Wrong SWR on 6m only? UPDATE SWR on all bands is out to lunch

[WM4CH]

I am getting a 1.3 SWR on 6 meters when the antenna shows 2.4 SWR. All the other bands work well.

But on 6 meters, I get no more than 1.3 SWR when it is confirmed by another radio and an antenna analyzer to be 2.4 and actually higher at higher power setting using another radio.

The SWR warning does not come up and the reverse power is very low, sub 1 watt even at 30 watts output.

Are there any 6 meter specific settings that may influence this?

6 meter reception seems to be fine.

I am wondering if this is a Thetis issue or a hardware issue.

S-ATT is 0 in receive and goes to -31 on transmit per the option.

I have read through both the Thetis manual and the 7000 manual and didn't see anything that would be in influence.

Just checking before I send it back to Doug. Seems like on 6 meters only, the reverse power measured is very low.

I bypassed everything and hooked up the antenna directly the the radio.

Thanks.

[WM4CH]

on noise level and on a received signal the difference between the 6m RX LNA on and off is 6 db.

Does that sound about right or is there maybe a problem with the 6m LNA?

[Phrotus]

May I suggest that you use a dummy load for issues such as this in order to take more variables out of the 'equation'.

Tom
W4TMW

[W2FBI]

May I suggest that you use a dummy load for issues such as this in order to take more variables out of the 'equation'.

Tom
W4TMW

Please excuse my ignorance. How might a dummy load help him isolate the difference between three SWR readings, where one is presumed erroneously low?

OP: No idea but in for the answer. I see you used 30 watts output - maybe a silly question but was that drive percentage or was it 30W measured on a meter somewhere? Just because I've myself, and seen others too, transmit in SSB and not have enough noise to actual modulate any power out and that would certainly result in an erroneously low SWR reading - because it would not actually be putting out enough power to get reflections despite the drive level due to the lack of audio to modulate.

[WM4CH]

May I suggest that you use a dummy load for issues such as this in order to take more variables out of the 'equation'.

Tom
W4TMW

Please excuse my ignorance. How might a dummy load help him isolate the difference between three SWR readings, where one is presumed erroneously low?

OP: No idea but in for the answer. I see you used 30 watts output - maybe a silly question but was that drive percentage or was it 30W measured on a meter somewhere? Just because I've myself, and seen others too, transmit in SSB and not have enough noise to actual modulate any power out and that would certainly result in an erroneously low SWR reading - because it would not actually be putting out enough power to get reflections despite the drive level due to the lack of audio to modulate.

using tune function of the radio.

too different MFJ power meters. They both show high SWR.

The radio doesn't

I think somehow the reverse power is not being sensed correctly or there is a setting or bug.

I don't understand how it can be bad only for 6 meters in hardware, unless something is unique to the hardware for 6 meters which is why I thought it might be a Thetis issue or settings issue

[WM4CH]

May I suggest that you use a dummy load for issues such as this in order to take more variables out of the 'equation'.

Tom
W4TMW

Well the dummy load has a very low SWR by nature.

So I am not following on how that will help.

[WA4SIX]

Some radios may be more sensitive to common mode currents.
Using a dummy load will negate those effects.
I would consider it the first step in diagnosis.

Ed

[Phrotus]

I'd like to add to Ed's comment......and also answer your question,

It is always good practice to use a dummy load for technical and practical reasons.

1) If you add a 50 ohm dummy load, take a reading and the problem remains? What does that mean?......or if the problem is eliminated? Don't forget, you are checking the ant. and transmission line and it's connectors in this situation.

2) When testing without a dummy load----> testing on the air..... is probably not going to make much QRM on a closed band in this case 6M. But in the case of an active band (HF band) it adds to the QRM ( tuner-uppers) we often hear on top of QSOs, which is bad practice, so using a dummy load
for diagnostics is always being a good neighbor.

You may want to add the dummy load so it can be switched in and out of line quickly.

3) In my opinion, it is a basic piece of ham radio gear.

73,
Tom

[WM4CH]

I'd like to add to Ed's comment......and also answer your question,

It is always good practice to use a dummy load for technical and practical reasons.

1) If you add a 50 ohm dummy load, take a reading and the problem remains? What does that mean?......or if the problem is eliminated? Don't forget, you are checking the ant. and transmission line and it's connectors in this situation.

2) When testing without a dummy load----> testing on the air..... is probably not going to make much QRM on a closed band in this case 6M. But in the case of an active band (HF band) it adds to the QRM ( tuner-uppers) we often hear on top of QSOs, which is bad practice, so using a dummy load
for diagnostics is always being a good neighbor.

You may want to add the dummy load so it can be switched in and out of line quickly.

3) In my opinion, it is a basic piece of ham radio gear.

73,
Tom

I have a dummy load that I switch in and out with a switch, so it is easy.

I have tried the dummy load and SWR is 1.1. The spec on the dummy load is less than 1.5 for 6m.
With the analyzer I get 1.4
on the IC-7300 I get 1.0

so what does that tell me?

The problem appears to be the radio not showing a high SWR and the protection not kicking in above 2.0 SWR because it never shows above 1.3 on a non-resonant antenna.

So what would be the next diagnostic step?

[W2FBI]

Exactly how does the SWR get measured?

[WM4CH]

Update:

The SWR is broken on all bands.

I never noticed because I use an autotuner and the autotuner does it's thing fast.

The autotuner is not a 6 meter tuner so I was trying to use the 160 meter doublet to tune to 6 meters and noticed before I even manually tuned (it is a modified Johnson Kilowatt Matchbox that I keep it tuned to 160 meters ) the SWR on the ANAN only showed 1.3 SWR while the stand alone power meter was very high.

That is how I noticed the problem.

Today I checked all the non-resonant bands and the SWR and Reverse power readings on the ANAN are way too low on all the non-resonant bands. As an example it shows only 1.9 SWR when the real SWR on 160m on the 80/40/20/10 fan dipole is over 8.

The reverse power measurement is reading inaccurately low producing a very wrong SWR.
The forward power reading appears correct.

So now I am thinking this is probably another hardware blown component.

Can anybody point me to the component on the schematics that measures reverse power?

[W2FBI]

REV_PWR on the PA/Filter board schematics seems to be relevant. First page of that doc, bottom right corner.
Looks like there's an op-amp LM358 for FWD_PWR U1009B and one for REV_PWR U1009A (edit: two sides of a dual op-amp I guess) which are ultimately fed to the SDR board via the 2x5 alex header.


You might be able to make more sense of it than I can. Looking up and downstream of that might shed more light on things that can be broken.

[W2FBI]

Since you're getting different values of SWR that get worse with worse SWR but not on the right scale, does that seem to implicate the op-amp itself as the issue?

[WM4CH]

Thanks for finding that

The likely problem is an the opamp or something else inline with the opamp that brings the signal to the input or biases the opamp.

This is now a hardware problem and I started a thread in the repair section.

https://community.apache-labs.com/viewtopic.php?f=43&t=4691

[WA4SIX]

Let me ask your setup.
Are you using an SWR/power meter between the tuner & antenna? If so, that is the wrong place to read SWR.
Try each band directly to the dummy load & see what the radio reads on all bands.

Ed

[W2FBI]

I don't know if we can yet say it's the op-amp, but it does sound plausible.

What I can't think of is a way for it to be damaged by the previous owner unless maybe he killed it when he tried to replace parts himself. (Did we ever get confirmation that was the explanation for that crappy soldering?) Normal usage it seems like it would be fairly difficult to fry without frying a lot more things. OTOH maybe it just failed.

There's a long way from RF to Thetis and I think we can do a lot more testing to narrow it down but damned if I know where to start right now. I'll take another look at my radio, the schematic, and Thetis later and see if anything comes to mind.

[WM4CH]

Let me ask your setup.
Are you using an SWR/power meter between the tuner & antenna? If so, that is the wrong place to read SWR.
Try each band directly to the dummy load & see what the radio reads on all bands.

Ed

The meter is between the amp and the tuner

it would never show swr change due to an antenna match if it wasnt it would just show the unmatched antenna SWR

the radio directly to the dummy load reads as it should 1.0 to 1.1 on all bands

I still do not understand how that helps diagnose the problem

if the real SWR is 8 and the radio reads 1.9

and when it is 3 and it reads 1.5

when it is 1.1 it will probably read 1.0 or 1.1

which it does on a resonant antenna or the dummy load

the forward power reads correctly and the reverse power does not.

[WM4CH]

maybe it is not an op amp

doesnt there need to be an internal coupler to sample the forward and reverse power?

I will look to see if I can find one on the circuit diagrams

[w9mdb]

Have you looked at Ref Pwr on the Thetis meter? What does for Fwd and Ref Pwr show?

[WM4CH]

Have you looked at Ref Pwr on the Thetis meter? What does for Fwd and Ref Pwr show?

yes
forward power corresponds to forward power on the MFJ meter

reflected power is very low compared to the MFJ meter

I think the problem is the radio is not measuring reflected power properly or the phase angle to produce the reflected power reading and proper SWR

[w9mdb]

Can you please quantify those values...."very low" doesn't show that detail.

[WM4CH]

Can you please quantify those values...."very low" doesn't show that detail.

I will post some numbers.

I also re-installed an old Thetis, same results.

[w9ac]

I will post some numbers. I also re-installed an old Thetis, same results.

FWIW, I see the same bizarre 6m SWR behavior with my 7000DLE. Thetis' SWR is all over the map when transmitting into an open circuit, changing the ANAN's ANT ports to open versus closed, but always reports 1:1 into a 50-ohm dummy load. In fact, the red square high SWR warning box never lights in Thetis no matter how bad the actual SWR on 6m. No issues with the same test on other bands.

Without digging into the hardware, it's difficult to localize the problem as hardware or something software-related (e.g., SWR interpolation or incorrect calibration on 6m). Frankly, I'm not too concerned although the concern is valid if relying on Thetis' high SWR protection limit.

It would be helpful to get test reports from other ANAN users with a description of the ANAN transceiver model being tested. A test using PowerSDR mRx may also be useful.

Paul, W9AC

[WM4CH]

Here are the numbers

All power was set on the dummy load to 10 watts via the MFJ-891 Meter.
The antenna is a fan dipole with wires for 80/40/20/10 meters. I also tune it to all bands 80-10 using the MFJ -998 Autotuner

I first checked the antenna at the freqs with theMFJ-259C Analyzer to check SWR
FP = forward power
RP=reflected power

The furthest right column is the ANAN reverse power reading in a percentage of what the expected reverse power reading is given the Analyzers SWR and the ANAN forward power readout.

It looks to me, except for 6 meters where the forward power is probably not very accurate, that the ANAN reflected power reading is consistently down close to 10% of expected reflected power which is approximately -10 db given that my ANAN power meter is not calibrated to a known good source and it is not a scientific instrument so there will be variable inaccuracies in the meter outputs.

Another comparison is that except for 6 meters, the ANAN reflected power is consistently in the ballpark of being only 10% of the MFJ measured reflected power.

SWR Chrt.png (93.84 KiB) Viewed 2781 times

[W2FBI]

So the reflected power is down ~10dB on every band. Huh.

[WM4CH]

Looking at the schematic, the radio employs a directional bridge to isolate Forward power voltage and Reverse power voltage using 2 op amps on the same LMR348 chip and then that voltage travels by cable to the processor.

So it could be anything from a poorly seated cable to a diode, to a cap, or transformer or the chip with 1 of the 2 op amps not op amping correctly.

I am going to open it up when I get a chance and re-seat the cable connections to start. I did recently move the radio in the shack so maybe a poorly seated connection got more poorly seated.