Last Oct I reported that I picked up a JPS ANC-4 noise canceller.
I reported that it offered no real improvement to the noise that
I experience (continous S9 level of bacon frying sound -not static
crashes). Several folks responded with both favorable and unfavorable
experiences.
Tom -W8JI offered to test my unit and post the results. The following
is a summary of his test as posted:
On 160 meters, the loss through the main antenna port was 5.38 dB.
That port appeared to be passive, and had good IMD performance. (In
comparison the DeMaw unit I have has 5.53 dB gain and the MFJ unit
about 3.1 dB loss.)
The "noise" port was another story. It overloaded at less than 40 mV
(-15 dBm) input regardless of gain setting, very poor IMD
performance. (The DeMaw QRN Squasher unit overloads at over one
volt at low gain settings, and the MFJ unit overloads at about
1/2 volt no matter what the gain setting).
The ANC-4 did shift phase quite well (340 degrees total phase
rotation) but unfortunately had over 23 dB amplitude drop as phase
was rotated through its range, and as high as 13 dB amplitude shift
even under the most favorable test conditions. This severe level
change with phase adjustment would make it VERY difficult
to find the right spot null on many signals and impossible to null
some signals that would otherwise be "nullable".
(In contrast the DeMaw unit has NO phase rotation at all and over
100 dB of unwanted amplitude shift as the phase control is
adjusted, while the MFJ unit has less than 1.5 dB of unwanted
amplitude shift and more than 326 degrees of phase rotation on 160.)
73, Tom W8JI
-----------------------
After a few emails with Tom, he sent me an MFJ noise canceller to try.
When I received the MFJ and hooked it up, I constructed a sloper "sense"
antenna from my tower (about 15 ft high and 25 ft of slope). I tuned
my xcvr to 40m.
TEST NO. 1:
I rolled my lawnmower between my 40m vertical (hytower) and the sloper.
I attached about 6 ft of wire to the sparkplug and cranked it up. The
lawnmower was about 75 ft equal distance from each antenna. The pulse
noise was S9 on my xcvr.
My noise blanker alone would drop the noise to S3 and cause distortion
on some strong sigs.
With the xcvr noise blanker off, the MFJ nulled the noise to S1-S2
(noise floor). There was no need to use the xcvr's blanker... so no
distortion on any signals.
I substituded my ANC-4 in place of the MFJ using the same sense antenna.
It nulled the noise to about S3-S4. The blanker dropped the noise an
additional S-unit. I could copy signals OK, but could hear the lawnmower
pulses in the background.
TEST NO. 2:
On 160m using my vertical transmit antenna my "frying" noise is S9+.
Using the MFJ with the same sense antenna has on 40m test, I couldn't
get much improvement. The good thing with the MFJ is that you have two
gain controls; one for the "sense" antenna and one for the "main" antenna.
I added another 30 ft wire to my sense antenna and with the gain fully
open (and preamp on) and the main antenna gain fully off, I could start
hearing the noise. [The two signals need to be close to same amplitude to
cancel.] Still no real improvement.
I changed the sense antenna to a 160m Inv-V on my tower. The same frying
noise now is S9 with the sense gain up. I started increasing the main
antenna gain to about 40% open and adjusted the phase. The noise
dropped like a log to about S4. Adusting both gains and phase I could get
the noise to S3 and hear signals with a much better S/N ratio. Good enough
to be able to operate on the band.
I substituted the ANC-4 for the MFJ. Using the same Inv-V sense antenna,
the best I could do is null the noise to about S7 which isn't much help.
[The ANC-4 doesn't have a main antenna gain control so you are limited in
balancing the level of both signals.]
IMPRESSIONS: I tested both units for an entire evening. The MFJ works!
I did purchase the ANC-4 used, but I feel it's OK. But to make either
unit work it must have the same signal on the sense ant as the main ant.
This means on 160m you must use a big sense antenna.
CAUTION!! Don't install the sense antenna too close to the transmit antenna.
Later I watched the lightbulb in the MFJ as I brought my xmtr power from
0 to 100 W. (I was worried because the Inv-V is close to my xmt vertical.)
I had no indication. I turned on my amp and started from 0 W and the
protection light popped at 200 W. I never did see it start to glow.
It was sure easier to replace the 12 V bulb than any transistor -that's
good! I dropped the ends of the 160m Inv-V and let them dangle on the
ground. I tested the MFJ again. Because the sense signal noise would only
go to S3 due to the less efficient antenna, I was not able to turn up the
main antenna gain very much. However, I was able to null the "frying" noise
to S1 and have signals pop up to S4 -a very good S/N ratio. I turned up
my amplifier slowly and I was able to operate with full output in heavy
noise and static conditions.
WHAT's NEXT: I contacted Tom -W8JI and offered to buy the MFJ. I'm
experimenting with a new sense antenna that goes over the front of my
house to get further away from the transmitting vertical in the backyard.
If I can get a good enough sense antenna that produces enough noise into
the canceller, look for me in the pileups......
This test/report reflects only my experience and not that of anyone else.
73, Dick -K5QY
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