ART-13 antenna loading

[W9BHI]

Got the ART-13 on the air last night.
Got good reports on signals and audio.
Can't get the SWR down below 1:5 to 1.
Dipped plate and tried external caps and adjusting the ant. tuner, won't go lower.
The tuner was set up on the Valiant so I know it was matched to 50 ohms and was at 1:02 to 1.
Any thoughts on what the ART-13 output needs to tune better?
I know that 1:5 to 1 is not that bad but I would like to get it better.
Thanks,
Don W9BHI
 

[wa3dsp]

1.5:1 isn't bad but if you were able to get it flat with another RF source it might indicate higher harmonic or spurious content in the the source with the higher SWR. Did you swing the tuner through its range or just try to touch it up from where it was with the other rig?

[WA2TTP Steve]

Hi Don,

Adding to what WA3DSP said in his post  about harmonic content. The following is copy of what I had posted back in 2009 about my Art-13 loading and harmonic issues.

Loading cap values.

On my ART 13 feeding a dummy load or my matched antenna I need about 1000 pf on 75 and about 300 on 40m.
I also looked at the output of the rig on my HP 8590L Spectrum Analyzer and noticed the second harmonic surpression was poor with light loading even if your getting near rated power output. A small increase in loading cap, say 10-15%, would result in a second harmonic decrease of another 20 or so DB over the 35 it started at. It also helped to surpress the sub harmonics of the VFO that appear in output.

I get about 135 watts output at 1150 volts B+.

Good Luck,
Steve
WA2TTP

[w1vtp]

Got the ART-13 on the air last night.
Got good reports on signals and audio.
Can't get the SWR down below 1:5 to 1.
Dipped plate and tried external caps and adjusting the ant. tuner, won't go lower.
The tuner was set up on the Valiant so I know it was matched to 50 ohms and was at 1:02 to 1.
Any thoughts on what the ART-13 output needs to tune better?
I know that 1:5 to 1 is not that bad but I would like to get it better.
Thanks,
Don W9BHI
 

The ART-13 presents a different source impedance than the Ranger.  It will be a back and forth exercise with the tuner with the ART-13.  I’ve yet to experience this effect myself but I expect to use some of the experienced advice from those here on the forum and others who have already put an ART-13 on the air.  My approach will be to tune the ART-13 up on a known good load. I expect to need to follow Steve’s advise in a previous post regarding adding what I think is a shunt capacitor across the output (Steve, please correct me if I missed the application of the additional cap).

After properly tuning up the ART-13 into the load, then I will hook up the antenna and match the xmtr to the antenna.  I do not think you can take the tuner from your ranger as is and expect the same performance due to the different source impedance between the Ranger and the ART-13.

This is an interesting thread to me because I have plans of putting an ART-13 on the air.

GL, Al

[W9BHI]

I have not adjusted the tuner through its range, just tried to touch it up and 1:48 to 1 is the lowest it will go.

Steve,
where do you have controls "D","C" and E set on 75 meters?
Some say set "C" to 5, some say 6.
I have some fixed transmitting mica capacitors (350, 400, 500Pf)
and a nice 50 to 500 Pf variable that I could use.

BTW, I used the 20 ohm shunt resistor in the power supply and the current meter is pretty close to what my digital meter reads.

Don W9BHI

[KA0HCP]

May I suggest a different approach?

-Forget what the 50ohm VSWR is on your tuner  meter.  The ART-13 can be happy working into a wide range of antenna impedances.  -

-Set the radio controls per the manual

-Key down, and adjust your tuner for maximum forward power.  Ignore the reflected and ignore the VSWR reading, since it is referenced to a 50ohm standard.

-Evaluate radio and tuner/power meter readings.

If you run out of adjustment on the tuner caps/inductor then readjust the radio controls, and attempt another tuner adjustment.

Approach 2:

-Get rid of tuner and work radio directly into antenna (coax)

Approach 3:

-Provide a higher feedline impedance to the radio by using balanced line, eg. 300, 450ohm, then balun to coax.


[EDIT]
Ok, I'll eat some of my words now that I've found my copy of the ATC manual.  Will still do more reading.

I do feel that hyper focusing on getting 1:1 VSWR, regardless of the radio and antenna is an exercise in perfectionism.

[WA2TTP Steve]

Don,
I can't help you with dial setting until early April, I'm at my Florida condo until then.

Al,
Your correct about the shunt loading.

Steve

[w1vtp]

<snip>

-Key down, and adjust your tuner for maximum forward power.  Ignore the reflected and ignore the VSWR reading, since it is referenced to a 50ohm standard.

<snip>

Not sure I agree with this.  The second you try to use the typical power meter into other than a non-reactive, 50 ohm load, the power meter (which is really a volt meter) will indicate all over the place.  If you get to this point just tune for best DC plate current (or should I say best loading for a plate modulated amplifier) and don't make any claims of RF power output.  Again, the experience of others who has done this before counts a lot

Al

[flintstone mop]

It wudda never hit me in the head about 2nd harmonic content that would present an SWR issue.
Anyway a spectrum Analyzer will show how much 2nd harmonic is there. Your 1.5:1 is not that bad at all. Do you have a MFJ antenna analyzer? If it reads the same at that exact freq, then the transmitter is not the cause, and nothing to worry about
Fred

[W9BHI]

The antenna is at 1:02 to 1 with the Johnson or the FT-950 using an Array Solutions Powermaster meter so it's not the antenna.

I put a scope on it last night to check modulation % and when I cranked up the horz sweep rate I noticed that the output waveform was very distorted.
Maybe it has some some harmonics.

Will try to check in on the Collins collectors net tonight.

Don W9BHI

[W9BHI]

Could it be parasitics?
The 813 has no suppressor.

Don W9BHI

[W9BHI]

Put 500 Pf on the cond post to gnd and it really cleaned up the output and put the SWR at 1:05 to 1.
It dropped the output 6 watts, no big deal.
Thanks to everyone who responded.
Don W9BHI