Keyboard Shortcuts
ctrl + shift + ? :
Show all keyboard shortcuts
ctrl + g :
Navigate to a group
ctrl + shift + f :
Find
ctrl + / :
Quick actions
esc to dismiss
Likes
- Loopantennas
- Messages
Search
|
Re: Wellbrook 50 ohm preamp to Files
¿ªÔÆÌåÓýMike, Since you told us you have an IMD test set, maybe you should build the two types and measure them, using same transistors and same current, and let us know the results.??? :) Steve On 10/15/2024 1:52 PM, vbifyz via
groups.io wrote:
|
|
Re: Looking for a good cheap antenna analyser
Hi Simon,
?
I think it depends upon what you are most likely to use it for, and how careful (or careless) you tend to be with kit.
?
Most of my applications are indoors, but I have used it up a tower without any problems., as it fits in my top pocket, it's easy to stow away whilst doing other things.
?
I also like to be able to store and export data for off-line analysis later, and for me this is a major consideration.
?
But if you want a simple-to-read instrument, with big controls, that you can use with gloves on, then maybe a basic, and more conventional, antenna analyser is a better option.
?
Horses for courses...
?
Regards,
?
Martin |
|
Re: Looking for a good cheap antenna analyser
Hi All
Thanks for inputs.. As it happens..( abit of back ground info here first. I am electrical and electronic engineer on 3 ferries very near Plymouth, also have a very good mechanical background..my immediate boss ( leading hand) has taken alot of interest into my ham radio exploit's. To which he just passed his exam and now is a ham! He just bought a nano vna and brought it into work..I like the swr plot against frequency plus obviously other features.) However..I feel I need one, but dont think it will replace the mfj up a ladder in the rain tuning a multi band Marconi T as have added another 200m ( 1250m or so now.) or so of radials. It¡¯s just too fiddley to use with one hand, plus far too fragile. So I think for hands on antenna tuning in field ( best swr with matching adjustments vs best resonance) the mfj is just fine..BUT for research/ planning the nano is required. Boss¡¯s cost ?80..($90?) not too bad.. Your thoughts please..thanks. Simon g0zen on Dartmoor, Devon |
|
Wellbrook 50 ohm preamp to Files
Andrew Ikin of Wellbrook for a short time offered a version of the ALA1530LN with an additional 9 dB gain Norton preamp in the receiver coupler--this version was called the ALA1530LNP. He developed this version which used two transformers.? I've uploaded the schematic into a new folder in the Files. /g/loopantennas/files/Wellbrook%2050%20ohm%20Norton%20Preamp He used the now-discontinued ZTX 327 transistor, but any good RF transistor can be used.
73, Steve AA7U |
|
Re: MLA-30+, the story continues!
#Small_receiving_loops_RX-only
On Tue, Oct 15, 2024 at 04:23 AM, Fred M wrote:
Would it be not less effort to use two well buffered X-tal Oscillators instead of an Si5351 followed by two x-tal filters?I have that, too. The numbers achieved with that setup were slightly worse, especially F1+F2 OIP2 (+90dBm). To be honest, I didn't buffer the oscillators that well, the max levels at the DUT input are only about -13dBm for each frequency, compared to -8dBm for Si5351a+filters. My design philosophy is "good enough is enough", Si5351a works and this is where I stopped.
?
73, Mike AF7KR |
|
Re: Null Depth versus Torsion
Paul,
?
I'm not clear as to the meaning of your term "... H cross horizontal is still zero", please explain.? ??
?
However, since a loop that is electrically-balanced to ground does not produce a response to an electric field, I would not expect the E-field to participate in the "tilted loop" response.
?
Have I misinterpreted your comment regarding the source of the imbalance?
?
? |
|
Re: Looking for a good cheap antenna analyser
The terminology and menu structure of the NANOs emulates the VNAs offered by the"big boys" .? I've used these for decades and find the NANOs very easy and quite friendly to use.? Consequently, the "up-the-tower" single-port VNAs feel clunky to me.? Dave - W?LEV On Tue, Oct 15, 2024 at 3:33?PM JohnG3PQA via <JohnG3PQA=[email protected]> wrote:
-- Dave - W?LEV |
|
Re: Looking for a good cheap antenna analyser
Hi John,
?
I agreed, we all have own personal favourites for various reasons, a lot depends upon our pattern of use.
?
Personally, I tend to find that I'm using my LiteVNA 64 and TinySA Ultra for more tasks than I thought I would, and a lot of my previous test kit hardly gets switched on, unless it's for a very specific purpose.
?
I find I also frequently use them as signal sources, which is something I'd not expected when I bought them.
?
Regards,
?
Martin |
|
Re: Looking for a good cheap antenna analyser
Martin,
All agreed and very true, but Simon was enquiring about an inexpensive antenna analyser rather than test bench device using NanoVNA Saver software etc.. The now obsolete devices have various advantages and disadvantages but may be able to be picked up cheaply.
Certainly the latest NanoVNAs have good batteries, bright screens, no problem using them outside if set up correctly. It is just a shame IMHO the menu structure and terminology of the Nanos has not been better written, but it looks as if I am in the minority here. I have a NanoVNA-F but rarely use it, the Sark is better outside and VNWA excellent device for accurate 2-port shack measurements but does not have its own screen of course. Ihave not found any problems with Win11 upgrades using the auto-installation program.
John |
|
Re: MLA-30+, the story continues!
#Small_receiving_loops_RX-only
On Mon, Oct 14, 2024 at 03:10 PM, vbifyz wrote:
Would it be not less effort to use two well buffered X-tal Oscillators instead of an Si5351 followed by two x-tal filters? I do it this way with a RF-2-tone generator proposed by DC4KU and are able to measure with a Siglent 3302 an IP3 up to 36 dBm without bandstop filters. To achieve a higher measuring dynamic range bandstop filters are mandatory. ?
DC4KU RF-two-tone generator (pdf in german, please use a translator)
?
regards
Fred |
|
Re: Null Depth versus Torsion
On Tue, Oct 15, 2024 at 01:28 AM, JohnT wrote:
Does this make sense?Good morning and thanks, JohnT :) Would it be right to understand the source of that imbalance would be from the E component, as H cross horizontal is still zero?
?
@Martin, day-dreaming eats up too much bandwidth. I really must put a sock in it. |
|
Re: Null Depth versus Torsion
Hi John,
?
That is assuming you are in the correct plane WRT the incident wave, and you will also have a reduction in the amplitude component, which I speculate will be -3dB when the offset is at 45 degrees, but which will subsequently be attenuated much more rapidly with further rotation, until a null is achieved at ?90 degrees.
?
Regards,
?
Martin |
|
Re: Null Depth versus Torsion
Good evening Paul,
?
Seems to me that if you were to "tilt" your square loop such that the upper horizontal leg were closer to the signal source and the lower leg were further away from the source, a phase difference would occur between the two horizontal legs which would degrade the cancellation occurring in the vertical legs and hence the depth of the null.? eg; if the sides of your loop were 0.1 lambda in length, tilting the loop by 45 degrees off-normal to Poynting vector of the incident wavefront would result in a phase difference between the two horizontal legs of 2*0.05*360deg*cos(45deg), or 25.5 degrees.? Does this make sense?
?
Best Regards,
John |
|
Re: MLA-30+, the story continues!
#Small_receiving_loops_RX-only
No matter what your IMD setup is, you need to run the measurement bypassing the DUT first, to see the capability of the setup.
My IMD bench is:
?- Si5351a generating F1=3.58 and F2=4.914MHz,? 4mA drive strength (important)
- 5-resonator xtal narrow bandpass filters, Cohn topology. I can slightly tweak the input frequencies to hit the maximum, it moves with temperature.
- hybrid power combiner
- step attenuator
- dummy aerial if the DUT is a loop preamp (in my case it is a 1:1:1 transformer and two 25/0.5 Ohm dividers, no reactive elements, flat response, 50dB CMRR up to 30MHz)
- here is the preamp under test
- 5-inductor bandstop filter, 2.5 .. 5.5MHz. F1/F2 Attenuation is about 35..40dB. All products of interest are outside of the stop band, but I measure their attenuation anyway to correct for it during the measurement. It is about 1 .. 1.5 dB.
- 20 or 40dB fixed attenuator to bring the signals within the range of the receiver
- Airspy HF+ Discovery
- HDSDR software
?
The floor (IMD detected without the DUT) is
+110dBm OIP2 at 2.24MHz (F2-F1)
+109dBm OIP2 at 8.5MHz (F2+F1)
+47dBm OIP3 at 2.24MHz (2*F1 - F2)
+39dBm OIP3 at 6.25MHz (2*F2 - F1) - this is the one which limits my measurements, I don't see it changing with LZ1AQ or other good preamp in the path. Probably limited by the Si5351a outputs cross-modulating.
?
73, Mike AF7KR |
|
Re: Null Depth versus Torsion
Hi Martin, thanks a lot for that.
?
Let's forget about torsion for now, and keep things simple.
?
My schoolboy visualisation must have terrible flaws, but goes something like this...
For simplicity, consider a square loop.
Consider only vertically polarised signals, so E is vertical and H horizontal in the plane of the wavefront. ?
With a loop broadside on to the wavefront, H does effectively nothing in the horizontal arms but induces identical currents in the two verticals. Hence complete cancellation.
?
Rotated 90 degrees, the horizontals are still unaffected, and verticals get *almost* the same current in each arm. Except for the tiny phase difference at front and rear. That differential accounts for PD at the feed point and is the received signal, weaker and weaker at longer wavelengths because of smaller phase difference (hence awful efficiency).
?
Now, broadside on again, *tilt* the loop a little. As before, horizontals make no contribution while by symmetry the almost-verticals still have similar induced current.
?
The only difference I can see is a tiny "would-be current gradient" between top and bottom of each arm - but still symmetrical. That is at odds with experiment because the null is no longer perfect (er, is that true?).
?
What is dumbo here missing?
Is there some E-field contribution we need to insert into the mix?
?
Very best
Paul
?
|
|
Re: MLA-30+, the story continues!
#Small_receiving_loops_RX-only
Hi Simon,
?
Mabe it's possible with later generation analysers that have a greater dynamic range, but most stuff available to hobby users isn't going to cut it.
?
I have a HP8563E, but it hardly gets turned on, as apart from the frequency coverage to 26GHz, it's not that much use for everyday stuff.
?
My tone sources are two crystal oscillators followed PA's and then by attenuators, individual absorptive band pass filters, a high power combiner and yet another attenuator, all built into a standalone box. I start off with 5w of RF and end up with 100mW at the output. The mini-Circuits combiners that are normally specified start to generate their own IP's at around +10dBm, and standard band pass filters don't present a 50 ohm match outside their passband, which can affect the generation of IMD products.
?
Even with this, and a decent set of notch filters, I have difficulty making repeatable IMD measurements, mainly because of leakage and minor phase shifts that affect the generation of IMD. It's hard enough at HF frequencies, and having in the past measured passive IMD, produced in cellular antennas, I know how much more difficult that can be.
?
You read the application notes from folks like Aligent / Keysight, and they make the test setup it looks easy, but at least for me, in a home workshop, it wasn't that straight forward.
?
However, I'm prepared to accept that your mileage may vary...
?
Regards,
?
Martin
?
On Mon, Oct 14, 2024 at 06:29 PM, rfsam wrote:
One just need a good "Big Box" Spectrum Analyzer (HP/Agilent/Keysight) with good LowPIM attenuator in front of it. |
|
Re: SOME MEASUREMENTS of a SML
Martin,
That's my go to calculator as well! :) Thanks, Simon On Mon, Oct 14, 2024 at 2:26?AM Martin - Southwest UK via groups.io <martin_ehrenfried@...> wrote:
|
|
Re: MLA-30+, the story continues!
#Small_receiving_loops_RX-only
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 |
|
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.?
|
to navigate to use esc to dismiss