Though not entirely convenient, an effective means of setting up a noise
bridge as a reference for tuning an antenna system to a specific impedance
is to make a test jig. Solder a 50-ohm resistor (I have found 51-ohm
resistors) between the center pin and the shell of a PL259 connector.
Connect this test plug to the "ANT" connector on the noise bridge and turn
on the bridge. (Obviously, be sure not to transmit!!
I have an old Palomar RX Noise Bridge. I can only assume that the controls
are about the same on newer bridges. Set the Reactance control for zero (no
inductive or capacitive reactance.) On my bridge, the pointer on the knob
would be pointing straight up. Then turn the resistance control to a point
where there is a null or the noise in the receiver goes away. Put a tactile
reference mark at that point if you can, or just be sure not to move the
controls until you have tuned the antenna.
Then disconnect the test plug and connect the antena tuner to the "ANT"
connector on the noise bridge and adjust the tuner for a null in the noise.
You should probably then mark the tuner controls so you can easily return to
that setting, or make a chart of the control positions and the frequency.
Obviously, this is not a procedure I want to go through evry time, but it is
a way of establishing reference settings on my own.
73.
Mike, K9AZS
----- Original Message -----
From: "Henry Brugsch" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, November 22, 2002 4:02 AM
Subject: Re: tuning up an antenna
> Hi Michael, depends on the rig you are working with.
> If the power supply is sufficiently low-rated, means that as the rig draws
> more current, the louder the hum from the laminations. Thus, out of tune,
> the more hum you get, the rig beginns dancing around on the table, screws
in
> the case begin to resonate, and smoke starts curling out of the system,
> until you correct the situation.
> When the current is at a reasonable level, the hum is generally almost
gone.
> But, it depends on the rig. Those old Globechiefs, and some of the others
> used as little as they could get away with, and so, just a bit out of
> resonence made a loud hum.
> This was one of these unforeseeable accidents that could never have been
> predicted, or even implemented by an engineer.
> The noise bridge you have could be used as a tuner-tuner.
> But, you'd need to preset the thing to a known resonance *I.E. a known
> resonent antenna, or 50 ohms.
> Then, don't touch the controls, use an atu, and tune for minimal noise.
> If you start trying to use the bridge to determine where the antenna is
> resonent, and moving the controls, its value will be lost. Unless you can
be
> sure where the true setting is for the correct resonence.
> Essentially, what I am trying to do is show you how to build a
tuner-tuner.
> I wish I had thought of this, when I had my original Palomar noise bridge
> many years ago. I could never get any real use out of it, because of the
> fact that I never set it to a known value, and worked from there.
> That would have been a lot smarter. But, Palomar jumped ahead of my
> thinking, and created the tuner-tuner.
> Now, the best situation would be a noise bridge with detents at a tested
50
> ohms, then you could preset the bridge by feeling the detent in the
control,
> and working from there. The best of both worlds. Even a bit of nail
pollish
> could help, but I tried this, and didn't like the inaccuracy of it.
> ----- Original Message -----
> From: "Michael Ryan" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Thursday, November 21, 2002 7:17 PM
> Subject: tuning up an antenna
>
>
> > Can a noise bridge which was once used on an old heath kit
> > HW-12 be used in conjunction with an antenna tuner for reading SWR?
> > I will try and describe it.
> > It has a switch on the lower front which slides back and forth to the
left
> > or right for turning on or off and a flat roguery knob next to the
> > switch. The connectors for antenna and so on are on the top. It also
has
> > a round raised speaker.
> > I would also like to know what to look for, when it comes to the power
> > supply hum, when the rig is loaded up for maximum out put.
> >
> > Thanks all:
> > Michael
>
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