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. . . HF QRM X-PHASE ELIMINATOR
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QRM ELIMINATOR
If you live in the city or close to industrial facilities, you probably have high RF-noise level on your HF radio receiver from local sources that causes interference and difficulties in receiving weak radio signals.
The solution is either to go out of city, in rural area far from RF-noise sources or to try this practical device and reduce or eliminate the local noise.
I have made this QRM-Eliminator from the Kit-complete that I have ordered on eBay, but you can easily make your own QRM eliminator too, removing or reducing RF-noise level coming to your radio receiver.
It really helps so that you can listen many more DX stations that are hiden in the ocean of noise.
The QRM Eliminator is inserted between transceiver and the antenna without any additional modifications to the radio. The unit has a built-in PTT control which enables the QRM-Eliminator to stay connected during transmit.
An additional auxiliary receiving antenna is required. It can be simply a few meters wire in the shak or outside.
The unwanted signal is received with both antennas. The QRM Eliminator allows you to adjust the phase angle as well as amplification in a way to cancel out the unwanted signal before it reaches the receiver front end. It's based on a totally innovative concept and cannot be compared to the normal 'noise blanker' performance.
The critical component, which determines how successful it will canceling the unwanted local RF-noise, is the 'noise antenna' connected to AUX. It has to be simple wire, inefficient at receiving DX signals of interest, but picking up local RF-noise, which is usually vertically polarised.
The AUX antenna should be short enough, so it can pick up only local RF-noise but not DX-signals, otherwise the noise cancelling efficiency will be lower.
The QRM Eliminator allows adjustment of the phase angle and amplification to cancel unwanted signals before they reach the receiver front end.
The unit has built-in PTT control to switch internal realys bypasing the signal path, so you can transmitt without damaging or frying the electronic components inside of the box during transmission. The maximum RF-power of the transmitter should not exceed 100W, so that can be handled by the relays used in this Kit-complete.
Do not transmitt with transceiver connected to the QRM-eliminator without PTT connector pluged under any circumstances!
- The main antenna should be connected to "MAIN" ANTENNA connector.
- Transceiver should be connected to "TRX" (transceiver connector)
- The auxiliary antenna should be connected to "AUX"
- Power supply 12V (13.8V)/150mA should be connected to 12V DC jack.
Best results can be achieved when the noise signal is with the same level on both antennas, when MAIN ANT GAIN-knob is turned fully counterclock-wise, if not, the AUX-antenna has to be changed/moved.
If you want to use a RF Power Amplifier, the QRM-Eliminator has to be connected between PA and transceiver.
When turned off, the main antenna is directly connected to your radio, you can transmit through the unit.
Instructions of use:
Turn on the unit, adjust MAIN ANT-Gain to have the noise signal with same level on both antennas, then adjust with the PHASE and AUX-Gain knobs, both alternatively, to achieve minimum noise. Then adjust the MAIN ANT-Gain knob for less noise. If not possible, readjust the PHASE and AUX-Gain knobs again until the minimum noise can be found.
The first try can be a bit difficult, but don't give up too early.
When the minimum of the local noise is found, it has to be nearly or totally gone, and DX signals can be heared. If the DX signal is gone as well, than it means that the AUX antenna picks up to much of the wanted signal together with the unwanted RF-noise. In that case, The AUX antenna has to be changed, moved or modified.
As all 3 knobs interact with each other, the adjustment can be a bit tricky, but at the end, the result can be great, so that we can hear many weak DX signals that we couldn't hear without this QRM-eliminator due to high local noise level.
Click on shematic above to see it in better resolution
I have purchased the Kit-complete from here.
The enclosure box and connectors I have boght from the local store for electronic components here in Macedonia.
There are many presentations available on YouTube which shows how this device works. Here are some links:
1. QRM Eliminator X-Phase in practice
2. QRM Eliminator X-Phase in practice
3. QRM Eliminator X-Phase in practice
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Mile Kokotov (2020)
MIle Kokotov, M.Sc. is industrial engineer manager and has a master`s degree in technical science with almost 40 years expirience in RF-technics. He is Acttual President of The Radio Amateur Society of Macedonia
Feel free to visit other articles and projects on his website
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