Bonehead: How do you tune an antenna with a noise bridge?
Jerald Pendleton
I've been told that some hams use a noise bridge to tune their antenna
using a transmatch. This has the advantage of not generating qrm while
you get the antenna to resonance.
How the heck do you do that?
In my case I have a MFJ antenna tuner that shows forward and reflected
power (and hence SWR). If I hook a noise bridge in in front of the
tuner it certainly not going to put out enough energy to drive the
swr meters.
Do I need one of those gadgets than measure antenna impedance? If so,
could someone point me a plans/kits for one (I've bought my last mfj)?
Many Thanks,
Jerry Pendleton
--
Jerald R. Pendleton Email: jer...@wrs.com, Personal Email: jrp...@netcom.com
The preceeding message represents only the opinon of the author. This
do not represent the opinions/positions of Wind River Systems, my mother,
my wife or my poodle.
Gary Coffman
>I may be displaying extreme ignorance here but....
>
>I've been told that some hams use a noise bridge to tune their antenna
>using a transmatch. This has the advantage of not generating qrm while
>you get the antenna to resonance.
>
>How the heck do you do that?
>
>In my case I have a MFJ antenna tuner that shows forward and reflected
>power (and hence SWR). If I hook a noise bridge in in front of the
>tuner it certainly not going to put out enough energy to drive the
>swr meters.
>
>Do I need one of those gadgets than measure antenna impedance? If so,
>could someone point me a plans/kits for one (I've bought my last mfj)?
A noise bridge *is* a gadget for measuring impedance (but not necessarily
antenna impedance). To tune a transmatch with a noise bridge, you put
the bridge inline between the receiver and the tuner, set the bridge
for an impedance of 50-j0, set the receiver to the frequency you want
to use, and tune the transmatch for a dip in received noise. You should
get a good sharp deep null when the tuner is adjusted correctly. Remember
to switch the bridge *out* of the line before you transmit, or you'll
have fried bridge for supper. :-)
Gary
--
Gary Coffman KE4ZV | You make it, | gatech!wa4mei!ke4zv!gary
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Tom Skelton
was
put out by Palomar Engineers. Here's the setup:
Attach your antenna to the 'output/antenna' of your tuner. Connect the 'input'
of your tuner to the "unknown" port/SO239 of the noise bridge. Connect the
"rcvr"
SO-239 to your receiver/transceiver.
Now, turn on the noise bridge and set the R (resistance) scale to 50 ohms and
set the Xc/Xl scale to 0 (zero). You should hear a rushing sound in your
receiver/transceiver. Adjust your tuner (leave the noise bridge alone) until
the noise in the receiver/transceiver is nulled. Your transceiver is now seeing
a 50 ohm match provided by your tuner. You can do this for any band you want to
operate, make up a chart, and basically set-and-forget unless you change your
antenna
dimensions.
MAJOR OBVIOUS WARNING: DO NOT TRANSMIT INTO THE
NOISE BRIDGE.
I hope this helps. cheers...
73, Tom WB4iUX
My posting is my view only and not AT&T's. But you know that!
DX IS !!!!!
And always will be.....
Jeffrey Allen LeBlanc
>>In article <CtyzA...@wrs.com> Jerald Pendleton writes:
>>I may be displaying extreme ignorance here but....
>>
>>I've been told that some hams use a noise bridge to tune their antenna
>>using a transmatch. This has the advantage of not generating qrm while
>>you get the antenna to resonance.
>>
>>How the heck do you do that?
>>
>was
>put out by Palomar Engineers. Here's the setup:
>Attach your antenna to the 'output/antenna' of your tuner. Connect the 'input'
>of your tuner to the "unknown" port/SO239 of the noise bridge. Connect the
>"rcvr"
>SO-239 to your receiver/transceiver.
>
>Now, turn on the noise bridge and set the R (resistance) scale to 50 ohms and
>set the Xc/Xl scale to 0 (zero). You should hear a rushing sound in your
>receiver/transceiver. Adjust your tuner (leave the noise bridge alone) until
>the noise in the receiver/transceiver is nulled. Your transceiver is now seeing
>a 50 ohm match provided by your tuner. You can do this for any band you want to
>operate, make up a chart, and basically set-and-forget unless you change your
>antenna
>dimensions.
>
>MAJOR OBVIOUS WARNING: DO NOT TRANSMIT INTO THE
>NOISE BRIDGE.
>
>I hope this helps. cheers...
>
>
>73, Tom WB4iUX
>My posting is my view only and not AT&T's. But you know that!
>DX IS !!!!!
>And always will be.....
>
>
for a reply.
Jeff, KB0FIX
--
----------------------------------------------------------------------------
| Jeffrey A. LeBlanc | In the immortal words of Socrates:
| jl19...@longs.lance.colostate.edu | "I drank what?!"
----------------------------------------------------------------------------
Sid Boyce
has one built in, just needs 12V, is fixed for 50 Ohms.
I had mine for a few years before I got curious and applied power to
just have a play and was surprised at the accuracy and ease of use.
There was also an article in QST or HamRadio that described how and
mentioned that even extra-Class hams could be heard tuning up on the
band when such a simple device works fine and silently.
By the way, in case anyone wonders, SEM is a company that has made
this type of equipment for many years and is based in the Isle-of-Man
(don't remember if that's the UK). They call it the EZ-TUNE, that way
they probably sell more than if they called it a noise bridge, theirs
has an RF sensing relay to switch the unit out when the transmitter is
keyed - as happened on occasions to me.
73
Sid ... G3VBV .... Amdahl(UK) ....
Rajiv Dewan
> Yes, that's what it is. Some commercial units like the SEM Z-MATCH
>has one built in, just needs 12V, is fixed for 50 Ohms.
>I had mine for a few years before I got curious and applied power to
>just have a play and was surprised at the accuracy and ease of use.
>There was also an article in QST or HamRadio that described how and
>mentioned that even extra-Class hams could be heard tuning up on the
>band when such a simple device works fine and silently.
BTW, the *noise* bridge does transmit - broadbanded noise albeit
at qrppp power levels. It is probably worse than lo leakage from
many receivers.
> By the way, in case anyone wonders, SEM is a company that has made
>this type of equipment for many years and is based in the Isle-of-Man
>(don't remember if that's the UK). They call it the EZ-TUNE, that way
>they probably sell more than if they called it a noise bridge, theirs
>has an RF sensing relay to switch the unit out when the transmitter is
>keyed - as happened on occasions to me.
Palomar, in US, has one too. It is called a tuner-tuner.
Best regards,
Rajiv
aa9ch/2
Jim Grubs, W8GRT
> a 50 ohm match provided by your tuner. You can do this for any band you want
> operate, make up a chart, and basically set-and-forget unless you change your
> antenna
> dimensions.
While this is true in theory, in practice there are a lot of things
that cause variations in correct tuner settings. The most obvious is
rainy weather.
--
jgr...@voxbox.norden1.com
'Two of the gravest general dangers to survival are the desire for
comfort and a passive outlook.' -- U.S. Army Ranger Handbook
Jim Grubs, W8GRT
> So, is the "Tuner Tuner" from Palomar just a noise bridge? Thanks in advance
> for a reply.
Yes, the advantages are it is preset for 50-j0 and has a handy co-ax
switch for taking it out of the line to the tuner. Most of the test
instrument type bridges have to have the co-ax disconnected by hand.
Michael J Dower
> >>I may be displaying extreme ignorance here but....
> >>
> >>I've been told that some hams use a noise bridge to tune their antenna
> >>using a transmatch. This has the advantage of not generating qrm while
> >>you get the antenna to resonance.
There's a design in "Solid State Design for Radio Amateurs" (ARRL / DeMaw et
al). I've used it - it works, too. Presents a reasonable match to the rig
during tune-up so that you can tune the proverbial wet string!
73's de VK2ENG in G-land
--
Michael J Dower
'Quoth the raven, "Never more".' ... Poe