It was necessary to reduce the gain in HF/IF reducing sensitivity of the transceiver to the limit and in the end I could hear only signals of very powerful stations that blocked the noise level. S-meter showed, when the transceiver is set to free frequency noise S9, sometimes +10 dB.


          Noise level without XPhase device

With the XPhase device:
The situation has changed dramatically. HF/IF gain stands at the maximum and I disable the gain control of the HF in the transceiver menu. DSP and NB work. S-meter now, as it should, shows "0" if there is no station signal. The signals of weak stations became audible, and powerful stations began to pass somewhat weaker than before, as I believe from the penetration of their signals into the AUX channel or more efficient operation of AGC.
The high noise level no longer "presses on the ears" and the degree of comfort at 80 and 40 meters became comparable to the 20 meter range.


          The same conditions, but with the connected XPhase device

          XI. Contents of delivery.


The complete set of delivery includes the collected and completely adjusted device XPhase and a short instruction manual.
Cords, connectors and adapter are not included in the delivery!

The XPhase device is intended for use in amateur equipment radio stations, read for people technically literate, for whom the solution of the data issues should not cause problems. In addition, all the transceivers are different. On the issue of how to connect XPhase to TRX on the PTT line, - see the manual on your TRX.

          XII. Economy.


Economics is a stubborn thing! When I came to the conclusion that I needed to produce such a device, I was forced to resort to economic calculations. And these calculations clearly showed that the cost of manufacturing One such device is extremely unprofitable, and with respect to acquisition material for the case and ordering a proprietary printed circuit board is not realistic. Another thing is wholesale, - making a small batch of devices. If you decide to make one such device for yourselves with your own hands, then the cost of purchasing materials for the case and parts, the manufacture of PCB, The cost of time for manufacturing, assembly and adjustment will cost several times more than the amount that I ask for this device - 100 EUR or 117 USD excluding of the cost of shipping. At the moment, there are 8 pieces of these devices. For purchasing please contact us via the feedback form on the Contacts page, pointing to the Subject: XPhase field. All the information necessary for the purchase of the device you will receive in the course of further correspondence.

          XIII. Prospects.


Any project or scheme is in motion, requires continuation, development. Demand generates supply. In this sense, I really liked the ideas as set forth by PA0NHC, with respect to the active noise ferrite antenna. I release XPhase devices in small batches, - 17 pieces each. At the moment, the PCB V3.1, taking into account the use of active noise ferrite antenna, as well as with the wiring of the stabilizer voltage. In the previous versions, the stabilizer was built in by hanging. If this, the first batch of XPhase will have the appropriate demand, I will do the next batch of instruments, on board V3.1 complete with an active noise ferrite antenna.
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