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Getting A Signal in the Basement? (antenna lead-in for AM BC and/or shortwave)
In the interest of my recent tinkerings with radios (both antique and
homebrew), I have put up an 80 foot straight wire antenna above the house. It sits about 35 feet up from, and horizontal to, the ground. I am using a lead in from one end made of insulated stranded copper wire (basically old speaker cable, about 18 guage I think). Right now, the lead-in wire comes down from the end of the antenna closest to the sun porch, and in through the storm window via a well-insulated bushing. Due to the location of this lead-in, this is the spot wherre I have been doing most of the tinkering with the radios. I also have a copper pipe ground rod in a nearby location so as to have as short a path to ground as possible.) It seems to work OK for now but I would ideally like to run the lead-in into my basement where my workshop is. I read somewhere (I think it might have been in reference to crystal sets) that you can use coax for an AM lead-in. Would this be better for a longer/more convoluted lead-in? Would I use the braded shield as the ground connection or would I run a separate ground back to my copper rod outside? What type of coax would be best for this sort of thing? I am interested in receiving both broadcast and shortwave. Any info on this matter would be most appreciated. thanks in advance, Dave |
David Forsyth wrote:
I read somewhere (I think it might have been in reference to crystal sets) that you can use coax for an AM lead-in. Would this be better for a longer/more convoluted lead-in? Not necessarily. If you need shielding for noise purposes that might be worthwhile but apart from that there's no advantage over just a single wire. The radios you're typically working on have high impedance inputs. In a random-wire installation, the total length of the wire IS the antenna. There is no lead-in per se. By using a shielded cable you are effectively shielding that portion of your antenna. I think you might find it won't work as well on BCB with the shield grounded and you would have to lift that at the radio end negating having it there in the first place. On shortwave freqs the loss of the cable in a mismatched state such as feeding a random wire (or an old hi-z radio) may also work against you. I'd go with the plain wire unless there is a noise problem that is being picked up by the vertical portion of the antenna. My 2c. -Bill |
David Forsyth wrote:
I read somewhere (I think it might have been in reference to crystal sets) that you can use coax for an AM lead-in. Would this be better for a longer/more convoluted lead-in? Not necessarily. If you need shielding for noise purposes that might be worthwhile but apart from that there's no advantage over just a single wire. The radios you're typically working on have high impedance inputs. In a random-wire installation, the total length of the wire IS the antenna. There is no lead-in per se. By using a shielded cable you are effectively shielding that portion of your antenna. I think you might find it won't work as well on BCB with the shield grounded and you would have to lift that at the radio end negating having it there in the first place. On shortwave freqs the loss of the cable in a mismatched state such as feeding a random wire (or an old hi-z radio) may also work against you. I'd go with the plain wire unless there is a noise problem that is being picked up by the vertical portion of the antenna. My 2c. -Bill |
--exray-- wrote:
I'd go with the plain wire unless there is a noise problem that is being picked up by the vertical portion of the antenna. Being a smarter than average bear (my own opinion of course :~) I figured I'd use coax to bring my long wire antenna into the house, and I'd ground the shield. Didn't work very well. Now I'm just using plain wires for each of the antenna and ground and it works very well. I'd say that my antenna outside the house is about 10-15' off the ground and runs for about 100' in a 50' x 50' "L" shape. -- regards from :: John Bartley 43 Norway Spruce Street Stittsville, Ontario Canada, K2S1P5 ( If you slow down it takes longer - does that apply to life also?) -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
--exray-- wrote:
I'd go with the plain wire unless there is a noise problem that is being picked up by the vertical portion of the antenna. Being a smarter than average bear (my own opinion of course :~) I figured I'd use coax to bring my long wire antenna into the house, and I'd ground the shield. Didn't work very well. Now I'm just using plain wires for each of the antenna and ground and it works very well. I'd say that my antenna outside the house is about 10-15' off the ground and runs for about 100' in a 50' x 50' "L" shape. -- regards from :: John Bartley 43 Norway Spruce Street Stittsville, Ontario Canada, K2S1P5 ( If you slow down it takes longer - does that apply to life also?) -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
Whichever way you go, be sure to put a lightning arrestor on the lead in.
David Forsyth wrote: In the interest of my recent tinkerings with radios (both antique and homebrew), I have put up an 80 foot straight wire antenna above the house. It sits about 35 feet up from, and horizontal to, the ground. I am using a lead in from one end made of insulated stranded copper wire (basically old speaker cable, about 18 guage I think). Right now, the lead-in wire comes down from the end of the antenna closest to the sun porch, and in through the storm window via a well-insulated bushing. Due to the location of this lead-in, this is the spot wherre I have been doing most of the tinkering with the radios. I also have a copper pipe ground rod in a nearby location so as to have as short a path to ground as possible.) It seems to work OK for now but I would ideally like to run the lead-in into my basement where my workshop is. I read somewhere (I think it might have been in reference to crystal sets) that you can use coax for an AM lead-in. Would this be better for a longer/more convoluted lead-in? Would I use the braded shield as the ground connection or would I run a separate ground back to my copper rod outside? What type of coax would be best for this sort of thing? I am interested in receiving both broadcast and shortwave. Any info on this matter would be most appreciated. thanks in advance, Dave -- Joe Leikhim K4SAT "Jazz is not dead. It just smells funny." -F.Z. |
Whichever way you go, be sure to put a lightning arrestor on the lead in.
David Forsyth wrote: In the interest of my recent tinkerings with radios (both antique and homebrew), I have put up an 80 foot straight wire antenna above the house. It sits about 35 feet up from, and horizontal to, the ground. I am using a lead in from one end made of insulated stranded copper wire (basically old speaker cable, about 18 guage I think). Right now, the lead-in wire comes down from the end of the antenna closest to the sun porch, and in through the storm window via a well-insulated bushing. Due to the location of this lead-in, this is the spot wherre I have been doing most of the tinkering with the radios. I also have a copper pipe ground rod in a nearby location so as to have as short a path to ground as possible.) It seems to work OK for now but I would ideally like to run the lead-in into my basement where my workshop is. I read somewhere (I think it might have been in reference to crystal sets) that you can use coax for an AM lead-in. Would this be better for a longer/more convoluted lead-in? Would I use the braded shield as the ground connection or would I run a separate ground back to my copper rod outside? What type of coax would be best for this sort of thing? I am interested in receiving both broadcast and shortwave. Any info on this matter would be most appreciated. thanks in advance, Dave -- Joe Leikhim K4SAT "Jazz is not dead. It just smells funny." -F.Z. |
If the antenna is the typical end-fed wire then the impedance will be
very high. Most AM radios have a high impedance input designed to match a random wire like that. If you use coax, the capacitance of the coax (center conductor to shield) will essentially short most of the signal to ground and little will get to the receiver. If you've ever opened up the coax used on car radios you'll find that it is a special high impedance coax. A small wire fits loosly thru an insulated tube with the shield around the outside. This keeps a relatively large spacing between the center conductor and the shield in order to minimize capacitance. |
If the antenna is the typical end-fed wire then the impedance will be
very high. Most AM radios have a high impedance input designed to match a random wire like that. If you use coax, the capacitance of the coax (center conductor to shield) will essentially short most of the signal to ground and little will get to the receiver. If you've ever opened up the coax used on car radios you'll find that it is a special high impedance coax. A small wire fits loosly thru an insulated tube with the shield around the outside. This keeps a relatively large spacing between the center conductor and the shield in order to minimize capacitance. |
Thanks for all who responded thus far (and sorry to be such a wellspring of
newbie questons). Yes, I must confess that there is no lightning arrestor installed as of yet! I was aware that one should install such a device at the time I put up the antenna, but I didn't have one handy, nor did I feel the need to invest in one. I was thinking that in the late fall/winter we really don't get any lightning here (north-east PA) and therefore I wouldn't really need a lightning arrestor until the Spring. I'm sure I'm probably wrong on this, though, as it was mainly a product of my Scots heritage getting the best of me. I guess it would be helpful to include some more specifics about what radios Im trying to feed with this antenna. Thus far, I have accumulated an A****er Kent "big box" Model 20, an A****er Kent 55-C (chassis only), an RCA Radiola 18, and a homebrew regen. This is my latest project. It uses a '36 screen grid tube as detector and a 6F8G as dual-stage audio driving a loudspeaker through an overly large Hammond OPT. So far I've only wound a coil for BC band and this thing works amazingly well. I plan on making some smaller coils for short wave (hopefully the solar storm stuff wont be long in staying). I also have future plans for a Grigsby-Grunow that was given to me to fix up, but it's on the distant horizon as of yet. So far nobody has complained about the large pile of radio-related crap in the sun porch, but Im sure it's a matter of time. I will probably have to route the antenna lead-in through a wall or two and around some bends and twists to get it into the workshop in the basement. I guess I was assuming I should use coax for this, but apparently not, from what everyone here is saying. I'm not as concerned about noise as I am about possible signal loss. Is this something to even be concerned about with a plain old insulated stranded wire lead-in routed through walls and such? I'm still new at this RF stuff (being a relatively recent convert from the realm of "AF"), so please bear with me, and thanks for all the helpful tips and suggestions! Dave |
Thanks for all who responded thus far (and sorry to be such a wellspring of
newbie questons). Yes, I must confess that there is no lightning arrestor installed as of yet! I was aware that one should install such a device at the time I put up the antenna, but I didn't have one handy, nor did I feel the need to invest in one. I was thinking that in the late fall/winter we really don't get any lightning here (north-east PA) and therefore I wouldn't really need a lightning arrestor until the Spring. I'm sure I'm probably wrong on this, though, as it was mainly a product of my Scots heritage getting the best of me. I guess it would be helpful to include some more specifics about what radios Im trying to feed with this antenna. Thus far, I have accumulated an A****er Kent "big box" Model 20, an A****er Kent 55-C (chassis only), an RCA Radiola 18, and a homebrew regen. This is my latest project. It uses a '36 screen grid tube as detector and a 6F8G as dual-stage audio driving a loudspeaker through an overly large Hammond OPT. So far I've only wound a coil for BC band and this thing works amazingly well. I plan on making some smaller coils for short wave (hopefully the solar storm stuff wont be long in staying). I also have future plans for a Grigsby-Grunow that was given to me to fix up, but it's on the distant horizon as of yet. So far nobody has complained about the large pile of radio-related crap in the sun porch, but Im sure it's a matter of time. I will probably have to route the antenna lead-in through a wall or two and around some bends and twists to get it into the workshop in the basement. I guess I was assuming I should use coax for this, but apparently not, from what everyone here is saying. I'm not as concerned about noise as I am about possible signal loss. Is this something to even be concerned about with a plain old insulated stranded wire lead-in routed through walls and such? I'm still new at this RF stuff (being a relatively recent convert from the realm of "AF"), so please bear with me, and thanks for all the helpful tips and suggestions! Dave |
Bob, is this something I could possibly be able to use in this application?
Where does one find such high-impedance coax? As an alternative, would it be possible to put an active device up near the antenna that would act as a buffer to feed a low-impedance line? Dave "Bob Lewis (AA4PB)" wrote in message ... If the antenna is the typical end-fed wire then the impedance will be very high. Most AM radios have a high impedance input designed to match a random wire like that. If you use coax, the capacitance of the coax (center conductor to shield) will essentially short most of the signal to ground and little will get to the receiver. If you've ever opened up the coax used on car radios you'll find that it is a special high impedance coax. A small wire fits loosly thru an insulated tube with the shield around the outside. This keeps a relatively large spacing between the center conductor and the shield in order to minimize capacitance. |
Bob, is this something I could possibly be able to use in this application?
Where does one find such high-impedance coax? As an alternative, would it be possible to put an active device up near the antenna that would act as a buffer to feed a low-impedance line? Dave "Bob Lewis (AA4PB)" wrote in message ... If the antenna is the typical end-fed wire then the impedance will be very high. Most AM radios have a high impedance input designed to match a random wire like that. If you use coax, the capacitance of the coax (center conductor to shield) will essentially short most of the signal to ground and little will get to the receiver. If you've ever opened up the coax used on car radios you'll find that it is a special high impedance coax. A small wire fits loosly thru an insulated tube with the shield around the outside. This keeps a relatively large spacing between the center conductor and the shield in order to minimize capacitance. |
Hi,
David wrote: Yes, I must confess that there is no lightning arrestor installed as of yet! it was mainly a product of my Scots heritage getting the best of me. Sounds familiar. Actually a lighting arrestor isn't worth much, and I'd suggest a large knife switch directly between the lead-in and ground. Your present antenna is ideal for broadcast reception since, as has been mentioned, most antique radios were designed with this sort of antenna in mind. Extending the lead-in to the basement will simply make it work better. The vertical part of the lead-in catches most of the signal. Keep it as far from power lines and noise sources as possible. If your ground is now farther away, you may lose some efficiency; my ground is a driven well in the basement. On short wave, things are different. I've used my inverted-L for short wave too, but never compared it directly against another antenna. Cheers, Alan |
Hi,
David wrote: Yes, I must confess that there is no lightning arrestor installed as of yet! it was mainly a product of my Scots heritage getting the best of me. Sounds familiar. Actually a lighting arrestor isn't worth much, and I'd suggest a large knife switch directly between the lead-in and ground. Your present antenna is ideal for broadcast reception since, as has been mentioned, most antique radios were designed with this sort of antenna in mind. Extending the lead-in to the basement will simply make it work better. The vertical part of the lead-in catches most of the signal. Keep it as far from power lines and noise sources as possible. If your ground is now farther away, you may lose some efficiency; my ground is a driven well in the basement. On short wave, things are different. I've used my inverted-L for short wave too, but never compared it directly against another antenna. Cheers, Alan |
David Forsyth wrote:
Bob, is this something I could possibly be able to use in this application? Where does one find such high-impedance coax? As an alternative, would it be possible to put an active device up near the antenna that would act as a buffer to feed a low-impedance line? Dave The trick in this recommendation is that the car radio feedline is a specific length (a few feet)and its capacitance is taken into account. -Bill "Bob Lewis (AA4PB)" wrote in message ... If the antenna is the typical end-fed wire then the impedance will be very high. Most AM radios have a high impedance input designed to match a random wire like that. If you use coax, the capacitance of the coax (center conductor to shield) will essentially short most of the signal to ground and little will get to the receiver. If you've ever opened up the coax used on car radios you'll find that it is a special high impedance coax. A small wire fits loosly thru an insulated tube with the shield around the outside. This keeps a relatively large spacing between the center conductor and the shield in order to minimize capacitance. |
David Forsyth wrote:
Bob, is this something I could possibly be able to use in this application? Where does one find such high-impedance coax? As an alternative, would it be possible to put an active device up near the antenna that would act as a buffer to feed a low-impedance line? Dave The trick in this recommendation is that the car radio feedline is a specific length (a few feet)and its capacitance is taken into account. -Bill "Bob Lewis (AA4PB)" wrote in message ... If the antenna is the typical end-fed wire then the impedance will be very high. Most AM radios have a high impedance input designed to match a random wire like that. If you use coax, the capacitance of the coax (center conductor to shield) will essentially short most of the signal to ground and little will get to the receiver. If you've ever opened up the coax used on car radios you'll find that it is a special high impedance coax. A small wire fits loosly thru an insulated tube with the shield around the outside. This keeps a relatively large spacing between the center conductor and the shield in order to minimize capacitance. |
David Forsyth wrote: Thanks for all who responded thus far (and sorry to be such a wellspring of newbie questons). Yes, I must confess that there is no lightning arrestor installed as of yet! I was aware that one should install such a device at the time I put up the antenna, but I didn't have one handy, nor did I feel the need to invest in one. I was thinking that in the late fall/winter we really don't get any lightning here (north-east PA) and therefore I wouldn't really need a lightning arrestor until the Spring. I'm sure I'm probably wrong on this, though, as it was mainly a product of my Scots heritage getting the best of me. Do yourself a favor: at the end of your antenna (inside the house) install a neon bulb and a 100K resistor in series, connected between the antenna and ground. Then, on a windy day, go watch the bulb. You can make your own static discharge unit: -----------\ /-------------- Copper \ / Copper Strip / \ Strip -----+-----/ \-----+-------- | | +---/\/\/\/-----+ 100K The points on the copper strips need to be sharp, not blunt, at the gap. Wire one strip to ground with #10 or larger copper wire, and the other strip to the antenna. Set the gap between the copper strips as narrow as you can. Solder a 100K resistor across the copper strips. |
David Forsyth wrote: Thanks for all who responded thus far (and sorry to be such a wellspring of newbie questons). Yes, I must confess that there is no lightning arrestor installed as of yet! I was aware that one should install such a device at the time I put up the antenna, but I didn't have one handy, nor did I feel the need to invest in one. I was thinking that in the late fall/winter we really don't get any lightning here (north-east PA) and therefore I wouldn't really need a lightning arrestor until the Spring. I'm sure I'm probably wrong on this, though, as it was mainly a product of my Scots heritage getting the best of me. Do yourself a favor: at the end of your antenna (inside the house) install a neon bulb and a 100K resistor in series, connected between the antenna and ground. Then, on a windy day, go watch the bulb. You can make your own static discharge unit: -----------\ /-------------- Copper \ / Copper Strip / \ Strip -----+-----/ \-----+-------- | | +---/\/\/\/-----+ 100K The points on the copper strips need to be sharp, not blunt, at the gap. Wire one strip to ground with #10 or larger copper wire, and the other strip to the antenna. Set the gap between the copper strips as narrow as you can. Solder a 100K resistor across the copper strips. |
Hi,
There is no simple answer to your problem as the impedances and frequency range involved are too great. However, as you are not intending to use the antenna to transmit with, take a look at this site and do a search on "LONG WIRE BALUN". http://www.maplin.co.uk/ If you are in the U.S. I am sure that there will be an equivalent item around somewhere. It is even possible that there is a design for one of these out on the net. The device is mis-named really and should be called something like an UNUN. Of course it is a kludge but what the hell as it should be better than a single wire or coax feed from your basement. Cheers - Joe, G3LLV |
Hi,
There is no simple answer to your problem as the impedances and frequency range involved are too great. However, as you are not intending to use the antenna to transmit with, take a look at this site and do a search on "LONG WIRE BALUN". http://www.maplin.co.uk/ If you are in the U.S. I am sure that there will be an equivalent item around somewhere. It is even possible that there is a design for one of these out on the net. The device is mis-named really and should be called something like an UNUN. Of course it is a kludge but what the hell as it should be better than a single wire or coax feed from your basement. Cheers - Joe, G3LLV |
After doing a lot of reading on the web about long wires, short wires,
inverted L's, impedance matching, baluns, ununs, onions, fundip, and who knows what else... I was thinking (run for cover please) Couldn't one simply use a small active device to buffer the straight wire antenna at the end where it tethers to Ye Olde Oak tree or whatever it's tied to? I was thinking you could even make it powered with a small gel cell or something and a solar cell to power it. Some sort of wide-band amplifier that would have a suitably high input impedance to accomodate the higher and varying impedance of the wire over the desired frequency range, and yet having a fixed 75 or 50 ohm output impedance to drive the coax that runs back to the house. Then you could use a transformer in the house at the receiver if it's the type that wants to be fed from a high-impedance. I would think this would get around the problem of an impedance matching transformer mismatching the antenna on frequncies where the antenna impedance drops significantly. Also it could provide perhaps some minimal gain to boot. Some of those commercial impedance matching transformers sell for over $50 US. So I would think a small buffer amp might not be too cost-ineffective. Dave |
After doing a lot of reading on the web about long wires, short wires,
inverted L's, impedance matching, baluns, ununs, onions, fundip, and who knows what else... I was thinking (run for cover please) Couldn't one simply use a small active device to buffer the straight wire antenna at the end where it tethers to Ye Olde Oak tree or whatever it's tied to? I was thinking you could even make it powered with a small gel cell or something and a solar cell to power it. Some sort of wide-band amplifier that would have a suitably high input impedance to accomodate the higher and varying impedance of the wire over the desired frequency range, and yet having a fixed 75 or 50 ohm output impedance to drive the coax that runs back to the house. Then you could use a transformer in the house at the receiver if it's the type that wants to be fed from a high-impedance. I would think this would get around the problem of an impedance matching transformer mismatching the antenna on frequncies where the antenna impedance drops significantly. Also it could provide perhaps some minimal gain to boot. Some of those commercial impedance matching transformers sell for over $50 US. So I would think a small buffer amp might not be too cost-ineffective. Dave |
David Forsyth wrote:
After doing a lot of reading on the web about long wires, short wires, inverted L's, impedance matching, baluns, ununs, onions, fundip, and who knows what else... I was thinking (run for cover please) Couldn't one simply use a small active device to buffer the straight wire antenna at the end where it tethers to Ye Olde Oak tree or whatever it's tied to? I was thinking you could even make it powered with a small gel cell or something and a solar cell to power it. Some sort of wide-band amplifier that would have a suitably high input impedance to accomodate the higher and varying impedance of the wire over the desired frequency range, and yet having a fixed 75 or 50 ohm output impedance to drive the coax that runs back to the house. Then you could use a transformer in the house at the receiver if it's the type that wants to be fed from a high-impedance. I would think this would get around the problem of an impedance matching transformer mismatching the antenna on frequncies where the antenna impedance drops significantly. Also it could provide perhaps some minimal gain to boot. Some of those commercial impedance matching transformers sell for over $50 US. So I would think a small buffer amp might not be too cost-ineffective. Dave If you want to put a preamp near the antenna, you can run a DC voltage up the coax by using RF chokes in the DC lines at both ends to isolate the RF, and series coupling capacitors to block the DC. That is how LNA/B/Cs are powered on most Sat TV receivers, and I have used it at 60 KHz, as well. You could use a Minicircuits chip that cost about $1.00 by adding a couple caps, a coil and a resistor. Their ERA or MAR series would do a good job, and the part is cheap enough that you can afford to replace it when lightning takes out your preamp. I have some rejected blank surface mount PC boards that will work for the part (They were laid out wrong, and engineering had to eat the cost). You can also do dead bug, or even use the old Vector Perfboard pins or standoffs and build it point to point. They do need a ground plane, but are quite stable. These parts have a 50 ohm output, so they will match either 50 or 75 ohm coax with little problems. You might need a low pass filter to remove out of band noise and signals to prevent overload, or if you want to have real fun built a remote tuner at the preamp. -- Michael A. Terrell Central Florida |
David Forsyth wrote:
After doing a lot of reading on the web about long wires, short wires, inverted L's, impedance matching, baluns, ununs, onions, fundip, and who knows what else... I was thinking (run for cover please) Couldn't one simply use a small active device to buffer the straight wire antenna at the end where it tethers to Ye Olde Oak tree or whatever it's tied to? I was thinking you could even make it powered with a small gel cell or something and a solar cell to power it. Some sort of wide-band amplifier that would have a suitably high input impedance to accomodate the higher and varying impedance of the wire over the desired frequency range, and yet having a fixed 75 or 50 ohm output impedance to drive the coax that runs back to the house. Then you could use a transformer in the house at the receiver if it's the type that wants to be fed from a high-impedance. I would think this would get around the problem of an impedance matching transformer mismatching the antenna on frequncies where the antenna impedance drops significantly. Also it could provide perhaps some minimal gain to boot. Some of those commercial impedance matching transformers sell for over $50 US. So I would think a small buffer amp might not be too cost-ineffective. Dave If you want to put a preamp near the antenna, you can run a DC voltage up the coax by using RF chokes in the DC lines at both ends to isolate the RF, and series coupling capacitors to block the DC. That is how LNA/B/Cs are powered on most Sat TV receivers, and I have used it at 60 KHz, as well. You could use a Minicircuits chip that cost about $1.00 by adding a couple caps, a coil and a resistor. Their ERA or MAR series would do a good job, and the part is cheap enough that you can afford to replace it when lightning takes out your preamp. I have some rejected blank surface mount PC boards that will work for the part (They were laid out wrong, and engineering had to eat the cost). You can also do dead bug, or even use the old Vector Perfboard pins or standoffs and build it point to point. They do need a ground plane, but are quite stable. These parts have a 50 ohm output, so they will match either 50 or 75 ohm coax with little problems. You might need a low pass filter to remove out of band noise and signals to prevent overload, or if you want to have real fun built a remote tuner at the preamp. -- Michael A. Terrell Central Florida |
Even the car radio type coax would probably have too much capacitance
for the length of run you'll need. Yes, you could put a preamp (actually an active impedance converter) near the antenna in order to drive standard 50-ohm coax cable. I classify it as an "impedance converter" because you probably don't need or want much gain, just the ability to match the coax impedance. On the broadcast band any gain will likely increase the noise level as much as the signals. If you don't have too much noise pick up from the house electrical wiring, etc you can probably just run a single wire feed line down into the basement. Keep it as far away as possible from any conductive material like rain gutters, etc. |
Even the car radio type coax would probably have too much capacitance
for the length of run you'll need. Yes, you could put a preamp (actually an active impedance converter) near the antenna in order to drive standard 50-ohm coax cable. I classify it as an "impedance converter" because you probably don't need or want much gain, just the ability to match the coax impedance. On the broadcast band any gain will likely increase the noise level as much as the signals. If you don't have too much noise pick up from the house electrical wiring, etc you can probably just run a single wire feed line down into the basement. Keep it as far away as possible from any conductive material like rain gutters, etc. |
In looking at some of the options I was pointed to on this matter, it seems
perhaps the first thing I should do is run a simple wire down into the basement as best I can and see how that fares. At least now Im armed with some alternative ideas should that method prove too lossy/noisy. thanks again to all who responded! Dave "Bob Lewis (AA4PB)" wrote in message ... Even the car radio type coax would probably have too much capacitance for the length of run you'll need. Yes, you could put a preamp (actually an active impedance converter) near the antenna in order to drive standard 50-ohm coax cable. I classify it as an "impedance converter" because you probably don't need or want much gain, just the ability to match the coax impedance. On the broadcast band any gain will likely increase the noise level as much as the signals. If you don't have too much noise pick up from the house electrical wiring, etc you can probably just run a single wire feed line down into the basement. Keep it as far away as possible from any conductive material like rain gutters, etc. |
In looking at some of the options I was pointed to on this matter, it seems
perhaps the first thing I should do is run a simple wire down into the basement as best I can and see how that fares. At least now Im armed with some alternative ideas should that method prove too lossy/noisy. thanks again to all who responded! Dave "Bob Lewis (AA4PB)" wrote in message ... Even the car radio type coax would probably have too much capacitance for the length of run you'll need. Yes, you could put a preamp (actually an active impedance converter) near the antenna in order to drive standard 50-ohm coax cable. I classify it as an "impedance converter" because you probably don't need or want much gain, just the ability to match the coax impedance. On the broadcast band any gain will likely increase the noise level as much as the signals. If you don't have too much noise pick up from the house electrical wiring, etc you can probably just run a single wire feed line down into the basement. Keep it as far away as possible from any conductive material like rain gutters, etc. |
"David Forsyth" wrote in message ...
In the interest of my recent tinkerings with radios (both antique and homebrew), I have put up an 80 foot straight wire antenna above the house. It sits about 35 feet up from, and horizontal to, the ground. I am using a lead in from one end made of insulated stranded copper wire (basically old speaker cable, about 18 guage I think). Right now, the lead-in wire comes down from the end of the antenna closest to the sun porch, and in through the storm window via a well-insulated bushing. Due to the location of this lead-in, this is the spot wherre I have been doing most of the tinkering with the radios. I also have a copper pipe ground rod in a nearby location so as to have as short a path to ground as possible.) It seems to work OK for now but I would ideally like to run the lead-in into my basement where my workshop is. I read somewhere (I think it might have been in reference to crystal sets) that you can use coax for an AM lead-in. Would this be better for a longer/more convoluted lead-in? Would I use the braded shield as the ground connection or would I run a separate ground back to my copper rod outside? What type of coax would be best for this sort of thing? I am interested in receiving both broadcast and shortwave. Any info on this matter would be most appreciated. thanks in advance, Dave Al Klase figured that our several years ago: http://www.webex.net/~skywaves/ANTENNA/antsys.htm Jiri Placek Boyertown, PA |
"David Forsyth" wrote in message ...
In the interest of my recent tinkerings with radios (both antique and homebrew), I have put up an 80 foot straight wire antenna above the house. It sits about 35 feet up from, and horizontal to, the ground. I am using a lead in from one end made of insulated stranded copper wire (basically old speaker cable, about 18 guage I think). Right now, the lead-in wire comes down from the end of the antenna closest to the sun porch, and in through the storm window via a well-insulated bushing. Due to the location of this lead-in, this is the spot wherre I have been doing most of the tinkering with the radios. I also have a copper pipe ground rod in a nearby location so as to have as short a path to ground as possible.) It seems to work OK for now but I would ideally like to run the lead-in into my basement where my workshop is. I read somewhere (I think it might have been in reference to crystal sets) that you can use coax for an AM lead-in. Would this be better for a longer/more convoluted lead-in? Would I use the braded shield as the ground connection or would I run a separate ground back to my copper rod outside? What type of coax would be best for this sort of thing? I am interested in receiving both broadcast and shortwave. Any info on this matter would be most appreciated. thanks in advance, Dave Al Klase figured that our several years ago: http://www.webex.net/~skywaves/ANTENNA/antsys.htm Jiri Placek Boyertown, PA |
David Forsyth wrote: In the interest of my recent tinkerings with radios (both antique and homebrew), I have put up an 80 foot straight wire antenna above the house. It sits about 35 feet up from, and horizontal to, the ground. I am using a lead in from one end made of insulated stranded copper wire (basically old speaker cable, about 18 guage I think). Right now, the lead-in wire comes down from the end of the antenna closest to the sun porch, and in through the storm window via a well-insulated bushing. Due to the location of this lead-in, this is the spot wherre I have been doing most of the tinkering with the radios. I also have a copper pipe ground rod in a nearby location so as to have as short a path to ground as possible.) It seems to work OK for now but I would ideally like to run the lead-in into my basement where my workshop is. I read somewhere (I think it might have been in reference to crystal sets) that you can use coax for an AM lead-in. Would this be better for a longer/more convoluted lead-in? Would I use the braded shield as the ground connection or would I run a separate ground back to my copper rod outside? What type of coax would be best for this sort of thing? I am interested in receiving both broadcast and shortwave. Any info on this matter would be most appreciated. thanks in advance, Dave Forget using coax or a preamp with that antenna. With an 80' wire antenna for AM and shortwave reception, there is nothing to be gained by their use, and you can degrade what you already have. Just add a static discharge unit, connect the wire to the receiver, and enjoy your antenna. If you want to make improvements, you can modify the antenna, and/or make an antenna tuner for it or use a different antenna. But as it stands today, it should give you plenty of signal for the use you have in mind. Running the wire into the basement is not a problem - just make sure you don't damage it, and route it away from metal objects. |
David Forsyth wrote: In the interest of my recent tinkerings with radios (both antique and homebrew), I have put up an 80 foot straight wire antenna above the house. It sits about 35 feet up from, and horizontal to, the ground. I am using a lead in from one end made of insulated stranded copper wire (basically old speaker cable, about 18 guage I think). Right now, the lead-in wire comes down from the end of the antenna closest to the sun porch, and in through the storm window via a well-insulated bushing. Due to the location of this lead-in, this is the spot wherre I have been doing most of the tinkering with the radios. I also have a copper pipe ground rod in a nearby location so as to have as short a path to ground as possible.) It seems to work OK for now but I would ideally like to run the lead-in into my basement where my workshop is. I read somewhere (I think it might have been in reference to crystal sets) that you can use coax for an AM lead-in. Would this be better for a longer/more convoluted lead-in? Would I use the braded shield as the ground connection or would I run a separate ground back to my copper rod outside? What type of coax would be best for this sort of thing? I am interested in receiving both broadcast and shortwave. Any info on this matter would be most appreciated. thanks in advance, Dave Forget using coax or a preamp with that antenna. With an 80' wire antenna for AM and shortwave reception, there is nothing to be gained by their use, and you can degrade what you already have. Just add a static discharge unit, connect the wire to the receiver, and enjoy your antenna. If you want to make improvements, you can modify the antenna, and/or make an antenna tuner for it or use a different antenna. But as it stands today, it should give you plenty of signal for the use you have in mind. Running the wire into the basement is not a problem - just make sure you don't damage it, and route it away from metal objects. |
David Forsyth wrote: In the interest of my recent tinkerings with radios (both antique and homebrew), I have put up an 80 foot straight wire antenna above the house. It sits about 35 feet up from, and horizontal to, the ground. I am using a lead in from one end made of insulated stranded copper wire (basically old speaker cable, about 18 guage I think). Right now, the lead-in wire comes down from the end of the antenna closest to the sun porch, and in through the storm window via a well-insulated bushing. SNIP Back considerably before the beginning of time, around 1940/1941, my uncle bought a fancy Sears Silvertone console with multiple bandspread shortwave bands and the lot. It came with instructions for using a substantial center-fed dipole antenna with twisted-pair two-wire feedline. Back in those days twisted-pair feedlines weren't much different from rubber insulated two-wire AC cords - ZIP cord hadn't appeared yet. The impedance probably wasn't far off from 75 ohms. The important point was that the balanced feed system and antenna reduced pickup of noise by the feedline. The close-spaced two-wire feed also made it less affected by routing. Your 80 feet is a small fraction of a wavelength anywhere in the AM broadcast band, so the antenna will be a high impedance no matter where you feed it. 300-ohm twinlead might be a start in today's world. Is shielded twinlead still available? The other choice for feeding a band dipole might be plastic ZIP cord. The insulation is not great, but a 1500 kHz, who cares? The spacing is close, giving less effect of close objects, but the impedance would thus be low. Just some thoughts, perhaps useless if you can't center-feed the antenna. |
David Forsyth wrote: In the interest of my recent tinkerings with radios (both antique and homebrew), I have put up an 80 foot straight wire antenna above the house. It sits about 35 feet up from, and horizontal to, the ground. I am using a lead in from one end made of insulated stranded copper wire (basically old speaker cable, about 18 guage I think). Right now, the lead-in wire comes down from the end of the antenna closest to the sun porch, and in through the storm window via a well-insulated bushing. SNIP Back considerably before the beginning of time, around 1940/1941, my uncle bought a fancy Sears Silvertone console with multiple bandspread shortwave bands and the lot. It came with instructions for using a substantial center-fed dipole antenna with twisted-pair two-wire feedline. Back in those days twisted-pair feedlines weren't much different from rubber insulated two-wire AC cords - ZIP cord hadn't appeared yet. The impedance probably wasn't far off from 75 ohms. The important point was that the balanced feed system and antenna reduced pickup of noise by the feedline. The close-spaced two-wire feed also made it less affected by routing. Your 80 feet is a small fraction of a wavelength anywhere in the AM broadcast band, so the antenna will be a high impedance no matter where you feed it. 300-ohm twinlead might be a start in today's world. Is shielded twinlead still available? The other choice for feeding a band dipole might be plastic ZIP cord. The insulation is not great, but a 1500 kHz, who cares? The spacing is close, giving less effect of close objects, but the impedance would thus be low. Just some thoughts, perhaps useless if you can't center-feed the antenna. |
R J Carpenter wrote: Back considerably before the beginning of time, around 1940/1941, my uncle bought a fancy Sears Silvertone console with multiple bandspread shortwave bands and the lot. It came with instructions for using a substantial center-fed dipole antenna with twisted-pair two-wire feedline. Back in those days twisted-pair feedlines weren't much different from rubber insulated two-wire AC cords - ZIP cord hadn't appeared yet. The impedance probably wasn't far off from 75 ohms. It's closer to 100 ohms, but the KEY phrase here is twisted. Zip cord and or twin lead isn't twisted (unless you twist it) and it's the twist that imparts the self sheilding. Jeff -- "They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." Benjamin Franklin "A life lived in fear is a life half lived." Tara Morice as Fran, from the movie "Strictly Ballroom" |
R J Carpenter wrote: Back considerably before the beginning of time, around 1940/1941, my uncle bought a fancy Sears Silvertone console with multiple bandspread shortwave bands and the lot. It came with instructions for using a substantial center-fed dipole antenna with twisted-pair two-wire feedline. Back in those days twisted-pair feedlines weren't much different from rubber insulated two-wire AC cords - ZIP cord hadn't appeared yet. The impedance probably wasn't far off from 75 ohms. It's closer to 100 ohms, but the KEY phrase here is twisted. Zip cord and or twin lead isn't twisted (unless you twist it) and it's the twist that imparts the self sheilding. Jeff -- "They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." Benjamin Franklin "A life lived in fear is a life half lived." Tara Morice as Fran, from the movie "Strictly Ballroom" |
Jeffrey D Angus wrote:
R J Carpenter wrote: Back considerably before the beginning of time, around 1940/1941, my uncle bought a fancy Sears Silvertone console with multiple bandspread shortwave bands and the lot. It came with instructions for using a substantial center-fed dipole antenna with twisted-pair two-wire feedline. Back in those days twisted-pair feedlines weren't much different from rubber insulated two-wire AC cords - ZIP cord hadn't appeared yet. The impedance probably wasn't far off from 75 ohms. It's closer to 100 ohms, but the KEY phrase here is twisted. Zip cord and or twin lead isn't twisted (unless you twist it) and it's the twist that imparts the self sheilding. Jeff And if anyone here knows twisted... ;-) -- Michael A. Terrell Central Florida |
Jeffrey D Angus wrote:
R J Carpenter wrote: Back considerably before the beginning of time, around 1940/1941, my uncle bought a fancy Sears Silvertone console with multiple bandspread shortwave bands and the lot. It came with instructions for using a substantial center-fed dipole antenna with twisted-pair two-wire feedline. Back in those days twisted-pair feedlines weren't much different from rubber insulated two-wire AC cords - ZIP cord hadn't appeared yet. The impedance probably wasn't far off from 75 ohms. It's closer to 100 ohms, but the KEY phrase here is twisted. Zip cord and or twin lead isn't twisted (unless you twist it) and it's the twist that imparts the self sheilding. Jeff And if anyone here knows twisted... ;-) -- Michael A. Terrell Central Florida |
The twist improves the ability to reject noise and signals picked up
by the balanced feed line but even untwisted, parallel lines do quite well. It is the fact that any signals are picked up by both lines equally and then cancel at the receiver input because they are in phase. |
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