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Author Topic: USB AND LSB ALIGNMENT  (Read 606 times)
KN6YA
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Posts: 10




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« on: December 29, 2007, 01:11:38 PM »

Seems this area gives me headaches. When I align my IC751 (has frequency display) per the manual or any SSB rig with a frequncy display, eg, by adjusting the PLL reference oscillator and upper and lower ssb oscillators, they never come out right and during contacts, others have to tune me in as I am off frequency. My freq counters (3 of them) are not calibrated and maybe thats the problem, so what I end up doing is aligning the upper and lower oscillators by listing for the best voice quality from other contacts and that seems to work the best. Maybe there is an easier way such as zero beating wwv but how, by zero beating upper and lower against WWV's tone. Ive tried this too but I her two tones and no zero beat.  Maybe theres a better way or maybe a trick I don't know.
Mark, KN6YA
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KB9CRY
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Posts: 4284


WWW

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« Reply #1 on: December 29, 2007, 02:00:00 PM »

My freq counters (3 of them) are not calibrated and maybe thats the problem


Yep, you got it.


Why worry about what your rig's frequency is displaying?

Personally I just tune in a station until they are zero-beated or until I like the sound of their voice and I call them and I'm always right on.  My rig may be 0.03 kc +/- from what the true frequency is but who cares.

And if I'm calling CQ, they all just tune the same and I never have trouble.  Many rig's counters will be off relative to another's.  I just don't worry about the minor details.  
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AC5UP
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Posts: 3812




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« Reply #2 on: December 29, 2007, 03:46:01 PM »

Many frequency counters use a 10 MHz clock and can be calibrated against WWV with an SWL receiver in AM mode and a few feet of wire. Pick a time when WWV on 10 MHz is sounding good using the 'few feet of wire' as an antenna. Turn on the freq counter and let it percolate for 30-60 minutes then lay or wrap a turn of the RX wire around the freq counter case. You should hear the counter's clock and WWV beating against each other. If not, and the counter has a 'Clock Out' BNC on the back, try connecting the free end of the RX wire though the smallest value cap you have in your junk box, something like 5pf, or a > 1 meg resistor to the clock port.

Adjust the frequency counter clock to zero beat against WWV. Exactly. If you can't hear the very lowest tones near zero beat, watch the S-Meter on the receiver for wiggle. Chances are you'll see a steady S-Meter needle at exact zero beat, slow wobble +/- a Hz or two.

As for the LSB and USB oscillators in your rig --- If alignment by the book doesn't play like it should, long ago and far away I had a Tempo 2020 that always sounded muddy and bassy on SSB RX. Aligned both oscillators by the book and it still sounded muffled. Best guess is the xtal filters had aged a shade off frequency. Just for the hell of it I tuned the RX to a quiet spot where I had nothing but band noise and peaked both trim caps for best audio balance. Not too bassy, not too tinny, just flat white noise in the midrange.

It worked. RX sounded good, TX reports likewise.

An alternate for those who need something more than 'sounds good' would be to align everything except the SSB offset and connect the freq counter across the speaker. Tune WWV straight up and wait until it cycles over to tone and clock ticks, then adjust the LSB and USB trim caps until you see the same tone freq as AM.
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AC5E
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Posts: 3585




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« Reply #3 on: December 29, 2007, 03:49:57 PM »

Well, my first receiver was within 50 kHz on 20 and below and 100 kHz on 11 and 10 Meters. We tuned the RX to the TX crystal, called CQ, and tuned around until we heard a reply. So WWV's pitch being different between USB and LSB seems a minor annoyance at most.

But if it really bugs you, tune in WWV, and set it so the  audio tone is the same on both USB and LSB.

73  Pete Allen  AC5E
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WA0LYK
Member

Posts: 85




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« Reply #4 on: December 29, 2007, 06:44:29 PM »

Your never going to get this right because of the design of the IC751.  I have one too and going through the alignment even with a frequency counter that's only 1 Hz off just doesn't do it.  There is too much interaction and the filter's passband has apparently drifted as mentioned above.

I just use another receiver to complete the alignment by making both sound like I want.  This will make your vfo reading off a little but in the end, I just forget about it and use it.  The actual frequency isn't real important as long as you stay away from the band edges.

Jim
WA0LYK
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K6AER
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Posts: 3468




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« Reply #5 on: December 29, 2007, 06:52:04 PM »

If your Upper and Lower SSB offset oscillators are to one side of the crystal filter or the other side you audio both receive and transmit will clip the high or lows. The ideal is to set the offset LO’s for a centered bandpass and for the audio to be center on the correct frequency.  Mind you if your crystal filter chain only passes 2.4 KHz of band width you will not be able to get more bandpass on the audio than what the filters can pass.

Now with your frequency counters out of calibration you might want to listen to a group of hams on a known frequency with new or recently calibrated radios. Most of the guys on 14.185 and 14.178 MHz have very new equipment and they are within 10 Hz.

Get on in the morning and they would be happy to help you get the radio centered. The probably will go off to the bottom of the band where no one will be bothered. Have the manual open to the correct page and the necessary oscillators marked for easy reference.

Most crystals age in the same direction (down) so theoretically you should only have to move the master oscillator to bring the secondary oscillators into the correct bandpass center.

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WA3SKN
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Posts: 5419




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« Reply #6 on: December 30, 2007, 09:44:46 AM »

To align ANYTHING you must start with a "known good reference source".  You don't have one.  So, WWV transmissions are the closest to a good frequenncy source you have available.  You can "zero-beat" to within cycles with this.  Do let your radio "warm up" before checking.
I would not be making any adjustments without "calibrated" test eqpt... there are too many adjustments you can do wrong!

-Mike.
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W2AEW
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Posts: 621


WWW

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« Reply #7 on: December 30, 2007, 11:09:05 AM »

FYI - Here's a document I wrote several years ago that talks about a few ways to use WWV to adjust your reference oscillator.

http://www.qsl.net/w2aew/adjustrig.htm

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K6AER
Member

Posts: 3468




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« Reply #8 on: December 30, 2007, 12:53:53 PM »

Gentleman,

Zero beating WWV so your frequency readout looks good will do no good if your offset Upper and Lower sideband oscillators are off frequency. You must have the offsets aligned properly before the frequency readout will mean anything. This means sweeping the audio to center the output bandpass on the proper IF frequency. The IF’s must be centered in the crystal filter and  IF chain or your audio will sound like …crap!

Then the IF must be centered on the second transmit mixer to the proper transmit frequency with the proper corresponding frequency readout.

The same has to be done for the receiver side as well.

Unless you have the necessary equipment and experience for this task I suggest you sent the radio in. The alignment should take less than an hour with a knowledgeable service shop.
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