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Narrow band antenna.
On Mar 13, 7:40 pm, Tom Bruhns wrote:
On Mar 13, 9:35 am, Artem wrote: Hello all. I'm looking how to make narrow band active antenna for 7 or 10.1mzh. My idea: I will use magnetic antenna with one loop. A one-turn loop of 3.14m cupper pipe with diameter 15mm has 2.687uH. With Varicaps of 192pf it will have resonance frequency of 7MHz. I will load this LC tank directly to Gate one of dual gate MOSFET.http://homepage.eircom.net/%257Eei9g...//homepage.eir... Should it work? I'll never seen such schematics. Usually people use transformers. But I will place this transistor directly inside gap in the loop of cupper pipe. The Gate of MOSFET will add only additional 2pf to Varicaps and it will be very easy to compensate. Sorry for English. You should probably download Reg Edwards' RJELoop3 and/or RJELoop1 programs, which will tell you that the conductor loss resistance of your loop will be about ten times the radiation resistance, How can calculate radiation resistance? resistance at 7MHz is skin effect http://circuitcalculator.com/wordpre...ct-calculator/ 0.028mm. for copper pipe 15mm in diameter: octave:1 15*3.14*0.028 ans = 1.3188mm^2 0.0155Om/m * 3.14m ans = 0.048670 Om. I think it's not bad. even counting the relatively low Q of varactor diodes, you'll have quite a bit of loss. On the other hand, even at 7MHz the atmospheric noise is so high that the loss won't be a significant problem so long as your amplifier is reasonably low noise. I'd recommend you use a C0G ceramic or possibly silvered-mica capacitor for most of the tuning capacitance, to keep the Q as high as possible (the losses as low as possible). You recommended did hot use varistors? I'm thinking about some kind http://www.toshiba.com/taec/componen...//273/1343.pdf 20 in parallel -------------------------------------- Ultra low series resistance: rs = 0.20 Ù (typ.) -------------------------------------- It will be 0.02 Om Reg suggests the Q for use at 7MHz will be around 2000, so the bandwidth is quite narrow. If the Q really is that high (polish the copper and coat it with a protective varnish or paint...), the parallel resonant impedance will be up around 200k ohms, so it should be a decent match to your FET amplifier. Make sure any loading at the gap is well above 200k ohms resistive, to keep from introducing significant additional loss. I'm thinking about soldering a box from FR4. If you want the antenna to also do a good job rejecting locally generated E field noise, you need to keep things well balanced. What you mean about balanced? Differential output? I should think about it. But at 7MHz, this is probably of marginal utility since any noise generators whose noise would be rejected would have to be very close to the antenna--within a few tens of meters. -- I've done similar amplifiers for multi-turn loops for LF, down around 150kHz, using a balanced JFET design directly across the loop, with good success. You can find the suggested programs athttp://www.zerobeat.net/G4FGQ/. And you likely would get some additional replies if you cross-post to rec.radio.amateur.antenna. Thank. Artem. |
Narrow band antenna.
On Mar 13, 9:09 pm, Artem wrote:
Sorry. ----------------------------------------------- Hello all. I'm looking how to make narrow band active antenna for 7 or 10.1mzh. My idea: I will use magnetic antenna with one loop. A one-turn loop of 3.14m cupper pipe with diameter 15mm has 2.687uH. With Varicaps of 192pf it will have resonance frequency of 7MHz. I will load this LC tank directly to Gate one of dual gate MOSFET. http://homepage.eircom.net/%257Eei9gq/rx_circ.html http://homepage.eircom.net/%257Eei9gq/mosifamp.GIF Should it work? I'll never seen such schematics. Usually people use transformers. But I will place this transistor directly inside gap in the loop of cupper pipe. The Gate of MOSFET will add only additional 2pf to Varicaps and it will be very easy to compensate. ----------------------------------------------- Artem. |
Narrow band antenna.
On Mar 13, 12:09 pm, Artem wrote:
On Mar 13, 7:40 pm, Tom Bruhns wrote: On Mar 13, 9:35 am, Artem wrote: Hello all. I'm looking how to make narrow band active antenna for 7 or 10.1mzh. My idea: I will use magnetic antenna with one loop. A one-turn loop of 3.14m cupper pipe with diameter 15mm has 2.687uH. With Varicaps of 192pf it will have resonance frequency of 7MHz. I will load this LC tank directly to Gate one of dual gate MOSFET.http://homepage.eircom.net/%257Eei9g...//homepage.eir... Should it work? I'll never seen such schematics. Usually people use transformers. But I will place this transistor directly inside gap in the loop of cupper pipe. The Gate of MOSFET will add only additional 2pf to Varicaps and it will be very easy to compensate. Sorry for English. You should probably download Reg Edwards' RJELoop3 and/or RJELoop1 programs, which will tell you that the conductor loss resistance of your loop will be about ten times the radiation resistance, How can calculate radiation resistance? resistance at 7MHz is skin effecthttp://circuitcalculator.com/wordpress/2007/06/18/skin-effect-calcula... 0.028mm. for copper pipe 15mm in diameter: octave:1 15*3.14*0.028 ans = 1.3188mm^2 0.0155Om/m * 3.14m ans = 0.048670 Om. I think it's not bad. See http://personal.ee.surrey.ac.uk/Pers...les/cloops.htm for info on calculating the radiation resistance. I believe that will be helpful. I assume Reg's RJELoop1.exe uses essentially the formula you'll find there. For your loop, that program says inductance is 2.69uH, conductor loss resistance is 46.2 milliohms, and radiation resistance is 5.7 milliohms. Although the conductor loss resistance (essentialy the same as you calculated above is "not bad," you need to consider it with relation to the very low radiation resistance. A current in the loop will dissipate far more power in the resistive loss than in the radiation resistance. You ideally will keep the loss resistance small compared with the radiation resistance, though for receiving (because of the very high level of atmospheric noise on HF and lower frequencies) it matters not nearly so much as for transmitting. When transmitting, you want your power to go into radio waves, not heat. When receiving you only need signal greater than noise, and it is relatively easy to make an amplifier with low enough noise figure that even an inefficient antenna will result in an amplifier output whose noise is dominated by the atmospheric noise received by the antenna. even counting the relatively low Q of varactor diodes, you'll have quite a bit of loss. On the other hand, even at 7MHz the atmospheric noise is so high that the loss won't be a significant problem so long as your amplifier is reasonably low noise. I'd recommend you use a C0G ceramic or possibly silvered-mica capacitor for most of the tuning capacitance, to keep the Q as high as possible (the losses as low as possible). You recommended did hot use varistors? I'm thinking about some kindhttp://www.toshiba.com/taec/components2/Datasheet_Sync//273/1343.pdf 20 in parallel -------------------------------------- Ultra low series resistance: rs = 0.20 Ù (typ.) -------------------------------------- It will be 0.02 Om So 0.02 ohms sounds like a small amount, but it's almost half as much as the resistance of the copper loop. This may not be a bad thing, because the Q is so high that the bandwidth will only be about 3.5kHz assuming a lossless capacitor, and with the added loss the Q will be lowered to perhaps 1400, allowing a slightly wider bandwidth. With so narrow a bandwidth you need to be concerned about the stability of the varicap diodes' capacitance. Still, I would think a very high Q fixed capacitor supplying most of the total capacitance would be a good thing. Use only enough varicap to cover the tuning range you want. So for example, with 2.69uH inductance, if you want to cover 7.00MHz to 7.30MHz, you need 192.2pF at the low end and 176.7pF at the high end, a range of a little less than 16pF. You should be able to do that easily with two of your suggested varicap diodes, perhaps a couple of fixed 82pF high Q caps, and a high Q trimmer such as a piston trimmer to trim the center of the range. Reg suggests the Q for use at 7MHz will be around 2000, so the bandwidth is quite narrow. If the Q really is that high (polish the copper and coat it with a protective varnish or paint...), the parallel resonant impedance will be up around 200k ohms, so it should be a decent match to your FET amplifier. Make sure any loading at the gap is well above 200k ohms resistive, to keep from introducing significant additional loss. I'm thinking about soldering a box from FR4. If you want the antenna to also do a good job rejecting locally generated E field noise, you need to keep things well balanced. What you mean about balanced? Differential output? I should think about it. It has more to do with the symmetry of the way the antenna is mounted. You want to make sure that the capacitance to ground from each side is as nearly the same as possible. You need to put the gap in the loop (the feedpoint) either at the top or at the bottom of the antenna, and for mounting it's often easier to put it at the top. That way you can clamp onto the middle of the bottom of the loop to mount to a pole... But if you have a balanced amplifier at the bottom and bridge the gap symmetrically across the box that amplifier is mounted in, it should also work well. I recommend to you the discussion about small loop antennas in King, Mimno and Wing's "Transmission Lines, Antennas and Waveguides." But at 7MHz, this is probably of marginal utility since any noise generators whose noise would be rejected would have to be very close to the antenna--within a few tens of meters. -- I've done similar amplifiers for multi-turn loops for LF, down around 150kHz, using a balanced JFET design directly across the loop, with good success. You can find the suggested programs athttp://www.zerobeat.net/G4FGQ/. And you likely would get some additional replies if you cross-post to rec.radio.amateur.antenna. Thank. Artem. Cheers, Tom |
Narrow band antenna.
On Mar 13, 9:44 pm, Tom Bruhns wrote:
On Mar 13, 12:09 pm, Artem wrote: On Mar 13, 7:40 pm, Tom Bruhns wrote: On Mar 13, 9:35 am, Artem wrote: Hello all. I'm looking how to make narrow band active antenna for 7 or 10.1mzh. My idea: I will use magnetic antenna with one loop. A one-turn loop of 3.14m cupper pipe with diameter 15mm has 2.687uH. With Varicaps of 192pf it will have resonance frequency of 7MHz. I will load this LC tank directly to Gate one of dual gate MOSFET.http://homepage.eircom..net/%257Eei9...//homepage.eir... Should it work? I'll never seen such schematics. Usually people use transformers. But I will place this transistor directly inside gap in the loop of cupper pipe. The Gate of MOSFET will add only additional 2pf to Varicaps and it will be very easy to compensate. Sorry for English. You should probably download Reg Edwards' RJELoop3 and/or RJELoop1 programs, which will tell you that the conductor loss resistance of your loop will be about ten times the radiation resistance, How can calculate radiation resistance? resistance at 7MHz is skin effecthttp://circuitcalculator.com/wordpress/2007/06/18/skin-effect-calcula... 0.028mm. for copper pipe 15mm in diameter: octave:1 15*3.14*0.028 ans = 1.3188mm^2 0.0155Om/m * 3.14m ans = 0.048670 Om. I think it's not bad. Seehttp://personal.ee.surrey.ac.uk/Personal/D.Jefferies/antennexarticles.... for info on calculating the radiation resistance. I believe that will be helpful. Thank. I'll try to understand what that mean tomorrow. I assume Reg's RJELoop1.exe uses essentially the formula you'll find there. For your loop, that program says inductance is 2.69uH, conductor loss resistance is 46.2 milliohms, and radiation resistance is 5.7 milliohms. Although the conductor loss resistance (essentialy the same as you calculated above is "not bad," you need to consider it with relation to the very low radiation resistance. A current in the loop will dissipate far more power in the resistive loss than in the radiation resistance. You ideally will keep the loss resistance small compared with the radiation resistance, though for receiving (because of the very high level of atmospheric noise on HF and lower frequencies) it matters not nearly so much as for transmitting. When transmitting, you want your power to go into radio waves, not heat. No transmitted. Only received. When receiving you only need signal greater than noise, and it is relatively easy to make an amplifier with low enough noise figure that even an inefficient antenna will result in an amplifier output whose noise is dominated by the atmospheric noise received by the antenna. Is the BF981 will be good enough for this? You recommended did hot use varistors? I'm thinking about some kindhttp://www.toshiba.com/taec/components2/Datasheet_Sync//273/1343.pdf 20 in parallel -------------------------------------- Ultra low series resistance: rs = 0.20 Ù (typ.) -------------------------------------- It will be 0.02 Om So 0.02 ohms sounds like a small amount, but it's almost half as much as the resistance of the copper loop. This may not be a bad thing, because the Q is so high that the bandwidth will only be about 3.5kHz assuming a lossless capacitor, and with the added loss the Q will be lowered to perhaps 1400, allowing a slightly wider bandwidth. With so I'm interesting in QRSS receiving. So narrow bandwidth is very useful because it will help suppress noise from PC with I will connect to radio. narrow a bandwidth you need to be concerned about the stability of the varicap diodes' capacitance. Still, I would think a very high Q fixed capacitor supplying most of the total capacitance would be a good thing. Use only enough varicap to cover the tuning range you want. So for example, with 2.69uH inductance, if you want to cover 7.00MHz to 7.30MHz, you need 192.2pF at the low end and 176.7pF at the high end, a range of a little less than 16pF. You should be able to do that easily with two of your suggested varicap diodes, perhaps a couple of fixed 82pF high Q caps, and a high Q trimmer such as a piston trimmer to trim the center of the range. Understand. Its uneasy to find high stable capacitor at this range. But maybe I can find vacuum capacitors or something like this. What you mean about balanced? Differential output? I should think about it. It has more to do with the symmetry of the way the antenna is mounted. You want to make sure that the capacitance to ground from each side is as nearly the same as possible. You need to put the gap in the loop (the feedpoint) either at the top or at the bottom of the antenna, and for mounting it's often easier to put it at the top. I think that gap at the bottom add more mechanical strength. And it should be easy to connect coaxial cable. That way you can clamp onto the middle of the bottom of the loop to mount to a pole... But if you have a balanced amplifier at the bottom and bridge the gap symmetrically across the box that amplifier is mounted in, it should also work well. It's mean two transistors ans transformer for connect this to the cable. Thank. |
Narrow band antenna.
On Mar 13, 1:18 pm, Artem wrote:
.... (snipping out a lot to keep this a reasonably length...) No transmitted. Only received. I understand, but my point is that an antenna is reciprocal: there is the same percentage loss in the copper resistance whether receiving or transmitting. .... Is the BF981 will be good enough for this? I would think almost any modern RF mosfet would be fine. You do not need very good noise figure for HF reception, even with an antenna with modest efficiency. Just make sure the amplifier input has high effective shunt resistance at the operating frequency-- greater than 200kohms--to preserve the high Q. .... Understand. Its uneasy to find high stable capacitor at this range. But maybe I can find vacuum capacitors or something like this. It should not be that bad. C0G dielectric (also called NPO) capacitors have a _maximum_ temperature coefficient of 30ppm/C. The diameter of the loop itself, and therefore its inductance, will change with temperature in the same range, I believe. C0G capacitors, especially surface mount type, also have extremely low effective series resistance. I've found some C0G SMT caps that seem to have very close to zero temperature coefficient--it varies from lot to lot, apparently depending on the exact mix of the dielectric. What do you suppose the temperature coefficient of the capacitance of varactor diodes is? Note: 100ppm change in capacitance causes 50ppm change in resonant frequency. That's 350Hz at 7MHz. You probably wouldn't even notice that. It's only about 10 percent of the 3dB bandwidth of the antenna. Cheers, Tom |
Narrow band antenna.
On Mar 13, 11:38 pm, K7ITM wrote:
It should not be that bad. C0G dielectric (also called NPO) capacitors have a _maximum_ temperature coefficient of 30ppm/C. The diameter of the loop itself, and therefore its inductance, will change with temperature in the same range, I believe. C0G capacitors, especially surface mount type, also have extremely low effective series resistance. I've found some C0G SMT caps that seem to have very close to zero temperature coefficient--it varies from lot to lot, apparently depending on the exact mix of the dielectric. What do you suppose the temperature coefficient of the capacitance of varactor diodes is? Note: 100ppm change in capacitance causes 50ppm change in resonant frequency. That's 350Hz at 7MHz. You probably wouldn't even notice that. It's only about 10 percent of the 3dB bandwidth of the antenna. Thank you very much. About about transformer (for connect coaxial cable). I can use any ferrite with small permeabilty? |
Narrow band antenna.
On Mar 14, 9:20 am, Artem wrote:
On Mar 13, 11:38 pm, K7ITM wrote: It should not be that bad. C0G dielectric (also called NPO) capacitors have a _maximum_ temperature coefficient of 30ppm/C. The diameter of the loop itself, and therefore its inductance, will change with temperature in the same range, I believe. C0G capacitors, especially surface mount type, also have extremely low effective series resistance. I've found some C0G SMT caps that seem to have very close to zero temperature coefficient--it varies from lot to lot, apparently depending on the exact mix of the dielectric. What do you suppose the temperature coefficient of the capacitance of varactor diodes is? Note: 100ppm change in capacitance causes 50ppm change in resonant frequency. That's 350Hz at 7MHz. You probably wouldn't even notice that. It's only about 10 percent of the 3dB bandwidth of the antenna. Thank you very much. About about transformer (for connect coaxial cable). I can use any ferrite with small permeabilty? Yes, that should be fine. I suppose a transformer will be a convenient way to better match the FET amplifier output to a transmission line. The transformer can be physically quite small. MiniCircuits and some others (CoilCraft; M/A-Com; ...) sell appropriate transformers, and of course they are easy to make if you have an appropriate core. Also you can feed power to the amplifier through the transmission line. The transformer secondary can return to a bypass capacitor instead of directly to ground, and your DC feed appears across that capacitor. The circuit I used for 150kHz loops used a shunt voltage regulator in the amplifier, and by feeding the other end with a controlled variable current, I could avoid problems with uncertain voltage drop in the line plus connectors, and also use the current through the regulator to control the tuning voltage on the varicap diodes. So everything was done through the transmission line. Cheers, Tom |
Narrow band antenna.
On Mar 14, 10:06 pm, Tom Bruhns wrote:
On Mar 14, 9:20 am, Artem wrote: On Mar 13, 11:38 pm, K7ITM wrote: It should not be that bad. C0G dielectric (also called NPO) capacitors have a _maximum_ temperature coefficient of 30ppm/C. The diameter of the loop itself, and therefore its inductance, will change with temperature in the same range, I believe. C0G capacitors, especially surface mount type, also have extremely low effective series resistance. I've found some C0G SMT caps that seem to have very close to zero temperature coefficient--it varies from lot to lot, apparently depending on the exact mix of the dielectric. What do you suppose the temperature coefficient of the capacitance of varactor diodes is? Note: 100ppm change in capacitance causes 50ppm change in resonant frequency. That's 350Hz at 7MHz. You probably wouldn't even notice that. It's only about 10 percent of the 3dB bandwidth of the antenna. Thank you very much. About about transformer (for connect coaxial cable). I can use any ferrite with small permeabilty? Yes, that should be fine. I suppose a transformer will be a convenient way to better match the FET amplifier output to a transmission line. I mean that I will use you suggestion about balanced amplifier. I'll use two FETs. I'll place one more tube from middle of the loop to the gap. And I will use this point as ground point for balanced amplifier. In this case I will have differential signal at FET Drains and I will need transformer for put this signal to coaxial cable. The transformer can be physically quite small. MiniCircuits and some others (CoilCraft; M/A-Com; ...) sell appropriate transformers, and of course they are easy to make if you have an appropriate core. Also you can feed power to the amplifier through the transmission line. The transformer secondary can return to a bypass capacitor instead of directly to ground, and your DC feed appears across that capacitor. The circuit I used for 150kHz loops used a shunt voltage regulator in the amplifier, and by feeding the other end with a controlled variable current, I could avoid problems with uncertain voltage drop in the line plus connectors, and also use the current through the regulator to control the tuning voltage on the varicap diodes. So everything was done through the transmission line. My cable only 10m long. So I this it would be unnecessary. And I will operate with three signals: 1. Varicaps voltages. 2,3 - voltages at secondary FETs gates. Cheers, Tom |
Narrow band antenna.
On Mar 14, 2:15 pm, Artem wrote:
.... I mean that I will use you suggestion about balanced amplifier. I'll use two FETs. I'll place one more tube from middle of the loop to the gap. And I will use this point as ground point for balanced amplifier. In this case I will have differential signal at FET Drains and I will need transformer for put this signal to coaxial cable. The transformer can be physically quite small. Yes...very good. That should help keep the loop nicely balanced, especially if you build it all very symmetrical. That one more tube can also then help support the loop mechanically. Good luck with your project! Cheers, Tom |
Narrow band antenna.
On Mar 15, 12:28 am, K7ITM wrote:
On Mar 14, 2:15 pm, Artem wrote: Yes...very good. That should help keep the loop nicely balanced, especially if you build it all very symmetrical. That one more tube Hi. I have some problem. I can't receive nothing except noise And self oscillation frequency. I have some photos. Could any give me some suggestions? Antenna: http://artembond.no-ip.info/apache2-...t/DSC_9427.JPG Chematics: http://artembond.no-ip.info/apache2-...t/DSC_9431.JPG Amplifier: http://artembond.no-ip.info/apache2-...t/DSC_9426.JPG |
Narrow band antenna.
In article , Artem wrote:
On Mar 15, 12:28 am, K7ITM wrote: On Mar 14, 2:15 pm, Artem wrote: Yes...very good. That should help keep the loop nicely balanced, especially if you build it all very symmetrical. That one more tube Hi. I have some problem. I can't receive nothing except noise And self oscillation frequency. I have some photos. Could any give me some suggestions? Antenna: http://artembond.no-ip.info/apache2-...t/DSC_9427.JPG Chematics: http://artembond.no-ip.info/apache2-...t/DSC_9431.JPG Amplifier: http://artembond.no-ip.info/apache2-...t/DSC_9426.JPG I think you need to narrow band those photos. greg |
Narrow band antenna.
On Mar 20, 10:07 pm, (GregS) wrote:
In article , Artem wrote: I think you need to narrow band those photos. Sorry for hosting. |
Narrow band antenna.
On Thu, 20 Mar 2008 12:58:02 -0700 (PDT), Artem
wrote: Hi. I have some problem. I can't receive nothing except noise And self oscillation frequency. Try choking both what are labeled "RF Out" and "Shield Cable." 73's Richard Clark, KB7QHC |
Narrow band antenna.
On Mar 20, 12:58 pm, Artem wrote:
On Mar 15, 12:28 am, K7ITM wrote: On Mar 14, 2:15 pm, Artem wrote: Yes...very good. That should help keep the loop nicely balanced, especially if you build it all very symmetrical. That one more tube Hi. I have some problem. I can't receive nothing except noise And self oscillation frequency. I have some photos. Could any give me some suggestions? Antenna:http://artembond.no-ip.info/apache2-...t/DSC_9427.JPG Chematics:http://artembond.no-ip.info/apache2-...t/DSC_9431.JPG Amplifier:http://artembond.no-ip.info/apache2-...t/DSC_9426.JPG :-) I saw the comment about "narrow-banding" the images. They were perhaps a little more than we needed, but it was nice to have something we could actually see. They did not take very long to download here, but someone with a slow connection may have troubles. One comment: usually you do not need much voltage gain. It is enough to get power gain with the FETs. That is, the received signal voltage across the gap of the loop, as resonated by the capacitors, should be high enough to be used with a good receiver. The problem is that the impedance is very high there. But that same high impedance makes for easy oscillation. From what you posted, it sounds like maybe you have identified an oscillation. If the AGC voltage is low enough, does the oscillation stop? The amplifier I built used two stages, an FET input stage and a buffer stage, and it had very low voltage gain--I am remembering about 3:1 or only 10dB, and maybe only 1:1 or 0dB including the output transformer, but quite a bit of power gain since it transformed the high loop impedance down to 50 ohms for the feedline. Also, there should be no need for the RF chokes from the gate-1 to source, if the loop is grounded at the bottom. If the loop is grounded at the bottom, the loop plus the RF chokes will short out the source-to-ground resistor. Maybe there is not a need to raise the source voltage above DC ground potential anyway. Also, it may help to NOT bypass the sources to ground, to allow some negative feedback. That may help stabilize the amplifier. If other things occur to me, I will post them... Cheers, Tom |
Narrow band antenna.
On Mar 21, 2:56 am, K7ITM wrote:
On Mar 20, 12:58 pm, Artem wrote: :-) I saw the comment about "narrow-banding" the images. They were perhaps a little more than we needed, but it was nice to have something we could actually see. They did not take very long to download here, but someone with a slow connection may have troubles. I'm move images to ImageShack http://img524.imageshack.us/my.php?image=dsc9427ib7.jpg http://img262.imageshack.us/my.php?image=dsc9431tv9.jpg One comment: usually you do not need much voltage gain. It is enough to get power gain with the FETs. That is, the received signal voltage across the gap of the loop, as resonated by the capacitors, should be high enough to be used with a good receiver. The problem is that the impedance is very high there. But that same high impedance makes for easy oscillation. From what you posted, it sounds like maybe you have identified an oscillation. If the AGC voltage is low enough, does the oscillation stop? Yes. It's stop. my main reason for this antenna is make very narrow antenna for city. I can't receive to my receiver almost nothing by big nose from computers, lamps and other things. But looks like this antenna did not help. Its amplify narrow-band noise. And even add more noise when oscillated. The amplifier I built used two stages, an FET input stage and a buffer stage, and it had very low voltage gain--I am remembering about 3:1 or only 10dB, and maybe only 1:1 or 0dB including the output transformer, but quite a bit of power gain since it transformed the high loop impedance down to 50 ohms for the feedline. Also, there should be no need for the RF chokes from the gate-1 to source, if the loop is grounded at the bottom. Source is not grounded for DC. For better transistors matching and overcurrent protection. If the loop is grounded at the bottom, the loop plus the RF chokes will short out the source-to-ground resistor. Maybe there is not a need to raise the source voltage above DC ground potential anyway. Also, it may help to NOT bypass the sources to ground, to allow some negative feedback. That may help stabilize the amplifier. Sources is not grounded. |
Narrow band antenna.
On Mar 21, 1:36 am, Richard Clark wrote:
On Thu, 20 Mar 2008 12:58:02 -0700 (PDT), Artem wrote: Hi. I have some problem. I can't receive nothing except noise And self oscillation frequency. Try choking both what are labeled "RF Out" and "Shield Cable." Thank. It's good idea. I'll try. |
Narrow band antenna.
On Mar 21, 3:08 am, Artem wrote:
On Mar 21, 2:56 am, K7ITM wrote: On Mar 20, 12:58 pm, Artem wrote: :-) I saw the comment about "narrow-banding" the images. They were perhaps a little more than we needed, but it was nice to have something we could actually see. They did not take very long to download here, but someone with a slow connection may have troubles. I'm move images to ImageShackhttp://img524.imageshack.us/my.php?image=dsc9427ib7.jpghttp://img262.imageshack.us/my.php?image=dsc9431tv9.jpg One comment: usually you do not need much voltage gain. It is enough to get power gain with the FETs. That is, the received signal voltage across the gap of the loop, as resonated by the capacitors, should be high enough to be used with a good receiver. The problem is that the impedance is very high there. But that same high impedance makes for easy oscillation. From what you posted, it sounds like maybe you have identified an oscillation. If the AGC voltage is low enough, does the oscillation stop? Yes. It's stop. my main reason for this antenna is make very narrow antenna for city. I can't receive to my receiver almost nothing by big nose from computers, lamps and other things. But looks like this antenna did not help. Its amplify narrow-band noise. And even add more noise when oscillated. The amplifier I built used two stages, an FET input stage and a buffer stage, and it had very low voltage gain--I am remembering about 3:1 or only 10dB, and maybe only 1:1 or 0dB including the output transformer, but quite a bit of power gain since it transformed the high loop impedance down to 50 ohms for the feedline. Also, there should be no need for the RF chokes from the gate-1 to source, if the loop is grounded at the bottom. Source is not grounded for DC. For better transistors matching and overcurrent protection. If the loop is grounded at the bottom, the loop plus the RF chokes will short out the source-to-ground resistor. Maybe there is not a need to raise the source voltage above DC ground potential anyway. Also, it may help to NOT bypass the sources to ground, to allow some negative feedback. That may help stabilize the amplifier. Sources is not grounded. Yes, unfortunately noise that is generated more than one or two wavelengths away from your antenna will be almost entirely electromagnetic by the time it reaches your antenna. Antennas do not differentiate between "electrically generated" and "magnetically generated" noise, when you are far enough that the electromagnetic field dominates over any near-field electric or magnetic field. The balanced small loop is good for rejecting electric-field noise only if (1) the noise is generated close to the antenna and (2) the antenna is close to the ground (so the electric field is guaranteed to be nearly vertical) -- -- where "close" means relative to a wavelength. So the small balanced loop is especially good for LF and VLF work. Perhaps someone else will have suggestions about what else you might try. Cheers, Tom |
Narrow band antenna.
On Mar 21, 6:26 pm, K7ITM wrote:
On Mar 21, 3:08 am, Artem wrote: Sources is not grounded. Yes, unfortunately noise that is generated more than one or two wavelengths away from your antenna will be almost entirely electromagnetic by the time it reaches your antenna. Antennas do not differentiate between "electrically generated" and "magnetically generated" noise, when you are far enough that the electromagnetic I did not hear nothing about electrically or magnetically photons. It's just photons. field dominates over any near-field electric or magnetic field. The balanced small loop is good for rejecting electric-field noise only if (1) the noise is generated close to the antenna and Yes. Computer, lamps etc close to antenna. (2) the antenna is close to the ground (so the electric field is guaranteed to be nearly 15 floor of 16-floor building. But I think that in this case "ground" are building walls. vertical) -- -- where "close" means relative to a wavelength. So the small balanced loop is especially good for LF and VLF work. my reason was make narrow-band antenna. For reject all out of band noise. Perhaps someone else will have suggestions about what else you might try. Cheers, Tom |
Narrow band antenna.
my reason was make narrow-band antenna. For reject all out of band noise. That is a very worthwhile objective. All that noise adds to the intermod noise and the sooner you can stop it, the better. In my youth I recall calling CQ on 42 mhz for a couple of weeks. Fortunately, a very sharp yagi and very low power saved me from a violation. John Ferrell W8CCW Beware of the dopeler effect (pronounced dope-ler). That's where bad ideas seem good if they come at you fast enough. |
Narrow band antenna.
On Mar 21, 10:02 am, Artem wrote:
On Mar 21, 6:26 pm, K7ITM wrote: On Mar 21, 3:08 am, Artem wrote: Sources is not grounded. Yes, unfortunately noise that is generated more than one or two wavelengths away from your antenna will be almost entirely electromagnetic by the time it reaches your antenna. Antennas do not differentiate between "electrically generated" and "magnetically generated" noise, when you are far enough that the electromagnetic I did not hear nothing about electrically or magnetically photons. It's just photons. :-) Oh, no, not photons again! When you are near to a source -- to a transmitting antenna or to a computer radiating noise -- the fields in general have not developed fully into electromagnetic waves -- photons if you wish. It is quite usual that, close to the source, either the electric or the magnetic field will dominate. Often from noise sources, the near field is predominantly electric, and a properly done loop antenna will reject that, responding only to the, um, photons. field dominates over any near-field electric or magnetic field. The balanced small loop is good for rejecting electric-field noise only if (1) the noise is generated close to the antenna and Yes. Computer, lamps etc close to antenna. (2) the antenna is close to the ground (so the electric field is guaranteed to be nearly 15 floor of 16-floor building. But I think that in this case "ground" are building walls. There is a hint he it is common that tall buildings incorporate a lot of steel, and that will likely act as a shield. I hope this antenna is not mounted inside! vertical) -- -- where "close" means relative to a wavelength. So the small balanced loop is especially good for LF and VLF work. my reason was make narrow-band antenna. For reject all out of band noise. A reasonable thing to do, though a good receiver with a low-distortion and fairly narrow-band front end should not have trouble with out-of- band signals (noise). Do you have a quantitative measure of just how strong this out of band noise is? I'd personally much rather use a preselection filter separate from the antenna, and close to my operating position, to reject out-of-band signals. Even though the antenna you have described has very high Q, I believe I could do better with a two or three resonator filter running at lower Q, since the slope of the attenuation versus frequency is much greater. Unless there was some especially strong signal in the band, I would at least consider a fixed-tuned bandpass filter that covered my band of interest, assuming that band is fairly narrow such as 7.0-7.1MHz. Can you tell that you are getting the expected antenna bandwidth, about 3kHz at the 3dB points at 7MHz? If the amplifier at the antenna has a tendency to oscillate, it very likely also has poor intermodulation performance. Be careful that it doesn't destroy the benefits you are trying to obtain. Cheers, Tom |
Narrow band antenna.
On Mar 22, 8:48 pm, K7ITM wrote:
15 floor of 16-floor building. But I think that in this case "ground" are building walls. There is a hint he it is common that tall buildings incorporate a lot of steel, and that will likely act as a shield. I hope this antenna is not mounted inside! It's not mounted at all. But for tests I'm put this antenna outside. vertical) -- -- where "close" means relative to a wavelength. So the small balanced loop is especially good for LF and VLF work. my reason was make narrow-band antenna. For reject all out of band noise. A reasonable thing to do, though a good receiver with a low-distortion and fairly narrow-band front end should not have trouble with out-of- band signals (noise). Do you have a quantitative measure of just how strong this out of band noise is? Not. Just not received. I'd personally much rather use a preselection filter separate from the antenna, and close to my operating position, to reject out-of-band signals. Even though the antenna you have described has very high Q, I believe I could do better with a two or three resonator filter running at lower Q, since the slope of the attenuation versus frequency is much greater. I will receive QRSS at all. And I think that it would be best way is using narrow-band antenna - filter - synchronous detector. there was some especially strong signal in the band, I would at least consider a fixed-tuned bandpass filter that covered my band of interest, assuming that band is fairly narrow such as 7.0-7.1MHz. Can you tell that you are getting the expected antenna bandwidth, about 3kHz at the 3dB points at 7MHz? I'm just testing. I will purchase RF generator in next week and test. Now I have only self-oscillation frequency. Antenna looks like working. I'm receiving a lots of Morse signals at 7.000 - 7050 Mhz. But I cant recognize any voice signal. This is receiving signal. Looks like narrow-band enough. This is not self oscillation. In self oscillation voltage a few volts. http://img148.imageshack.us/my.php?image=ds0000bu6.png This is schematics. I'm not sure that I'm correct use gual gate transistors. http://img210.imageshack.us/my.php?image=schbr1.jpg I'm not sure that using shielded cable and ferrite chocks is good idea. http://img171.imageshack.us/my.php?image=hwak2.jpg np0 caps. http://img370.imageshack.us/my.php?image=capsnf8.jpg |
Narrow band antenna.
COOL! All worked!
|
Narrow band antenna.
On Mar 23, 11:48 pm, Richard Clark wrote:
On Sun, 23 Mar 2008 12:39:35 -0700 (PDT), Artem wrote: Antenna looks like working. I'm receiving a lots of Morse signals at 7.000 - 7050 Mhz. But I cant recognize any voice signal. Side Band? No. Out of band. I'm now add varicaps and all working! Antenna really very narrow. I'm not sure that using shielded cable and ferrite chocks is good idea. Not enough choking and needs to be repeated a quarter wave down the choked wire(s). It's 7Mhz. quarter wave is 10 miters. I'm use choking: between amplifier and antenna between transformer and coax cable. For amplifier power wires and gain control. |
Narrow band antenna.
On Sun, 23 Mar 2008 12:39:35 -0700 (PDT), Artem
wrote: Antenna looks like working. I'm receiving a lots of Morse signals at 7.000 - 7050 Mhz. But I cant recognize any voice signal. Side Band? I'm not sure that using shielded cable and ferrite chocks is good idea. Not enough choking and needs to be repeated a quarter wave down the choked wire(s). 73's Richard Clark, KB7QHC |
Narrow band antenna.
On Sun, 23 Mar 2008 14:42:22 -0700 (PDT), Artem
wrote: I'm not sure that using shielded cable and ferrite chocks is good idea. Not enough choking and needs to be repeated a quarter wave down the choked wire(s). It's 7Mhz. quarter wave is 10 miters. Then again at the far end of the wire(s). I'm use choking: between amplifier and antenna between transformer and coax cable. For amplifier power wires and gain control. I've observed that, and I have observed it is not enough from your photo - if you still have self-oscillation. Your pictures do not reveal any choking of the RF Out cable. As for the diagonal arm for "ground." This is fine insofar as it being placed in the electrical middle of the antenna loop (a ground), but all this rat's nest of wiring throws the concept of balance out the window. I see in earlier pictures where you clean that up with careful routing, but it seems much too busy. This leads me into the comments following: On another note, the AGC seems overly elaborate, especially when all that wire could be introducing the self-oscillation. Further, wiring in power seems another invitation to problems when a 9V battery would solve that too. Local power would discard the need for the ground coming from the loop's perimeter, eliminate unnecessary AGC, reduce the complexity of choking, lower gain (it obviously has too much), and give you only one coax coming from the antenna. You need to solve the self-oscillation through removing complexity. When you accomplish that, THEN that is the time to add it back in, one thing at a time. You will probably discover all those features and design gimmicks are not worth it. 73's Richard Clark, KB7QHC |
Narrow band antenna.
On Sun, 23 Mar 2008 14:27:49 -0700 (PDT), Artem
wrote: COOL! All worked! It would seem no further advice is necessary, much less my last bit of wisdom on the topic. It would help if you were to elaborate as to what actually killed the oscillation. 73's Richard Clark, KB7QHC |
Narrow band antenna.
On Mar 24, 3:24 am, Richard Clark wrote:
On Sun, 23 Mar 2008 14:42:22 -0700 (PDT), Artem wrote: I'm not sure that using shielded cable and ferrite chocks is good idea. Not enough choking and needs to be repeated a quarter wave down the choked wire(s). It's 7Mhz. quarter wave is 10 miters. Then again at the far end of the wire(s). I'm use choking: between amplifier and antenna between transformer and coax cable. For amplifier power wires and gain control. I've observed that, and I have observed it is not enough from your photo - if you still have self-oscillation. Your pictures do not reveal any choking of the RF Out cable. It's inside. Nearby BNC socket. As for the diagonal arm for "ground." This is fine insofar as it being placed in the electrical middle of the antenna loop (a ground), but all this rat's nest of wiring throws the concept of balance out the window. I think that some disbalance should compensate differencial amplifier on transistors. I see in earlier pictures where you clean that up with careful routing, but it seems much too busy. This leads me into the comments following: On another note, the AGC seems overly elaborate, especially when all that wire could be introducing the self-oscillation. Further, wiring in power seems another invitation to problems when a 9V battery would solve that too. Local power would discard the need for the ground Yes. But FETs draw more that 10ma each. coming from the loop's perimeter, eliminate unnecessary AGC, reduce the complexity of choking, lower gain (it obviously has too much), and give you only one coax coming from the antenna. Cable length is not problem. I'm living in apartment. I can put antenna outside the window. But not on the roof. I can make power supply over coax cable. I can put Atmega8 (en example) to amplifier and add DACs for operate varicaps, AGC. I can add rectifier and filter for detect self-oscillation and automatics reduce AGC. But it's not necessary. |
Narrow band antenna.
On Mar 24, 5:45 pm, Richard Clark wrote:
As for the diagonal arm for "ground." This is fine insofar as it being placed in the electrical middle of the antenna loop (a ground), but all this rat's nest of wiring throws the concept of balance out the window. I think that some disbalance should compensate differencial amplifier on transistors. That makes no sense whatever. Disbalance mean in-phase signal on gate 1 FETs. differencial will not amplify this signal. Sounds like a lot of unnecessary complexity. The one thing you repeat is varicaps, but I don't see them. I have. I just did now how them because this is trivial. |
Narrow band antenna.
On Mar 24, 5:45 pm, Richard Clark wrote:
As for the diagonal arm for "ground." This is fine insofar as it being placed in the electrical middle of the antenna loop (a ground), but all this rat's nest of wiring throws the concept of balance out the window. I think that some disbalance should compensate differencial amplifier on transistors. That makes no sense whatever. Disbalance mean in-phase signal on gate 1 FETs. differencial will not amplify this signal. Sounds like a lot of unnecessary complexity. The one thing you repeat is varicaps, but I don't see them. I have. I just did now how them because this is trivial. |
Narrow band antenna.
On Mar 24, 4:59 pm, Artem wrote:
I just did now how them because this is trivial. I did not show varicaps because this is trivial. Sorry. |
Narrow band antenna.
On Mar 24, 4:59 pm, Artem wrote:
I just did now how them because this is trivial. I did not show varicaps because this is trivial. Sorry. |
Narrow band antenna.
On Mar 24, 4:59 pm, Artem wrote:
I just did now how them because this is trivial. I did not show varicaps because this is trivial. Sorry. |
Narrow band antenna.
On Mon, 24 Mar 2008 04:32:39 -0700 (PDT), Artem
wrote: I've observed that, and I have observed it is not enough from your photo - if you still have self-oscillation. Your pictures do not reveal any choking of the RF Out cable. It's inside. Nearby BNC socket. Which defeats the choking. As for the diagonal arm for "ground." This is fine insofar as it being placed in the electrical middle of the antenna loop (a ground), but all this rat's nest of wiring throws the concept of balance out the window. I think that some disbalance should compensate differencial amplifier on transistors. That makes no sense whatever. another invitation to problems when a 9V battery would solve that too. Local power would discard the need for the ground Yes. But FETs draw more that 10ma each. That is trivial. However, you can bias for less because you don't need that much drain current. coming from the loop's perimeter, eliminate unnecessary AGC, reduce the complexity of choking, lower gain (it obviously has too much), and give you only one coax coming from the antenna. Cable length is not problem. I'm living in apartment. I can put antenna outside the window. But not on the roof. I can make power supply over coax cable. I can put Atmega8 (en example) to amplifier and add DACs for operate varicaps, AGC. I can add rectifier and filter for detect self-oscillation and automatics reduce AGC. But it's not necessary. Sounds like a lot of unnecessary complexity. The one thing you repeat is varicaps, but I don't see them. 73's Richard Clark, KB7QHC |
Narrow band antenna.
On Mon, 24 Mar 2008 07:59:50 -0700 (PDT), Artem
wrote: I think that some disbalance should compensate differencial amplifier on transistors. That makes no sense whatever. Disbalance mean in-phase signal on gate 1 FETs. differencial will not amplify this signal. This is still a strain in language as you have done nothing to describe what the "compensation" is for. The circuit of your schematic is fully differential in a bridge configuration, so saying it will not amplify still makes no sense. To offer a deliberate imbalance to a balanced circuit gives rise to astability which is the first hallmark of oscillation - especially in an amplifier with too much gain, and too much current drain - or a lockdown. I get every impression that this bridge configuration arrived from some sense of "ground" that then drove the need for the cross piece to the midpoint of the loop. That point is "ground", but only as an electrical neutral to the loop. It carries no other "ground" distinction and you could have as easily built a single MOSFET amplifier rather than a bridge configuration. A split shield around the loop (or integrating it into the design) would have simplified AGC and control lines too. You tried to incorporate some of the split shield design into this when you enclosed the amplifier and made a socket connection, but you defeated the benefit of the choke at the same time with a zero net gain (the choke, as built, has no use). Sounds like a lot of unnecessary complexity. The one thing you repeat is varicaps, but I don't see them. I have. I just did now how them because this is trivial. They are not shown in your schematic. I don't see them in your photos. Making them operational is adding yet more lines, although I can see they would be necessary for your purposes. Providing the decoupled varicap bias into a balanced circuit is not trivial at all, and offers the prospects of returning to that self oscillation. There will be something like half a dozen components for that alone. HOWEVER, this is all beside the point unless your design breaks into oscillation again. You haven't informed us how you cured that since you announced you had solve all your problems. 73's Richard Clark, KB7QHC |
Narrow band antenna.
On Mar 24, 10:02 pm, Richard Clark wrote:
On Mon, 24 Mar 2008 07:59:50 -0700 (PDT), Artem wrote: I think that some disbalance should compensate differencial amplifier on transistors. That makes no sense whatever. Disbalance mean in-phase signal on gate 1 FETs. differencial will not amplify this signal. This is still a strain in language as you have done nothing to describe what the "compensation" is for. The circuit of your schematic is fully differential in a bridge configuration, so saying it will not amplify still makes no sense. To offer a deliberate It will not amplify signal in-phase signal. It's same like differential amplifier. I get every impression that this bridge configuration arrived from some sense of "ground" that then drove the need for the cross piece to the midpoint of the loop. That point is "ground", but only as an electrical neutral to the loop. It carries no other "ground" Yes. It's "Ground" only for bridge amplifier. distinction and you could have as easily built a single MOSFET amplifier rather than a bridge configuration. A split shield around It's more difficult for me. It's looks more simply for me to build fully symmetrical amplifier. the loop (or integrating it into the design) would have simplified AGC and control lines too. You tried to incorporate some of the split shield design into this when you enclosed the amplifier and made a socket connection, but you defeated the benefit of the choke at the same time with a zero net gain (the choke, as built, has no use). I have. Sounds like a lot of unnecessary complexity. The one thing you repeat is varicaps, but I don't see them. I have. I just did now how them because this is trivial. They are not shown in your schematic. I don't see them in your photos. Making them operational is adding yet more lines, although I can see they would be necessary for your purposes. http://img245.imageshack.us/my.php?image=d3du5.jpg |
Narrow band antenna.
On Sun, 23 Mar 2008 12:39:35 -0700 (PDT), Artem
wrote: On Mar 22, 8:48 pm, K7ITM wrote: 15 floor of 16-floor building. But I think that in this case "ground" are building walls. There is a hint he it is common that tall buildings incorporate a lot of steel, and that will likely act as a shield. I hope this antenna is not mounted inside! It's not mounted at all. But for tests I'm put this antenna outside. vertical) -- -- where "close" means relative to a wavelength. So the small balanced loop is especially good for LF and VLF work. my reason was make narrow-band antenna. For reject all out of band noise. A reasonable thing to do, though a good receiver with a low-distortion and fairly narrow-band front end should not have trouble with out-of- band signals (noise). Do you have a quantitative measure of just how strong this out of band noise is? Not. Just not received. I'd personally much rather use a preselection filter separate from the antenna, and close to my operating position, to reject out-of-band signals. Even though the antenna you have described has very high Q, I believe I could do better with a two or three resonator filter running at lower Q, since the slope of the attenuation versus frequency is much greater. I will receive QRSS at all. And I think that it would be best way is using narrow-band antenna - filter - synchronous detector. there was some especially strong signal in the band, I would at least consider a fixed-tuned bandpass filter that covered my band of interest, assuming that band is fairly narrow such as 7.0-7.1MHz. Can you tell that you are getting the expected antenna bandwidth, about 3kHz at the 3dB points at 7MHz? I'm just testing. I will purchase RF generator in next week and test. Now I have only self-oscillation frequency. Antenna looks like working. I'm receiving a lots of Morse signals at 7.000 - 7050 Mhz. But I cant recognize any voice signal. This is receiving signal. Looks like narrow-band enough. This is not self oscillation. In self oscillation voltage a few volts. http://img148.imageshack.us/my.php?image=ds0000bu6.png This is schematics. I'm not sure that I'm correct use gual gate transistors. http://img210.imageshack.us/my.php?image=schbr1.jpg I'm not sure that using shielded cable and ferrite chocks is good idea. http://img171.imageshack.us/my.php?image=hwak2.jpg np0 caps. http://img370.imageshack.us/my.php?image=capsnf8.jpg Please see the US ARRL frequency chart he http://www.arrl.org/FandES/field/reg...ands_color.pdf 7000 to 7050 MHz is RTTY and Morse code only. If you want voice, probably SSB try 7125 to 7300 MHz. |
Narrow band antenna.
On Mar 25, 7:29 am, JosephKK wrote:
Please see the US ARRL frequency chart he http://www.arrl.org/FandES/field/reg...ands_color.pdf 7000 to 7050 MHz is RTTY and Morse code only. If you want voice, probably SSB try 7125 to 7300 MHz. I'm in Europe. We have only 7000....7100. |
Narrow band antenna.
On Mon, 24 Mar 2008 15:40:53 -0700 (PDT), Artem
wrote: This is still a strain in language as you have done nothing to describe what the "compensation" is for. The circuit of your schematic is fully differential in a bridge configuration, so saying it will not amplify still makes no sense. To offer a deliberate It will not amplify signal in-phase signal. It's same like differential amplifier. This still makes no sense. You have not described what you are "compensating" for, and differential amplifiers amplify without distinction to "in-phase" or "out-of-phase." If it did, you are not using the right topology because you are using operational amplifier terminology - the circuit is not an operational amplifier, even by discrete components. They are not shown in your schematic. I don't see them in your photos. Making them operational is adding yet more lines, although I can see they would be necessary for your purposes. http://img245.imageshack.us/my.php?image=d3du5.jpg Nice close-up. Choking of some of the lines seems OK, but not the coax. So, now where is the schematic of the biasing for these varicaps? If those two clear insulation lines are going to the loop, it is going to be hard to apply DC to a dead short - or does that black shroud cover more than the varicaps? 73's Richard Clark, KB7QHC |
Narrow band antenna.
On Mar 25, 9:33 pm, Richard Clark wrote:
On Mon, 24 Mar 2008 15:40:53 -0700 (PDT), Artem wrote: This is still a strain in language as you have done nothing to describe what the "compensation" is for. The circuit of your schematic is fully differential in a bridge configuration, so saying it will not amplify still makes no sense. To offer a deliberate It will not amplify signal in-phase signal. It's same like differential amplifier. This still makes no sense. You have not described what you are "compensating" for, and differential amplifiers amplify without distinction to "in-phase" or "out-of-phase." If it did, you are not using the right topology because you are using operational amplifier terminology - the circuit is not an operational amplifier, even by discrete components. They are not shown in your schematic. I don't see them in your photos. Making them operational is adding yet more lines, although I can see they would be necessary for your purposes. http://img245.imageshack.us/my.php?image=d3du5.jpg Nice close-up. Choking of some of the lines seems OK, but not the coax. http://img370.imageshack.us/my.php?image=d2eb0.jpg Could you find in this picture choke? So, now where is the schematic of the biasing for these varicaps? If those two clear insulation lines are going to the loop, It's lines from resonance loop to amplifier. it is going to be hard to apply DC to a dead short - or does that black shroud cover more than the varicaps? Now my Antenna in broken. I will fix my antenna mad make a web for schematics, software for calculation? etc. PS: Could anyone know, What I can receive in QRSS, 7 MHz in Europe on this http://www.radiointel.com/review-degende1103.htm receiver? |
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