Ive owned many phasing rigs starting with a HB W2EWL, all the Central
Electronics, and a pair of HT-37's.
While a single tone can be used to get a good indicated null it is only at
that one frequency. It is better to use two tones. If that isnt possible
then use a tape loop or digital recorder with a fairly flat speech
recording. Something recorded off the BCB with good AVC works well. Then
adjust and make sure the high frequencies are suppressed as well as the low.
Carl
KM1H
----- Original Message -----
From: <[EMAIL PROTECTED]>
To: "Discussion of AM Radio in the Amateur Service"
<[email protected]>
Sent: Wednesday, November 28, 2007 8:49 AM
Subject: RE: [AMRadio] Halli HT37 Phasing Mod problem
----- Original Message -----
Subject: RE: [AMRadio] Halli HT37 Phasing Mod problem
Date: Tue, November 27, 2007 21:16
From: "Gary Schafer" <[EMAIL PROTECTED]>
The best way that I have found to align phasing rigs is to talk into the
mike while listening to the opposite side band and tune things for
minimum
(best side band suppression). A nice long ooooooh works good. You will
need
to switch side bands and do the same on the other as they interact. You
can
tune it for really great suppression on one side band while the other one
won't be so great.
Find the point where the suppression is nearly equal on each side band
while
listening to the opposite side.
Never owned an HT-37, but have played with various other phasing-type
rigs, one of them home-grown (by me).
Here's a few more ideas:
Use your scope to trace a "Lissijous figure" - in this case a circle - to
dial in the correct phase and amplitude relationship between the two
quadrature audio channels. You'll wand to feed a sine wave into the audio
input of the rig for this; a 1Kc tone should work OK. Make sure you don't
overdrive the audio stages! Also, with the same setup, you can use a
selective receiver (something with a bandpass of 500Kc/s or less) to sift
out the lower sideband (1 KHz below the transmit (virtual) carrier
frequency), carrier (which should be very weak, but probably audible)),
and the upper sideband.(1 KHz above the carrier freq.). Tune in the
sideband you want to suppress and null it out. Then tune in the opposite
sideband, select the other sideband on the transmitter, and do the same.
There will be a compromise between ultimate opposite sideband suppression
and getting the best suppression possible for both USB and LSB operation.
I've never used the Lissajous figure method myself, but it makes sense it
should work. I've used the 2nd method several times.
73/GL,
-Larry/NE1S
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