Re: Topband: Mag loop 400W if possible.
Depends upon small wire resistance change as it heats up. On Mon, 16 Nov 2015 10:30:50 -0500, Tom W8JI wrote: > Loss is I squared R. as the current is lowered then loss drops rapidly. That isn't true. Loss as a percentage or as a ratio to applied power is exactly the same in a linear system. 6 dB loss is 6 dB loss whether at 1 milliwatt or 1 megawatt. _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Mag loop 400W if possible.
Loss is I squared R. as the current is lowered then loss drops rapidly. That isn't true. Loss as a percentage or as a ratio to applied power is exactly the same in a linear system. 6 dB loss is 6 dB loss whether at 1 milliwatt or 1 megawatt. _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Mag loop 400W if possible.
It does not take a lot of RF if conditions are right. A few years ago I received a little 40 meters QRP transceiver for Christmas. Did not have a 40 meter antenna at the time. listened on my Beverage antenna, and everything was working OK. just for the heck of it, called a European and he came right back 559. I told him I was working QRP , the next transmission told him I was using a Beverage antenna and he signed off rapidly. 'Difficult to believe' Loss is I squared R. as the current is lowered then loss drops rapidly. 73 Bruce-k1fz www.qsl.net/k1fz/bogantennanotes.html On Mon, 16 Nov 2015 08:27:17 -0500, Tim Shoppa wrote: I have examined the RFI situation at some local apartment-bound ops on 40M and I swear when they work into their loop that it is their apartment wiring that is radiating, and not the loop antenna. It's gotta be worse on 160M. A guest op at a local contest superstation reported how hard it was to work DX the first morning on the high bands, then went to check out the antenna switching after a local with just a wire (aka me) was working the DX before him. He found out that all the QSO's he had that morning up to that point had been worked with a Heathkit Cantenna dummy load :-). Yes, it is very possible to work stations just using a Cantenna! (Possibly circa 30-40 dB down leaking into the beam, but I'm guessing feedline radiation can be similar too.) Tim N3QE _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Mag loop 400W if possible.
I have examined the RFI situation at some local apartment-bound ops on 40M and I swear when they work into their loop that it is their apartment wiring that is radiating, and not the loop antenna. It's gotta be worse on 160M. A guest op at a local contest superstation reported how hard it was to work DX the first morning on the high bands, then went to check out the antenna switching after a local with just a wire (aka me) was working the DX before him. He found out that all the QSO's he had that morning up to that point had been worked with a Heathkit Cantenna dummy load :-). Yes, it is very possible to work stations just using a Cantenna! (Possibly circa 30-40 dB down leaking into the beam, but I'm guessing feedline radiation can be similar too.) Tim N3QE On Sun, Nov 15, 2015 at 7:59 AM, jonathan white < jonathan.whit...@btinternet.com> wrote: > Hi I am in a bit of trouble I will be mooing to a flat/apartment ,so can > anyone give me details of a mag loop that will fit in a room and also be > able to be taken apart and resembled on a beach,will use big vac cap 1000pf > 40kv Russian type,any takers,and please dont laugh I love topband. > 73`s Jon g8ccl > _ > Topband Reflector Archives - http://www.contesting.com/_topband > _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Mag loop 400W if possible.
Well everyone .going to view an apartment/flat in UK! Tomorrow and the seawall is less than 5mins away.The estuary of the river Crouch in Essex,UK. So will be able to run 100 watts of wsjt or whatever and qrp loop ant,for when its cold and wet.Ialso am trying to get a contest location notfar from new qth. thanks everyone. 73`s Jon On 15/11/15 21:03, Richard (Rick) Karlquist wrote: On 11/15/2015 4:59 AM, jonathan white wrote: Hi I am in a bit of trouble I will be mooing to a flat/apartment ,so can anyone give me details of a mag loop that will fit in a room and also be able to be taken apart and resembled on a beach,will use big vac cap 73`s Jon g8ccl For the beach, get a collapsible telescoping pole and make a vertical on the beach. Add a loading coil and a couple of radials and you're on the air. Way better than a loop. Rick N6RK _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Mag loop 400W if possible.
On 11/15/2015 4:59 AM, jonathan white wrote: Hi I am in a bit of trouble I will be mooing to a flat/apartment ,so can anyone give me details of a mag loop that will fit in a room and also be able to be taken apart and resembled on a beach,will use big vac cap 73`s Jon g8ccl For the beach, get a collapsible telescoping pole and make a vertical on the beach. Add a loading coil and a couple of radials and you're on the air. Way better than a loop. Rick N6RK _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Mag loop 400W if possible.
On Sun, Nov 15, 2015 at 12:44 PM, jh-...@sbcglobal.net wrote: > Use the largest, heaviest hardline you can find. if you use hardline at all, it ought be be VERY BIG hardline! If the largest you can find is (for example) 7/8", that's simply not big enough, unless you are willing to put up with the reduced efficiency or make the loop much larger. What is needed for an efficient STL (small in terms of wavelength) is big copper pipe. And if we use aluminum it needs to be even bigger than copper. The entire STL --the loop itself, the tuning capacitor, and the connections between them MUST have extremely low ohmic resistance vs. the radiation resistance. That almost always means large, expensive vacuum variables with wide copper strap connecting it to the loop. Braided copper is out of the question, it will heat due the enormous currents flowing in the loop. Such an efficient STL also has extremely narrow bandwidth. Think that over carefully, especially if you plan on using SSB. Also, rethink your resources. I ran Top Band from a 2nd story apartment > with a full-sized inverted L hidden in a tree, with radials running down > the sides of the bldg., and worked 93 countries with 100-600W. > Bingo! An inverted-L is really the way to go. 73, Mike www.w0btu.com _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Mag loop 400W if possible.
On Sun,11/15/2015 10:44 AM, jh-...@sbcglobal.net wrote: Use the largest, heaviest hardline you can find. Also, rethink your resources. I ran Top Band from a 2nd story apartment with a full-sized inverted L hidden in a tree, with radials running down the sides of the bldg., and worked 93 countries with 100-600W. 73 and GL, JH W6UQZ Yes on all counts. My neighbor, W6GJB, has built a portable high power magnetic loop from eight 4-ft sections of the modular portable military surplus 2-in antenna masts. Four sections have two 45 degree bends in them, and serve as corners, and fit together to form a small loop. Four straight sections are added between the bent sections to form a larger loop. He's tuning with some big rotary plate capacitors in parallel with fixed high voltage caps from my junk box. I agree with others that the usefulness of an indoor loop will be quite limited. W6GJB has done fairly well running QRP with the smaller "Alex Loop" on 40M and above from hotel rooms in wood frame buildings. 73, Jim K9YC _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Mag loop 400W if possible.
Use the largest, heaviest hardline you can find. Also, rethink your resources. I ran Top Band from a 2nd story apartment with a full-sized inverted L hidden in a tree, with radials running down the sides of the bldg., and worked 93 countries with 100-600W. 73 and GL, JH W6UQZ From: jonathan white To: TOPBAND@contesting.com Sent: Sunday, November 15, 2015 4:59 AM Subject: Topband: Mag loop 400W if possible. Hi I am in a bit of trouble I will be mooing to a flat/apartment ,so can anyone give me details of a mag loop that will fit in a room and also be able to be taken apart and resembled on a beach,will use big vac cap 1000pf 40kv Russian type,any takers,and please dont laugh I love topband. 73`s Jon g8ccl _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Mag loop 400W if possible.
It's *possible* to construct an STL (small transmitting loop) with fairly good efficiency. But *NOT* one for 160 meters that fits inside a house! :-) I have a web page about STLs with lots of linked pages at www.w0btu.com/magnetic_loops.html Take particular note of the first two links there to Owen Duffy's site and what he has to say. No telling what problems an indoor STL could cause. It could couple to the AC wiring and damage connected appliances. In the late 1970s a dipole in our apartment caused some interesting effects! Incandescent lamps lit up dimly, even though the wall switch was off. We could hear a loud hum from a neighbor's stereo through the floor when we transmitted. And our Heathkit digital clock went bonkers. Enough said. 73, Mike www.w0btu.com _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Mag loop 400W if possible.
I forget to add that the EZNEC simulation showed the gain of this loop to be about -10.8 dBi on 1.8 MHz. Matching network loss not included. Jerry On 11/15/2015 10:46 AM, Tom W8JI wrote: His 400W TX power will likely be ~10 watts ERP if he does a good job on construction. 390W will be nothing but heat. :) - Original Message - From: "Barry N1EU" To: "topBand List" Sent: Sunday, November 15, 2015 8:59 AM Subject: Re: Topband: Mag loop 400W if possible. Wish you all the best with the antenna project Jon but not sure your apartment neighbors are going to love your indoor 400W on topband ;-) 73, Barry N1EU On Sun, Nov 15, 2015 at 12:59 PM, jonathan white < jonathan.whit...@btinternet.com> wrote: Hi I am in a bit of trouble I will be mooing to a flat/apartment ,so can anyone give me details of a mag loop that will fit in a room and also be able to be taken apart and resembled on a beach,will use big vac cap 1000pf 40kv Russian type,any takers,and please dont laugh I love topband. 73`s Jon g8ccl _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband - No virus found in this message. Checked by AVG - www.avg.com Version: 2014.0.4842 / Virus Database: 4447/11004 - Release Date: 11/15/15 _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Mag loop 400W if possible.
His 400W TX power will likely be ~10 watts ERP if he does a good job on construction. 390W will be nothing but heat. :) - Original Message - From: "Barry N1EU" To: "topBand List" Sent: Sunday, November 15, 2015 8:59 AM Subject: Re: Topband: Mag loop 400W if possible. Wish you all the best with the antenna project Jon but not sure your apartment neighbors are going to love your indoor 400W on topband ;-) 73, Barry N1EU On Sun, Nov 15, 2015 at 12:59 PM, jonathan white < jonathan.whit...@btinternet.com> wrote: Hi I am in a bit of trouble I will be mooing to a flat/apartment ,so can anyone give me details of a mag loop that will fit in a room and also be able to be taken apart and resembled on a beach,will use big vac cap 1000pf 40kv Russian type,any takers,and please dont laugh I love topband. 73`s Jon g8ccl _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband - No virus found in this message. Checked by AVG - www.avg.com Version: 2014.0.4842 / Virus Database: 4447/11004 - Release Date: 11/15/15 _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Mag loop 400W if possible.
Your country may not have the same RF safety rules that we have in the US. For the US those rules are at this link http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/oet65b.pdf The mag loop will be limited by the magnetic field strength along a line perpendicular to the plane of the loop. In the US that limit for general population is 2.19/f amps per meter, or for 1.8 MHz 1.21 amps per meter. An EZNEC simulation of a 10 ft diameter loop at 1.8 MHz made with 1 inch diameter copper pipe, and with the bottom of the loop 5 ft above ground and with 400 watts applied shows that the magnetic field exceeds USA safety limits for general population at 11.5 ft from the loop. That's for 100% duty cycle. Reduce the duty cycle to 50% and the safe distance becomes 10 ft. If you improve the low efficiency of this loop (4.95%) that safe distance increases. I hope we don't have the discussion again of what is, and is not safe, because I doubt that there is anyone on this forum qualified to make that judgement. Regardless of what is safe, or is not, we in the US have to abide by the rules in that document. I don't know what the rules are in the UK. Jerry, K4SAV On 11/15/2015 9:29 AM, K4SAV wrote: I forgot to mention. 10 ft diameter loop is about the smallest loop that will tune with your 1000 pf cap. A 10 ft loop needs 843 pf. Use 2 inch diameter pipe and you need 982 pf. You can see that with AA5TB's calculator. Jerry, K4SAV On 11/15/2015 9:18 AM, K4SAV wrote: I like to use AA5TB's calculator to get a quick estimate for mag loops. http://www.aa5tb.com/loop.html#cal Also see http://www.aa5tb.com/loop.html Example: 10 ft diameter loop made from 1 inch diameter copper pipe, 0.05 ohms added resistance 1.8 MHz efficiency = 4.95% Bandwidth = 1.5 kHz Cap voltage = 10 kV peak with 400 watts applied (That will get much higher if you improve the efficiency) You would have to model it in NEC and calculate the near field to get the safe operating distance. Jerry, K4SAV On 11/15/2015 6:59 AM, jonathan white wrote: Hi I am in a bit of trouble I will be mooing to a flat/apartment ,so can anyone give me details of a mag loop that will fit in a room and also be able to be taken apart and resembled on a beach,will use big vac cap 1000pf 40kv Russian type,any takers,and please dont laugh I love topband. 73`s Jon g8ccl _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Mag loop 400W if possible.
I forgot to mention. 10 ft diameter loop is about the smallest loop that will tune with your 1000 pf cap. A 10 ft loop needs 843 pf. Use 2 inch diameter pipe and you need 982 pf. You can see that with AA5TB's calculator. Jerry, K4SAV On 11/15/2015 9:18 AM, K4SAV wrote: I like to use AA5TB's calculator to get a quick estimate for mag loops. http://www.aa5tb.com/loop.html#cal Also see http://www.aa5tb.com/loop.html Example: 10 ft diameter loop made from 1 inch diameter copper pipe, 0.05 ohms added resistance 1.8 MHz efficiency = 4.95% Bandwidth = 1.5 kHz Cap voltage = 10 kV peak with 400 watts applied (That will get much higher if you improve the efficiency) You would have to model it in NEC and calculate the near field to get the safe operating distance. Jerry, K4SAV On 11/15/2015 6:59 AM, jonathan white wrote: Hi I am in a bit of trouble I will be mooing to a flat/apartment ,so can anyone give me details of a mag loop that will fit in a room and also be able to be taken apart and resembled on a beach,will use big vac cap 1000pf 40kv Russian type,any takers,and please dont laugh I love topband. 73`s Jon g8ccl _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Mag loop 400W if possible.
I like to use AA5TB's calculator to get a quick estimate for mag loops. http://www.aa5tb.com/loop.html#cal Also see http://www.aa5tb.com/loop.html Example: 10 ft diameter loop made from 1 inch diameter copper pipe, 0.05 ohms added resistance 1.8 MHz efficiency = 4.95% Bandwidth = 1.5 kHz Cap voltage = 10 kV peak with 400 watts applied (That will get much higher if you improve the efficiency) You would have to model it in NEC and calculate the near field to get the safe operating distance. Jerry, K4SAV On 11/15/2015 6:59 AM, jonathan white wrote: Hi I am in a bit of trouble I will be mooing to a flat/apartment ,so can anyone give me details of a mag loop that will fit in a room and also be able to be taken apart and resembled on a beach,will use big vac cap 1000pf 40kv Russian type,any takers,and please dont laugh I love topband. 73`s Jon g8ccl _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Mag loop 400W if possible.
Hi Jon, There are a lot of reasons why you can't do it. But you will need a physically large loop for the little 1000pF cap. Start with 8 foot diameter and maybe up to twelve feet. My loops are round and a twelve foot loop probably won't fit between the floor and ceiling of your flat. Make it oval with the same length (not diameter) for the loop. You can use coaxial cable for a loop that you can roll up. Then you can stow, transport, and reassemble it. Do you really want to be immersed in the near field from your 400 watt transmitter? 73, Bill KU8H On 11/15/2015 07:59 AM, jonathan white wrote: Hi I am in a bit of trouble I will be mooing to a flat/apartment ,so can anyone give me details of a mag loop that will fit in a room and also be able to be taken apart and resembled on a beach,will use big vac cap 1000pf 40kv Russian type,any takers,and please dont laugh I love topband. 73`s Jon g8ccl _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Mag loop 400W if possible.
The question always is the amount of area inside the loop and keeping the most distance between opposing sides. There are no tricks or magic. It is all about low resistance and maximum physical size. More loss will help it handle more power for a given capacitor voltage, but you don't want that. All of the tricks like helical winding or multi turns to make a loop "work better" never actually help, and actually hurt. That's why all the commercial loops settle on a single largest possible conductor and largest size design. The biggest electrical issues will be connection resistances and how well current and voltages are balanced in the loop, especially in relationship to the feedline and any mast. 73 Tom - Original Message - From: "jonathan white" To: Sent: Sunday, November 15, 2015 7:59 AM Subject: Topband: Mag loop 400W if possible. Hi I am in a bit of trouble I will be mooing to a flat/apartment ,so can anyone give me details of a mag loop that will fit in a room and also be able to be taken apart and resembled on a beach,will use big vac cap 1000pf 40kv Russian type,any takers,and please dont laugh I love topband. 73`s Jon g8ccl _ Topband Reflector Archives - http://www.contesting.com/_topband - No virus found in this message. Checked by AVG - www.avg.com Version: 2014.0.4842 / Virus Database: 4447/11000 - Release Date: 11/14/15 _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Mag loop 400W if possible.
Wish you all the best with the antenna project Jon but not sure your apartment neighbors are going to love your indoor 400W on topband ;-) 73, Barry N1EU On Sun, Nov 15, 2015 at 12:59 PM, jonathan white < jonathan.whit...@btinternet.com> wrote: > Hi I am in a bit of trouble I will be mooing to a flat/apartment ,so can > anyone give me details of a mag loop that will fit in a room and also be > able to be taken apart and resembled on a beach,will use big vac cap 1000pf > 40kv Russian type,any takers,and please dont laugh I love topband. > 73`s Jon g8ccl > _ > Topband Reflector Archives - http://www.contesting.com/_topband > _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: Mag loop 400W if possible.
Hi I am in a bit of trouble I will be mooing to a flat/apartment ,so can anyone give me details of a mag loop that will fit in a room and also be able to be taken apart and resembled on a beach,will use big vac cap 1000pf 40kv Russian type,any takers,and please dont laugh I love topband. 73`s Jon g8ccl _ Topband Reflector Archives - http://www.contesting.com/_topband
