loopantennas@groups.io

Re: Steve ugly-build LZ1AQ using MPS2222 sweeps uploaded to Photos

#20291

Dave,

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As far my acknowledgement of usung VNA for measurement small impedances or resistors of 0.1 ohms value allows to reach about 0.04 % accuracy.?

However, for low resistance values that you mentioned shall be used a different method by connecting between CH0 and CH1 ports of VNA ( so called I- method by measiring S21 or current through your resistor). This technique has 0.01 %.

I guess you can measure ohmic resistors not radiation resistance

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Raphael

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Re: Steve ugly-build LZ1AQ using MPS2222 sweeps uploaded to Photos

#20290

Chavdar,

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I am sorry I forgot to mention another point. I can understand why you have been using Norton equivalent circuit for a prove how great works active small loop antenna in short current mode. The low resistive input of amplifier cancels the reactive influence of loop antenna and regardless what series arms in simulator are used - we will get flat ( frequency independent ) frequency response.

On other hand using Thevenin circuit it does not? prove the above said because you do not have a control mechanism allowing the source voltage to follow the frequency in acordance to Faraday' law of induced current. So, the frequency response is not "frequency flat" ( indepenent from frequency ) more but skewed down with the frequency increase.

My understanding has been usage of dummy aerial circuit with a receiver in our technical business always? ignores that applied test signal shall follow Faraday's law.?

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Raphael?

Re: Steve ugly-build LZ1AQ using MPS2222 sweeps uploaded to Photos

#20289

Hi Chavdar,

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With all my respect to you spending a lot of time exploring loop antennae with amplifiers I am in disagreement with your "simulator" design.

For all practical means we have been using as a source voltage generators, thus for testing active antennae their equivalent circuit? should be Thevenin's circuit.

Yes, we can transform from Thevenin to Norton circuit but it is pure theoretical move.

We agreed that value of current source in Norton's is related to voltage source in Thevenin's as I sc = V oc / Z ant because of equal power condition requirement for this transform.

Using as series arms in your simulator relatively high in value resistors 1 Kohm, it cannot be? anticipated that really was created Norton's circuit because the current source does not reach the required current level? when 1 Kohm >> Z ant in frequency range of interest from f lc ( low-cut off ) to up to f0 ( resonance point ).

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Regards,

Raphael

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Re: MLA-30+, the story continues! #Small_receiving_loops_RX-only

#20288

Hi Martin & Fred,

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Thanks for the article links. I will dig into them later.

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At this moment, I don't have notch filters for the 5-30 MHz range that I want to measure. To quickly verify whether the IP is internal to the TinySA, I will try to increase its attenuation to see if the displayed IMD reduces.?

What I find hard to understand is why the measured OIP3 is 30 dBm at 20 MHz (see graph), but progressively drops as the frequency pair is lowered, and finally reaching 16 dBm at 5 MHz. My expectation is internally generated IMD should be quite constant over frequency. On the other hand, if the external & internal IMD are combining constructively and destructively at different frequencies, as Martin has speculated, I would expect the OIP3 trace to be wavy. Or did I miss something?

Anyway, more investigation is required to understand the setup's eccentricities.

At the project onset, I thought it would take 1 month max to build a working active loop, but now it has already taken a year of my life ?. What a deep rabbit hole!

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73, Chin-Leong Lim, 9W2LC

Re: Steve ugly-build LZ1AQ using MPS2222 sweeps uploaded to Photos

#20287

To Raphel

Sorry , 10- 20 times larger from? the loop impedance.

The Northon is ok - the current source is the short circuit current.? Zloop >>Rin so we ignore current through the loop.

Chavdar lz1aq

Re: MLA-30+, the story continues! #Small_receiving_loops_RX-only

#20286

On Sun, Oct 6, 2024 at 07:32 PM, <biastee@...> wrote:

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What's your test setup, and how do validate it ?

FY6900 function gen, Minicircuits ZSC-2-4 hybrid combiner, & TinySA. I admit I haven't validated the setup.

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Hi Chin-Leon Lim
Measurements of high IP3 values are challenging. It is very likely that the measured IM products will be created in Tiny SA itself, not in the DUT. Your limitation is the internal IP of the Tiny SA

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regards, Fred

Re: MLA-30+, the story continues! #Small_receiving_loops_RX-only

#20285

Hi Leong,

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OK thanks for that.

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From experience, I don't think you will be able to achieve the required performance of your test setup without building fundamental frequency notch filters to place on you analyser input.

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Ideally you need to be able to measure signal levels below -100dBm, in the presence of test signals at 0dBm or more. Even with a high end SA, this is asking a lot.

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Steve and Everett wrote this useful practical guide for Siglent.

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https://www.siglenteu.com/application-note/inter-modulation-distortion-imd-testing/

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I think the variation you are seeing is due to the external and internal IP generation aiding and abetting each other as the phase and amplitude relationships vary with frequency.

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In the old days of analogue TV transmitters, we used to deliberately generate IP products at low level, and inject them into the RF transmission chain, to null out IP's that were being produced in the high power amplifier stages. We called this feed-forward correction.

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Regards,

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Martin

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Re: SOME MEASUREMENTS of a SML

#20284

In receive mode the resistance increase due do the skin effect could be neglected for simplifiaction. It is disproportionanally lower than the frequency dependent increase of the inuctive reactance.

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regards

Fred

Re: MLA-30+, the story continues! #Small_receiving_loops_RX-only

#20283

Hi Martin,

LZ1AQ's |OIP3-P1dB| vs. freq

73, Chin-Leong Lim, 9W2LC

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Re: MLA-30+, the story continues! #Small_receiving_loops_RX-only

#20282

On Sun, Oct 6, 2024 at 10:52 AM, Martin - Southwest UK wrote:

Good work, but the LZ1AQ IOP3 looks far too low.

Hi Martin,

Sharp eyes! ?

You r correct, the LZ1AQ OIP3 looks too small. I think the problem lies in the large variation with freq - the OIP3 varies from 16 dBm at 5 MHz to 30 dBm at 20 MHz. In contrast, the competition - MLA-30+, M0AYF & PA0FRI have flatter OIP3 variation.

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My normal sanity check is to check that the IOP3 is typically 10 to 15dB higher than the P1dB value.

The |OIP3 - P1dB| in the table looks deceptively small because it is the worst case value, taken at different frequencies, i.e. P1dB is taken at 20 MHz, while OIP3 is at 5 MHz. If the OIP3-P1dB is taken at the same frequency, say 20 MHz, the delta is a more believable 15 dB (see this graph). When I find the time, I will create another graph showing |OIP3-P1dB| vs. freq - hopefully, it will clarify things.

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What's your test setup, and how do validate it ?

FY6900 function gen, Minicircuits ZSC-2-4 hybrid combiner, & TinySA. I admit I haven't validated the setup.

Hi Everett, thanks for sharing your measurement results.

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73, Chin-Leong Lim, 9W2LC.

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Re: SOME MEASUREMENTS of a SML

#20281

I have.? I considered including skin effect, but chose to keep the measurements away from that.? Of course, that is also frequency dependent and even makes radiation resistance worse - if it could get any lower.....

This has got me go'n.? This time around I didn't want to delve into frequency dependent measurements as that takes more thought and care tham making DC measurements.

Possibly someone can dig up the DC resistance of standard 0.5-inch copper tubing and same for copper pipe of same dimensions.?

Dave - W?LEV

Show quoted text

On Sun, Oct 6, 2024 at 11:19?PM Dan Clementi via <dan=[email protected]> wrote:

Dave, I believe you've neglected skin effect.

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Dave - W?LEV

Re: SOME MEASUREMENTS of a SML

#20280

Dave, I believe you've neglected skin effect.

SOME MEASUREMENTS of a SML

#20279

Consider:

1)? The DC resistance of the loop is constant.? It's independent of frequency.? That's one of the distinguishing characteristics of pure resistance vs. reactance.

2)? The radiation resistance of the loop varies with frequency.? However, it is a very small fraction of an ohm, typically around 0.001 ohms (that's a mΩ or milliohm using proper abbreviations) or less.? This is what spoils tuned loops for efficiency.

The DC resistance of my 0.5-inch copper tubing loop of 36-inches diameter (circumference of 113.10-inches) can be calculated.? I measured 7.007 Amperes through the loop with a voltage drop across the loop of 46.3 mV (millivolts).? So the DC resistance is (Ohm's Law):

? ?? R = V / I = 0.0463 volts / 7.007 Amperes = 6.61 mΩ (6.61 milliohms) or 0.00661 ohms.? ?

Another measurement yielded 4.123 Amperes through the loop with a voltage drop across the loop of 29.5 mV (29.5 millivolts).? Once again:

? ?? R = V / I = 0.0295 volts / 4.123 Amperes = 7.17 mΩ (7.17 milliohms) or 0.00717 ohms.

And for statistical significance:? measured 1.60 Amperes through the loop with a voltage drop across the loop of 9.98 mV (9.98 milivolts) or 0.00998 volts.? Again:

???? R = V / I = 0.00998 volts / 1.60 Amperes = 6.24 mΩ (6.25 milliohms) or 0.00624 ohms.

The numerical average of these three readings is:

???? R AVG = [6.61 + 7.17 + 6.24] mV / 3 = 6.66 mΩ (6.67 milliohms) or 0.00667 ohms.

???? AVG R = [ 0.00661 + 0.00717] / 2 = 6.89 mΩ (6.89 milliohms) or 0.00689 ohms.

This compared to a radiation resistance of 0.001 (1 milliohm) or less ohms, I believe makes a reasonable first-order argument for constant current vs. frequency.

Now we need a good measurement of radiation resistance to validate this argument.? Using a VNA for such low resistances is challenging.? I'll think of something.? Any other ideas?

I could feed a known amount of RF energy and actually measure the current induced through the loop.? I have several home made current probes that I can easily calibrate.? Other ideas and/or techniques are welcome along with contributions of others in measuring various parameters of SMLs.? .?? .?? .?? Please?

Dave - W?LEV

Re: Steve ugly-build LZ1AQ using MPS2222 sweeps uploaded to Photos

#20278