Description:
Problems with local QRM on HF? often the answer is "yes". no matter if it's the elevator controller or an arcover on the
high voltage line next to the garden.
most trouble comes from the local electronics, computers, television, power supplies or else. with this amazing accessory
local QRM can be phased out, even when it's up to S9. no need to know where the noise comes from, could be the own
packet radio machine or a welding machine some 100m away from you.
The QRM-Eliminator is inserted in your antenna line, no need to modify your radio. It has a PTT-connection on the back,
so it can be in line while transmitting. A second auxiliary antenna must be connected, ideal would be a small antenna
close to the source of the noise, for example a small loop close to the elevator control, or some meters of wire some-
where in the shack or near the main antenna. keep the antenna short enough, otherwise it will pick up your wanted signal
in shortwave as well as the noise. The unwanted signal is picked up by both antennas with a different phase and both
signals can be added and phased out, a clear frequency is left for your receiver.. not comparable with a noise blanker.
Frequency range: 3.5 MHz...60 MHz. Size: 150x55x60mm, Connections: 3xUHF-Jack for main antenna, auxiliary antenna
and radio. RCA-jack for PTT. Supply needed: 13.8V/250mA.
Connections:
transmit antenna to "MAIN ANT"
Transceiver to "TRX"
auxiliary antenna to "AUX ANT"
nearly every antenna is useable, local QRM can be picked up with a bad antenna. you can use another HF antenna or
even the 2m antenna with only the center pin connected or some meter of wire behind the shelf in the shack.
best results can be achieved when the noise signal is same level on both antennas when GAIN-knob is turned fully
clockwise, if not, try to change / move the second antenna. Do not use an aux antenna which also picks up the signal you
want to hear, otherwise this signal is pahsed out too!
for testing the Signal just connect every antenna directly to the radio, then insert the QRM-Eliminator.
supply Voltage 13.8V / 250 mA to the "12V" DC jack, center is plus.
when transmitting through the QRM-Eliminator connect the PTT-Line from the back of your radio where normally your
PA is connected. PTT is active when center pin is grounded. Do not connect to the PTT-key on your microphone! Max.
power rating is 200W. if you want to use an amp, the QRM-Eliminator is to be connected between amp and exciter.
Take care, the aux antenna may not be too close to the main antenna, otherwise your own TX signal can damage the
unit.
When turned off, the main antenna is directly connected to your radio, you can transmit through the unit.
Usage:
turn on the unit, adjust GAIN to have the noise signal with same level on both antennas, then adjust with the both PHASE
knobs the noise, both alternatively, to a minimum of noise. then adjust the GAIN knob for less noise. if not possible, read-
just the phase knobs again until the minimum can be found. A bit difficult at first try, don't give up to early!
when found a minimum the local noise has to be nearly or totally gone and the wanted signal will be left over. if this signal
is gone as well => the aux. antenna picks up to much of the wanted signal AND of the noise, change /modify the antenna.
as all 3 knobs interact with each other, the adjustment can be a bit tricky.
when you believe, the unit does not work....
use your antenna analyser as signal generator, put it somewhere in the shack. connect both antenna jacks with a little
banana lead and check for a S9 signal from your analyser. then with GAIN fully clockwise, the signal must be phased out
after adjusting the 2 PHASE knobs.
Control LED: since end of 2018 we deliver the MK2 version, which also includes a control LED. Red/orange shows the
unit is powered and ready for adjustment. When PTT is activated, the LED switches to green.
QRM-Eliminator
Order-No. 26000
WiMo Antennen und Elektronik GmbH
Am Gäxwald 14, D-76863 Herxheim Tel. (07276) 9668-0 FAX 9668-11
http://www.wimo.com e-mail: [email protected]
