Hi Tod: I stand corrected. After reviewing my notes, I seldom found a
situation where the power line noise pulses were stable enough or consistent
in nature thus making it very difficult to adjust the PHASE AND WIDTH
controls to effectively blank the annoying pulses.
I see in my notes that it actually worked quite well for my XYL's mix-master
but I fixed that with a few capacitors across the motor.
Life on 160 is a challenge and that is what makes it so special. Only those
willing to accept the challenge stick around and they tend to be amazing
individuals.
73 Markus VE7CA
--
Markus Hansen
VE7CA, North Vancouver, BC CANADA
Web site: http://www.shelbrook.com/~ve7ca/
On Thu, Nov 26, 2009 at 12:06 PM, Tod - ID <tod@k0to.us> wrote:
> Markus:
>
> The circuit does not require that the noise be on your power line -- in
> fact
> it is preferable that it is not on that line.
>
> What it does do is to use your power line to supply the 120 Hz clock for
> the
> mutivibrator pulse generator. The pulse output of the multivibrator circuit
> controls a circuit that is in series with the RF input to the receiver and
> separate from the multivibrator pulse generating circuitry.
>
> The timing of the start of the generated pulse used to cut off the RF input
> to the receiver is adjusted using the PHASE potentiometer so that when the
> radiated line noise reaches your antenna and is heading for your receiver
> the pulse generated by the multivibrator circuit will "cut" off the RF
> starting at the beginning of the spike on the RF line. The WIDTH
> potentiometer adjusts the duration of the cut off period so that the
> incoming spike is over before the RF reception is restored.
>
> The beauty of the circuit is that you can adjust the start time and the
> duration of the RF cut off so that only that part of the incoming RF that
> contains a noise spike is affected.
>
> All of the circuitry is 'outside' of your receiver so there is no need to
> modify the receiver and, in fact, you can use the receiver noise blanker as
> well as the external one.
>
> Because there may be more than one source of radiated noise it is quite
> feasible to have two of the multivibrator pulse generator circuits each
> driving the same RF gating [cut off] circuit. Each multivirbrator has its
> own PHASE and WIDTH controls so you can adjust them independently to blank
> two different sources.
>
> My personal preference is to use the circuit to drive and external RF
> gating
> circuit rather than to cut into the receiver and connect it to the internal
> noise blanker circuit of the receiver. The internal noise blanker might be
> needed to remove electric fence noise which I would suspect is not synched
> with the power line 60 Hz. I don't have such noise so I don't know if this
> is true.
>
> You mention a "noise canceller" and I am guessing that might refer to a
> device which uses a sense antenna to provide noise that is 'cancelled'
> using
> a unit such as the DX Engineering NCC-1 or the MFJ-1026. I have used both
> and have the NCC-1 presently. The 'cancellation' process nulls both the
> noise and the desired signal -- especially if they are in the same general
> direction. I use a preamp to restore the signal level after the nulling
> process but that still leaves weak signals with a S/N that I wish was
> better.
>
> Like the RX antenna rule -- more than one method for eliminating noise is
> desirable.
>
> The best method of course is, as you state, eliminate the noise at the
> source.
>
> Tod, K0TO
>
>
>
>
>
> > [mailto:topband-bounces@contesting.com] On Behalf Of Markus Hansen
> > Subject: Re: Topband: Noise
> >
> > Hi Tod. I built this cct many years ago and found it unsatisfactory
> compared to the noise blanker in my receiver. It requires a high level
> of
> > power line noise spikes on the power line coming into your shack before
> it will trigger the blanker diodes and that
> > caused a lot of IMD. Put a scope on your 110 V line into you
> > QTH and see if you can see any power line spikes on your 110
> > volt line. If not the noise you are receiving may be quite
> > some distance away some your QTH being radiated instead of
> > induced along the AC line into you shack.
> >
> > Of course the best solution is locate the power line noise
> > source and try to get it fixed.
> >
> > The next best solution is a noise canceller which is inserted
> > between the receiver and the receive antenna and it doesn't cause IMD.
> >
> > Markus VE7CA
>
>
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160 meters is a serious band, it should be treated with respect. - TF4M
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