YouKits FG-01 Analyser Calibration?

[VK2GOM]

I'm just wondering if anyone has attempted to calibrate a YouKits FG-01 antenna analyser?

Doing some tests on 40m, my HF SWR/Power meter is inline with my ATU which itself has cross needle Power/SWR metering, and both agree with each other when putting RF to the antenna to find lowest SWR. Then, unplugging the radio and connecting the analyser, it reckons my lowest SWR match is then about abother 90kHz down the band.

If I then re-adjust the ATU so the analyser sees a good match, and then plug the radio back in and fire up some RF, the SWR is now up around 2.5:1.

Incidentally, the rudimentary SWR monitoring meter in the radio (FT817) also agrees with my power meter / ATU cross meter combo.

There's obviously some disparity between the three measurement methods (2x meters, and the radio) which all concur, and the analyser.

I can only assume the analyser is not calibrated correctly.

Are there any simple methods to calibrate it?

73 - Rob VK2GOM / GW0MOH

[VK2OMD]

Ah, the problem of the man with two watches who is now uncertain of the time!

I made some suggestions but I was thinking you had the SARC 110.

There is some discussion in the manual about calibration using some pots.

It seems to treat Z as a scalar quantity, that should have a lot of appeal to hams.

Owen

[VK3BQ]

What does a known 50ohm load show. Would that help? Mine thinks it's 48ohms. A r+a 5w dummy load. But I have a Bnc to n adaptor in line also.

[VK2JDH]

I can only assume the analyser is not calibrated correctly.

Are there any simple methods to calibrate it?

73 - Rob VK2GOM / GW0MOH

Are you getting some RF or interfence back down the antenna upsetting the measurement?

[VK2GOM]

I might try another test with my magnetic loop, since tuning on that is very sharp, and compare the analyser and my SWR/Power meter.

If things don't agree, I can see an eBay sale coming on!

73 - Rob VK2GOM / GW0MOH

[VK6ZFG]

The antenna analysers readings need to be interpreted with some reservations.

The output signal generated by the commonly available antenna analysers are usually not very clean (varies with frequency used). This lack of clean singnal can influence the reading obtained.

The antenna analysers are an aid but not a precision measuring instrument. You need to take this into account. If you do not, you may finish up wasting a lot of time chasing non existant problems.

[VK2JDS]

perhaps the frequency counter function in the analyser isnt reading the correct frequency?

you can listen to the carrier coming from the analyser on your 817 and see if its on frequency Rob..

surely it couldnt be that simple though.. what about an assembly problem, like excessive lead lengths on component legs etc?
73

[VK2GOM]

I can hear the chirp of the analyser on the Rx and see it on my Spec An. The pulses are quite wide, but do appear to be in the ballpark frequency.

I also tried connecting the analyser directly to my Motorola microwave dummy load via an N to BNC adaptor - so no coax at all, it says SWR: 1.0, Z = 48R, so it appears to be 2R 'out'.

I wonder if I should tweak the 'Z' pot inside and bring it back to 50R? The pots are microscopic. I'd probably need to sand down one of my phenolic trimmers to fit them.

73 - Rob VK2GOM / GW0MOH

[VK2AVR]

I suspect you have common mode issues. Does the resonant frequency change at all when you touch the analyser vs placing it on a desk isolated from everything else (including your body)? I've seen an OCF dipole fed with a voltage balun swing about 500kHz when I touched the analyser's enclosure. When measuring a properly fed antenna with a cold feedline it was rock solid no matter what.

48R for a 50R load.. who cares. Not enough to make a difference. SWR is correctly reading as 1.0.

[VK5LTD]

Have others encountered similar inaccuracies with youkits device? Did the manufacturer provide any support
I'm looking into analysers at present and youkits is reasonably priced and generally well reviewed. The issues above is a concern.
Others Im looking at are the Rigexpert & another new offiering KVE-60

[VK2OMD]

Have others encountered similar inaccuracies with youkits device? Did the manufacturer provide any support
I'm looking into analysers at present and youkits is reasonably priced and generally well reviewed. The issues above is a concern.
Others Im looking at are the Rigexpert & another new offiering KVE-60

These things range from a device that really isn't any more than an oscillator with SWR meter (and that is really useful for a lot of things), with or without scanning and graphic display in a hand portable package to full blown two port VNAs with quite advanced measurement capacity and abiity to download the data to a PC and further analyse / plot it.

If you don't truly understand transmission lines, then the first level may suffice as the more advanced capability might just cause confusion (see http://owenduffy.net/blog/?p=1907 for an anecdote... this guy was doing well until he decided to put his analyser to use).

If you intend using the thing to learn more about transmission lines, move up the range.

Notwithstanding all that, I would recommend something that has accuracy over a range outside that which you intend to use. For example, if you only want it for HF, get a device that goes to at least 50MHz because solving problems on 28MHz benefits from seeing behaviour both sides of the target.

The ability to download and share the scan is useful, you may be able to share your measurements with someone remotely who can help you to understand them.

Don't even think of a device which does not properly measure the sign of reactance. Almost no one who thinks they have a reliable simple method of determining the sign of reactance in the general case truly understands the problem. If experts have problems determining the sign of reactance, beginners have no hope.

As far as cost goes, something that is affordable but doesn't do what you want is not good value.

Owen

[VK3APW]

Rob,
for what it is worth, I have seen '50' ohm dummy loads measure anything from 48 to 53 ohms. You just can't assume that your dummy load will be exactly 50 ohms. I have checked my Youkits against a HP4193 VIM, and it appears to be very close. I have also experienced, AM broadcast stations interference, with a MFJ analyzer's results, ( which is widely known ), and filters are available to assist with.
In short, I don't believe you can expect too much from these type of devices.

Regards

Peter vk3apw

[VK2OMD]

... I have also experienced, AM broadcast stations interference, with a MFJ analyzer's results, ( which is widely known ), and filters are available to assist with.

That susceptibility to interferece stems from the use of broadband detectors in the instruments.

Some modern instruments use techniques to select the analyser's signal over others and so are less subject to interference, see descriptions of some of the AIM and Rigol analysers for examples.

Something to keep in mind when buying as external filters are a bothched workaround for the problem.

Owen

[VK5LTD]

The appeal of these new generation is the visual representation of antenna resonance points across a range of frequencies, impedance and sharpness of the resonance. I could plot this manually by just taking readings at 25 Khz spacings I suppose but the technology is available to do this with these instruments.

Unlesss you are a keen antenna builder, I don't know how much use these devices are. If it's a setup, check resonance and leave in place situation, the device would only used very occasionally. Maybe an Grid dip meter might suffice for my purposes rather than spend $200-$300 on an analyser.

Youkits did respond to me and state there were 2 variable resistors that can be used for adjustment/calibration

[VK2OMD]

The appeal of these new generation is the visual representation of antenna resonance points across a range of frequencies, impedance and sharpness of the resonance. I could plot this manually by just taking readings at 25 Khz spacings I suppose but the technology is available to do this with these instruments.
...

A chap had a 40m quarter wave ground mounted monopole, and wanted to use it on the US CW section of 80m, and the question was what type of feed arrangement would give good efficiency and what bandwidth might it have.

The chap used a MFJ noise bridge to measure impedance at the monopole feed point across their 80m band. $300 for an analyser was not in his budget at the time.

The measured R,X data has a few bumps in it (the green VSWR line is calculated. It provided sufficient information to design an L matching network.

Can the FG-01 dispaly R and X (including sign of X)? If not, it could not be used for this project.

The ubiquitous MFJ-259B can display R and |X|, and you could reasonably assume that X will be negative for an eighth wave monopole.

Above is calculated impedance at the shack end of 30m of LMR400 with the L network at the base of the antenna. VSWR bandwidth is about 100kHz, line loss is below 0.5dB in that region. (It might look a mess, but if you focus on 3.5-3.6MHz, it is good and that was the objective.

With an MFJ-259B, you would be struggling to work out the sign of X in measurements at this point.

The design was implemented and measured, and it reconciled with the predictions.

These things can be done with simple instruments and knowledge, or with more sophisticated instruments and knowledge. It might seem tedious, but it worked and the humble noise bridge was better suited to the task than many analysers. You could not do this with a GDO.

Owen