Re: Topband: How to detune a wire Inverted L? How to 'detune'electrical fence
Tom appreciate sharing your thoughts. I see there are different ways. Considering the TX Antenna will most likely be half wave feed away from the radio, the most appealing to me at the moment seems to be opening the feed line in the shack, on the PA input/ TRX output cable, as PA in RX mode will be by-passed. Opening the line on the 100w side of cable does not seem to represent significant challenge for the relays (I can use the garden variety I have in the junk box). I am in a process of doing a small switching box with relays that will be 'manually' controlled by a foot switch as the PA is rather old and does not have fast relays to enable TRX controlled QSK, so I will anyway need a foot switch to operate with PA. The PA has already been shipped to the island earlier. Inside the box I have already installed a switch and variable cap which in RX mode will allow one of the following: Open/ Short/ Shunted with a switchable inductance L / Shunted with variable Capacitor/ Shunted with LC. This will hopefully allow to find a suitable combination empirically in event of the feed line cable being slightly longer than a half wave. Failing that I could relocate the box outside to where the 1/4 or 3/4 feed line point is, extend the control cable and short it in RX mode - considering the relay contacts would need to stay open in TX mode, assume most of garden variety relays with space between the contacts of 3mm or so should provide the required isolation. For a variable Cap I am using 3 x 445 pf broadcast radio cap, no particular voltage rating as it will be switched in RX only. The TX ant coax cables have already been shipped to the island so I will only be able to do some approximate trials in my back yard with a similar length coax. 73 Tomas, VK2CCC On Fri, Aug 16, 2013 at 8:17 AM, Tom W8JI w...@w8ji.com wrote: ** A poor man's version of L worked satisfactory for me in 2010 VK9LL operation, without any tuner at the base, the bottom terminal of the vertical wire directly connected to the center conductor of the coax cable. I had around 90m ??? of feedline going from the shack to TX antenna, to bring the TX antenna to the clear. It was not a perfect match (I had a MiniVNA with me ant taken measurements but dont remember the feedpoint impedance straight of my head). What you do really depends on what you are comfortable with doing. One case requires a control line and remote relay, the other moves stuff inside or close to the shack. One possible solution is to add a T connector 1/4 wave electrical from the antenna, and short it there with a relay. The relay has to handle higher voltages but almost no current, provided you time it right. Another is to go 1/2 wave away, and just open the line for RX. This requires a higher current lower voltage series relay. Provided you time it right. Timing is a huge issue with some radios, and no problem with others. Many radios can just use the TX line used to key amplifiers. Others will actually require an external sequencing or interlock system (which is no easy task for multiple modes). What would the methodology be to calculate the load at the shack end to detune it TX ant? Would inserting any significant X move the TX ant resonance point further way do the detuning job? I would do it emerically, by using the coax you intend to use at a home test setup. Exactly how you do it depends entirely on the test equipment you have and how comfortable you are. It can be done with almost no equipment and a little skill, or less skill and more equipment. The location of TX ant for 2013 operation is about 60m away from the shack. Another idea expressed was if the L is fed with a half wave, the open terminal at the shack end during RX would transform into an open contact at the feedpoint making the L float above the ground? That's correct, although it can be made to work with any cable length if you use an inductor, a capacitor, or an open or short. One of the four will open any length line at the antenna. So would a properly located stub. There are a dozen ways to do it, and the choice depends on what you can do and want to do, more than what works. 73 Tom _ Topband Reflector
Re: Topband: How to detune a wire Inverted L? How to 'detune'electrical fence
Q1) Would a simple relay disconnecting the vertical wire at the TX antenna feedpoint be good for detuning TX antenna? (I am using a piece of wire attached to 18m Spidermast for the vertical section) and another piece of horizontal on the top. Q2) Are there any practical solutions for detuning TX antenna by using some circuitry at the shack end instead? Q3) What in practice could be done about the impact of the electrical fence? (other then moving RX antenna as far away as possible/ and considering using a shielded coax loop / or Waller Flag to 'null' the fence out?) Assuming it is a 1/4 wave L, anything that electrically opens the base of the antenna at the feedpoint with maximum possible impedance detunes the L. Depending on any networks or transmission lines between the detuning switch and the element, the optimum termination at the switch might be almost anything. It is quite possible to detune the antenna from the shack, although it will generally require a certain value of inductance or capacitance to be switched in. I detune my 200 ft tower, fed through an L network, about 50 feet from the element and L network with a short. Tom _ Topband Reflector
Re: Topband: How to detune a wire Inverted L? How to 'detune'electrical fence
Sounds like a robust relay, just above the feed-point would de-tune the L rather nicely. At least that was my thought. Probably simpler and more straightforward than trying to detune it in the shack. Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI Sent: Thursday, August 15, 2013 10:39 AM To: Tomas Magyla; topband@contesting.com Subject: Re: Topband: How to detune a wire Inverted L? How to 'detune'electrical fence Q1) Would a simple relay disconnecting the vertical wire at the TX antenna feedpoint be good for detuning TX antenna? (I am using a piece of wire attached to 18m Spidermast for the vertical section) and another piece of horizontal on the top. Q2) Are there any practical solutions for detuning TX antenna by using some circuitry at the shack end instead? Q3) What in practice could be done about the impact of the electrical fence? (other then moving RX antenna as far away as possible/ and considering using a shielded coax loop / or Waller Flag to 'null' the fence out?) Assuming it is a 1/4 wave L, anything that electrically opens the base of the antenna at the feedpoint with maximum possible impedance detunes the L. Depending on any networks or transmission lines between the detuning switch and the element, the optimum termination at the switch might be almost anything. It is quite possible to detune the antenna from the shack, although it will generally require a certain value of inductance or capacitance to be switched in. I detune my 200 ft tower, fed through an L network, about 50 feet from the element and L network with a short. Tom _ Topband Reflector _ Topband Reflector
Re: Topband: How to detune a wire Inverted L? How to 'detune'electrical fence
Short of expensive fast vacuum relays, what sort of readily available T/R (not QSK) relays handle QRO power at non-50-ohm points? If it was purely 50 ohms, I wouldn't feel bad using a big ice cube relay. But I suspect that on many bands the voltages at the base of the antenna would easily jump the air gap in that kind of relay. I'm thinking not just of detuning the transmit antenna but also general band change activities that right now I go over to the L network at the base of the antenna to do. That's the wall of my shack so not a huge distance but it would be cool to do band change activities all from the operating seat rather than go over to the wall and move banana plugs like I do right now. Tim N3QE -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Charlie Cunningham Sent: Thursday, August 15, 2013 10:49 AM To: 'Tom W8JI'; 'Tomas Magyla'; topband@contesting.com Subject: Re: Topband: How to detune a wire Inverted L? How to 'detune'electrical fence Sounds like a robust relay, just above the feed-point would de-tune the L rather nicely. At least that was my thought. Probably simpler and more straightforward than trying to detune it in the shack. Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI Sent: Thursday, August 15, 2013 10:39 AM To: Tomas Magyla; topband@contesting.com Subject: Re: Topband: How to detune a wire Inverted L? How to 'detune'electrical fence Q1) Would a simple relay disconnecting the vertical wire at the TX antenna feedpoint be good for detuning TX antenna? (I am using a piece of wire attached to 18m Spidermast for the vertical section) and another piece of horizontal on the top. Q2) Are there any practical solutions for detuning TX antenna by using some circuitry at the shack end instead? Q3) What in practice could be done about the impact of the electrical fence? (other then moving RX antenna as far away as possible/ and considering using a shielded coax loop / or Waller Flag to 'null' the fence out?) Assuming it is a 1/4 wave L, anything that electrically opens the base of the antenna at the feedpoint with maximum possible impedance detunes the L. Depending on any networks or transmission lines between the detuning switch and the element, the optimum termination at the switch might be almost anything. It is quite possible to detune the antenna from the shack, although it will generally require a certain value of inductance or capacitance to be switched in. I detune my 200 ft tower, fed through an L network, about 50 feet from the element and L network with a short. Tom _ Topband Reflector _ Topband Reflector _ Topband Reflector
Re: Topband: How to detune a wire Inverted L? How to 'detune'electrical fence
Well, it sounded like Thomas wanted to de-tune the L, so it wouldn't interfere with his receive antenna when receiving. Assuming that he's only using the L for 160, he would be switching at a high-current, modest voltage point. So a substantial relay would be appropriate, I think. I wouldn't recommend hot-switching, though. Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Shoppa, Tim Sent: Thursday, August 15, 2013 10:58 AM To: Charlie Cunningham; 'Tom W8JI'; 'Tomas Magyla'; topband@contesting.com Subject: Re: Topband: How to detune a wire Inverted L? How to 'detune'electrical fence Short of expensive fast vacuum relays, what sort of readily available T/R (not QSK) relays handle QRO power at non-50-ohm points? If it was purely 50 ohms, I wouldn't feel bad using a big ice cube relay. But I suspect that on many bands the voltages at the base of the antenna would easily jump the air gap in that kind of relay. I'm thinking not just of detuning the transmit antenna but also general band change activities that right now I go over to the L network at the base of the antenna to do. That's the wall of my shack so not a huge distance but it would be cool to do band change activities all from the operating seat rather than go over to the wall and move banana plugs like I do right now. Tim N3QE -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Charlie Cunningham Sent: Thursday, August 15, 2013 10:49 AM To: 'Tom W8JI'; 'Tomas Magyla'; topband@contesting.com Subject: Re: Topband: How to detune a wire Inverted L? How to 'detune'electrical fence Sounds like a robust relay, just above the feed-point would de-tune the L rather nicely. At least that was my thought. Probably simpler and more straightforward than trying to detune it in the shack. Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI Sent: Thursday, August 15, 2013 10:39 AM To: Tomas Magyla; topband@contesting.com Subject: Re: Topband: How to detune a wire Inverted L? How to 'detune'electrical fence Q1) Would a simple relay disconnecting the vertical wire at the TX antenna feedpoint be good for detuning TX antenna? (I am using a piece of wire attached to 18m Spidermast for the vertical section) and another piece of horizontal on the top. Q2) Are there any practical solutions for detuning TX antenna by using some circuitry at the shack end instead? Q3) What in practice could be done about the impact of the electrical fence? (other then moving RX antenna as far away as possible/ and considering using a shielded coax loop / or Waller Flag to 'null' the fence out?) Assuming it is a 1/4 wave L, anything that electrically opens the base of the antenna at the feedpoint with maximum possible impedance detunes the L. Depending on any networks or transmission lines between the detuning switch and the element, the optimum termination at the switch might be almost anything. It is quite possible to detune the antenna from the shack, although it will generally require a certain value of inductance or capacitance to be switched in. I detune my 200 ft tower, fed through an L network, about 50 feet from the element and L network with a short. Tom _ Topband Reflector _ Topband Reflector _ Topband Reflector _ Topband Reflector
Re: Topband: How to detune a wire Inverted L? How to 'detune'electrical fence
De-tuning an electric fence is something I have thought about (I have some here). Two possible ideas (these are not proven - so I won't say solutions). If the fence doesn't need to be active while detuned - you can break it up into odd multiples of quarter wavelengths (mind your velocity factors). If the fence does need to be active - you can do step #1 - but then put some kind of choke in series of the places you break it up. The one beverage I have near electric fences doesn't run too close to the wires except at one point where they are nearly perpendicular. Tree N6TR On Thu, Aug 15, 2013 at 7:57 AM, Shoppa, Tim tsho...@wmata.com wrote: Short of expensive fast vacuum relays, what sort of readily available T/R (not QSK) relays handle QRO power at non-50-ohm points? If it was purely 50 ohms, I wouldn't feel bad using a big ice cube relay. But I suspect that on many bands the voltages at the base of the antenna would easily jump the air gap in that kind of relay. I'm thinking not just of detuning the transmit antenna but also general band change activities that right now I go over to the L network at the base of the antenna to do. That's the wall of my shack so not a huge distance but it would be cool to do band change activities all from the operating seat rather than go over to the wall and move banana plugs like I do right now. Tim N3QE -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Charlie Cunningham Sent: Thursday, August 15, 2013 10:49 AM To: 'Tom W8JI'; 'Tomas Magyla'; topband@contesting.com Subject: Re: Topband: How to detune a wire Inverted L? How to 'detune'electrical fence Sounds like a robust relay, just above the feed-point would de-tune the L rather nicely. At least that was my thought. Probably simpler and more straightforward than trying to detune it in the shack. Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI Sent: Thursday, August 15, 2013 10:39 AM To: Tomas Magyla; topband@contesting.com Subject: Re: Topband: How to detune a wire Inverted L? How to 'detune'electrical fence Q1) Would a simple relay disconnecting the vertical wire at the TX antenna feedpoint be good for detuning TX antenna? (I am using a piece of wire attached to 18m Spidermast for the vertical section) and another piece of horizontal on the top. Q2) Are there any practical solutions for detuning TX antenna by using some circuitry at the shack end instead? Q3) What in practice could be done about the impact of the electrical fence? (other then moving RX antenna as far away as possible/ and considering using a shielded coax loop / or Waller Flag to 'null' the fence out?) Assuming it is a 1/4 wave L, anything that electrically opens the base of the antenna at the feedpoint with maximum possible impedance detunes the L. Depending on any networks or transmission lines between the detuning switch and the element, the optimum termination at the switch might be almost anything. It is quite possible to detune the antenna from the shack, although it will generally require a certain value of inductance or capacitance to be switched in. I detune my 200 ft tower, fed through an L network, about 50 feet from the element and L network with a short. Tom _ Topband Reflector _ Topband Reflector _ Topband Reflector _ Topband Reflector
Re: Topband: How to detune a wire Inverted L? How to 'detune'electrical fence
Well, Tomas If you are comfortable using Smith Charts, you could work out some reactance for any length of feedline to detune the antenna. Other than your 1/2 wave approach, another approach would be to use an electrical 1/4 wave or 3/4 wave feedline and short it in the shack with a relay when receiving. That would present an open at the antenna terminals when the 1/4 or 3/4 wave line is shorted, thereby detuning the antenna completely. GL! 73, Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tomas Magyla Sent: Thursday, August 15, 2013 1:44 PM To: Tom W8JI Cc: topband@contesting.com Subject: Re: Topband: How to detune a wire Inverted L? How to 'detune'electrical fence Tom it is a 1/4 wave L, with the vertical section dictated by a 18m Spidermast telescopic rod. A poor man's version of L worked satisfactory for me in 2010 VK9LL operation, without any tuner at the base, the bottom terminal of the vertical wire directly connected to the center conductor of the coax cable. I had around 90m ??? of feedline going from the shack to TX antenna, to bring the TX antenna to the clear. It was not a perfect match (I had a MiniVNA with me ant taken measurements but dont remember the feedpoint impedance straight of my head). I would be more tempted to use the same poor man's version as I will be cutting the handle of my toothbrush to fit all the radio gear into the 14kg airline baggage allowance. What would the methodology be to calculate the load at the shack end to detune it TX ant? Would inserting any significant X move the TX ant resonance point further way do the detuning job? The location of TX ant for 2013 operation is about 60m away from the shack. Another idea expressed was if the L is fed with a half wave, the open terminal at the shack end during RX would transform into an open contact at the feedpoint making the L float above the ground? Thanks heaps Tomas VK2CCC On Fri, Aug 16, 2013 at 12:39 AM, Tom W8JI w...@w8ji.com wrote: Q1) Would a simple relay disconnecting the vertical wire at the TX antenna feedpoint be good for detuning TX antenna? (I am using a piece of wire attached to 18m Spidermast for the vertical section) and another piece of horizontal on the top. Q2) Are there any practical solutions for detuning TX antenna by using some circuitry at the shack end instead? Q3) What in practice could be done about the impact of the electrical fence? (other then moving RX antenna as far away as possible/ and considering using a shielded coax loop / or Waller Flag to 'null' the fence out?) Assuming it is a 1/4 wave L, anything that electrically opens the base of the antenna at the feedpoint with maximum possible impedance detunes the L. Depending on any networks or transmission lines between the detuning switch and the element, the optimum termination at the switch might be almost anything. It is quite possible to detune the antenna from the shack, although it will generally require a certain value of inductance or capacitance to be switched in. I detune my 200 ft tower, fed through an L network, about 50 feet from the element and L network with a short. Tom _ Topband Reflector _ Topband Reflector
Re: Topband: How to detune a wire Inverted L? How to 'detune'electrical fence
On 8/15/2013 7:39 AM, Tom W8JI wrote: Depending on any networks or transmission lines between the detuning switch and the element, the optimum termination at the switch might be almost anything. If the antenna is close to a quarter wave, one rather easy termination is t make the feedline either a shorted quarter-wave or an open half-wave of transmission line. A halfwave of RG8/RG213 for 160M won't have much loss, and a simple antenna relay box (like W2VJN's 2X1 Top Ten box, which runs on 12VDC) would make it quite easy to rig. So simply add enough coax to reach either of those lengths and add the relay and control line that provides the short or open in RX mode. The downside of this, of course, is that you can't listen on the TX antenna for diversity. . 73, Jim K9YC _ Topband Reflector
Re: Topband: How to detune a wire Inverted L? How to 'detune'electrical fence
FYI, I see on the Max Gain site (and local to me) that he is out of the RJ1A series of relays. tnx Mike / W5JR Alpharetta GA On 8/15/2013 1:39 PM, JC N4IS wrote: Tim The issue with the relay at the antenna is the time to close the contacts and avoid RF hot switch. I'm using a Jennings RJ1A-26S for years, just 4-6 milliseconds to close. Or you can use a sequencer, or a winkey2 with cw lead time and PTT2 for the amplifier. http://www.mgs4u.com/RF-Microwave/vacuum-relays-SPDT.htm Regards Carlos N4IS _ Topband Reflector _ Topband Reflector
Re: Topband: How to detune a wire Inverted L? How to 'detune'electrical fence
On 8/15/2013 10:39 AM, JC N4IS wrote: The issue with the relay at the antenna is the time to close the contacts and avoid RF hot switch. Yes. You might solve that by using PTT from the radio, which for most modern rigs, occurs 8-10 msec before RF, and in some rigs the delay is adjustable (K3, FT1000-series are some I know of). 73, Jim K9YC _ Topband Reflector
Re: Topband: How to detune a wire Inverted L? How to 'detune'electrical fence
A poor man's version of L worked satisfactory for me in 2010 VK9LL operation, without any tuner at the base, the bottom terminal of the vertical wire directly connected to the center conductor of the coax cable. I had around 90m ??? of feedline going from the shack to TX antenna, to bring the TX antenna to the clear. It was not a perfect match (I had a MiniVNA with me ant taken measurements but dont remember the feedpoint impedance straight of my head). What you do really depends on what you are comfortable with doing. One case requires a control line and remote relay, the other moves stuff inside or close to the shack. One possible solution is to add a T connector 1/4 wave electrical from the antenna, and short it there with a relay. The relay has to handle higher voltages but almost no current, provided you time it right. Another is to go 1/2 wave away, and just open the line for RX. This requires a higher current lower voltage series relay. Provided you time it right. Timing is a huge issue with some radios, and no problem with others. Many radios can just use the TX line used to key amplifiers. Others will actually require an external sequencing or interlock system (which is no easy task for multiple modes). What would the methodology be to calculate the load at the shack end to detune it TX ant? Would inserting any significant X move the TX ant resonance point further way do the detuning job? I would do it emerically, by using the coax you intend to use at a home test setup. Exactly how you do it depends entirely on the test equipment you have and how comfortable you are. It can be done with almost no equipment and a little skill, or less skill and more equipment. The location of TX ant for 2013 operation is about 60m away from the shack. Another idea expressed was if the L is fed with a half wave, the open terminal at the shack end during RX would transform into an open contact at the feedpoint making the L float above the ground? That's correct, although it can be made to work with any cable length if you use an inductor, a capacitor, or an open or short. One of the four will open any length line at the antenna. So would a properly located stub. There are a dozen ways to do it, and the choice depends on what you can do and want to do, more than what works. 73 Tom _ Topband Reflector
