LZ1AQ LNA and a 1.2 meter copper loop antenna.

With G8JNJ strongly recommending it, I finally got around to making the LZ1AQ loop. The schematic and PCB layout along with the BOM I used..., is available to anyone interested here:
and LZ1AQ, the designer's documentation is located here: http://www.lz1aq.signacor.com/docs/wsml/wideband-active-sm-loop-antenna.htm

The prototype board is working @ http://ka7u.no-ip.org:8074 part of the time. I'll leave it up while the weather permits as the prototype board is a bit large to fit in the electrical box under the antenna. The new layout of the boards is smaller and will work better for the enclosures. The prototype does not have a balun to match the 100 ohm balanced twisted pair to the coax, but I have a printed circuit board being made to provide that matching unit at the receiver input. It can be found on the first shared URL above.  This LNA and feed system has significantly reduced the common mode noise that the other antenna amplifiers all seem to exhibit. See the attached images for a better description of what is going on.

So next will be the MFJ clone loop antenna. Hi Hi.



  • My dyslexia is manifest... LZ1AQ CHAVDAR LEVKOV, is the designer of this loop amplifier. He is from Bulgaria, not New Zealand. Being unable to edit the post, this correction will need stand as a correction. The loop at http://ka7u.no-ip.org:8074 is currently using this amplifier design and probably will for the foreseeable future. Chavdar has some great insights on his blog referenced above and if you decide to use this amplifier with your DIY loop antenna, it is well worth reading. Chavdar provided some information to help me to optimize this loop for frequencies between 0-30MHz. I've incorporated most of them in the PCB available here: https://easyeda.com/doxnairobi/
    Perhaps I could do more with FTP shield grounding and local mode suppression on the power supply pair, so think about that if you are building this amp.
  • I edited the post for you..
  • Hi Ron,

    Reducing the loop inductance (for a given size) is something worth trying if you want to improve the performance still further on the HF bands (>10MHz).

    This is less critical when you are using a loop amplifier with a fairly high input impedance, but in the LZ1AQ design it is only in the region of a few ohms (which is great for the LF bands), so loop inductance becomes a critical factor as you go up in frequency.

    You can either make the loop a lot 'fatter' to reduce the inductance, connect several same size loops in parallel (but spaced by a few inches), or cross-connect four or more independent loops together.

    Chavdar has good notes on this subject on his website.



    Martin - G8JNJ
  • Hi Marco,

    I'm also using the LZ1AQ loop amplifier, but my signal levels are no where nearly as good as yours.


    I understand that you are using four crossed loops ?

    Can you describe your loop antennas configuration in more detail as I'd like to see if I can replicate your setup.

    Here are my loops.

    More info on this web page.



    Martin- G8JNJ
  • A report on the ongoing experimenting with the home brew ZL1AQ loop amplifier and the commercial version. I have now made a total of 6 LZ1AQ amplifiers, 3 using matched 2N2222 transistors and 3 using 2N5109 transistors. I've experimented with single loops and dual loops in orthogonal planes like the image in G8JNJ's post above. According to my observations of the noise floor using the KiwiSDR, the amps using the 2N5109 transistors exhibit a better noise floor by a considerable margin, over 10dBm on 160 meters and observably more on the lower frequencies. Generally, the entire 30 MHz band spread is noticeably improved with the 2N5109 transistors. The 2N2222 transistors I used had a typical HFE of 214.

    The commercial version that I purchased has considerably more gain than the DIY model but once again it also has a higher noise floor and the additional gain has required notch filters to reduce local high powered stations, that the DIY boards don't require, as they have less gain. The commercial board is very sensitive at VLF and is very nice with many options that make it ideal for a wider variety of antenna configurations.

    I have two problems with the boards currently available at https://easyeda.com/doxnairobi/zl1aq-loop-amp-ron-morell , I used the 2N2222 footprint and it makes it a bit tight to use the 2N5109, and if you use a RJ45 socket that accepts cords horizontal to the board, it will be incorrect, so use the RJ45 socket that plugs in from the top. I might get around to changing these two issues... It takes me about 4 hours to make the amp and the balun RJ45 to BNC board. https://easyeda.com/doxnairobi/2-1_balun , and again, I've got the RJ45 plug backwards if you use a horizontal plug. There is nothing stopping you from modifying these boards before having them produced. The last order was $2.00 for 10 boards + shipping and the parts I ordered. The parts weren't much either. Mostly it just takes time to figure out how to do it and wait for them to show up.

    I've worked with 4 different amp designs and I think the LZ1AQ is quite competitive with the other designs. Thanks to G8JNJ for recommending it.
  • I just finished installing a 1.2 meter copper loop with a commercial LZ1AQ amplifier. The station is in Central Italy.

    The overload indicator was up all the time so I temporarily installed a 15dB attenuator (by Mini-Circuits). The indicator is now off but I was wondering if it was a good idea and/or if it would be better to use a HPF to attenuate broadcasting stations below ~2MHz.

    Can anybody else share their experiences in this regard?

    Thank you

    The kiwi is available here: http://k1fm.us:8073
    Feel free to check it out and tell me what you think, if you wish
  • edited December 2018
    I have the commercial version LZ1AQ. It is not currently in service, but it works much like yours on a 120cm diameter x 1" copper pipe loop. I do not have LW broadcast stations, so MW are the ones that overload my antenna here. Generally, if the signal is less than -25dBm on the KiwiSDR spectrum scale, then it does not overload the KiwiSDR. I did not see the OV light on your station so I don't think you are not having overload, at least not at this time. I did have the noise you are seeing above 9MHz. I changed the balun/power inserting board to one of my own, and the noise was greatly reduced, so I boxed that commercial balun board. Looking at it again, I wonder if it would benefit with more turns, like 14x10 for a 2:1 ratio. It might be worth a try. I notice spurs in the 20 MHz regions that are outstanding. These spurs seem to be produced by our networks and KiwiSDR network connection contributes to them. It was found by Nick W1NJC that setting the KiwiSDR to 10 base T speeds reduced the amplitude of these spurs. We did this with these software modifications:

    213 apt-get install ethtool
    220 vi /etc/rc.local
    #!/bin/sh -e
    # rc.local
    # This script is executed at the end of each multiuser runlevel.
    # Make sure that the script will "exit 0" on success or any other
    # value on error.
    # In order to enable or disable this script just change the execution
    # bits.
    # By default this script does nothing.

    ethtool -s eth0 speed 10 duplex full

    exit 0

    221 reboot

    If it works for you, the 60 KHz spaced spurs will be reduced. We also decided that the spurs are picked up by the antenna, so moving the antenna far away from the network and household noise sources was a great help. In my case 250 feet did reduce interference greatly.

    I am using a DIY version of LZ1AQ amplifier and changed transistors to 2N5109 which were pair matched for hfe and the bias on each pair was checked for same voltage, thus improving the differential effect attenuating common mode noise. The commercial version has more gain, a higher noise floor, but I think better sensitivity from VLF on up, so even though the noise floor is higher, I think the SNR is generally better, but this is just an impression, I haven't worked it enough to know. Seems I've spent so much time working other noise problems that I haven't got around to critically comparing the amps. My DIY LZ1AQ amp lives at:
  • Ron,
    Thank you for the promt reply.
    Holy cow, your setup puts mine to shame!...
    Unfortunately I cannot put my hands on my receiver as it is located in Europe while I am in the US.
    I will however definitely try to set 10 base on the eth card.
  • Alain,
    You have a fine business receiver. Lots of good and readable signals. The problems you have will get reduced as you get to it. It is a process.
  • edited December 2018
    Hi Alain,

    This circuit may help. It is placed on the KiWi RF input and rolls off the gain at MF and also incorporates a simple MF BC band notch.

    The items marked 1 & 2 are the 50 Ohm input and output ports (treat them as coax connectors with a grounded screen). Component legs connected to a common ground are indicated with the triangular shaped three horizontal parallel bar symbols.

    The basic circuit is a 10dB Tee attenuator formed by the three resistors.

    The values chosen for the attenuator sets the maximum attenuation at the lowest frequency. You can increase or decrease the amount of attenuation by altering the value of the resistors. I chose 10dB as it seems to provide the best compromise in terms of optimizing the amplitude of signal levels VS S/N ratio when using typical antennas.

    The 330pF capacitor and 330nH inductor set the frequency at which the attenuation starts to decrease.

    The 100pF capacitor resonates with the 330nH inductor at around 30MHz to help reduce any residual attenuation at that frequency.

    As the frequency increases the reactance of the capacitor decreases, and the reactance of the inductor increases and this gradually disconnects the attenuator network.

    The circuit is typically used in cable TV networks to compensate for increasing coax attenuation with frequency. Amplifiers will have compensation to provide rising gain with frequency in order to offset the cable losses. If you want more background look up Zobel network


    On the output of the equaliser, a simple series tuned circuit notches out the MF signals centered on approx 900KHz with a notch depth of approx 25dB. The bandwidth and notch depth are determined by the component 'Q' and L/C ratio.

    I have built quite a few for various KiWi owners. It usually solves the problem of MF band overload for folks who are using loops without unduly affecting the overall performance.


    Martin - G8JNJ
  • Martin,
    Thank you very much for your suggestion. I might try to build one on SMD directly with male-female SMA connectors.
  • Martin,
    The Zobel configuration is interesting. Here's what I get from QUCS about it:

    Just to show that, like Unix, there are always multiple ways to solve a problem, here's another.
    I've been using a different configuration with similar flexibility of attenuation and HPF corner. Both approaches tend to have a 'bump' at the corner but either might be useful. Again from QUCS:

    I find that I end up looking at the maximum (aggregate) signal over the whole spectrum from an antenna-in-question and set the attenuator appropriately. The Kiwi OVC comes on around -14 dBm at the SMA connector. If one signal is dominant, allowing for peak/average variations due to modulation as well as the sum from any other large signals, this might have an attenuator 6-10 dB more than might be indicated from the strong station alone.

    After choosing that attenuator I run it and see what I think. Sometimes there may be a single "big guy" that needs whacking apart from the attenuator which reduces the entire LF/MF spectrum. Here in Fort Collins, I am only four wavelengths away from a monster - WWVB at 60 kHz. For it I do as you do and add a single series trap.

    This approach requires looking at each antenna/location situation on a case-by-case basis but does give pretty good results.

    Glenn n6gn
    Fort Collins, CO
  • Hi Glen,

    I note that that you get a peak at around 20MHz.

    You have a 330pF in place of 100pF (C2).

    The peak should be at around 30MHz to reduce the loss on 10m and roll off slightly above it.

    This is an actual sweep of the circuit as built.

    As you say, more than one way of implementing the required curve.

    The values were chosen to deal with overload from specific MF BC stations and also help to 'level' the output from active loop antennas (and others) which tend to have more than enough gain on the LF bands but usually not quite enough on the HF bands. On the LF bands the natural noise floor is about 30dB higher than on the HF bands, so adding 10dB of slope usually doesn't make much difference in terms of the RX S/N ratio, but it does help reduce overload problems from strong BC stations on the lower frequencies.

    I've provided a few of these to other KiWi owners who were having problems, and this simple circuit has usually fixed it.

    I also have more complex filter designs which I use on my KiWi's, but they cost a bit too much for me to build, test and ship for most folks liking.


    Martin - G8JNJ
  • Here's a close up of the MF band filtering.

    Marker lines 3 & 4 show the limits of the MW BC band in Europe.


    Martin - G8JNJ
  • Ooops, that's what I get for doing it too quickly! Here it is with the 100 pf.

    one can move the peak around to suit.

    I think it would be helpful if Kiwi operators who have a public presence and are able to do it would put this sort of information on their splash page. Doing so would allow absolute calibration of a given signal (in whatever antenna is being selected). If one knows the antenna factor, such as is the case with LZ1AQ antennas, AND the filtering/attenuation response ahead of the Kiwi, and if the Kiwi S-meter/walterfall calibration is set then signals and noise, in either S units, dBm or volts/meter could be deduced.

    Doing this at all frequencies requires a plot/measurement of this sort but, as can be seen, measurement/model agreement can be very good and this really need not be difficult IF the antenna factor is known.

    Glenn n6gn
  • edited December 2018

    Dreamed about my comment on the commercial balun/power board and remembered problems I found with the CAT6 shield to RJ45 connection. So I took another look at that commercial LZ1AQ balun. There is no difference visible between the waterfall screenshots. So the problem I was experiencing at that time was feedline related and not balun/inserter board related. I scratched my comments about this in the earlier post. But, back to the problem I had with the shielded 4 pair feedline, I had a balun board inline that did not have a shielded RJ45 jack while the feed line had a shielded plug. It worked fine. I placed the commercial LZ1AQ balun board inline and the bandspread exploded with noise. Of course I went back to the board with the unshielded jack. Later I made new designed balun/power boards that use shielded RJ45 jacks. These new units had the same noise as the LZ1AQ. After investigating, I discovered the shield on the feed line did not have a good connection to the shielded plug. Replacing the plug and making sure the drain wire and shield were in solid contact with the metal portion of the crimp solved the problem. It is worth noting that the RJ45 jack on the commercial LZ1AQ amplifier board is unshielded. So the amplifier board ground is not common with the shield on the feed line. I believe this was a design feature to isolate common mode currents and also because both the ground and vcc are fed through inductors which changes the voltage potential from the feeds by the resistance of the inductors.

    So before you look at attenuation, double check your feed line connections.

  • edited December 2018
    I put 20 dB of attentuation inline, more than enough, then went and looked at the strongest signals in the AMBC band, making note of the signal strength. A little math on those can tell a story.
  • >
    >I think it would be helpful if Kiwi operators who have a public presence and are able to do it would put this sort of information on their >splash page. Doing so would allow absolute calibration of a given signal (in whatever antenna is being selected). If one knows the antenna >factor, such as is the case with LZ1AQ antennas, AND the filtering/attenuation response ahead of the Kiwi, and if the Kiwi S->meter/walterfall calibration is set then signals and noise, in either S units, dBm or volts/meter could be deduced.

    Ha, I don't think I could easily do that with mine. There is just too much filtering and splitting going on.

    Here's my notch filter response (with no equalisation). This reduces the level of signals in most BC bands, which are typically 10 to 20dB stronger than the amateur and utility stations in the adjacent bands.


    Martin - G8JNJ
  • Thankfully, I only have to filter 3 MF AMBC TX and do so with notches that are not otherwise very impactful. That's on WA2ZKD here in Rochester NY. WA2ZKD/1 in Rockport Maine lives without filters. Both stations use Pixel Loops although I'll be switching to something else soon here in NY.
  • I'm suggesting just publishing the filter/atten response and saying where the S meter is calibrated. Put a note in about the antenna factor if you know it. Let the user put it together and calculate the field strength. As long as the information is there, it can easily be done.

    Glenn n6gn
  • I'd like to point out that setting the eth card to 10-base-T made a huge difference in terms of noise. Thanks Ron for letting me know.
    I also would like to point out that living in NYC is probably one the worst spots in the world in terms of noise, broadcasting overloading and ....

    [continuing editing this post after 1 hour]
    Well, I hope you will forgive the off topic but this is the most unbelievable post I have written in my life. As I was writing the above part, the power went out and the Internet too. At the same time the night sky lit up as if it was day and it stayed lit for about one minute. People started running, screaming in the streets. Shortly after myself and my wife took an emergency radio kith with batteries (which is stored in a metallic box) and run to a safe place underground.
    It turned out to be a massive explosion at an electric plant nearby.

    Well, as I was saying NYC is the worst in terms of noise, broadcasting overload and fear of nuclear armageddon.

    Glad to be here... Now back to KiwiSDR talks!
  • Wow! I would have been concerned too!

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