8778	2013-07-04 19:06:29	101	Inductive reactance of a Current Balun?
Message	Date	From	Subject
Hi, Current Balun:- the inductive reactance of the windings prevents common mode currents from flowing and ensures a balanced output. What should be the inductive reactance of a Current Balun (for HF frequency range)? Some authors say it should be 10 times the load impedance at the lowest frequency of operation, some say it should be four times, while Andy Griffith (W4ULD) says it must be twice the highest ohmic value of the load expected. Regards, Amin
8779	2013-07-04 19:46:45	Jim Miller	Re: Inductive reactance of a Current Balun?
http://audiosystemsgroup.com/RFI-Ham.pdf also: http://fermi.la.asu.edu/w9cf/articles/balun.pdf take time to read bios of both authors. 73 jim ab3cv
8787	2013-07-05 22:50:25	101	Re: Inductive reactance of a Current Balun?
Hi Jim, Thank very much for your advice & links. Last night, I made a current balun with inductive reactance of 1k ohms at the lowest intended frequency (1.87 Mhz). For receiving only, I use BN-43-3312 binocular core with Al of 5,400 with 4 round of winding through. I get 85uH ( i.e. 1,000 ohms @ 1.87 Mhz and 3,743 ohms @ 7.01 Mhz - by calculation). Bravo, I have a very very quite antenna. When I tune to a SW broadcasting station, splendid! Hardly hear any background noise/interference. When I tune to a 40m band SSB station, also hardly hear any background noise/interference but signal strength drops about 3-4 scale of S-meter! Is it normal or something wrong with my balun? Please advise! Regards, Amin
8788	2013-07-06 06:20:22	Jim Miller	Re: Inductive reactance of a Current Balun?
Please describe your antenna and feedline all the way to your receiver so that I can understand your situation better. jim ab3cv
8789	2013-07-06 15:57:35	101	Re: Inductive reactance of a Current Balun?
Hi Jim, I use a loop antenna with about 20 meter (60 feet) length. Shape is irregular rectangle, while plane is irregular horizontal & vertical. I hang the antenna
8790	2013-07-06 16:14:49	Jim Miller	Re: Inductive reactance of a Current Balun?
What is the feedline that you used and how did you construct the current mode choke? jim ab3cv
8791	2013-07-06 16:57:24	101	Re: Inductive reactance of a Current Balun?
Hi Jim, The feedline is RG-58A (I think) and the choke is actually the 1:1 current balun built with very high inductive capacitance:- For receiving only, I use BN-43-3312 binocular core with Al of 5,400 with 4 round of winding through. I get 85uH ( i.e. 1,000 ohms @ 1.87 Mhz and 3,743 ohms @ 7.01 Mhz - by calculation). Regards, Amin
8792	2013-07-06 17:51:49	Jim Miller	Re: Inductive reactance of a Current Balun?
Of course there's no sure way of knowing what is causing your symptoms but it is possible that your previous choke wasn't as effective and was allowing your feedline to act as an extension of your antenna. There's also the possibility that your current choke though inductively reactive is resonating with the capacitive reactance of the feedline forming a low impedance and unwanted path on the outside of the coax. Jim Brown recommends making the choke out of materials which ensure a high resistance as well as reactance to minimize the current flowing on the outside of the coax. To do that he recommends more like 5K impedance and with equal parts reactance and resistance. If you have the materials I'd recommend trying to make the choke higher impedance in reactance and loss to see if the effect changes. good luck jim ab3cv
8793	2013-07-06 20:17:42	101	Re: Inductive reactance of a Current Balun?
Hi Jim, Thanks for your recommendation. What I'll do is to cascade the 1:1 current balun to double the impedance but I'm afraid of wanted signal being attenuated as well. Regards, Amin
8796	2013-07-08 19:49:44	Andy	Re: Inductive reactance of a Current Balun?
If it's a well made current balun, desired signal picked up by the loop antenna shouldn't be attenuated at all. Andy
8797	2013-07-08 21:04:56	101	Re: Inductive reactance of a Current Balun?
Hi Andy, I agree with you too. I've built many current baluns (with low inductive capacitance), the result certifies it. But when I incorporate the choke capability (with high inductive capacitance), I face the problem. What I must investigate further is "what is the relationship between high impedance (due to high inductive reactance) and signal loss (at various frequencies)" i.e. not the current balun characteristic per se but it's choke characteristic. Andy, it would be very much appreciated if you could advise me the websites or articles that I can proceed further
8798	2013-07-09 07:06:28	Ed Manuel	Re: Inductive reactance of a Current Balun?
Amin, If you have not read it already, search for article: Common-Mode Chokes by Chuck Counselman, W1HIS One of the "bibles" IMHO Ed, N5EM _____
8799	2013-07-09 07:35:20	101	Re: Inductive reactance of a Current Balun?
Hi Ed, I've got it and in fact I've built many of Fig.#1 (or Fig.#4 Page 21) & have been using with my main antenna with great success. Now I try to modify it in the form of balun as Fig.#6 (Page 31) and my version is 85 uH using binocular coil (for receiving only). But still not yet be successful - everything is attenuated including the wanted signal! That's why I come to the club for help. Regards, Amin
8800	2013-07-09 21:02:49	Andy	Re: Inductive reactance of a Current Balun?
What kind of line (or wires) did you use for this new balun? Andy
8801	2013-07-09 22:31:50	101	Re: Inductive reactance of a Current Balun?
Hi Andy, It is magnet/enamelled wire.
8802	2013-07-11 05:12:58	PY8ELO - Silva	Toroid cores for Balun
Hi all, I am looking for FT240-61 and FT300-61 cores but it is very hard to find here in Brazil. Can somebody help me please? Thanks in advance and Best regards, Silva. ************************************** Brazilian Ham Radio - ARRL Member Callsign: PY8ELO Name: Silva Grid Locator: GI25ar Address: POBOX 151 CEP 68180030 ITAITUBA - PA - BRAZIL ************************************** "The quieter You become the more You are able to hear"
8803	2013-07-11 11:44:11	Todd F. Carney / ...	Re: Toroid cores for Balun

8804	2013-07-11 11:44:21	Gustavo Villada	Re: Toroid cores for Balun
Hi Silva, I found a couple in ebay, also this site: http://kitsandparts.com/toroids.php have a nice stock (but not the ones that you are locking) regards and 73 Gus LU6AGV
8805	2013-07-11 19:56:55	Andy	Re: Toroid cores for Balun
> http://kitsandparts.com/toroids.php have a nice stock (but not the > ones that you are locking) He does have one of them (the FT240-61). Don't know how well it works to ship to Brazil. His order form does have a choice for "All other countries". I'm told he (W8DIZ) ships orders fast. Regards, Andy
8806	2013-07-13 04:21:23	PY8ELO - Silva	Re: Toroid cores for Balun
Hi Andy and all, thanks a lot for your reply. I already has purchase a couple of cores. Kind Regards, Silva. On 11-07-2013 23:56, Andy wrote: > > > http://kitsandparts.com/toroids.php have a nice stock (but not the > > ones that you are locking) > > He does have one of them (the FT240-61). > > Don't know how well it works to ship to Brazil. His order form does > have a choice for "All other countries". I'm told he (W8DIZ) ships > orders fast. > > Regards, > Andy > > -- ************************************** Brazilian Ham Radio - ARRL Member Callsign: PY8ELO Name: Silva Grid Locator: GI25ar Address: POBOX 151 CEP 68180030 ITAITUBA - PA - BRAZIL ************************************** "The quieter You become the more You are able to hear" [Non-text portions of this message have been removed]