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#1
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Matching transformer comparison?
Anyone have a way of measuring the varying efficiencies of the
following? Let's say 5 to 20 MHz frequency range. This would be the base number for comparison, assign it a one: a: Straight connection of a random long wire antenna The others... b: The same long wire connected through a television (75/300 ohm variety) c: Same antenna with a 9:1 ratio transformer I'm assuming everything else remaining the same. I'm interested in the variation, shown ratio wise, between the above. Are there any handy online calculators for this? mike |
#2
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Matching transformer comparison?
m II wrote:
Anyone have a way of measuring the varying efficiencies of the following? Let's say 5 to 20 MHz frequency range. This would be the base number for comparison, assign it a one: a: Straight connection of a random long wire antenna The others... b: The same long wire connected through a television (75/300 ohm variety) c: Same antenna with a 9:1 ratio transformer I'm assuming everything else remaining the same. I'm interested in the variation, shown ratio wise, between the above. Are there any handy online calculators for this? mike http://amateur-radio-wiki.net/index....le=Calculators |
#3
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Matching transformer comparison?
dave wrote:
http://amateur-radio-wiki.net/index....le=Calculators dammit, dave. If I felt like working at it, I would have gone across the room and picked out a BOOK. Then on to finding the HP41...Why can't we just be spoon fed all the time? It works for all the News I get these days. On a more serious note, this link was in there..thank you. http://www.g8ajn.tv/balun.ht mike |
#4
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Matching transformer comparison?
On Jun 26, 1:16*am, m II wrote:
- Anyone have a way of measuring the varying - efficiencies of the following? - Let's say 5 to 20 MHz frequency range. - - This would be the base number for comparison, assign it a one: - - a: Straight connection of a random long wire antenna OK so this is your starting point "Basic Standard" with an assigned Unit Value of One [1] Therefore this is not about 'efficiency' but Relative Merit. - The others... - - b: The same long wire connected through - a television (75/300 ohm variety) Depends on the relative quality a design of the TV Matching Transformer. Plus the quality of the Coax Cable and a good earthen Ground. 1 - A 'good-one' will reduce some of the apparent noise coming from the basic long wire antenna : So that is a +One-Half [+1/2] 2 - A 'good-one' will reduce some of the AM/MW Band Signals coming from the basic long wire antenna : So that is a +One-Half [+1/2] Relative Merit Unit Value of One + One-Half + One-Half for a Total of Two [2] --- to One - c: Same antenna with a 9:1 ratio transformer First most of the very broadband 9:1 Matching Transformers that are shown for Shortwave Radio Listening (SWL) are also designed to cover the AM/MW/BCB down to 500 kHz and SW Bands up to 30 MHz. These usually recommend about a 10-Turn Primary for the Feed-Line to the Radio and about a 30-Turn Secondary for the Antenna side. Note - That you set a 5 MHz lower 'limit' so you might want to cut the number of turns in half and have a 5 -Turn Primary with a 15 Turn Secondary. A good 9:1 Matching Transformer : 1 Will reduce much of the apparent noise coming from the basic long wire antenna : So that is a +One [+1] 2 - Will reduce much of the AM/MW Band Signals coming from the basic long wire antenna : So that is a +One [+1] Relative Merit Unit Value of One + One + One for a Total of Three [3] --- to One - I'm assuming everything else remaining the same. As am I : Same Long Wire Antenna +plus+ * Same good earthen Ground# # Note - Many SWL'ers only use an in the house Water Pipe Ground with their Long Wire Antenna -so- Going from an in the house Water Pipe Ground to a good outside 8-Ft earthen Ground Rod may be another +One [+1] all by itself for those who make the switch to an outside 8-Ft earthen Ground Rod. * Same Coax Cable# # Note - Many SWL'ers only use an Insulated Wire for their Feed-in-Line from their Long Wire Antenna -so- Going from an Insulated Wire to a Coax Cable may be another +One [+1] all by itself for those who make the switch in the Feed-in-Line. - I'm interested in the variation, shown ratio wise, - between the above. Are there any handy - online calculators for this? Online Calculators will give you Generated Numbers for a given set of parameters; and not Relative Ratios {side-by-side comparisons -aka- Relative Merit} . - - mike iane ~ RHF |
#5
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Matching transformer comparison?
RHF wrote:
- c: Same antenna with a 9:1 ratio transformer First most of the very broadband 9:1 Matching Transformers that are shown for Shortwave Radio Listening (SWL) are also designed to cover the AM/MW/BCB down to 500 kHz and SW Bands up to 30 MHz. These usually recommend about a 10-Turn Primary for the Feed-Line to the Radio and about a 30-Turn Secondary for the Antenna side. Note - That you set a 5 MHz lower 'limit' so you might want to cut the number of turns in half and have a 5 -Turn Primary with a 15 Turn Secondary. Both the examples you give have a three to one ratio. If this is a nine to one example, I must be missing something in your explanation. Please enlighten me. mike |
#6
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Matching transformer comparison?
On 6/27/10 13:07 , m II wrote:
RHF wrote: - c: Same antenna with a 9:1 ratio transformer First most of the very broadband 9:1 Matching Transformers that are shown for Shortwave Radio Listening (SWL) are also designed to cover the AM/MW/BCB down to 500 kHz and SW Bands up to 30 MHz. These usually recommend about a 10-Turn Primary for the Feed-Line to the Radio and about a 30-Turn Secondary for the Antenna side. Note - That you set a 5 MHz lower 'limit' so you might want to cut the number of turns in half and have a 5 -Turn Primary with a 15 Turn Secondary. Both the examples you give have a three to one ratio. If this is a nine to one example, I must be missing something in your explanation. Please enlighten me. The impedance ratio is what matters, here. More or less uniform impedance across the desired spectra produces more or less uniform performance at the radio input. The impedance ratio of a transformer is equal to the square of the turns ratio. A 3:1 turns ratio produces a 9:1 impedance ratio. Now, a transformer's optimum frequency range will depend on a number of factors. The specific material used in the core is one. That's why there are so many different types of core material. The actual number of turns is another. The type of wind is a third. For these reasons, and that the impedance ratio is too narrow for the SW bands, a 75-300 TV transformer is not exactly a good choice for shortwave listening. Although it may produce passable results at some frequencies if there are no other options. mike |
#7
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Matching transformer comparison?
D. Peter Maus wrote:
On 6/27/10 13:07 , m II wrote: RHF wrote: - c: Same antenna with a 9:1 ratio transformer First most of the very broadband 9:1 Matching Transformers that are shown for Shortwave Radio Listening (SWL) are also designed to cover the AM/MW/BCB down to 500 kHz and SW Bands up to 30 MHz. These usually recommend about a 10-Turn Primary for the Feed-Line to the Radio and about a 30-Turn Secondary for the Antenna side. Note - That you set a 5 MHz lower 'limit' so you might want to cut the number of turns in half and have a 5 -Turn Primary with a 15 Turn Secondary. Both the examples you give have a three to one ratio. If this is a nine to one example, I must be missing something in your explanation. Please enlighten me. The impedance ratio is what matters, here. More or less uniform impedance across the desired spectra produces more or less uniform performance at the radio input. The impedance ratio of a transformer is equal to the square of the turns ratio. A 3:1 turns ratio produces a 9:1 impedance ratio. Now, a transformer's optimum frequency range will depend on a number of factors. The specific material used in the core is one. That's why there are so many different types of core material. The actual number of turns is another. The type of wind is a third. For these reasons, and that the impedance ratio is too narrow for the SW bands, a 75-300 TV transformer is not exactly a good choice for shortwave listening. Although it may produce passable results at some frequencies if there are no other options. [...] Good information all around. But it's also important to remember that a random wire will have an impedance which will vary hugely with frequency. (If you get many wavelengths long, the impedance variations with frequency do start to smooth out.) The free demo antenna modeling program called EZNEC will figure the impedance for you, in addition to actually showing you the antenna pattern geometry for almost any wire configuration. A matching transformer can help or hinder signal transfer (which matters surprisingly little on the noisier bands below about 10 MHz), and definitely DC shorts and DC isolates the antenna and radio input. If you really want maximum signal transfer on a wide band of HF frequencies with a random wire, the best way to go would be to add an adjustable antenna coupler to peak things up (in other words, to match impedances), varying the settings for each band of interest. With all good wishes, Kevin, WB4AIO. -- http://kevinalfredstrom.com/ |
#8
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Matching transformer comparison?
On Jun 27, 11:07*am, m II wrote:
RHF wrote: - c: Same antenna with a 9:1 ratio transformer First most of the very broadband 9:1 Matching Transformers that are shown for Shortwave Radio Listening (SWL) are also designed to cover the AM/MW/BCB down to 500 kHz and SW Bands up to 30 MHz. *These usually recommend about a 10-Turn Primary for the Feed-Line to the Radio and about a 30-Turn Secondary for the Antenna side. Note - That you set a 5 MHz lower 'limit' so you might want to cut the number of turns in half and have a 5 -Turn Primary with a 15 Turn Secondary. - Both the examples you give have a three - to one ratio. If this is a nine to one example, - I must be missing something in your explanation. - - Please enlighten me. - - mike Mike [M II], Basically the Ratio is the Square of the Turns -ex- 1x1 = 1 & 3x3 = 9 -so- 10T & 30T = 100:900 ~ 1:9 Many/most Shortwave Listeners(SWL) Matching Transformers use a Ratio of 9:1 for Random {Long Wire} Antennas and for Dipole Antennas a Ratio of 4:1 http://en.wikipedia.org/wiki/Balun Please note that your standard TV Matching Transformer is 300 Ohms to 75 Ohms ~ 4:1 -so- the 300 Ohms side is 4 * The Square Root of 4 is 2 * * the 300 Ohms side would have 2-Turns [2X] -and- the 75 Ohms side is 1 * The Square Root of 1 is 1 * * the 75 Ohms side would have 1-Turns [1X] -note- Usually for VHF&UHF TV Signals not many Turns are required as for the lower HF Radio Signals of 30 MHz and all the way down to 500 kHz in the AM/MW BCB. -fwiw- some SWL'ers will take the very small TV Matching Transformer Ferrite Binocular Cores {Two Holes} and rewind them with very thin Wire to make them into SWL Matching Transformers. http://www.surplussales.com/Inductor...FerMisc-5.html Since these are Ferrite Binocular Cores {Two Holes} they require half the turns as the common One Hole http://www.surplussales.com/Inductor...FerToro-3.html Round Donuts {Toroidal}. http://en.wikipedia.org/wiki/Toroida...d_transformers Some claim to get 5T & 15T on one of these very small TV Matching Transformer Ferrite Binocular Cores going through each of the Two Holes. I however have only been able to get 3~4 & 9~12 in these very small cores. http://www.hard-core-dx.com/nordicdx...eed/feed1.html Making your own Shortwave Listeners(SWL) Matching Transformers : |
#9
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Matching transformer comparison?
RHF wrote:
Thanks to both of you for the 'square of the turns ratio' bit. I have found some old computer mother boards and these things are crawling with ferrite cores suitable for rewinding. Some of them have a trifiliar (weird word) wrap on them which will be coming off. I've pulled them out and will be winding them soon. tertiary mike III |
#10
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Matching transformer comparison?
m II wrote:
trifiliar When I use non existent words like that , I have to pay them extra and make them mean what I want. michael lewis carroll II |
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