Re: Topband: RX antenna transformer winding
I have used plastic coffee stirrers from the fast food joints; they start out smaller and they cost the same... ;-) 73, geo - n4ua On Wed, Aug 21, 2013 at 11:48 AM, n0...@juno.com wrote: From recent postings: I started using Teflon sleeves in windings because I ran out of small Teflon wire wrap wire I was using. Without Teflon on the wires, and with normal mag wire, the enamel was easily scratched. Not only that, lightning would punch through from enamel to core, or from wire to wire. ** Telon is easily nicked, the type of wire used in modern vehicles is very robust but with the sleeves plain ole magnet wire works well and allows even smaller winding bundles. RE: binocular cores and sleeving I didn't have the right size of Teflon sleeves in my junque drawer, so I cut appropriate lengths of used soda straws from McD's, slit them lengthwise, then cut off the excess (lengthwise). Then I curled the cut straw sections and pushed them through the cores. The result is a near perfect fit with a slight overlap at the lengthwise cuts. The overlaps can be oriented toward the outside of the core so the wire won't have a tendancy to open up the overlap. 73, Charlie, N0TT _ Topband Reflector _ Topband Reflector
Re: Topband: RX antenna transformer winding
I've been using Radio Shack 30 AWG insulated wire (wire wrap wire) to wind my binocular cores for RX antennas. It comes in 50 foot spools, and you can buy it in Blue, Red, or White. This insulated wire has made winding of my binocular cores a real pleasure. No more worries about scratching the enamel coating on the magnet wire that used to drive me nuts, and no more messing around removing the enamel coating on the ends (I just use normal cheap wire strippers to remove the insulation on the ends of the wires for connection purposes). Have never had problems using this wire without the use of plastic/teflon sleeves (but I was also not attempting to keep the primary and secondary turns separate (using sleeves) for purposes of reduced capacitance between the windings in my applications) Here are the Radio Shack part numbers for the wire I use : Red : 278-501 White : 278-502 Blue : 278-503 Cost is $5.49 per spool. 73, Don On Wed, Aug 21, 2013 at 12:46 PM, George Dubovsky n4ua...@gmail.com wrote: I have used plastic coffee stirrers from the fast food joints; they start out smaller and they cost the same... ;-) 73, geo - n4ua On Wed, Aug 21, 2013 at 11:48 AM, n0...@juno.com wrote: From recent postings: I started using Teflon sleeves in windings because I ran out of small Teflon wire wrap wire I was using. Without Teflon on the wires, and with normal mag wire, the enamel was easily scratched. Not only that, lightning would punch through from enamel to core, or from wire to wire. ** Telon is easily nicked, the type of wire used in modern vehicles is very robust but with the sleeves plain ole magnet wire works well and allows even smaller winding bundles. RE: binocular cores and sleeving I didn't have the right size of Teflon sleeves in my junque drawer, so I cut appropriate lengths of used soda straws from McD's, slit them lengthwise, then cut off the excess (lengthwise). Then I curled the cut straw sections and pushed them through the cores. The result is a near perfect fit with a slight overlap at the lengthwise cuts. The overlaps can be oriented toward the outside of the core so the wire won't have a tendancy to open up the overlap. 73, Charlie, N0TT _ Topband Reflector _ Topband Reflector _ Topband Reflector
Re: Topband: RX antenna transformer winding
I've also had very good results using wire-wrap wire for winding small RF transformers. Pretty easy to work with - and it's rugged. Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of mstang...@comcast.net Sent: Wednesday, August 21, 2013 2:01 PM To: topband@contesting.com Subject: Re: Topband: RX antenna transformer winding I use wire wrap wire when winding small cores. The Kynar insulation is tough and resists nicking. http://www.jameco.com/webapp/wcs/stores/servlet/StoreCatalogDrillDownView?l angId=-1storeId=10001catalogId=10001search_type=jamecoallfreeText=wire+w rap+wire OT: Wire wrapping was very popular in the 60's and the 70's before the advent of multilayer printed circuit boards. It was very reliable. The backplane of the Apollo Guidance Compluter was connected via wire wrap. You can see an example at the Infor Age Museum in Wall, NJ. http://w2dtc.com/2011-0522-infoage/2011-0522-0061.jpg Mike N2MS _ Topband Reflector _ Topband Reflector
Re: Topband: RX antenna transformer winding (pure resistance transformation issues)
I had additional offline conversations with Rick (N6RK), and Carl (KM1H), and below is my official response to my original post about RX antenna transformer windings and complex impedance measured on the primary side of the transformer depending on how they are wound. Rick N6RK said The way out of this dilemma is to use a smaller toroid core than the 1.14 inch diameter core you currently have. But I saw the complex impedance phenomena even with smaller diameter cores (using different grade of material), and here is my actual FT 50-43 data as an example. FT50-43 measured data as follows (windings on opposite side of the core from each other) : Pri = 5 T, Sec = 20 T, 1K load resistor R= 42, X = 25, 1.8 Mhz, Capacitance = 5 pf R= 51, X = 24, 3.5 Mhz R= 57, X = 32, 7 Mhz When I used two FT50-43 cores configured to make a binocular core, I obtained the following results : Pri = 3 T, Sec = 12 T, 1K load resistor R= 38, X = 21, 1.8 Mhz R= 50, X = 1, 3.5 Mhz R= 52, X = 0, 7 Mhz Rick also said : the small amount of leakage inductance you are seeing even with the large core with separated windings is nothing to worry about. I agree with this unless you are trying to phase RX antennas, and then the complex impedance becomes a critical factor to deal with, and that's why I feel it's important to understand (know) that this phenomena exists. Rick also said : I would rather tolerate that and get the benefit of the reduced capacitance from winding to winding. Appears everyone agrees that a very low capacitance between windings (between primary and secondary winding) is near (if not at the very the top) of the list of desired properties of the RX antenna transformer. This is also supported by statements in the ON4UN Low-Band DXing book. Carl (KM1H) goes to great lengths to reduce the capacitance between windings on the binocular cores that he uses on his RX antennas per his following statement : Teflon tubes for each winding and that brought the C way down by compressing each winding in the smallest tube that I could get the wires thru and then forcing a toothpick thru to force the most separation. Thanks to Rick and Carl for the technical discussions we had. 73, Don Kirk (wd8dsb) _ Topband Reflector
Re: Topband: RX antenna transformer winding (pure resistancetransformation issues)
Unless you have a system with pretty high common mode impedances, winding spacing means nothing. ** Contrary to what you have stated elsewhere Where? Please quote it in enough context to see the meaning. I'll certainly clairfy it or correct it if possible, because I don't want to mislead anyone. _ Topband Reflector
Re: Topband: RX antenna transformer winding (pure resistance transformation issues)
On 8/20/2013 1:00 PM, Tom W8JI wrote: By squeezing or spreading turns to change mutual coupling between turns, a T157-2 core can have almost 2:1 impedance shift! That tells us it has considerable flux leakage. So-called self-shielding and it's inverse, leakage flux, also depend on permeability, which in turn depends on the material and the frequency of interest. Fair-Rite data sheets for their materials clearly show the variation of permeability with frequency. And when we squeeze or spread turns we are also changing stray C of the winding. 73, Jim K9YC _ Topband Reflector
Re: Topband: RX antenna transformer winding (pure resistancetransformation issues)
- Original Message - From: Tom W8JI w...@w8ji.com To: topband topband@contesting.com Sent: Tuesday, August 20, 2013 4:00 PM Subject: Re: Topband: RX antenna transformer winding (pure resistancetransformation issues) SNIP Unless you have a system with pretty high common mode impedances, winding spacing means nothing. ** Contrary to what you have stated elsewhere The primary reason I (and DXE) isolate windings with Teflon tubes is to reduce lighting damage, and to greatly reduce assembly damage. If the system has pretty high common mode impedances there might be some small advantage in pushing windings apart, but the primary-secondary capacitance is never going to be important in Beverages or other low or modest common mode impedance antennas. Balancing a small loop might be an issue. ** Common mode is an overworked response for perceived ailments. I took your low capacitance suggestions a step further after carefully measuring C and frequency response for maintaining high directivity and F/B. Many Topband operators use their Beverages above 2 MHz. I started using Teflon sleeves in windings because I ran out of small Teflon wire wrap wire I was using. Without Teflon on the wires, and with normal mag wire, the enamel was easily scratched. Not only that, lightning would punch through from enamel to core, or from wire to wire. ** Telon is easily nicked, the type of wire used in modern vehicles is very robust but with the sleeves plain ole magnet wire works well and allows even smaller winding bundles. Since I was more interested in performance rather than production problems I took the time to evaluate a large number of variations. Carl KM1H _ Topband Reflector
Topband: RX antenna transformer winding (pure resistance transformation issues)
Digging back through the archives I found lots of discussion about the best transformer to use with flags, pennants and beverages. The discussions included material type, and style (toroid vs. binocular), but I found no mention about problems regarding the use of conventional toroid cores in which a pure resistive load on the secondary appears to be a complex impedance (resistance and inductance) on the primary side of the transformer when having the primary turns on one side of the core and the secondary turns on the opposite side of the core (which appears to be the recommended method of winding if using toroid cores for this purpose). I then noticed that the only recommended transformer configuration I measured that would provide a pure resistance on the primary when having a pure resistive load on the secondary was the transformer constructed with a binocular core as recommended by W8JI and others, and creating a binocular core using two side by side toroid cores also worked fine in my testing. I then decided to try spreading my secondary winding (20 turns) on the toroid core over approximately 330 degrees of the toroid core (FT 114-77), and then overlay my primary winding (5 turns) on top of the secondary and again spread it over the 330 degrees of the toroid core. Doing this fixed my transformation problem (now my primary was just resistive when the secondary had a pure resistive load. Here is some data to help explain the issue (the R and X values is the impedance measured on the primary side of the transformer with the 1 K resistance connected to the secondary of the transformer). FT114-77, Pri = 5 T, Sec = 20 T, primary and secondary separated (opposite sides of the core), 1K resistive load on secondary. R = 57 ohms, X = 18 ohms, Freq = 1.8 Mhz R = 58 ohms, X = 34 ohms, Freq = 3.5 Mhz FT114-77, Pri = 5 T, Sec = 20 T, primary and secondary over lay (using 330 degrees of the core), 1K resistive load on secondary. R = 56 ohms, X = 0 ohms, Freq = 1.8 Mhz, insertion loss = -0.54 dB R = 53 ohms, X = 0 ohms, Freq = 3.5 Mhz Note : measured capacitance primary to secondary = 5 pf, capacitance not measured at RF BN-73-202, Pri = 3 T, Sec = 12 T, 1K resistive load on secondary. R = 59 ohms, X = 0 ohms, Freq = 1.8 Mhz, insertion loss = -0.30 dB R = 57 ohms, X = 0 ohms, Freq = 3.5 Mhz Note : measured capacitance primary to secondary = 9 pf, capacitance not measured at RF Has anyone else stumbled upon the above phenomena, and am curious why there has been no mention of it before (or if there has been it's very hard to find)? I'm very happy with the performance of my binocular core transformers, but I'm technically inquisitive. 73, Don Kirk (wd8dsb) _ Topband Reflector
Re: Topband: RX antenna transformer winding (pure resistance transformation issues)
On 8/16/2013 8:06 AM, Don Kirk wrote: discussions included material type, and style (toroid vs. binocular), but I found no mention about problems regarding the use of conventional toroid cores in which a pure resistive load on the secondary appears to be a complex impedance (resistance and inductance) on the primary side of the The way out of this dilemma is to use a smaller toroid core than the 1.14 inch diameter core you currently have. This is a RECEIVING antenna after all. What you are seeing is leakage inductance. The leakage inductance should scale linearly with core diameter. The capacitance should also scale. Having said that, the small amount of leakage inductance you are seeing even with the large core with separated windings is nothing to worry about. I would rather tolerate that and get the benefit of the reduced capacitance from winding to winding. Rick N6RK _ Topband Reflector
