Excellent! That is good news. I must admit, I am curious to know what was wrong with the original controller. As for changing the feedline, don't bother, the difference in attenuation is insignificant. In order for there to be a noticeable difference in the signal strength at the receive end, you would need at least a 3dB improvement, which is half an S-point, and even that would probably not be all that noticeable. The other thing that feedline loss does is mask the antenna's real SWR, tending to make the system seem better than it really is. But again, this would only be noticeable for a significant change of feedline loss. For example, RG-8X is specified as 0.9dB/100' @ 10MHz, and 2.1dB/100' @ 50MHz, RG-213 is 0.62dB/100' @ 10MHz, and 1.5dB/100' @ 50MHz. At 10MHz therefore the difference is 0.3dB and if you read my previous post you will understand when I say that fractions of a dB are of no consequence. Even though the loop does not cover 50MHz, the difference there is only 0.6dB, again, insignificant, so leave well alone, there is no benefit to changing. Remember the engineering advice, "Don't Fix What Ain't Broke!" Anyway, I am glad that your problem is resolved, we had fun doing some detective work, and I'm always glad to try and help. Now go and have some fun!

73, Adrian, 5B4AIY

Hi Adrian,

Well, I received the new ATU 2.0 this afternoon and I have good news! The controller now finds my Baby Loop during the Auto Detect Routine which would thrill me to no end if that was all. But, I can now make nice large jumps in frequency without the dreaded SWR or Motor faults.

My testing is still in the preliminary phase but it sure is a lot better performance than it was before. Still have a bit of a noise hump on 40m but it's pretty flat on 20m so not sure what that is about. Like I said before, I had those before with my MFJ Loop so perhaps it's a local thing.

I'm still thinking of upgrading my feed line to RG213, but looked up the specs and really would not gain much in loss, plus it's not as flexible as RG8U.

I want to thank you again for your help with this, you have been a big help for sure!

73 Jim K4ECP

OK, I have now made some measurements of my controller. Using a precision 50 ohm dummy load known to be better than 1.05:1 from DC through to 3GHz, this was connected with a very short piece of coax to the ANT socket of the controller, and, using the TEST facility the SWR was measured. At all frequencies from 6,600kHz to 9,000kHz it measured 1.0:1. From 10,000kHz to21,000kHz it was 1.1:1, and from 22,000kHz to 29,800kHz it was 1.2:1. This shows the intrinsic accuracy of the C-M controller's SWR bridge. The same test was then repeated using my scruffy MFJ 100W dummy load, and from 6,600kHz to 9,000kHz it was 1.1:1, from 10,000kHz to 29,800kHz it was 1.2:1. I then inserted a known good 20m length of Ultraflex-7 and repeated the tests, with no change, showing that the cable was good. Yesterday I measured the output power of my controller and it was +11dBm +/-0.5dB over the entire frequency range using my Siglent spectrum analyser. Bear in mind that the C-M controller does not need to actually 'measure' the SWR - in all probability it simply uses the reflection bridge's reflected voltage, the SWR is calculated and displayed merely as a convenience for the user. At least, if I were designing it that's what I would do. This then should give you a baseline as to the accuracy of the measurements you are making. As I said, the ACCURATE, and I stress ACCURATE and REPEATABLE measurement of RF power is a challenging task, and for amateur equipment if you are within +/-10% you are doing well. As you go higher in frequency, the challenge increases. Even professional power meters are not usually specified to better than +/-0.5dB. As my old professor in university was fond of saying with a dismissive wave of his hand, "There's no such thing as a fraction of a dB in RF measurements! You'll be lucky to get the same measurement 2 days in a row!" Add to that the fact that most digital instruments indicate their results to an excessive degree of precision, and it's no wonder there is a certain amount of confusion. I certainly always had to remind my technicians that just because it displays the result to 3 decimal places does not mean it is accurate to 3 decimal places! Accuracy and resolution are two different things. OK, I've had my morning rant, I feel so much better now.

Adrian, 5B4AIY

Hi, Jim,

Yes, there are some aspects of your feedline sweep that bear further investigation. As a (now retired) professional satellite communications systems engineer I have to say that accurate and repeatable measurement of RF power, and SWR are some of the more 'challenging' things to deal with. If your feedline is new, has properly fitted connectors, and, most important, is completely free from sharp kinks, then there is little reason to suspect it. If you compare your findings with the sweep I posted, you will see that in my case my feedline is flat, the SWR is less that 1.05:1 everywhere, but, this was using a precision 50 ohm dummy load guaranteed flat to 3GHz. So your irregularities might well be due to the MFJ load itself, at least if its anything like my MFJ dummy load. Equally, if you made these measurements using the TEST facility of the C-M controller as I suggested, then we are assuming that it is reasonably accurate as well. You can cross-check your readings by using your Flex radio as both the signal source and the measurement. If you get essentially the same results then it is probably the dummy load, after all, the MFJ dummy load is not a precision device. You can further check this by using a short piece of coax and connecting it directly to the Flex and making some measurements. You do not have to repeat all the frequencies, just those that are a bit on the high side for this test. If your Flex shows the same results using a short length of coax, then it is probably the MFJ load. You could also put the MFJ dummy load directly on the ANT connector of the C-M controller and check it at a few frequencies to see what the intrinsic accuracy of its internal SWR bridge is. I'll put my precision dummy load on my controller and make a few measurements for comparison and get back to you. I have to say, this is an interesting exercise. More to follow.....

Adrian, 5B4AIY

C-M finally agreed that the ATU is probably at fault after seeing the sweep that I sent them. So I am just waiting to hear from the vendor that I purchased it from. I also did the feed line sweep and it was not as flat as I expected. However, the only 50 ohm load I had was an MFJ...However I think it's acceptable -

I have a 50 ohm load and will run the same test today to check the feed line

73 Jim K4ECP

Hi, Jim,

Yes, your SWR is not unreasonable. If you turn it into a graph:-

then you can see that apart from the 2:1 point the rest is OK. True, it is not as flat as I would have liked, but it is not unworkable. As for the frequencies between about 18 and 21 MHz, yes, I can see why the loop might have a problem there, but I have seen worse, and the loop has worked. As I said previously, provided that far from resonance the SWR is high and constant, then the tuning algorithm will easily locate the resonance point. I presume that these results were obtained using the Ciro-Mazzoni controller. What is more revealing is measuring the SWR with a dummy load at the end, which takes into account the feedline. Although this is best done with a swept-frequency analyser, it is possible to do it with the C-M controller. Simply terminate the loop end of the feedline with a good 50 ohm dummy load, and then using the TEST mode enter the various frequencies and observe the resultant SWR. Tedious, to say the least, because in order to enter the next frequency you have to press the BACKSPACE key, and then press and hold the / key to re-enter the test mode, but it can be done.

Adrian, 5B4AIY

Hi Adrian,

Tech Support requested that I do a frequency sweep with the loop in it's present location which is attached. I don't see any issue with the loop, feed line or location that is causing an SWR issue, do you???

Hi Adrian,

Great information thanks...while looking at the display while it's tuning I can see where some of that action is occurring. It seems happy with any frequency in the 40m band as it tunes 7MHz frequencies quickly and accurately, Anything other than that, it seems to have a problem. Sometimes 20m is fine and other times trying to tune any 20m frequency is a real bitch. And pretty much forget anything higher than 18MHz.

I see what you are saying about feedline issues...however I did replace my feedline just a week or so ago with no change in my situation. I had the exact same issue with the new feedline as I did the feedline with the splice. I keep going back to the spurious nature of the ATU. Just like the feedline not being flat confusing the alogorithm, I think a dirty generator could possibly cause the same thing. Undoubtedly you are much more familiar with these systems than I and it seems that your work has to do with something along these lines.

73 Jim

Hi, Jim,

Although Ciro-Mazzoni have not shared their source code with me, there are only a small number of ways this sort of thing can work. I have written the software for similar systems, and typically when far from resonance the algorithm expects the SWR to be both high and constant. In this state the actuator would be driven at maximum speed and the SWR constantly monitored until a reduction is observed. At this point the algorithm would switch to the fine tune mode where the actuator would be stepped in small increments. At each step the SWR is measured and compared to the previous value. If it is less, then another step is made in the same direction. Eventually either the measured SWR is the same as the previous step or there is an increase (a reversal) which means that you have reached the resonance point. In the case of the C-M loop the frequency is also switched either side of the resonance point presumably to ensure that you have reached the optimum point. The algorithm can be confused if the feed line is not flat. If the algorithm detects that the SWR increases at some point then it assumes that you have passed the resonance point and will now reverse the motor direction and search for a reduction in SWR in the opposite direction. Eventually the actuator will be driven into its electrical limit, the motor current will reduce to zero which will be detected by the controller and the famous 'MOTOR FAIL' error message delivered and the controller shuts off. So again, if your system constantly seems to be driven in the wrong direction, despite the motor sense being correct, then this points to some sort of feedline impedance discontinuity. This can only really be measured or displayed using a graphic antenna analyser or a vector network analyser. What you do is disconnect the loop from the feedline and terminate it with a good 50 ohm dummy load. Then measure the SWR at various frequencies and verify that it is 1:1 everywhere in this condition. With a swept frequency network analyser this is simple to do.

This is a plot of my Ultraflex feedline when terminated in 50 ohms, using a RigExpert analyser, and, as you can see it is nice and flat everywhere. Also attached is my overall SWR.

Adrian,

I just re-read your original post, and you were having the same issue that I am that when making a large frequency move, it drives to the minimum position and throws the SWR error. You found a feedline problem and it was solved. I also had a splice, however my coupler was pristine...clean and tight. You are using RG213 and I am using RG8U. My run is 125' and my run is also new as I just replaced it less than 2 weeks ago.

C-M is aware of what I'm using for feedline and has not said that they think it's an issue. I would be willing to spend the extra $$$ for a 213 run if it would help.

What I don't understand is why it would drive to the opposite direction than it needs to go in. Is the controller that stupid that it does not know which direction it needs to drive??? I can't believe that it is - So something must glitch it somehow to make it do what it is doing - I would really like them to explain to me why it's doing what it's doing...

Hi Adrian,

Just checked manually and the polarity of the motor wiring is correct - 7 open and 1 close. It just seems so odd that when I command it to auto tune from 20m to 10m instead of loop "opening" it goes to the minimum capacitor position. I can manually tune any 10m frequency with excellent SWR. I sent C-M all the ATU 2.0 pictures with all the spurs and have been asking them do they think it's at fault...nothing yet.

Hi, Jim,

OK, if you have not managed to get it to auto-detect, then the controller will not have determined the correct 'sense' of the actuator wiring. You will need to make sure that it is connected in the correct sense manually. Go to the TEST facility, and press the 9 key and observe which way the actuator moves. If it opens the antenna then you have to correct sense, if it tries to close the antenna, then simply reverse the motor connections. The keys are, 9 - fast open, 8 - medium speed open, 7 - slow open, 3 - fast close, 2 - medium speed close, and 1 - slow close.

I must apologise for not getting you to check your firmware revision earlier, I had assumed that you had the latest version as you had just purchased it. It simply goes to show, Never Assume - It Makes An Ass Out Of U & Me!, and, I fell into the trap. My apologies.

Adrian, 5B4AIY

Hi Adrian,

I heard back from tech support and they asked which version of software I was using in the ATU saying that 4.05 was buggy. It came with 4.05 so I upgraded to 4.06 and there was some improvement...It still fails Auto Detect but it does try now to tune from 20m to 10m! Before it would just immediately throw the SWR error, now it actually displays the tuning screen on the Flex and the motor drives the capacitor but in the WRONG direction. It drives it closed instead of further open - and the of course throws the SWR error - At least there is SOME forward movement -

73 Jim K4ECP

Here's another odd one, this was displayed on the Flex while I was in TEST Mode manually tuning 24.930

Hi Jim,

Yuk! That looks really dirty. Attached are my tuning signal and band using the same frequencies as you

AS you can see, my tuning signal is quite clean, but notice the small spur at about 14.360, and another at about 14.240, compare that with the same thing without the tuning signal.

As you can see, there is quite a difference between your generator's output signal and mine. I really think you have a controller problem. I have examined the tuning signal with my Tekronix scope, and it is essentially a square waveform. Similarly, when examined with my Siglent spectrum analyser, it is fairly clean. I'll do some tests and post a screen shot of its spectral purity.

73, Adrian 5B4AIY

Hi Adrian,

OK, unplugged PS and noise hump still there, also had an MFJ Magnetic Loop before this one and had a hump with that one as well. Must be something to do with my setup I guess - Thanks for the thought though! Oh, C-M supplied a 2 amp supply.

73 Jim

OK...will explore that. Here is pic of controller cross fed into Flex, looks nasty to me -

Hi, Jim,

Overnight a thought fell into my head, probably because there was nothing to stop it. My setup is different than your because I am not using a C-M 24V PSU. I found that they were very noisy, and so I designed a linear 24V/2A PSU, and that's what I use. To see if it is the PSU, tune as before, but then disconnect the PSU or switch it off at the mains, and see if your 'noise bump' disappears. Also, check the rating, some loops were supplied with a 24V/1A supply, but that cannot always supply the peak current pulse, and later antennas are supplied with a 2A supply. I would recommend a 24V/2A linear supply to eliminate all possibility of noise. At my QTH here in the mountains the background noise level is around S2/S3 on 20m as there is absolutely no industry or other sources of electrical noise, it's very quiet. Even 40m after dark is quiet! The 24V PSU does not need to be regulated, as the 24V is only used by the H-Bridge motor controller IC and the actuator. There is an internal regulator the drops the voltage down to that required by the electronics. In fact the actuator's motor will operate down to very much lower voltages, so precise regulation is unimportant. As long as it can supply the initial peak current pulse and has an output voltage of at least 20V it will work fine, and will be free of noise.

73, Adrian, 5B4AIY

I also cross fed generator into the Flex and it looked a lot more spurious than yours did, but I was in SSB and not CW so will also try in CW to see how it looks.

Hi Jim,

Well, I'm mystified. I am attaching some images of my setup.

This is what mine looks like, 20m after dark, antenna tuned to 14.175. No noise hump.

Generator cross-feed into receiver, note, S9+40db

Also the generator output at 14.175. I will be most interested in what Tech Support has to say.

73, Adrian, 5B4AIY

Adrian,

For what it's worth, I measured the actuator while at 14.175 and I also have 8cm.

73, Jim

OK, I did what you suggested and checked the generator power in CW mode and it was fine...I was using SSB mode and that why I was showing only S9.

Also, the SWR on the Flex was very low with the loop tuned to 14.175...

Finally, the third picture shows the "noise hump" on 40m...the hump on 20m is less pronounced -

I'm also communicating with C-W Tech Support on this issue and will be curious what they come up with in the morning - Thanks so much for your help on this Adrian, it's much appreciated

Hi, Jim,

No I intended you to move the actuator using the TEST mode. When you check the signal level, make sure you tune it in. In the CW mode it should be tuned to the carrier, but tune around to get the highest reading. It sounds as if your generator output is low, and that certainly would cause extreme tuning difficulties, as well as a failure of the auto-detection.

Adrian

Did you mean to use test mode without the generator to initially tune the loop to 14175? If so how do I do that without the generator coming on. I can use test mode to tune to 14175 by watching the SWR and checking it with the tune on my Flex and the SWR is nill. the generator spike goes up to the top of the panadapter, however the signal strength is only about S9...Certainly not as high as yours at S9+40...since it's the middle of the night here, I will have to wait until morning to check the actuator distance.

Oh what a sad tale! OK, let's straighten out some things. First, the type of ground you have makes no difference to the way the loop operates as far as tuning and auto-detection are concerned. I also have a 'Stealth' loop, and it makes no difference if I use it by my pool, on the gravel or concrete by my garage, on on dry dirt at my portable location. Indeed, where we live here in Cyprus, the ground conditions are probably very similar to yours. Yesterday for example, the high was 38C or, 100F, and our ground is now parched and dry as a bone. So we can eliminate the type of ground. It is certainly true that placing a ground mat stretching out at least 1 loop diameter can help, but it is not necessary, if you cannot auto-detect your antenna, and are having other tuning problems, then I can assure you that it's not your location or type of ground. It's a pity I'm not your neighbour, just think how easy this would be if I came around with my controller, network analyser, and some other test equipment, we could fix this issue in a matter of minutes! As far as the TEST mode is concerned, C-M have not really explained what that percentage figure means, nor is there any obvious way of altering it. So, let's try an eliminate the antenna. Tune your Flex to say the centre of the 20m band, 14,175kHz, and in the CW mode. Now tune the antenna by using the TEST mode and using the SLOW buttons, (1 to close/lower the frequency, 7 to open/increase the frequency) you should be able to detect a distinct and sharp increase in the noise level as the antenna is tuned to your transceiver's frequency. Now, using only a low power, say, 10W, find out what the SWR is, and tune around to find the minimum, it should be of the order of 1.4:1. Assuming that your antenna can be tuned, and can accept power and the SWR is low, then this pretty much eliminates both the antenna and the feeder. Now we need to examine the controller. Using the TEST mode, when prompted for a frequency, enter 14.175kHz, the centre of the 20m band. As soon as you press the enter key you should see a large signal peak at exactly 14.175kHz on your panadapter display. The amplitude should be something near 40dB above S9 or even slightly higher. This would prove that the internal generator is working, is producing the correct frequency, and is of roughly the right amplitude. I tried this just now and verified that this works. To give you an idea where the mechanical position of the actuator is, I am attaching a picture of my actuator tuned to 14.175kHz.

If this test fails or you cannot get the antenna to tune to this frequency, or any other, then, sadly, you have a warranty problem.

Adrian, 5B4AIY

Hi again Adrian,

One more idea...I live in the SW US which is in the desert and our landscaping is probably different that what you would see in Europe. We have gravel instead of grass. I am wondering if the gravel is not as reflective as bare ground would be...Do you think that this may be part or all of my problem??

I am thinking of going to the hardware store and picking up some metal screening to act as a ground plane...what do you think?? Oh by the way, I just tried lowering the loop to just under 4 feet above ground and no joy -

Hi, Jim,

It looks as if your loop is quite close to a wall or other structure, that is also not good. It should be several metres clear of any structures, especially if they have rebar or other metalwork. Equally, it should not be insulated from its mounting pole. As far as resonant frequency drift, the loop's resonant frequency is temperature sensitive. Not really surprising, it is made from aluminium, which has a high coefficient of expansion. As a result, as the temperature increases the loop expands, opening the capacitor and increasing the frequency. The effect is most noticeable on 20m and 17m, and my measurements indicate that the shift is of the order of about 10kHz/degree C (See attached graph)

I would be most interested in a picture of what you see on your panadapter. However, as you have a panadapater, it would be easy to check the internal generator's output and frequency using the TEST feature of the controller. When you get back post the images, and we can discuss this further.

73, Adrian

Hi Adrian,

I replaced the feedline over the weekend and I think the drifting issue is a bit better. Odd that you don't see the hump on your Flex on the panadapter...when I get back from my business trip I will try and post a picture of what I am seeing...perhaps "hump" is not correct terminology! Anyway, thanks for the advise regarding the tightness of the U loop bolts...mine are snug and not real tight, will

tighten those more for sure.

I believe I may have found another issue with my installation...I am using a tripod and about a 2 foot piece of steel pipe to a Yaesu 450 rotator and then from there about a two foot piece of fiberglass pipe from the top of the rotator to the loop bracket...according the C-M tech support that is a no-no so I need to fix that. The fiberglass pipe is what I had so I used it. So basically the loop is insulated from the rest of the structure. So all together I am about 6' off the ground to the bottom of the loop.

73 Jim

Hi Adrian,

Thanks for responding so quickly...This is a new installation and it has not worked correctly yet! I received the loop last Wednesday and have been trying to make it work since then. However, thanks so much for the information. I have feedline on order and will replace when it arrives and hopefully things get better. My rig is a Flex 6400 so hopefully it's not at fault. Also, I have another issue that you may have seen before - My SWR seems to drift...on the Flex there is a pan adapter and when the loop is resonate, there is a "noise hump" that is displayed on the pan adapter. After a certain length of time that "noise hump" will drift either up frequency or down frequency by 20 KHz or so. Sometimes it's quick and sometimes the drift is slower. I am wondering if it's the heat of the day, but I would think that really should not be happening at all with such an expensive loop. I have contacted the tech support guys about this and they are working the issue, but I am wondering if you have experienced this before in a loop and if you have what the fix was.

73 Jim

Hi, Jim,

First, it is not necessary to use RG-213 for the feeder. I only used it because I had it available. My present feeder is Ultraflex-7, but RG-58, RG-8X is perfectly good. It certainly sounds from your description that you have a cable problem. If you have another length of cable, not necessarily of the same length, then try that. In my case it was quite easy for me to test the antenna out in the garden using a mains extension lead, a temporary short length of RG-58, and a twisted pair cable for the actuator connection. If this works, then clearly you have a cable fault. If this does not work, then we need to get more information. There is really little that can go wrong with the antenna, but, using a multi-meter, measure the resistance between outer and inner of the RF cable connected to the antenna. It should show essentially a short-circuit at DC. You could also measure right at the antenna itself, and this should definitely be a short-circuit there. If you do not have an antenna analyser, then we need to use another method to see if we can tune the antenna and measure the resultant SWR. You can drive the antenna's actuator with any DC voltage between about 6V and 24V, so, connect your transceiver directly to the antenna, and tune it to the centre of, say, 40m. Now, using a twisted pair connected to the motor, user the voltage of your transceiver's power supply and drive the antenna until you hear a distinct increase in noise from the receiver. If you have a separate adjustable power supply adjust its voltage to very slowly move the antenna's actuator. As the motor is isolated, you can reverse the direction by simply reversing the supply voltage. Once you have manually tuned the antenna to the transceiver's frequency, using only the lowest power, see what the SWR is. You will probably have to tune around until you find the lowest SWR. It should be quite low in the range of about 1.4:1. If this is OK, then it proves that the antenna is resonant, and offering a good match to the transceiver. Believe me, this is a LOT simpler with an antenna analyser! Now check the ATU. In the RECEIVE mode, there should be a direct connection between the centre pin of the transceiver connection and the antenna connection. Assuming that we do not have an actual antenna fault, next connect the transceiver to the ATU, and the ATU to the loop, and restore the motor connection. Using the keypad, enter the frequency to which the transceiver is tuned. You should be able to hear the loop tuning signal at about S9+50dB or more. If not then your ATU is faulty. I am assuming that at one time your setup worked! Let me know how you get on.

Adrian, 5B4AIY

Hi Adrian,

I am having the exact same issue with a new Baby Loop but I am using RG8x instead of 213. My run is about 125' and I do have a splice but the coupler is in pristine shape. I do have a solid run of 8x on order...is it necessary to use 213 for the loops? If so that is what I will use but it is spooky that I am having the exact same issue with it not being able to identify the loop to not being able to tune a large frequency increment. Unfortunately I do not have an analyser so I will just assume that the feedline is bad and replace it.

73 Jim K4ECP Rio Rancho, NM USA