Jumping back to your March 10th post on this thread, the DXE RPA-1 circuit, looks to be a simple and inexpensive circuit. I have been comparing it to
https://www.okdxf.eu/lankford/Norton-2N5109.pdf. This circuit is much more trouble to build, or so it would appear, but not really that much more work and especially now that I have the low cost PCB service with low cost parts.
I should probably quit experimenting with these LNA circuits and move on to something else, but my last order of Wellgood boards are lost in the mail somewhere, and I have friends waiting on me for their project boards. The LZ1AQ beta boards should be here next week and as you are using them, I expect they are probably as good as it will get for these antenna types.
Many thanks for all these valuable comments.
I'm also thinking in buying the lz1aq kit to improve my HF reception. I listen mainly from 5MHz to 15MHz SSB mode.
Any tips regarding the loop diameter and thickness for my case? I understand that the father the better to reduce loop inductance, just would like to have your valuable tips concerning my situation for the best results for 5-15MHz.
Or better to look to another solution?
The LZ1AQ amp is quite good. If you buy the commercial version it is designed to use either 1 loop or 2 loops. If you use 2 loops the SNR should improve by 3 dB. I have not yet used 2 loops but do plan to soon and I do have a commercial version of the LZ1AQ amp (but I have not yet used it). I have been using 1 inch diameter soft drawn copper for loops, but it does not seem much better than 1/2 inch soft drawn copper tubing. I think Heliax would also make a fine loop. There is no reason to use copper if you have a source of aluminum tubing, you can use that. I currently have a LZ1AQ home made amp running a single 1.2 meter diameter loop at http://ka7u.no-ip.org:8074 . If you are a builder and enjoy that, you might be interested in ordering low cost boards and parts here: https://easyeda.com/doxnairobi/ , look at the LZ1AQ Loop Amp and the RJ-BNC Balun. Note the commercial boards from LZ1AQ will be superior to these boards and of course are already assembled and tested. Ron KA7U
As Ron has already said, if you can connect two or more loop in parallel, or use a 'Fat' loop you will improve the performance, especially on frequencies above 10MHz.
You are aiming for as low a value of inductance as possible, combined with as large an area as possible.
LZ1AQ has produced some very good notes on the subject.
I was using the 'Fat' loop shown on the above web page, but the Winter storms damaged it, so it's currently awaiting a rebuild.
@K7AU - Ron I tried building a GALI-74 amplifier. The input impedance at around 1MHz was greater than 250 Ohms (for just one device). It reduces to a more sensible value above about 10MHz, but a pair of them would be less than ideal as a loop amplifier. Thsi is probably why the LZ1AQ performs better.
Many thanks for the replies. Indeed, after some research I found that pex-al-pex tubing is cheap and good to build loop antennas. I can source it cheap locally with diameters of around 20mm. I'm thinking in cross parallel loops arrangement in LZ1AQ. I plan to buy the kit mounted and tested instead of building myself. It will give me more confidence and probably will be better in terms of reception performance vs building myself. Copper tubing is more expensive and alu tubing will be very difficult to bend with about 1" diameter. Maybe I'll go for 1.27m loops as I can find here 4m of pex-al-pex tubing just ready to buy. Or four square loops maybe... decisions...
If you are only building one 'thin' loop don't make it too big a diameter.
The natural noise floor on the LF bands is fairly high, so once you have a loop big enough to hear the noise on the LF bands there is no advantage in making it any bigger, as the extra inductance (or in the worst case self resonance due to a combination of loop inductance and end capacitance) will seriously degrade the performance on the HF bands, where the natural noise floor is low, and you can benefit from any improvement in overall sensitivity.
Basic question. Is the active loop mostly for improved LF performance and limited space situations? I read quite a bit about them but not too much on how they compare to a passive large wire loop. Given enough space, which way would one want to use?
I have a Pixel active loop which I choose to help minimize AMBC OV at my QTH. Even a passive antenna can get whacked here and so I use notches in the AM band. The loop does help null some of the ones I don't notch.
Active antennas tend to be popular with folks who don't have the space for larger antennas, or who need to site them away from local interference sources or maybe use the loop directivity to 'null' out local BC stations or other specific noise sources.
A big passive loop can work very well, it's large perimeter can provide a fairly wideband match if you use a suitable ratio impedance matching transformer.
There is some directivity, so you may get some nulls in certain directions on certain frequencies.
Try Googling "sky loop antenna" and you should be able to get plenty of ideas.
However as Jim has already stated, with a bigger antenna, you may need to add some notch filters to reduce the signal levels on some BC bands.
I have a near-corner fed vertical delta loop, 75 ft apex up, base 10 foot from ground, 4:1 currently with some future tests to see if a different ratio may be better. Besides getting a nearby Invisible Fence RFI issue fixed, its done well enough, broadcast seems tame. Just checking to see if there was argument/use case I had missed. Thanks!
I was not very happy with the one I assembled. It seemed the common mode noise was higher than it should have been. I studied that and think the 2 GALI-74 amps are not balanced. I used 1% resistors, but the voltages are quite different across the two amps. So the differential effect is not working due to the unbalance between them. I have not found a way to check these small devices for equal performance prior to soldering them to the board. With the LZ1AQ amp I found the transistor balance at each stage has a profound affect on the performance of the differential amp in as much as the common mode noise is greatly decreased with balance. I also found the spurious signals were greatly reduced with balance. I think these type of spurs are 3rd order distortion products? Anyway, the LZ1AQ circuit seems stable and linear across the spectrum and most of the spurs are actually radiated signals from other devices in and about the premises. The input voltage has more filtering on the LZ1AQ board than the GALI-74 board and that may also be a shortcoming on the GALI-74 board. Just as an aside, I think the HiLetgo amp that I started with uses a mimic amplifier but I don't know which one. For a simple circuit it does very well, but exhibits more common mode noise and spurious signals than the LZ1AQ circuit. Of course it does not have input voltage filtering except for the one RF blocking inductor that I scabbed on.
Oh the joys of hacking away at circuits. Hi Hi Ron - KA7U
The reduction in IP products with improved amplifier balance are likely to be mostly 2nd order products.
One trick you could try is to place a 1:1 voltage balun (a pair of bilfilar windings with the end of winding one connected to the start of winding two ) across the amplifier input with the center tap to ground. You may need to experiment with the number of turns and type of ferrite but this is likely to be just as effective (and easier to construct) as an isolating input transformer with a grounded center tap on the secondary (amplifier input) side.
@G8JNJ Martin, I tested the LZ1AQ amp here today and compared the tests with the Hiletgo amp test results. Don't know why I didn't do this sooner but anyway:
The noise floor on the LZ1AQ is typically -10dBm lower than the Hiletgo. So generally the LZ1AQ does better S/N ratio by about 10dBm. But I was very surprised at the performance between 1.8MHz and 7.0MHz. Below 300KHz the LZ1AQ is much better than the Hiletgo amp. Would you take a look at the input filter and output circuit and let me know if you see something that I could change to improve the performance of this LZ1AQ amp in that 1.8-7.0 MHz frequency range? I really like the LZ1AQ for common mode rejection and low noise floor.
@G8JNJ Martin, I used a transmitter set for 5 watts into a 50 ohm load. First testing the Hiletgo amp for received signal and then placing the LZ1AQ in the same location and direction and checking again. It should provide a relative indicator of the difference in amplifier gain at a given frequency. The reduced sensitivity on a given frequency could be the result of the transmitter and 50 ohm setup, but the difference in received signal should be relative. Ron - KA7U
Comments
Attachments:
https://forum.kiwisdr.com/uploads/Uploader/53/aa664eef2a7544390b2342231c751e.png
I'm also thinking in buying the lz1aq kit to improve my HF reception. I listen mainly from 5MHz to 15MHz SSB mode.
Any tips regarding the loop diameter and thickness for my case? I understand that the father the better to reduce loop inductance, just would like to have your valuable tips concerning my situation for the best results for 5-15MHz.
Or better to look to another solution?
Best regards
Thanks in advance
https://easyeda.com/doxnairobi/ , look at the LZ1AQ Loop Amp and the RJ-BNC Balun. Note the commercial boards from LZ1AQ will be superior to these boards and of course are already assembled and tested.
Ron
KA7U
As Ron has already said, if you can connect two or more loop in parallel, or use a 'Fat' loop you will improve the performance, especially on frequencies above 10MHz.
You are aiming for as low a value of inductance as possible, combined with as large an area as possible.
LZ1AQ has produced some very good notes on the subject.
http://active-antenna.eu/tech-docs/3_ActiveAA_Antena_11.pdf
There are also more note and pictures on my Active Antenna's web page.
https://www.g8jnj.net/activeantennas.htm
I was using the 'Fat' loop shown on the above web page, but the Winter storms damaged it, so it's currently awaiting a rebuild.
@K7AU - Ron I tried building a GALI-74 amplifier. The input impedance at around 1MHz was greater than 250 Ohms (for just one device). It reduces to a more sensible value above about 10MHz, but a pair of them would be less than ideal as a loop amplifier. Thsi is probably why the LZ1AQ performs better.
Regards,
Martin - G8JNJ
The problem with the loop was not the loop itself, but the support structure and loop mount, but I do live on top of a hill....
Regards,
Martin - G8JNJ
Indeed, after some research I found that pex-al-pex tubing is cheap and good to build loop antennas. I can source it cheap locally with diameters of around 20mm. I'm thinking in cross parallel loops arrangement in LZ1AQ. I plan to buy the kit mounted and tested instead of building myself. It will give me more confidence and probably will be better in terms of reception performance vs building myself.
Copper tubing is more expensive and alu tubing will be very difficult to bend with about 1" diameter.
Maybe I'll go for 1.27m loops as I can find here 4m of pex-al-pex tubing just ready to buy. Or four square loops maybe... decisions...
If you are only building one 'thin' loop don't make it too big a diameter.
The natural noise floor on the LF bands is fairly high, so once you have a loop big enough to hear the noise on the LF bands there is no advantage in making it any bigger, as the extra inductance (or in the worst case self resonance due to a combination of loop inductance and end capacitance) will seriously degrade the performance on the HF bands, where the natural noise floor is low, and you can benefit from any improvement in overall sensitivity.
Regards,
Martin - G8JNJ
A big passive loop can work very well, it's large perimeter can provide a fairly wideband match if you use a suitable ratio impedance matching transformer.
There is some directivity, so you may get some nulls in certain directions on certain frequencies.
Try Googling "sky loop antenna" and you should be able to get plenty of ideas.
However as Jim has already stated, with a bigger antenna, you may need to add some notch filters to reduce the signal levels on some BC bands.
Regards,
Martin - G8JNJ
I did build a prototype GALI-74 loop amp.
https://easyeda.com/doxnairobi/NEW-gali-74-loop-amp
I was not very happy with the one I assembled. It seemed the common mode noise was higher than it should have been. I studied that and think the 2 GALI-74 amps are not balanced. I used 1% resistors, but the voltages are quite different across the two amps. So the differential effect is not working due to the unbalance between them. I have not found a way to check these small devices for equal performance prior to soldering them to the board. With the LZ1AQ amp I found the transistor balance at each stage has a profound affect on the performance of the differential amp in as much as the common mode noise is greatly decreased with balance. I also found the spurious signals were greatly reduced with balance. I think these type of spurs are 3rd order distortion products? Anyway, the LZ1AQ circuit seems stable and linear across the spectrum and most of the spurs are actually radiated signals from other devices in and about the premises. The input voltage has more filtering on the LZ1AQ board than the GALI-74 board and that may also be a shortcoming on the GALI-74 board. Just as an aside, I think the HiLetgo amp that I started with uses a mimic amplifier but I don't know which one. For a simple circuit it does very well, but exhibits more common mode noise and spurious signals than the LZ1AQ circuit. Of course it does not have input voltage filtering except for the one RF blocking inductor that I scabbed on.
Oh the joys of hacking away at circuits. Hi Hi
Ron - KA7U
The reduction in IP products with improved amplifier balance are likely to be mostly 2nd order products.
One trick you could try is to place a 1:1 voltage balun (a pair of bilfilar windings with the end of winding one connected to the start of winding two ) across the amplifier input with the center tap to ground. You may need to experiment with the number of turns and type of ferrite but this is likely to be just as effective (and easier to construct) as an isolating input transformer with a grounded center tap on the secondary (amplifier input) side.
Regards,
Martin - G8JNJ
Martin,
I tested the LZ1AQ amp here today and compared the tests with the Hiletgo amp test results. Don't know why I didn't do this sooner but anyway:
Hiletgo LZ1AQ
28.5MHz -69dBm -43dBm
24.9MHz -63dBm -48dBm
21.2MHz -48dBm -36dBm
18.1MHz -44dBm -57dBm
14.2MHz -54dBm -50dBm
10.12MHz -53dBm -58dBm
7.15MHz -57dBm -62dBm
5.33MHz -59dBm -75dBm
3.75MHz -67dBm -83dBm
1.9MHz -90dBm -101dBm
The noise floor on the LZ1AQ is typically -10dBm lower than the Hiletgo. So generally the LZ1AQ does better S/N ratio by about 10dBm. But I was very surprised at the performance between 1.8MHz and 7.0MHz. Below 300KHz the LZ1AQ is much better than the Hiletgo amp. Would you take a look at the input filter and output circuit and let me know if you see something that I could change to improve the performance of this LZ1AQ amp in that 1.8-7.0 MHz frequency range? I really like the LZ1AQ for common mode rejection and low noise floor.
Ron - KA7U
Attachments:
https://forum.kiwisdr.com/uploads/Uploader/35/e7a400996680b932067ec3cd234f9d.png
That doesn't look correct.
What did you use as the signal source and what was the test setup ?
Regards,
Martin - G8JNJ
Martin,
I used a transmitter set for 5 watts into a 50 ohm load. First testing the Hiletgo amp for received signal and then placing the LZ1AQ in the same location and direction and checking again. It should provide a relative indicator of the difference in amplifier gain at a given frequency. The reduced sensitivity on a given frequency could be the result of the transmitter and 50 ohm setup, but the difference in received signal should be relative.
Ron - KA7U
OK, I think you are suffering from some close in near field measurement issues.
The problem is that close to the source the E Field and H field are not unified.
http://www.rfcafe.com/references/electrical/images2/wave-impedance-measures-relative-strength-electric-magnetic-fields.gif
You need to build a simple broadband TX loop to use as the signal source, and ensure that the TX loop is aligned with the RX loop.
http://www.w1tag.com/FSM_CAL.pdf
Regards,
Martin - G8JNJ