Hi, Dan,

I have used an automotive product sold here called Copper-Eze. It is an anti-seize grease that is loaded with very fine copper dust particles. You should be able to find a similar product, it is a grease and has a distinct coppery look to it. You liberally smear this on the bolt threads as well as on the contacting surfaces after they have been wire brushed to be clean and shiny, and the bolt up tight. I also smear this on any outside PL-259 threads, and even in the constant sunshine and harsh conditions here have not had any plugs that have seized.

73, Adrian, 5B4AIY

Dan,

You need a compound that prevents corrosion of the joined surfaces while maintaining conductivity between those surfaces... Jet-Lube SS-30 Pure Copper Anti-Seize from DX Engineering or comparable product should work just fine.

73,

Fred

Great fix finally, congrats. Please make sure that you applied/coated some oxide paste where the solid sheet "steel metal" contact both sides of the loop antenna. Otherwise, it may develop oxidation & conductivity issue due to dissimilar metal composition contacting two different bare metal surfaces.

Dan - KM6VMR

My problem has been resolved. After extensive problem determination of the ATU and capacitor with Ciro support (who is fantastic), I decided to go over the entire antenna assembly - more specifically the bottom of the antenna where the two halves come together.

It was an assembly error on my part. The 'spring steel' connector between the bottom halves was not connected on one side. It was folded under. As soon as I connected it I got an SWR of 1.1 on 80m.

All SWR and tuning problems are resolved.

Hi Adrian,

Been thinking this through and please see the photos below;

Above screen shots are from my antenna analyzer with the antenna in the fully closed position (using manual mode). Before making adjustments, if I knew the low-end calibration point for the actuator motor, I could adjust to achieve that. Moreover, I would like to know the upper end so I can be sure I am meeting that mark as well.

To reiterate, I have no problems with upper bands 20m and 40m. Well, this is not totally true - as the SWR slowly creeps up with each subsequent tuning cycle. I can 'reset' it by fully opening the antenna manually.

Using manual mode, I was able to get a reading for 3.5 KHz. Notice that the antenna is no longer resonant at the low end of 80m.

Using my antenna analyzer and a dummy load at the end of the feed line from the inside of my shack to the antenna, I got 1.0-1.1 SWR for 80m and 40m (3.5KHz to 7.5kHz,) and 1.1-1.2 SWR for 20m (14.5KHz). So I know my antenna wire is good from an SWR standpoint.

As mention, I am using 12g stranded copper wire for the actuator motor to ATU.

I am awaiting an official answer from the support line on what my next steps should be. But am interested in all ideas and information from anyone to help solve this mystery.

Hi Adrian,

This makes perfect sense. I have been thinking that the actuator motor sensors are defective or that as you so perfectly explained, it is attempting to move beyond its limits.

I have have even come up with a plan to adjust the actuator in baby steps as you suggest. There is a “clamp” (steel plate) with 4 screws that secures the actuator motor. The plate appears a little bent as if it’s been over-tightened.

i am on day 2 of a 6 day-on stretch at work (12 hour shifts in an ER as an RN) and then will be visiting my sister out of state for a few days - so I will not be able to try this until after the 9th Of January.

When I am able to make the adjustment I will report back. In the meantime if you have any additional information or suggestions, please let me know.

Thanks!

73,

Fred

Hi, whilst I do not have a MIDI antenna, there are some commonalities with respect to the controller and the BABY loop. The MOTOR FAIL error message indicates that there is no current being drawn by the motor. It is significant in your case that you have to use the manual mode and drive the antenna out of the error. The actuator is equipped with two limit switches that prevent the motor stalling if you attempt to drive it too far in either direction. These switches are normally closed, but if you drive the actuator to its electrical inner or outer limit, then the appropriate switch opens placing a diode in circuit which will be reverse biased. By reversing the polarity of the drive voltage you can drive it out of the limit. From your description it sounds as if you are driving the antenna into its inner limit at frequencies below 4MHz. This suggests that you need to alter the position of the actuator to allow the antenna to close without reaching the inner electrical limit. In the case of the BABY loop, this is governed by the position of the clamp on the motor casing, I do not know how the actuator of the MIDI loop is mounted. Have a close look and see if there is any adjustment as there should be to take account of manufacturing tolerances. Bear in mind that quite a small change of position will change the resonant frequency by quite a lot, so only make small movements. Having replaced the actuator twice now for my loop my preferred method is to drive the motor on the bench to its inner electrical limit and then mount it on the loop and carefully adjust the position of the clamp until the antenna is resonant below its nominal lower frequency limit. In my case the lower limit is 6,600kHz, so I set the lower electrical limit to 6,550kHz to ensure that the antenna trips the electrical limit before hitting a hard mechanical limit so that the motor cannot stall. The SWR problem is another matter. The gamma match adjustments are solely to achieve a good match at resonance. Since the loop is electrically very short in comparison to a wavelength, at resonance the loop is simply a parallel tuned circuit, and is resistive. At the capacitor the voltage and current relationships are such that this is very high impedance point, whereas diametrically opposite there is a neutral point. As you move around the circumference of the loop from the neutral point the voltage/current relationship alters, and at some point it will have a ratio that is equal to 50 ohms, and this is what the gamma match does. The User Manual contains some information on making this adjustment, but before cutting metal I would examine the SWR across the entire frequency range first. As long as it is less than about 1.8:1 then leave it alone. Most amplifiers and transceivers can easily operate with SWRs up to about 2:1. Only if the SWR is above about 2:1 across the entire frequency range would I consider adjusting the gamma match. In summary, you should attend to the MOTOR FAIL error before attempting any matching adjustments, and that looks as if you need to adjust the position of the actuator to ensure that the inner electrical limit switch operates when the antenna position is such as to give a resonant frequency slightly lower than the lower nominal frequency limit.

73, Adrian, 5B4AIY