959B SSB SWR

[144inBama]

While hitting some skip today, I noticed my SWR on SSB are horrible. 1.1 on AM pretty much across the band with the amp on or off.... SSB... 1.2 to 1.6 with amp on and 1.2 to 1.8 with the amp off. Now the radio meter, which matches the MFJ-880 in AM doesn't change, it's only the MFJ (between the amp and antenna) that gives me the high SWR. The antenna is a 1.1-1.2 using the MFJ-259, Soooo.... Where do I look to solve this issue?

 

[sp5it]

SWR is mode independent.
Mike

 

[144inBama]

SWR is mode independent.
Mike

So I need to check SWR on AM then SSB and split the difference?

 

[OldTech03]

So I need to check SWR on AM then SSB and split the difference?

Try this adjustment set the swr while fully modulating SSB whistle while calibrating the SWR meter then switch to test the SWR's while talking with MFJ . The radios internal swr meter is auto calibrating so it compensates for the difference in power from AM to SSB.

 

[sp5it]

So I need to check SWR on AM then SSB and split the difference?

You even don't need the radio to check SWR and tune antenna. I usually do it in FM or AM with modulation down to 0.
Mike

 

[Captain Kilowatt]

So I need to check SWR on AM then SSB and split the difference?

SWR is SWR regardless of mode. SWR changes with frequency, not mode. Check in AM mode with DEAD carrier and be happy. Disregard anything the meter shows if trying to test in SSB mode with normal voice. Unless you recalibrate the meter EACH time you change power level the apparent SWR will change as well. SSB has more power out than AM therefore the apparent SWR will change.

 

[sp5it]

Get cross needle meter and you can see SWR on SSB

 

[Handy Andy]

to 2nd CK's comment,

When your radios SWR shoots up in SSB, on voice peaks - and not an AM - seem to be flat...you need to remember the power levels - both are a range of spectrum (Frequencies) but one has a LOT of power in only one small portion of it. The other mode (AM/FM) is broad banded but still only uses a specific width of spectrum - audio takes over the rest of the filtered width.

I need you to understand the above so as you work your SWR controls - try to use a good audio peaking sounds (no, not whistle - "ahh", "cha - cha" something with a strong sharp sound to make the SWR reading in Calibrate peak up high enough so you can set it without flooding the meter and potentially damaging it.

Remember too, at the Auto setting this thing tends to shoot up - simply due to the process, so if you can avoid using the built in SWR meter and use a Cross needle or more dedicated EXTERNAL SWR meter with it being Calibrated to your SSB peaks - it's far easier. That is To 2nd @sp5it comment...

BUT, then too, too much audio can cause harmonics and ruin your day using an amp sensitive to input levels. Your EXTERNAL SWR meter will show this - and they are from harmonics the system generates - be aware.

So observe and adjust audio drive accordingly so you the radio and your amp live to see another day.

 

[144inBama]

Get cross needle meter and you can see SWR on SSB

That's what I'm using. The MFJ-880 is a cross needle

 

[Handy Andy]

Your EXTERNAL SWR meter will show this - and they are from harmonics the system generates - be aware.

Can't stress this enough - back down the Audio or adjust that ALC to push down those peaks a little harder to reduce the effects you see in the SWR meters - they are the REFLECTIONS, from A set of harmonics being produced from the system - reflecting back to your system from the antenna which can't - it is not - tuned for it.

 

[144inBama]

Just finished playing around with the antenna. Using a dummy load my SWR is the same on SSB as it is on AM..... Now, while connected to the antenna on SSB and modulating, my SWR started at 1.5 and sloooowly declined to 1.1 as I talk, the same as AM. In AM with a 100 watt dead key, my SWR is 1.3 then drops to 1.1 on modulation which is normal from my understanding. I'm almost wondering if the mag mount is partially responsible for this....not having a good enough ground initially and as I transmit, it searches for a better magnetic grounding grid? Once it reaches 1.1 on SSB, every key after that, on modulation it starts at 1.5 and instantly drops to 1.1 and maintains it.

 

[Crawdad]

Whenever SSBing, I monitor the reflected power rather than SWR. I know that if the reflected power stays low antenna system (and SWR) is A-OK. When checking SWR I do it in a mode with a carrier, recalibrating at different power levels.

 

[144inBama]

I can't calibrate mine, it's auto calibrating.

 

[Crawdad]

Since I have only a lowly single needle MFJ872 I have to calibrate........

 

[338_MtRushmore]

This sounds like the peak reading circuit just isn't that great. The ameritron meters are the only cross needle meters I know of that actually read pep accurately.