12639	2016-04-10 15:20:55	Lasse Moell	Ferrite properties
Message	Date	From	Subject
I have to ask the group for some help! My understanding of ferrite behavour is far too shallow. Is it possible to have non-reversible change the properties of ferrite due to too much power (voltage?) and becoming more non-linear? It seems my antenna balun (HyGain BN86) is generating a very harmonic rich signal, as noted by the nearby military airbase. Measuring the transmitter output shows a very clean signal into a dummy load, and it becomes very dirty once I have the antenna attached. Cheers Lasse SM5GLC
12640	2016-04-10 16:03:30	Chris Trask	Re: Ferrite properties
You can permanently damage ferrites if the temperature exceeds the Curie point. What happens is dependent on the material and the thermal stress. > >I have to ask the group for some help! >My understanding of ferrite behavour is far too shallow. > >Is it possible to have non-reversible change the properties of ferrite due >to too much power (voltage?) and becoming more non-linear? > >It seems my antenna balun (HyGain BN86) is generating a very harmonic rich >signal, as noted by the nearby military airbase. Measuring the transmitter >output shows a very clean signal into a dummy load, and it becomes very >dirty once I have the antenna attached. > Chris When the going gets weird, the weird turn pro - Hunter S. Thompson
12641	2016-04-10 16:22:57	Andy	Re: Ferrite properties
Another source of harmonic generation is a marginal electrical contact, making a point-contact diode. It's said that it can even be physically separate from one's antenna and feedline (such as a chain-link fence nearby). It can take very little harmonic radiation to be heard by someone who is listening. Do you know by measurements that your harmonic content actually increases, or is this a subjective observation? Andy
12642	2016-04-10 19:38:52	Graham / KE9H	Re: Ferrite properties
You can drive ferrite into a non-linear state, which will cause it to generate harmonics, if you are exceeding the rated maximum flux in the core. It will typically get hot while doing this. If it gets too hot, things go downhill fast. (see Curie Temperature) Flux density inside the core is proportional to Ampere-Turns divided by the cross section of the core. It can be too much power, creating too many Amperes, or a bad design, that used too many turns for the design, or not having enough ferrite to spread the flux out. Or running a design at a lower impedance than intended, without lowering the power to compensate for the increased current. The solution is normally to use a (much) bigger core, and check that you don't have any significant heating. It could be permanent heat damage to the core, or magnetization of the core, or most likely, you just have a bad design or mis-application. Use a bigger core, and use a design by someone that understands how to design and apply ferrites. --- Graham / KE9H ==
12643	2016-04-10 20:17:23	Russell Shaw	Re: Ferrite properties

12644	2016-04-10 20:31:12	Russell Shaw	Re: Ferrite properties

12645	2016-04-11 01:03:22	Lasse Moell	Re: Ferrite properties
Thank You for all information guys! I have tried to measure, but it is somewhat difficult as the antenna is some 10 meters away and I cannot hook up to a measurement system. I had to revert to use a simple VHF antenna and look at the levels in my shack. I do see up to -40 dBm at 126 MHz which is a bit too much for my likeing. The balun (commercial HyGain BN86) will be replaced with large choke and then compared to levels previously seen. I will investigate this further... /Lasse SM5GLC 11 april 2016 01:22:16 +02:00, skrev Andy ai.egrps@gmail.com [emrfd] : Another source of harmonic generation is a marginal electrical contact, making a point-contact diode. It's said that it can even be physically separate from one's antenna and feedline (such as a chain-link fence nearby). It can take very little harmonic radiation to be heard by someone who is listening. Do you know by measurements that your harmonic content actually increases, or is this a subjective observation? Andy
12646	2016-04-11 08:48:21	w3lpl2000	Re: Ferrite properties
Lasse, While your HyGain BN86 is one possible source of harmonic generation, there are many other possibilities. You could temporarily remove the balun to determine if its the culprit. My friend had severe TVI that suddenly appeared in his neighborhood after several years of no TVI at all. The problem turned out to be a neighbor who installed a preamp on his television antenna. The overloaded preamp radiated strong harmonics throughout the neighborhood. Another friend has similar harmonic generation problems that were isolated to corroded joints in his greenhouse close to his antennas. 73 Frank W3LPL
12664	2016-04-18 16:27:37	Lasse Moell	Re: Ferrite properties
So far no luck... I have removed the balun and its ferrite, and the spurious signal is still there. Have spent the evening running around with a portable spectrumanalyzer, lap-top and a directional antenna (i.e. R&S HE200). Now if I at a distance measure a level of the harmonic, I see -85 dBm and then replace the transmitter/LPF with a signal generator attached to the HF antenna, I have to set its level to -20 dBm to read the same -85 dBm. I thought it should be a walk in the park to pin-point the source. It seems to come from my house/antenna.... but as soon as I get close I can wave the antenna and get all sorts of readings. At one time I thought it may be my TV antenna... as the level I see with DF antenna pointing to the TV was clearly high. But no change when I removed the TV coax. All wires in my house seems to have the energy, mains phone etc... I'm running out of ideas... /Lasse SM5GLC 11 april 2016 10:03:18 +02:00, skrev 'Lasse Moell' lasse.moell@webdog.se [emrfd] <emrfd@yahoogroups.com>: Thank You for all information guys! I have tried to measure, but it is somewhat difficult as the antenna is some 10 meters away and I cannot hook up to a measurement system. I had to revert to use a simple VHF antenna and look at the levels in my shack. I do see up to -40 dBm at 126 MHz which is a bit too much for my likeing. The balun (commercial HyGain BN86) will be replaced with large choke and then compared to levels previously seen. I will investigate this further... /Lasse SM5GLC 11 april 2016 01:22:16 +02:00, skrev Andy ai.egrps@gmail.com [emrfd] : Another source of harmonic generation is a marginal electrical contact, making a point-contact diode. It's said that it can even be physically separate from one's antenna and feedline (such as a chain-link fence nearby). It can take very little harmonic radiation to be heard by someone who is listening. Do you know by measurements that your harmonic content actually increases, or is this a subjective observation? Andy
12667	2016-04-18 22:05:36	Andy	Re: Ferrite properties
Does it correlate with your transmitter transmitting? It's not there all the time, is it? Maybe the RF is getting into the power lines and rectifying there. Another experiment to consider is to shut off all power in the house, and use the portable signal generator. It would likely rule out any active device in the house being responsible for the harmonic. Andy
12668	2016-04-18 23:14:35	Lasse Moell	Re: Ferrite properties
The level do correspond to transmitter output, but not linear. And it should not be dB for dB when non-linear. When trying to find the source, it is more like distributed PIM (passive IM) and both mains and phone line carries the signal. But I still have to find where the nonlinearity is created. I need 10-20 watt o/p to generate a strong enough IM to detect. See if I can find some time today... Cheers Lasse SM5GLC 19 april 2016 07:04:56 +02:00, skrev Andy ai.egrps@gmail.com [emrfd] : Does it correlate with your transmitter transmitting? It's not there all the time, is it? Maybe the RF is getting into the power lines and rectifying there. Another experiment to consider is to shut off all power in the house, and use the portable signal generator. It would likely rule out any active device in the house being responsible for the harmonic. Andy
12672	2016-04-19 07:17:38	Rod KM6SN	Re: Ferrite properties
Lasse, There is a directive antenna that is ideal for your application. It is called a Villard Cage. I have used such an antenna to locate the source of power line noises; it is so accurate that it is possible to identify which cross-arm on a power pole is causing the noise. It is so accurate that it is possible to determine which side of the cross-arm has the problem. I have uploaded a picture of one such example along with construction notes to the EMRFD files section. Please pardon the poor quality picture- the best I could get under the circumstances. Please let me know if I need to supply additional information. Rod KM6SN The construction of a Villard Cage is: 1. Make a short dipole
12673	2016-04-19 07:18:05	Clark Martin	Re: Ferrite properties
Start by turning off all circuit breakers (or pull the fuses). If the signal goes away, start turning the breakers back on one by one. Clark Martin KK6ISP Yet another designated driver on the information super highway. >
12674	2016-04-19 08:21:02	Graham / KE9H	Re: Ferrite properties
Do you have a lightening arrestor in series with your coax? If so, remove it, temporarily, and repeat the test. --- Graham / KE9H ==
12675	2016-04-19 13:40:20	Lasse Moell	Re: Ferrite properties
Rod, interesting stuff... Apparenlty Mike Villard W6YX designed this for OTH stuff... but very little to be found, at least when I tried to search for it! How about making a simple drawing? Are the ends of the dipole joined to the cage? Any "magic" size for the cage that circumvent the dipole? And finally, feeding, does it differ in impedance from a "normal" dipole? Cheers Lasse SM5GLC 19 april 2016 04:14:59 +02:00, skrev Rod KM6SN rod.km6sn@wildblue.net [emrfd] : Lasse, There is a directive antenna that is ideal for your application. It is called a Villard Cage. I have used such an antenna to locate the source of power line noises; it is so accurate that it is possible to identify which cross-arm on a power pole is causing the noise. It is so accurate that it is possible to determine which side of the cross-arm has the problem. I have uploaded a picture of one such example along with construction notes to the EMRFD files section. Please pardon the poor quality picture- the best I could get under the circumstances. Please let me know if I need to supply additional information. Rod KM6SN The construction of a Villard Cage is: 1. Make a short dipole
12676	2016-04-19 13:45:55	Lasse Moell	Re: Ferrite properties
No, just straight coax to the antenna. The more I try to locate the radiating component, the more confused I become. Tonight, highest readings were close to chimney, where an old steel pipe runs from the cellar up to roof. Way to big to be in resonace, but maybe along with a suitable mast secured to the chimeny, and the aluminium sheets round the chimney. Never expected PIM (passive intermodulation) to this hard to locate! /Lasse SM5GLC 19 april 2016 17:21:00 +02:00, skrev 'Graham / KE9H' ke9h.graham@gmail.com [emrfd] : Do you have a lightening arrestor in series with your coax? If so, remove it, temporarily, and repeat the test. --- Graham / KE9H ==
12677	2016-04-19 14:02:22	Jim Strohm	Re: Ferrite properties
Hi Rod Can you add some details about using the Villard cage? It looks simple enough -- a VHF AM receiver with a dipole attached to the receiver, floating inside the cage and insulated from it. The cage itself resembles one arm of a cage dipole. How do you hold and point it? Do you put it on a stick, or do you hold it in your hands? I'm guessing that you use the amplitude of the received signal to tell you that you've got a bead on your culprit. Thanks and 73 for any additional info you can share. Jim N6OTQ
12678	2016-04-19 14:03:05	Rod KM6SN	VHF direction finding
Lasse, There is a directive antenna that is ideal for your application. It is called a Villard Cage. It can be used to very accurately locate the source of a VHF signal, including close-in signal locating. The antenna has very deep and narrow bidirectional nulls off the ends. To preserve the sharp pattern it is necessary to have the signal strength indicator inside the Cage. I have uploaded a picture of one such example along with construction notes to the EMRFD files section. In that writeup I said that any receiver can be used; however, it must be a receiver that can indicate signal strength. An FM receiver would not work very well. A simple VHF AM receiver is suitable, as the changes in amplitude are extreme, and can easily be recognized by listening to the audio out. Regards, Rod KM6SN
12679	2016-04-19 15:09:43	Rod	Re: Ferrite properties
Lasse, Yes, Mike Villard came up with the design. I found it in some obscure document over 30 years ago. The CAGE wires are all bonded together at the ends. The dipole is suspended in the axial center of the cage, and the dipole does NOT connect to the cage ends. My CAGE is 48 inches (122 cm)long, and that length was arbitrarily selected. The dipole in my CAGE is about 45 inches (114cm) long. It is made of insulated #22 hookup wire, and where the two dipole halves come together in the center I just twisted the two wires together to make a twisted-pair line, mostly to apply tension to the dipole. . The twisted wire section is about 4 inches (10.2 cm) long, and it is soldered to an RCA phono socket. Perhaps in overkill, I used nylon monofilament fishing line to tie the tightly-looped ends of the dipole to the corresponding ends of the CAGE. I opened up the Radio Shack VHF Aircraft receiver, disconnected the whip connections, and soldered in a section of RG174 coax about 12 inches (30.5 cm) long. Arbitrarily, I made a 3 turn balun in the RG174 coax, by coiling three turns in about a 2cm diameter. Then I soldered an RCA phono plug onto the RG174, and plugged it in to the RCA socket which is attached to the twisted-pair line from the dipole. Thee Radio Shack VHF receiver is physically suspended COMPLETELY INSIDE the cage close to the dipole feedpoint. I emphasize NO attempt was made to do any impedance matching, and NO attempt was made to select the dipole length to be resonant at a specific frequency. It is probably resonant somewhere in the VHF aircraft voice band. This is simply a sense antenna, and it is not selected for performance, just convenience. The magic happens because of the Villard CAGE shielding. I hope this description serves in lieu of a drawing. Let me know if I need to supply additional detail. Good Luck, and Cheers, Rod KM6SN
12680	2016-04-19 15:10:33	Rod	Villard Cage usage
Hi Jim, In a previous post I added more detail about the Villard Cage construction. To use the apparatus, just grab the CAGE in about the center, and aim the end of the CAGE towards the suspected area. I held the CAGE close to my head, with the ends pointed straight "forward" and "backward", so I could hear the audio out from the receiver. I turned my whole body to get azimuth rotation. I simply tilted the CAGE to get elevation rotation. It is a fun widget to use, and extremely effective for direction finding. Remember, you are looking for a NULL, and the NULL will be profound and angularly narrow. Rotate in AZ and EL slowly, or you can miss the target completely. Good Luck, and Cheers, Rod KM6SN
12681	2016-04-19 23:36:27	Lasse Moell	Re: Ferrite properties
Rod, thanks for the explanation. Looks very interesting and doable... only thing that may be a bit tricky is to have the receiver inside the cage... Right now I am using a small spectrum analyzer and a PC to view and analyze the spur signal. I may try the cage and cheat trying to extract a feeder from the cage, even at a reduced performance. Still very interesting device and a perfect week-end project! Cheers Lasse SM5GLC 19 april 2016 23:27:28 +02:00, skrev Rod rod.km6sn@wildblue.net [emrfd] : Lasse, Yes, Mike Villard came up with the design. I found it in some obscure document over 30 years ago. The CAGE wires are all bonded together at the ends. The dipole is suspended in the axial center of the cage, and the dipole does NOT connect to the cage ends. My CAGE is 48 inches (122 cm)long, and that length was arbitrarily selected. The dipole in my CAGE is about 45 inches (114cm) long. It is made of insulated #22 hookup wire, and where the two dipole halves come together in the center I just twisted the two wires together to make a twisted-pair line, mostly to apply tension to the dipole. . The twisted wire section is about 4 inches (10.2 cm) long, and it is soldered to an RCA phono socket. Perhaps in overkill, I used nylon monofilament fishing line to tie the tightly-looped ends of the dipole to the corresponding ends of the CAGE. I opened up the Radio Shack VHF Aircraft receiver, disconnected the whip connections, and soldered in a section of RG174 coax about 12 inches (30.5 cm) long. Arbitrarily, I made a 3 turn balun in the RG174 coax, by coiling three turns in about a 2cm diameter. Then I soldered an RCA phono plug onto the RG174, and plugged it in to the RCA socket which is attached to the twisted-pair line from the dipole. Thee Radio Shack VHF receiver is physically suspended COMPLETELY INSIDE the cage close to the dipole feedpoint. I emphasize NO attempt was made to do any impedance matching, and NO attempt was made to select the dipole length to be resonant at a specific frequency. It is probably resonant somewhere in the VHF aircraft voice band. This is simply a sense antenna, and it is not selected for performance, just convenience. The magic happens because of the Villard CAGE shielding. I hope this description serves in lieu of a drawing. Let me know if I need to supply additional detail. Good Luck, and Cheers, Rod KM6SN
12684	2016-04-20 06:55:54	Rod KM6SN	Re: Ferrite/Villard Cage
Lasse, You are welcome. I love sharing tools and techniques. You just might be able to get away with bringing the feeder out of the cage on twisted pair, with a very effective common-mode choke (broad-band balun)where it exits the cage. A better choice might be a broadband RF transformer at the cage exit point, and use twisted pair (or some form of balanced line) from the transformer to the specan, with a common-mode choke balun at the specan. Not sure what to recommend for the choke balun. The VHF receiver can be a simple SSB receiver. Any form of amplitude detector will do. Because the nulls are so deep, it is easy to 'measure' them solely by listening to the RX audio. If you are using a PC to view the signal, the PC is probably emitting tons of RF at VHF also, be aware. Is the specan USB powered? Could the PC/specan combination be emitting RF that is creating erroneous measurements? Cheers, Rod KM6SN
12687	2016-04-20 08:31:56	winston376	Re: Ferrite properties
Rod, Very interesting info. Wondering whether this is used to track down broadband noise as opposed to a narrowband emitter? Thanks for sharing. Alex
12692	2016-04-21 08:52:00	Rod KM6SN	Re: Ferrite properties
Alex, You are welcome. I have used it to track down power line noise, which is broadband in nature because it is comprised of a low frequency fundamental rich in harmonics, with harmonics up into VHF. I simply picked a VHF harmonic, and located its source. It is easier to locate power line noise at VHF than LF. Rod KM6SN
12696	2016-04-22 09:01:43	winston376	Re: Ferrite properties
Rod, Understand now the VHF RX part of the method. At my location, 20 M suddenly (last 2 months) got wiped out with broadband as well as narrowband emitters to the southwest of me. On 20 M, I've DF'd the source(s) to utility poles carrying low, high tension powerlines as well as broadband cable service. Your recommendations come at an opportune time...thanks again. Alex