Adjust SSB offsets without test equipment ... (DX959)

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willee
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Adjust SSB offsets without test equipment ... (DX959)

Post by willee » Saturday 29th Nov 2008, 0:06

Here is a way to align your SSB transmit offsets without ANY test equipment.
I used this on my Galaxy DX-959 but it should work with any radio.
Just be sure you are adjusting the correct points.

Assuming your AM frequency is OK, Have a friend with a good ham receiver listen on your frequency while you talk and adjust L24 for USB and L25 for LSB.
Have him on the telephone and he can tell you when you sound like you are "on frequency" in the SSB mode.
This is not as precise as using good test equipment but it will work just fine as long as HIS radio is in good adjustment.

Be sure not to adjust L21 and L22 by mistake ... these are for the receiver not the transmitter.

I had a problem using my frequency counter on TP6.
There was no test post soldered in the hole and when I attached the Freq counter the receiver audio went out.
I suspect the meter (a HP unit) was loading the circuit somehow.

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The Defpom
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Adjust SSB offsets without test equipment ... (DX959)

Post by The Defpom » Saturday 29th Nov 2008, 9:07

A good way to avoid loading the circuit down if you are not connecting through a scope is to have a small value ceramic capacitor in series with the counter probe, something like 5-10pF is usually suitable.

Also come more comments, L23(AM), L24 (USB)and L25 (LSB) are the 10.7MHz I.F. offsets, these rarely go far off frequency, and tend to only need adjustment if someone has messed with them.

L20 (AM), L21 (USB), L22 (LSB) are the loop oscillator offsets, which usually do require adjustment.

Using a second (known to be on frequency) radio to adjust for correct sounding audio on SSB is usually good enough, but if you have a frequency counter, it is best to do it that way.

willee
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Adjust SSB offsets without test equipment ... (DX959)

Post by willee » Saturday 29th Nov 2008, 14:36

Thanks Scott.
I tried a few small caps but they all gave the same results.
Reciever audio would blank out as soon as I touched the lead to the test point.

This DX959 is a fairly new radio but it idoes not have the new Mosfet finals ... if that has anything to do with it.
I also find it strange there is no post soldered into the TP6 hole like the other test points have.

Also found that the VCO adjustment VC1 had no effect on the frequency at pin 8 of IC3. I is a touch low at 10.23800 mhz.

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Rick
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Adjust SSB offsets without test equipment ... (DX959)

Post by Rick » Saturday 29th Nov 2008, 22:47

Well this all made me chuckle. About setup using a receiver and a telephone.

TP6 is only used to setup the carrier osc in SSB and only in TX mode.
The AM carrier test point is TP5, which is the output of the Balance Mod IC6.

Ranger has not fitted a TP6 for many years now, and you use the resistor R160 has the test point.

VC1 is not the VCO adjustment.
VC1 setup the 10.24000 MHz ref frequency, the best way to do this is to monitor the frequency at the collector of Q25 while adjusting VC1.

Note
There are two VC1 in this radio, the other one is on the frequency counter module, DO NOT ADJUST this one.
Rick.

willee
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Adjust SSB offsets without test equipment ... (DX959)

Post by willee » Sunday 30th Nov 2008, 3:05

Rick, I am glad I brought a smile to your face.

Actualy, All I needed to do was get the SSB transmitter on frequency.
I can not read a freq by hooking a freq meter to TP6. (even with a cap)
The only other way I could think of was calling my buddy and having him "tune me in" by ear with his new IC-756 ProIII.
It worked just fine.

I doubt the AM freq could be set that way but fortunately the freq meter works OK on that test point.

The VC1 adjustment did nothing to change the freq at IC3 pin 8 as called out in the alignment procedure (from CB Tricks).
They call it the VCO adjustment.
I dont know why but it would not change the freq.

I am certinaly not the sharpest knife in the drawer when it comes to electronics I am learning every time I take on a project like this and do appreciate all the help you and the other real radio techs here are offering. Being able to do some servicing and adjustment on my radio saves me money, time, and gives me a better working radio.

Now if I can just clear up the adjustment procedure for setting the driver and final bias current I will be one happy CB'er.
The procedure on CB Tricks says different than the service manual downloaded from this site.

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Rick
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Adjust SSB offsets without test equipment ... (DX959)

Post by Rick » Sunday 30th Nov 2008, 8:46

If your radio has a 2SC2166 driver then set the bias for 50mA using TP9 and TP8.
If your radio has a 2SC1969 final then set the bias for 100mA using TP9 and TP7.
Both bias are setup USB mode with no modulation in TX
Rick.

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Adjust SSB offsets without test equipment ... (DX959)

Post by bob85 » Sunday 18th Jan 2009, 15:57

the best method of aligning offsets is to use a counter to get you in the ballpark then fine tune for correct audio frequency response,
using just a counter does not take into account that the centre frequency and skirt shape of the ssb filter is not perfect, the counter method is a cb thing, the old method was to adjust offsets for equal rf output at two audio frequencies say 300hz and 2300hz, doing it with an experienced ear ensures the best sound every time, using a counter does not :wink:

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