Fairly new to HF, MFJ-941D Tuner has me all confused...

[N1RKR]

OK, here's the situation...

I have a 10 meter dipole in the back yard, about 22 feet up at the center, with the "wings" out at about 45 degree downward angle... I am told that with this tuner, it should be no problem to match 15 and 20 meters... So, I'm trying 15 meters...

So I went step by step by the manual...

A jumper coax goes from my transmitter (IC-745) to a simple power/swr meter (I'll get into why later), then out of that to the transmitter input on the MFJ-941D, and then out the Coax 1 port to my dipole.

From there, the manual explains what the INDUCTANCE knob does, and explains that "A" is minimum, and "L" is maximum. Then the Transmitter matching knob and the antenna matching knob. OK, I'm good so far. It then says that the transmitter must be tuned for a 50 ohm load for the band in operation, and to do this "by connecting the 50 ohm load to the BYPASS COAX connector and turning the antenna switch to the BYPASS position..."

Does this mean I have to buy a dummy load? Is that the only way to do it? That seems wrong to me. Am I read it wrong? And if I'm reading it right, how would I go about knowing whether the impedance is right or not? *confused*

So the next step in the manual says to set the transmitter matching knob and the antenna matching knob to TDC (3.5 in this case). It then says to rotate the inductor selector knob until maximum noise is obtained. It doesn't matter what I set that to, the noise doesn't seem to change at all. *more confused*... OK, so I left it at "A" for now...

Then it says to alternatively rotate the transmitter and antenna knobs to get the best SWR. And here's where the extra meter comes in. I use the SWR meters (one in the tuner, and the other one) to watch it go down. Then when I'm done, I re-calibrate the SWR meters for the forward to infinity, and recalculate the SWR based on the new forward setting. This works fine on the "extra" SWR meter, but the tuner's SWR meter won't let me set the swr sensitivity high enough in FWD mode to get it to the infinity mark, and are therefore unable to calculate proper SWR using that meter...

But, using my "other" meter, and the original reading on the tuner's SWR meter before I tried to recalculate the fwd infinity setting, I get it down to about a 1.8:1.

Now the next hiccup. The way the SWR meter in the radio itself is set, you set a knob to the set position, and use the RF POWER knob to set "infinity". Infinity works out to be about the 30 watt power setting, and when I use that to calculate SWR, the radio says the SWR is about 2.5:1... I then re-check using my extra meter, and it says 2.0:1... Any idea why these aren't the same?

I'm reluctant to transmit on full power because though everything I can see says that it's within the safe SWR range, I can't be sure I'm not messing something up and I don't want to blow up my radio...

So, please, someone with more experience than I have, read this over and let me know if there's anything glaringly obvious that I'm missing, and explain the missing piece from the "50 ohm tuning" thing? I'm sure the 6 page manual is written for people who have used tuners in the past, and I haven't, so there's something I'm missing there.

Thanks

N1RKR/AG

 

[vkrules]

I'm looking at the mfj-941 d you have the single needle meter right?Ok first of all you don't need a dummy load to check SWR and you set the tuner to bypass if you don't want to use the tuner, that as the the name suggests, bypasses the tuner . Put the tuner in swr mode select fwd .adjust the swr sensitivity so you see the needle is on the set mark. Switch from fwd to reflect thats your SWR Don't change the drive level.

 

[vkrules]

You should be able to get fsd (set mark) on that tuner with just a few watts. (manual says 5 watts) . My self I always peak for noise before hitting the tx ,it gets the swr in the ball park, also it's good practice to use as low a power setting as you can and still get a fsd while tuning or checking swr. You should hear a difference+++ Just had a thought no change in noise and can't get fsd on the tuner, are your patch cables ok? And yes it is common to see different swr readings with more that 1 meter in line


From there, the manual explains what the INDUCTANCE knob does, and explains that "A" is minimum, and "L" is maximum. Then the Transmitter matching knob and the antenna matching knob. OK, I'm good so far. It then says that the transmitter must be tuned for a 50 ohm load for the band in operation, and to do this "by connecting the 50 ohm load to the BYPASS COAX connector and turning the antenna switch to the BYPASS position..."


That I think might be reference to tuning older valve radios when we could tune the output impedance.

 

[Lil'Yeshua]

I have the MFJ-971. It might help you to turn down the rf gain while adjusting(listening)the tuner for the highest noise level. Again,on mine,I set mine for the highest noise level and a fairly low swr and I used an additional power meter to make sure that the wattage output from my tuner coincides with my radio's established deadkey power into a dummy load.

Note:I read somewhere that says my 971 won't read anything accurately wattage wise below 10 watts deadkey.

But these are my observations.

 

[N1RKR]

VKRules, yes, I have the "D" model which has the single needle meter. The "E" model has the dual needles...

OK, now that I've got a little more use out of it, and have been able to talk to some of the guys in my local radio club, I think I've narrowed down most of my problems...

What works for me is to set the "transmitter matching" and "antenna matching" knobs to TDC (3.5), and the "inductor selector" to A...

Then I turn the inductor knob one click at a time until I get the best receive signal. This is my starting point...

Since HF is pretty much all SSB, and you can't take an swr reading in SSB mode (no carrier), at this point I'll switch over to FM mode and drop my power level to 15ish watts. I then flip the transmit switch and use the swr meter on the tuner to take an initial swr reading.

I then start with the "antenna matching" knob, which I move slowly up and down to find which drops the swr. When I get it as low as possible, then I adjust the "transmitter matching" knob to get it lower.

I still have my "extra" swr/power meter in line, and at this point, with the SWR as low as possible, I turn up the power on the radio just a bit (50ish watts), and then play with the transmitter matching and antenna matching knobs to see if I can get any more power out of it. I'll sacrifice a bit of SWR to gain some output power. As long as the SWR stays below 2:1, I'm happy.

At this point, I flip the transmit switch back off, go back to USB (or LSB) mode, and turn the power up to full.

This has been working for me so far.

 

[W5LZ]

When you change the power output of that transmitter you will also have to recalibrate that SWR meter. If you don't do that re-calibrating then your SWR readings will not be accurate.
This doesn't concern the question you asked but it's a pretty good idea anyway.
Your 10 meter antenna with the legs drooping 45 degrees isn't a very good idea, that 'droop' will definitely affect the antenna's input impedance (on any band), it won't be what you tend to expect or told it should be.
I think you will also find that if you use an antenna made for the lowest band of interest it will be easier to make work on higher frequencies, than if made for a higher frequency and used on a lower frequency. It's more a matter of what you can put up to start with, sometimes room just isn't available.
- 'Doc

 

[Browningman]

OK, here's the situation...

I have a 10 meter dipole in the back yard, about 22 feet up at the center, with the "wings" out at about 45 degree downward angle... I am told that with this tuner, it should be no problem to match 15 and 20 meters... So, I'm trying 15 meters...

Your dipole antenna is too close to the ground and too short for 20 meters...

So I went step by step by the manual...

A jumper coax goes from my transmitter (IC-745) to a simple power/swr meter (I'll get into why later), then out of that to the transmitter input on the MFJ-941D, and then out the Coax 1 port to my dipole.

From there, the manual explains what the INDUCTANCE knob does, and explains that "A" is minimum, and "L" is maximum. Then the Transmitter matching knob and the antenna matching knob. OK, I'm good so far. It then says that the transmitter must be tuned for a 50 ohm load for the band in operation, and to do this "by connecting the 50 ohm load to the BYPASS COAX connector and turning the antenna switch to the BYPASS position..."

Does this mean I have to buy a dummy load? Is that the only way to do it? That seems wrong to me. Am I read it wrong? And if I'm reading it right, how would I go about knowing whether the impedance is right or not? *confused*

All hams should own a true 50 ohm dummy load and they should calibrate their SWR meter into the dummy load, not zero it to the antenna - since the antenna is not 50 ohms if it needs to be tuned.

So the next step in the manual says to set the transmitter matching knob and the antenna matching knob to TDC (3.5 in this case). It then says to rotate the inductor selector knob until maximum noise is obtained. It doesn't matter what I set that to, the noise doesn't seem to change at all. *more confused*... OK, so I left it at "A" for now...

Then it says to alternatively rotate the transmitter and antenna knobs to get the best SWR. And here's where the extra meter comes in. I use the SWR meters (one in the tuner, and the other one) to watch it go down. Then when I'm done, I re-calibrate the SWR meters for the forward to infinity, and recalculate the SWR based on the new forward setting. This works fine on the "extra" SWR meter, but the tuner's SWR meter won't let me set the swr sensitivity high enough in FWD mode to get it to the infinity mark, and are therefore unable to calculate proper SWR using that meter...
You do not use multiple SWR meters to tune a antenna tuner..
The internal antenna tuner / SWR meter is only going to show you the tune in the jumper between the radio and the antenna tuner.. You can't tune something once it has already been tuned..

But, using my "other" meter, and the original reading on the tuner's SWR meter before I tried to recalculate the fwd infinity setting, I get it down to about a 1.8:1.

Now the next hiccup. The way the SWR meter in the radio itself is set, you set a knob to the set position, and use the RF POWER knob to set "infinity". Infinity works out to be about the 30 watt power setting, and when I use that to calculate SWR, the radio says the SWR is about 2.5:1... I then re-check using my extra meter, and it says 2.0:1... Any idea why these aren't the same?

I'm reluctant to transmit on full power because though everything I can see says that it's within the safe SWR range, I can't be sure I'm not messing something up and I don't want to blow up my radio...

So, please, someone with more experience than I have, read this over and let me know if there's anything glaringly obvious that I'm missing, and explain the missing piece from the "50 ohm tuning" thing? I'm sure the 6 page manual is written for people who have used tuners in the past, and I haven't, so there's something I'm missing there.

Thanks

N1RKR/AG

Find yourself a REAL HAM that can Elmer you.
Get rid of the MFJ junk and the CB radio junk - you are a ham now, you need to buy at the very least a off-center fed 80 meter dipole.
A 10 meter dipole antenna just isn't going to cut it if you want to work the HF Bands,,,

Just because you can tune something so the transmitter doesn't burn up doesn't mean that it is working or working properly.
If you choose to use dipole antenna's - put up a Fan Dipole antenna or multiple frequency dipoles for each band you wish to operate.

You need to get your antenna's as high up in the air as possible..
This means an investment in some type of pipe or tower or fiberglass tubes to get more elevation - or moving to a different neighborhood that has tall trees.

My question would be why you chose to try to use a 10 meter dipole on 20 meters when you could make a 20 meters dipole and not have these problems.

And to finish my rant - forget about the G5RV - it is not going to work for you unless you get all of it at least 40' off the ground..

 

[Browningman]

When you change the power output of that transmitter you will also have to recalibrate that SWR meter. If you don't do that re-calibrating then your SWR readings will not be accurate.
This doesn't concern the question you asked but it's a pretty good idea anyway.
Your 10 meter antenna with the legs drooping 45 degrees isn't a very good idea, that 'droop' will definitely affect the antenna's input impedance (on any band), it won't be what you tend to expect or told it should be.
I think you will also find that if you use an antenna made for the lowest band of interest it will be easier to make work on higher frequencies, than if made for a higher frequency and used on a lower frequency. It's more a matter of what you can put up to start with, sometimes room just isn't available.
- 'Doc

The only thing we are concerned with is the Voltage - hence VSWR - not SWR.
When checking the VSWR we should always start with the lowest amount of power available - since VSWR will change with more voltage. So no - you are incorrect when you say that this person should recalibrate their meter when they increase power..

Your advice of using the longest possible antenna - for the lowest band the OP wishes to operate on is sound advice.

A 10 meter dipole needs to be at least 30' off the ground in order to get it to work properly. 40' would be even better.

For working 10, 12, 15, 17 meters - your needs would be better served using a Solorcon, Antron 99 antenna..
When I raised mine to 40' and added 120 ground radials, 40 for 20, 40 for 15 and 40 for 10 meters, I was able to get my Solorcon 99 to tune up the whole way to 20 meters.

 

[N1RKR]

I suppose I should explain myself a bit further...

Find yourself a REAL HAM that can Elmer you.
Get rid of the MFJ junk and the CB radio junk - you are a ham now, you need to buy at the very least a off-center fed 80 meter dipole.
A 10 meter dipole antenna just isn't going to cut it if you want to work the HF Bands,,,

None of the equipment I use is/was CB equipment. I haven't touched a CB in 20+ years. And I know I'm a ham now. I've been a ham for that 20 years that I haven't been on the CB, thanks... That being said, I recently became interested in HF work. A couple months ago I finally broke down and bought an HR-2510 to use here at the house (which, despite what the CB idiots think, is a 10 meter radio that most people convert to 11 meters, and is NOT a CB). At the time, I was only a Technician, so a bit of 10 meters was pretty much my only HF option. To go with that 2510, and to get on the air quickly, I bought a premade 10m dipole (yes, I know, I know, I should have built one, but this was easy and cheap - intended to get me on the air quickly with a minimum of fuss).

And, some people prefer an inverted V instead of straight out. Makes it a bit directional, even if the SWR does take a small hit. Believe it or not, this dipole does pretty good even being lower than I would like it. Either way, I knew this would be a temporary antenna while I figured out what I wanted to do...

During this time I had been studying the General Class ARRL book off and on, with the intention of eventually upgrading... Though at this point I hadn't really put any emphasis on it...

Then I stumbled upon an IC-745 bundle on Craigslist for a decent price. It had been there for awhile, so I made the guy an offer, and he accepted it. I figured, if nothing else, it'd give me a bit more power on 10 meters...

Well, long story short, yesterday (5/24) I sat for and passed my general class exam. The guy I bought the 745 from let me borrow his MFJ-941d tuner, and that led me to here. I know I'm going to get a bunch of loss because of where I started (short antenna trying to tune for lower frequencies)... This is by no means a permanent setup. I'm pretty sure that ultimately I'm going to be putting up an OCF 80 Meter dipole. That'll give me 80, 40, 20 and 10 without a tuner, and then I can tune 12, 15, 17 and 160. I have no interest in 30 and 60...

You need to get your antenna's as high up in the air as possible..

And the new dipole that I put up will be more than 20ish feet above the ground. Again, the current antenna was never meant to be permanent, so it didn't make sense to waste a bunch of energy on putting a temporary dipole way up in the trees. The new 80m dipole will definitely be up in the trees. Most of the trees that line the edge of my property are probably 40-45ish feet high.

You do not use multiple SWR meters to tune a antenna tuner..

The reason I have both the tuner and the SWR meter is so that the tuner can show the SWR as I tune, and the other meter shows power output. I'm not using them as two separate SWR meters.... *shrug*

 

[W5LZ]

Browningman,
"The only thing we are concerned with is the Voltage - hence VSWR - not SWR.
When checking the VSWR we should always start with the lowest amount of power available - since VSWR will change with more voltage. So no - you are incorrect when you say that this person should recalibrate their meter when they increase power.."

At least you got part of the above right, one method of calculating SWR is by using voltage. The other method is by using current. Oddly enough, you can't measure 'SWR' directly because it's a 'man-made' measurement, a contrived thingy.
Sorry, I'm not mistaken when I said to re-calibrate an SR meter if you change the level or output power. I think every non-self-calculating SWR meter will tell you to exactly that in their instructions. That's how the meter works, you know, by comparing forward and reverse power or voltage. That's an indirect way of comparing impedances, since you can't measure them directly by using anything as simple as an SWR meter.
I have to say you are right about using lower power levels to measure SWR. An impedance mismatch can cause there to be some very high voltages present, so keeping the applied power/voltage low to start with is a pretty good idea. But then, power level has nothing to do with changing SWR, but it has a lot to do with the capabilities/ratings of the meter doing the measuring. If the meter can handle it, multiplying the power by a factor of 10 won't change the SWR. But it sure makes a difference in the accuracy of the meter reading that SWR, and why the manufacturer's recommend re-calibrating for changes in power levels.
So, while I certainly do make mistakes, this isn't one of them...
- 'Doc

 

[Road Squawker]

...VSWR will change with more voltage. So no - you are incorrect when you say that this person should recalibrate their meter when they increase power..

When I... added 120 ground radials, 40 for 20, 40 for 15 and 40 for 10 meters, I was able to get my Solorcon 99 to tune up the whole way to 20 meters.

remind me to never take your advice.

 

[N1RKR]

So, while I certainly do make mistakes, this isn't one of them...
- 'Doc

While I didn't include that in my message, Before I flip my transmit switch back off, I do turn up the power (since in theory the SWR is good) and re-calibrate the SWR meter for the higher power level.

I do not know if this is needed, but since the meter does measure the ongoing SWR, and since I've noticed that when going back to the calibration mode that it's different than it was on lower power, then it can't hurt to reset it for the higher power level...

 

[w9cll]

For working 10, 12, 15, 17 meters - your needs would be better served using a Solorcon, Antron 99 antenna..
When I raised mine to 40' and added 120 ground radials, 40 for 20, 40 for 15 and 40 for 10 meters, I was able to get my Solorcon 99 to tune up the whole way to 20 meters.

You're a Ham now, get rid of the CB junk.....

 

[Beetle]

Try increasing the power WITHOUT increasing the voltage or changing the resistance/impedance in any real (i.e. not on paper) situation.