Home |
Search |
Today's Posts |
#1
|
|||
|
|||
Static 9:1 balun
I am doing the same thing myself, but let's think about the anti-static
feature which uses a Ne-2 bulb a 10K resistor and IIRC a .01 capacitor The NE-2 is a NEON tube...They don't conduct, they FIRE like a Thyratron, they are gas discharge tubes...like a stone age Zener diode. The NE-2 ( when I used them in strobe-light power supplies, fired at 65 volts and until it reached 65 volts, it did NOTHING. Reading recent references I see it is listed as a 105-125 V device...perhaps that's for optimum "brightness"...I just know it FIRES at 65 ac volts. at any rate the 10K resistor is a good order of magnitude too low in my opinion...The reference ( a xeroxed page from a catalog listing all the neon tubes characteristics) says the bulb needs a 200K resistor for a 65V AC firing voltage (RF is AC) or 90V DC firing voltage. Can we have some practical experience here from the "listeners" about whether the resistors should be 10K or 200 K ? Yodar "-=jd=-" wrote in message .. . I'm a newcomer to SWL and I've been perusing the boards and the various sites. Lots of interesting info to be found all over - perhaps too much info. I'm quite possibly a good example of the adage that a little knowledge can sometimes be a dangerous thing. So, I'm thinking of the following to reduce noise while listening inside the house (with a Grundig YB400PE): The plan is to string 100-feet of #14 wire from a 14-foot post next to the house to a tree (about 130-feet away and 30-feet up) with about 30- feet +/- of rope on the post end of the wire. I'll connect coax from the end of the wire to a project box; from the project box to a ground-rod; from the ground-rod to the receiver. About the project box: It was raining and I was bored. I took the anti-static design from the AMANDX site (www.angelfire.com/mb/amandx/static.html) And the 9:1 balun from the hard-core-dx/nordicdx site (http://www.hard- core-dx.com/nordicdx/antenna/feed/9_1balun.html) And I've combined both designs into one box. The way I did it was to connect the capacitor from the static filter to the antenna side of the balun (hope that makes sense). Oh, it looks like hell, but I'm thinking it might actually work ok. I'm hoping to string it all up as soon as Tropical Storm "Bill" blows through and see if there's any difference from the built-in and wind-up antennas. Given that I am (admittedly) a totally green newbie and have *no* clue about the theory behind the random wire antennas, the anti- static filter or baluns, I'm wondering if anyone may have any advice they may like to offer regarding what I have planed, other than gales of derisive laughter... JD -- "Who are you going to believe, me or your lyin' eyes?" -Groucho Marx |
#2
|
|||
|
|||
Aren't all parts of those 9:1 baluns at DC ground already?
If your co-ax is well grounded you don't need the capacitor. On Tue, 01 Jul 2003 02:56:06 -0000, "-=jd=-" wrote: core-dx.com/nordicdx/antenna/feed/9_1balun.htm |
#3
|
|||
|
|||
If I understand you correctly, you propose to put coax between the end of
your wire and the project box containing the balun (autotransformer). I would recommend moving the box to the end of the wire, and using the run of coax going back to the receiver to "come down" from the box to the ground. This would, I admit, give you a problem of how to make the ground connection to the coax shield at the antenna end; you could use a grounding block, which requires your coax run to have connectors at this point, or you need to do some "surgery" to the coax to take off the outer covering without cutting the shield (for this, go to a sewing shop and look at the tool called a "seam ripper", and you may see how to use it to "uncover" coax shield). This is a slightly funny antenna, the wire together with the exterior of the coax shield, creates a grounded Inverted-L that has its feedpoint not at the ground stake, but at the balun. I've been playing with the idea of winding a coil with the coax at the ground stake (back-of-envelope calculations say 200 uH) which makes this antenna self-decoupling: at high frequencies, the high reactance disconnects the "bottom" of the antenna from the ground, and it's a bent dipole; at low frequencies, the low reactance makes it an Inverted-L. One antenna for LW to 30MHz? You asked for ideas... -- R F Wieland Newark, DE 19711-5323 USA 39.68N 75.74W Icom R75 Heathkit GR-81 Inverted-L in the attic Reply to wieland at me dot udel dot edu |
#4
|
|||
|
|||
Joe Strain wrote: I am doing the same thing myself, but let's think about the anti-static feature which uses a Ne-2 bulb a 10K resistor and IIRC a .01 capacitor The NE-2 is a NEON tube...They don't conduct, they FIRE like a Thyratron, they are gas discharge tubes...like a stone age Zener diode. The NE-2 ( when I used them in strobe-light power supplies, fired at 65 volts and until it reached 65 volts, it did NOTHING. Reading recent references I see it is listed as a 105-125 V device...perhaps that's for optimum "brightness"...I just know it FIRES at 65 ac volts. at any rate the 10K resistor is a good order of magnitude too low in my opinion...The reference ( a xeroxed page from a catalog listing all the neon tubes characteristics) says the bulb needs a 200K resistor for a 65V AC firing voltage (RF is AC) or 90V DC firing voltage. Can we have some practical experience here from the "listeners" about whether the resistors should be 10K or 200 K ? Yodar 10k is a good value for the resistor. In this application the resistor is in parallel with the bulb. Its purpose is to bleed off any static that generates. In this case, lower is better, but you want to keep the value well above ( 10X ) the impedance of whatever is connected. When there is a nearby strike, more voltage will be generated on the antenna. When the voltage exceeds 90 volts, the lamp fires. It discharges the antenna until the voltages drops below 65 volts. After that, the resistor bleeds off the rest. When using the lamp as a pilot light, the resistor is in series with the bulb. This is done to limit current. Too much current and the bulb's life is shortened. As another poster mentioned, a balun tends to put everything at ground potential anyway. None of this is sufficient to handle a direct strike. Also a sufficiently large nearby strike could still cause damage to a radio. Enjoy Craig |
#5
|
|||
|
|||
-=jd=- wrote: On 01 Jul 2003, craigm wrote: Joe Strain wrote: ...snip... Can we have some practical experience here from the "listeners" about whether the resistors should be 10K or 200 K ? Yodar 10k is a good value for the resistor. In this application the resistor is in parallel with the bulb. Its purpose is to bleed off any static that generates. In this case, lower is better, but you want to keep the value well above ( 10X ) the impedance of whatever is connected. When there is a nearby strike, more voltage will be generated on the antenna. When the voltage exceeds 90 volts, the lamp fires. It discharges the antenna until the voltages drops below 65 volts. After that, the resistor bleeds off the rest. When using the lamp as a pilot light, the resistor is in series with the bulb. This is done to limit current. Too much current and the bulb's life is shortened. As another poster mentioned, a balun tends to put everything at ground potential anyway. None of this is sufficient to handle a direct strike. Also a sufficiently large nearby strike could still cause damage to a radio. Enjoy Craig I was hoping someone would verify that the resistor is parallel with the bulb - I had second thoughts after reading Joe's post. As for lightning protection, I'm thinking that if a lightning strike hits that close or directly, I'm probably screwed regardless. I'll opt for disconnecting the ant. when not in use. I have now strung the whole affair up. As previously stated, except that from the 14' post at the house to only about 8' up the the tree for now (I'll need a sling-shot to hit the 30' mark). Even so, the difference is remarkable! The drop-off in ambient noise is remarkable. I tried the three different antennas (dx mode) while tuned to 10mhz and found that: Coax-Fed Random Wire - clear as a bell and signal meter was maxed on 5 and stayed there (scale 1 - 5). I'm presuming the coax feed along with the 30' rope extending the antenna way from the house were the significant factors as I disconnected the static-filter/balun unit and could not tell a bit of difference (with my uncalibrated ear-ball). Seemed to be similar results on other freqs. Built-In Aerial - The stations was in and out, I could pick up a beep occasionally over the noise. Signal meter fluctuated from 1 to 3, but I think that was more the noise level. Wind-up Ant: Worse than the Aerial. Nothing but noise. Signal meter fluctuated from 2 to 4. Either that particular freq did not present the circumstances where the static-filter/balun would be worthwhile -or- the static-filter/balun really doesn't do much for me regarding reception improvement. In any event, it doesn't seem to have an effect either way, so no harm done that I can tell. That, and winding it salvaged an otherwise rainy afternoon... So I'm wondering if a balun is a waste of time on a random wire for SWL only. At least, in the case of Joe Listener just sticking a length of wire up - not in the case of big beverages or some other "formal" (lack of a better word) antenna rig... Are you sure you have the balun/matching transformer wired and connected properly? JD -- "Who are you going to believe, me or your lyin' eyes?" -Groucho Marx |
#6
|
|||
|
|||
-=jd=- wrote: On 02 Jul 2003, N8KDV sneezed on the keyboard, resulting in: -=jd=- wrote: ...snip... So I'm wondering if a balun is a waste of time on a random wire for SWL only. At least, in the case of Joe Listener just sticking a length of wire up - not in the case of big beverages or some other "formal" (lack of a better word) antenna rig... Are you sure you have the balun/matching transformer wired and connected properly? I'm fairly confident that I do, but I can't say it is exact. I'd like to examine a known good one before I would hazard claiming I got it 100% right. I know I have the leads absolutely correct, as per the design in (http://www.hard-core-dx.com/nordicdx/antenna/feed/9_ 1balun.html). The only question is in the wraps. They are done neatly and do not overlap. It took me a few tries to get the wraps on like I wanted - evenly spaced, no overlap, snug against the choke... However, depending on how you count the wraps, I have either (30)10) wraps -or- (30-1/2)10-1/2) wraps. I have no idea if that would make a difference and would defer to the groups advice. Err... I also don't know if this makes any difference either, but I used the square ferrite choke from Radio Shack, as I could not find a round one anywhere locally. Ah... therein may lie the problem... as much as people have argued with me in the past about this, I can only say that all ferrite cores are not created equal... I do appreciate the feedback! Thanks, JD |
#7
|
|||
|
|||
-=jd=- wrote:
On 01 Jul 2003, craigm wrote: Joe Strain wrote: ...snip... snip I have now strung the whole affair up. As previously stated, except that from the 14' post at the house to only about 8' up the the tree for now (I'll need a sling-shot to hit the 30' mark). Even so, the difference is remarkable! I used to use a sling shot - I've found it's easier to launch my antennas by tossing a 5 ounce lead fishing weight with some fishing line over a branch, and then pulling up my rope. It's even easier if you know someone who used to be a pitcher. "The strike zone is that fork about 35 feet up." snip So I'm wondering if a balun is a waste of time on a random wire for SWL only. At least, in the case of Joe Listener just sticking a length of wire up - not in the case of big beverages or some other "formal" (lack of a better word) antenna rig... JD Baluns do improve impedance matching, but just having the ferrite they're normally wound on close to the coax will help reduce RFI too. With an outdoor antenna, most of the RFI you're picking up is probably finding it's way to the antenna on the shield of the coax. The ferrite acts like a choke to help filter it out. Regards, Mark |
#8
|
|||
|
|||
N8KDV wrote: -=jd=- wrote: On 02 Jul 2003, N8KDV sneezed on the keyboard, resulting in: -=jd=- wrote: ...snip... So I'm wondering if a balun is a waste of time on a random wire for SWL only. At least, in the case of Joe Listener just sticking a length of wire up - not in the case of big beverages or some other "formal" (lack of a better word) antenna rig... Are you sure you have the balun/matching transformer wired and connected properly? I'm fairly confident that I do, but I can't say it is exact. I'd like to examine a known good one before I would hazard claiming I got it 100% right. I know I have the leads absolutely correct, as per the design in (http://www.hard-core-dx.com/nordicdx/antenna/feed/9_ 1balun.html). The only question is in the wraps. They are done neatly and do not overlap. It took me a few tries to get the wraps on like I wanted - evenly spaced, no overlap, snug against the choke... However, depending on how you count the wraps, I have either (30)10) wraps -or- (30-1/2)10-1/2) wraps. I have no idea if that would make a difference and would defer to the groups advice. Err... I also don't know if this makes any difference either, but I used the square ferrite choke from Radio Shack, as I could not find a round one anywhere locally. Ah... therein may lie the problem... as much as people have argued with me in the past about this, I can only say that all ferrite cores are not created equal... Not sure whether you've read this article or not: http://members.aol.com/DXerCapeCod/z_transformers.pdf I do appreciate the feedback! Thanks, JD |
#9
|
|||
|
|||
Ah... therein may lie the problem... as much as people have argued with me in the past about this, I can only say that all ferrite cores are not created equal... I must have missed those threads on that Steve, can you expound a little on that? Do you feel the rat shacks cores are suffice? -- ~*~*~Monitoring the Spectrum~*~*~ ***GO BEARCATS*** ~~~Hammarlund129X/140X~~~ **Heathkit Q MUltiplier** GE P-780 |
#10
|
|||
|
|||
Robert F Wieland wrote: If I understand you correctly, you propose to put coax between the end of your wire and the project box containing the balun (autotransformer). I would recommend moving the box to the end of the wire, and using the run of coax going back to the receiver to "come down" from the box to the ground. Yes. And it depends on how the transformer is wound/connected. The ones I use here use a separate ground from the feedpoint. (So, what I'm using are two ground rods, feedpoint, from the transformer, and at the shack from the receiver.) The winding off the toroid from the wire itself is totally separate from the winding that goes to the coax. Now, it is possible to connect the grounds at the transformer (ala MLB) and avoid the ground at the feedpoint. I've used/made them both ways, but I prefer the two ground method. This would, I admit, give you a problem of how to make the ground connection to the coax shield at the antenna end; I run the coax near the end into a Transi-trap... ground that, and after that the only ground is from the receiver. you could use a grounding block, which requires your coax run to have connectors at this point, or you need to do some "surgery" to the coax to take off the outer covering without cutting the shield (for this, go to a sewing shop and look at the tool called a "seam ripper", and you may see how to use it to "uncover" coax shield). This is a slightly funny antenna, the wire together with the exterior of the coax shield, creates a grounded Inverted-L that has its feedpoint not at the ground stake, but at the balun. I've been playing with the idea of winding a coil with the coax at the ground stake (back-of-envelope calculations say 200 uH) which makes this antenna self-decoupling: at high frequencies, the high reactance disconnects the "bottom" of the antenna from the ground, and it's a bent dipole; at low frequencies, the low reactance makes it an Inverted-L. One antenna for LW to 30MHz? You asked for ideas... -- R F Wieland Newark, DE 19711-5323 USA 39.68N 75.74W Icom R75 Heathkit GR-81 Inverted-L in the attic Reply to wieland at me dot udel dot edu |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Parallel balun problem with wire loop | Antenna | |||
Balun question... | Scanner | |||
Adding a 2:1 balun to a multi-band dipole | Antenna | |||
Horizontal loop - balun or no balun ? | Antenna | |||
Balun Grounding Question ? | Antenna |