Just wanted to give my 2c in regard to IMD/IP3 measurements as I did and continue doing lots of them at my work.
?
30-40dBm IP3/OIP3 measured levels are not that high. One just need a good "Big Box" Spectrum Analyzer (HP/Agilent/Keysight) with good LowPIM attenuator in front of it. No Bandstop/notch filters are really needed! Signal Combiner can produce some IMDs but usually they are pretty low for those levels of desired measured IP3. Bandpass filters for F1 and F2 are also not needed along with attenuators between those filters and Combiner. Actually if filters are used I'd recommend increasing the attenuators to 10dB each. Instead of Bandpass filters normally we would use an Isolator (circulators with termination on top). But.... that's mostly for VHF+ frequencies. Not sure if proper isolators do even exist for LF/MW/HF frequencies. So, filters may be the best F1/F2 solution before Combiner.
Now, my main work IP3 bench is capable of measuring IP3/OIP3 levels of up to 90-100dBm with ~2W of F1 and F2 each... That's pretty much measuring IP3 of passive components where everything matter including connector cleanliness and proper torque (sometimes overtorquing helps!). At those levels you cannot use lump components for filters and combiners and cavity stuff is the only thing that worked for me. For example I'm using celltower cavity diplexers/duplexers for F1 and F2 mixing and a big double cavity rejection filter in front of the Spectrum Analyzer (tuned to reject CW at F1 and F2 with rejection of close to 100dB). Big negative of such setups is inflexibility. You need to swap bench components to change the frequency or have multiply setups for each frequency of interest. And of course LF-HF and cavity filters probably cannot coexist due to the size :) But any of that is not needed when you measure amplifiers.
In regard to TinySA Ultra. It's a great thing but would be my #1 suspect for creating the intermods on it's own. So, with TinySA one indeed may need rejection filters in front of it... If anything I'd probably use an SDR with good front end for the task like that instead of TinySA.
?
Thanks,
Simon
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Re: Steve ugly-build LZ1AQ using MPS2222 sweeps uploaded to Photos
John and Andrew are both correct.
If modeled as a voltage source in series with inductance, you will find the output voltage into a resistive load is independent of frequency above a certain threshold, just as with the parallel current source model.
This is because the loop voltage source EMF increases linearly with frequency at 6 dB/octave (induced voltage is proportional to rate of change of the magnetic flux, so when you differentiate the sin(wt) the flux rate of change becomes -w*cos(wt)) and voltage divider formed by the loop's inductive reactance (which doubles per octave) in series with the amplifier input resistance?decreases the signal at the amplifier input at the same 6 dB/octave if the frequency is sufficiently high such that the amplifier input impedance is much less than the inductive reactance of the loop.? In other words, the 6 dB/octave rising voltage output is canceled by the -6 dB/octave voltage divider effect and the net voltage input into the loop amplifier is constant with frequency.
This series model predicts the same behavior as a parallel current source, so either may be used provided you take care to get the maths correct.
The simplistic -6 dB/octave LR voltage divider assumes, as mentioned earlier,? that the loop's inductive reactance is large compared with the input impedance of the amplifier.
Jack K8ZOA
?
All,
?
Here is a good article by another member how? a hardwired simulator shall be designed to take in account that induced e.m.f. for given field strength shall be proportional to frequency. That shall work for both layouts voltage source with series inductor or current source with shunt inductor.?
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Re: SOME MEASUREMENTS of a SML
On 10/14/2024 3:26 AM, Martin - Southwest UK via groups.io wrote: I find the
Interactive loop calculator to be quite handy for actual loop design, if you want to quickly try changing a few different parameters to see what sort of ball-park difference it would make as a trade-off between efficiency, power handling, and ease of construction. Yes, Miguel's loop calculator is very handy. Setting the input values with sliders isn't very precise, but you can usually get close enough to get useful results.
As a bonus, you can also model multi-turn loops too, which is handy for use on the LF bands.
Comment: When changing the value of N, the calculator keeps the loop diameter constant, so the loop length changes, as does everything calculated from that value.? If your goal is to reduce the size of a loop for LF and low-frequency-HF work, for example, you probably want to keep the loop length constant, so a change needs to be made to the loop diameter to compensate. In my STLcalc program, the latter approach is used. 73, Gus - KB0YH
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Re: SOME MEASUREMENTS of a SML
Hello again Mark.
On Sun, Oct 13, 2024 at 01:27 PM, Augie "Gus" Hansen wrote:
1) The item Jim called Loop Diameter is actually the
Loop Length.
?Hi Gus,
?
I mistakenly said "Diameter" when I meant perimeter (I did
enter the correct perimeter in the calculator).
Yes, I like the use of "perimeter" because it works for all shapes.
Circumference is for circles, although it is often used for octagon
and other nearly circular shapes.
In my STLcalc program I use "Loop Length", and emphasize that the
total length includes the tuning capacitor body length and any
jumpers used to connect the cap to the main loop.
I didn't know about the 66pacific.com calculator's
error in computing inductance.? Thanks for bringing awareness
to this.?
Several times over the past four years or so I have sent information
to the 66pacific webmaster / majordomo about this issue, but have
never gotten a reply, nor has anything been done to modify the web
app. I've also described the issue in a couple of QSO Today Expo
sessions on small transmitting loop antennas to warn users about it.
Any results (Q, BW, efficiency, cap voltage, tuning cap value and
voltage) calculated from a wrong reactance value are all wrong.
I reran the numbers using this calculator: ??
?The inductive reactance increased substantially but the
radiation and loss resistances stayed the same.
If the loop length and conductor diameter don't change, the Rrad and
Rloss values remain the same (assuming the same material). STLcalc
shows Reactance = 104.48 Ohms for an octagon, and 105.17 Ohms for a
circle. The program also accounts for loss in the cap and any
connections, and any soldered or welded joins in the loop conductor.
66pacific only calculates for the octagon shape and doesn't account
for any of those other losses.
Wishing you success with your loop project,
Gus, KB0YH
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Re: Null Depth versus Torsion
Hi Paul,
?
At first sight, it seemed like a simple calculation, but it's not.
?
The change in amplitude produced by the twist may be calculated, but the change in phase is more difficult to quantify. It could be modelled, but I suspect in "real life" other factors such as interaction with nearby objects, cable routes etc. would make it much less predictable.
?
My guess is that, if you introduced a 180 degree twist, you would end up with a near omni response and circular polarisation, but signal levels in the original main lobe would be reduced by 3dB, and a figure of 8 or 360 degree twist would tend to cancel all signals, but I may be wrong.
?
I'm sure that someone cleverer than me can provide a definitive answer, but it's an excellent question.
?
Regards,
?
Martin
?
On Mon, Oct 14, 2024 at 11:47 AM, Paul White wrote:
But we can twist a loop all the way to a figure-8. Anyone up for *that* challenge hehe?
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Re: Looking for a good cheap antenna analyser
On Sat, Oct 12, 2024 at 10:16 AM, Simon wrote:
Have a mfj 259b
I think someone mentioned? recommending the AA-55 Zoom by RigExpert.
?
Unlike some of the MFJ products that may use a broadband detector, I observed that the AA-55 Zoom uses a narrow band detector that allowed the AA-55 to ignore nearby AM radio station signals that otherwise affect instruments using broadband RF detection techniques in their circuitry.
?
With the AA-55 Zoom I was able to tune within 1 kHz of a radio station at 1700 kHz (just below the 160m ham band) and work without interference to measurements. When tuned TO the station frequency of 1700 kHz, I could observe obvious 'beat note' behavior as evidenced by 'bouncing values' on the AA-55 Zoom's display.
?
The signal power when my large loop was tuned to 1700 kHz was around -1 dBm (just under 1 milliWatt) as measured on an HP 8591E (which passed internal Self Cal tests using its front panel CAL OUT signal source) spectrum analyzer. When the large 160m loop is tuned to 1900 kHz in the 160m band, signal power (from the 1700 kHz station) was observed to be around -20 dBm.
?
I can recommend the AA-55 Zoom or similar architecture single-port S-11 style instruments without hesitation based on its ability to 'ignore'? nearby RF signal sources (at least on the 160m band and at the RF signal level I observed.)
?
Note: I was unable to use a Boonton Model 260A "Q Meter" to measure the (large) loop antenna's inductance on account of it using a broadband RF detector internally.
?
de AA5CT Jim
?
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On Sat, Oct 12, 2024 at 12:11 PM, Everett N4CY wrote:
There is no way to run a proper IMD without a band stop filter that rejects the 2 tones and a band pass filter for each of the tones.
A decade back, I made use of an old tube-type Stoddart NM-22A Field Strength EMI/RFI receiver for this purpose, as, a tuned RF front end serves the purpose of fundamental filtering or notching. Beware using broad-band SDR receivers for this application w/o taking similar precautions (of course) as one would for a broad band Spec An.
?
Anything as broad in response as a spectrum analyzer is going to require assurances (such as outboard LP/HP/BP filtering) to assure the Spec An is not overloaded, or its dynamic range is not exceeded.
?
I was running tests on an active antenna mounted on a car. The 'antenna' (wire) was about 30 inches and driving the gate of an JFET. I could vary the bias point and observe 3rd order distortion products as created by several local AM radio stations in the area? ... different circuit configurations were tried, including buffer stages following the JFET input amplifier/Source follower stage. Sorry, no detailed notes were taken of this quick proof-of-concept testing.
?
de AA5CT Jim
?
?
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Null Depth versus Torsion
When using flexible conductors, we need some arrangement to keep the loop flat.
Any significant torsion or twist presumably affects null depth.
So just wondering if anyone has done the calculations?
?
Small deviations from the plane are obviously the most interesting.
But we can twist a loop all the way to a figure-8. Anyone up for *that* challenge hehe?
?
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Re: SOME MEASUREMENTS of a SML
I find the
?
?
Interactive loop calculator to be quite handy for actual loop design, if you want to quickly try changing a few different parameters to see what sort of ball-park difference it would make as a trade-off between efficiency, power handling, and ease of construction.
?
As a bonus, you can also model multi-turn loops too, which is handy for use on the LF bands.
?
Regards,
?
Martin
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Re: SOME MEASUREMENTS of a SML
On Sun, Oct 13, 2024 at 01:27 PM, Augie "Gus" Hansen wrote:
1) The item Jim called Loop Diameter is actually the Loop Length.
?Hi Gus,
?
I mistakenly said "Diameter" when I meant perimeter (I did enter the correct perimeter in the calculator).
?
I didn't know about the 66pacific.com calculator's error in computing inductance.? Thanks for bringing awareness to this.? I reran the numbers using this calculator: ?? ?The inductive reactance increased substantially but the radiation and loss resistances stayed the same.
?
? ? ?Loop Diameter?Perimeter: 113 inches (9.417 ft)
? ? ?Conductor Diameter:? 0.5 inches
? ? ?Frequency: 7 MHz
?
Calculated values:
?? ?Loss Resistance: .050 Ohms.
? ? Radiation Resistance:? .004 Ohms
? ? Inductive Reactance:? 74.6 Ohms? 110 Ohms
?
Mark?
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Re: SOME MEASUREMENTS of a SML
My loop diameter is 36-inches.? That makes the circumference 113-inches.? That's what I measured.
Dave - W ?LEV
On Sun, Oct 13, 2024 at 7:02?PM Mark Whittington AG5RT via <mark-whittington= [email protected]> wrote:
On Mon, Oct 7, 2024 at 10:22 AM, Jim wrote:
Verification would be welcome.
I put the loop dimensions in an online calculator often used to design small transmit loops ()
?
? ? ?Loop Diameter: 113 inches (9.417 ft)
? ? ?Conductor Diameter:? 0.5 inches
? ? ?Frequency: 7 MHz
?
I got the same resistance:
?
? ? Loss Resistance: .050 Ohms.
? ? Radiation Resistance:? .004 Ohms
? ? Inductive Reactance:? 74.6 Ohms
?
My opinion echoes the point made by Fred.? For receive applications, the loss resistance is so much smaller than the inductance reactance (1/1400 in this case), it can be reasonably neglected.?
?
- Mark
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Re: Steve ugly-build LZ1AQ using MPS2222 sweeps uploaded to Photos
Hi Mark,
?
I reviewed your response:
?
1. The introduced two isolation resistors 1 Kohms each cannot be considered as a part of dummy aerial because any dummy aerial equivalent circuit should include only real antenna lumped element values ( that is the ABC of design concept of dummy aerials ).
2. There is a misconception between dummy aerials and simulation models.
3. In simulation model for a small loop antenna, especially for short current application mode, none has introduced an acceptable layout of it.
4. The simulation model should be built based on the published known equation of voltage divider consisting of two arms - lumped inductance of antenna and resistive input of amplifier and applied induced voltage, based on Faraday's law. The practical difficulty to construct such simulator is the induced voltage is linearly proportional to the frequency.
?However, the physical simulators have been? published here do not take into consideration the mentioned above condition. Simply those simulators do not have a control mechanism, allowing the applied voltage from generator source to follow the frequency change accordingly.
On other hand dummy aerials have been used only for measurement of frequency responses, allowing to apply from signal generator constant values with frequency changes of interest.?
In my opinion, for simulation of antenna systems would be better to use current induced method, like Martin proposed, with two coupled together in near-field loop antennae with one important condition for an improvement for this technique - the current in the transmit antenna shall be controlled with frequency be almost constant
in value.?
?
Regards,
Raphael
? ??
?
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Re: SOME MEASUREMENTS of a SML
Mark, there are two things to check in
the message shown below:
1) The item Jim called Loop Diameter is actually the Loop Length.
2) The 66pacific.com calculator, since it was released long ago,
has the calculation of inductance wrong. As the conductor diameter
is reduced, the inductance, and therefore the inductive reactance,
should go up, not down. The calculated value is nearly correct
only near a 0.95 inch diameter, and goes in the wrong direction
from there. Compare 66pacific to STLcalc, LoopCalc, and other "mag
loop" programs to see the problems introduced by having the
inductance value wrong.
On 10/7/2024 4:02 PM, Mark Whittington AG5RT wrote:
toggle quoted message
Show quoted text
On Mon, Oct 7, 2024 at 10:22 AM, Jim wrote:calculated
incorrectly
Verification would be welcome.
I put the loop dimensions in an online calculator often
used to design small transmit loops ()
?
? ? ?Loop Diameter: 113 inches (9.417 ft)
? ? ?Conductor Diameter:? 0.5 inches
? ? ?Frequency: 7 MHz
?
I got the same resistance:
?
? ? Loss Resistance: .050 Ohms.
? ? Radiation Resistance:? .004 Ohms
? ? Inductive Reactance:? 74.6 Ohms
?
...
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Re: Stainless-Steel Loop with Wellgood 4.1 Amplifier
Unfortunately, I have no plans for this.
I have built two of these antennas. One has been sold. I will also sell the second one after extensive testing.
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Re: Stainless-Steel Loop with Wellgood 4.1 Amplifier
I cannot measure this. Unfortunately I don't have such a measuring device. I am not a technician.
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Re: Stainless-Steel Loop with Wellgood 4.1 Amplifier
Very good reception.
1.5m over Ground.
?
/g/loopantennas/photo/298235/3840297?p=Name%2C%2C%2C20%2C2%2C0%2C0
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Re: Steve ugly-build LZ1AQ using MPS2222 sweeps uploaded to Photos
On Tue, Oct 8, 2024 at 07:08 AM, Raphael Wasserman wrote:
Do I miss anything ?
Hi Raphael,
?
Your analysis is correct.? You could get there a little more directly:
?
? ? ? (generator level)? = (Isc)*(R_dummy_areal)
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? =(0.707mA)*(2K Ohms)
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? = 1.414V
?
The dummy areal is a linear system.? At a reduced drive level the short circuit current output would be reduced by the same about.? The purpose of the simulation was to determine the flatness of the loop's short circuit current with respect to frequency.? The relatively strong field strength used (1V/m) was chosen arbitrarily.
?
Mark
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Re: Steve ugly-build LZ1AQ using MPS2222 sweeps uploaded to Photos
On Mon, Oct 7, 2024 at 02:16 PM, Mark Whittington AG5RT wrote:
I reran the simulation with the load point located at three different positions: bottom side, front side, and back side.? I obtained the following results:
Location of tabulated results: ? /g/loopantennas/files/One%20meter%20loop%20simulation%20EZNEC%20PRO/Short%20Circuit%20Currents%20of%20Octagonal%20Loop.pdf
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Re: SOME MEASUREMENTS of a SML
On Mon, Oct 7, 2024 at 10:22 AM, Jim wrote:
Verification would be welcome.
I put the loop dimensions in an online calculator often used to design small transmit loops ()
?
? ? ?Loop Diameter: 113 inches (9.417 ft)
? ? ?Conductor Diameter:? 0.5 inches
? ? ?Frequency: 7 MHz
?
I got the same resistance:
?
? ? Loss Resistance: .050 Ohms.
? ? Radiation Resistance:? .004 Ohms
? ? Inductive Reactance:? 74.6 Ohms
?
My opinion echoes the point made by Fred.? For receive applications, the loss resistance is so much smaller than the inductance reactance (1/1400 in this case), it can be reasonably neglected.?
?
- Mark
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Re: Steve ugly-build LZ1AQ using MPS2222 sweeps uploaded to Photos
On Sun, Oct 6, 2024 at 04:55 AM, §é§Ñ§Ó§Õ§Ñ§â §Ý§Ö§Ó§Ü§à§Ó wrote:
??So I will suggest to Mark to ?do another calc.: ?at resonance frequency ?to move the load point at 90 deg on the side of the loop and ?see the value of this current. ?I have made some very rough model of this receiving loop at resonance point? ( creating e.m. field with a small vertical dipole far away from the loop)? and the current at the loop side is almost 1.5 ?times higher than the current at ?point in the bottom of the loop. ?When the loop is "small" the current must be uniform in any point of the loop.
Chavdar, your rough model seems to be correct.? I obtained the following results:
?
?
Before, when the feed point was at the bottom of the loop, the short circuit current (i.e. the Norton equivalent source current) was only 0.4 dB higher at resonance relative the low frequency current.? With the feed point on the side nearest the incoming wave, it is 4.1 dB higher. ? With the feed point on the side farthest from the incoming wave, it is 3.8 dB higher.? ?Similarly, at 30 MHz, it is 1.5 dB?
higher relative low frequency in both cases whereas before it was only 0.2 dB higher.
?
Dan, thanks for running the simulation with your more circular loop.? I will try this experiment with your file and see if it produces similar results.? Your conductor diameter was 25.4mm whereas mine was only 3.3mm, so that might make a difference.
?
- Mark
?
?
?
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Augie "Gus" Hansen