Antenna Work
I have been having some RFI and antenna issues at the house here. I have experimented with antennas for years. One thing to keep in mind is almost all of my antennas are or have been in the attic - outside antennas are mostly a no-no here.
The first attic antenna I ever used was a 40m dipole zig-zagged around the attic space next to my room (second floor, one wall opens to an attic space). This never did well.
I used a screwdriver antenna mounted to my truck with about 150' of cable running to it for many years - this worked and I worked the world on it, but hooking it up and disconnecting it every time I came home or went back out was a real pain. I still have this option, and I run a lot of mobile HF these days with my FT-857D.
At some point in the past 3-4 years I stuck a 40m dipole in the attic above my room (along the peak of the roof - the best place inside to put it, or as much of it I could fit there). This is a decent antenna. I have made a ton of QSO's on it. However, the antenna covers one band and 40m usually has a high noise level - s5-s9 depending on conditions.
In my quest for a multi-band antenna I took a small piece of wire, very thin (not as thin as magnet wire, this is copper and insulated. I can't remember where I got it or what it was from), and tossed it up over the roof and tied it off to a tree on the other side of the property (mind you, the tree is only 10' high). Then I used part of the gutter system of the house as a counterpoise and loaded it up with a tuner. This worked, but caused some RFI - especially on 20m. I could turn things on and off when keying up that I probably never even found!
So I put up a loop antenna last year. This wraps around the entire attic space above my room - it covers the whole house, as much as the attic covers. I would say it is 200-250' long. I fed this with ladder line and ran it to my tuner. This antenna works pretty well on all bands since it uses the tuner, but it causes RFI - I notice it on my TV on 20m. However, I was using this antenna one day and my neighbor came over and complained about RFI on his TV. So now a whole new can of worms has been opened.
I also put up a 6m ground plane. This little antenna works great when the band opens. I have worked Nevada, Florida, out East to Maine, and most of the South/South East (EM land). It doesn't work as well as a beam antenna, but considering my circumstances it works pretty well.
Then, after the RFI issue with my neighbor I found it happens on 10m for sure. I didn't try any other bands other than 6 and 10. I think I was on 6m when I had the initial complaint and was only working 6 and 10 that day. After a high-pass filter and an Amidon F240-K ferrite core the RFI on 6 was gone but 10 was still there. So I put a ground plane antenna up, resonant for 10 meters. I think I was still getting in to the TV but I checked that before I left for my trip, which was over 3 weeks ago now. I will have to re-visit that one.
So, after some consulting with a friend of mine, Steve, on the RFI issue he suggested I try to get resonant antennas up. Having a resonant antenna with low SWR will go a long way to helping out on the RFI issue. The loop that I was using on all bands was being forced to radiate on non-resonant frequencies - which could be a leading cause of the problem. The antenna works, ham radio speaking, but causes other problems. Being in a compromised situation (the attic space for antennas) really makes this hard - it would be much easier to put a resonant antenna up outside such as a vertical, a set of dipoles, a fan dipole, or the best would be beam antennas on a tower! However, considering where I am - that can't happen.
So the creativity starts. After hearing a few of the odd-ball setups Steve has done in the past (fan dipoles, a vertical grounded to the water heater and run up through the second floor of an apartment, tiny magnet wire strung up in trees with a fishing sinker, etc) I thought the one that would be the easiest to do is a fan radiator grounded to some duct work in the attic. I had my 40m dipole up in the attic so I originally was going to do the fan dipole idea, however that is twice as much work as a set of 1/4 wave radiators. You take half of a fan dipole and run that off the duct work as a counterpoise (1/4 wave radiators on all bands connected to a single feed point).The duct work goes back in the house to all kinds of things, so there is no shortage of a counterpoise. I figured this would do the trick for sure.
I got to work on this (about 4 weeks ago now). I used an SO-239 chassis with the 4 bolt holes. I cut in to the rafter brace for the duct work (which was screwed in to the duct in two places - good electrical connection) for the SO-239 to fit and drilled holes for two bolts. Then I soldered a loop to the center pin (maybe 1/2") so I had room to solder on all of my radiators. Then I started fanning them out and tacking them in place wherever I put them.
Well, it isn't that easy. Apparently there is a lot of interaction between the wires where I strung them up. I have been having a lot of issues trying to tune the mess. One change here affects everything else there.
I had Steve come over yesterday and take a look at everything to see if he could come up with some ideas. After a trip to the attic he said my radiators were too close and to fan them out more. So that will be the next step to my project. I will have to get up there when it is cool enough to work (at night). The attic sure does get HOT!
That sounds easy enough, right? Well I am sure I will run in to some more problems on this one! It really is a mess of an antenna, but if I can get it to work that would be a big relief.
Just for the heck of it, Steve wanted to take a walk around the house to see if there were any other odd-ball things to consider. Sure enough, he found one - part of the gutter system (separated from everything else on the back side) has a downspout that runs a few inches from a spigot. The spigot is connected to the rest of the plumbing (all copper!) in the house = fabulous ground. The gutter system would make a nice radiator, fed against the plumbing, on some frequency.
So I gave this a shot. I got out another SO-239, some wire, a strip of braided ground strap, and a hose clamp and connected everything together. This setup makes an excellent antenna on 20m! It has a flat SWR across the whole band. It even resonates with about a 1.5:1 SWR on 60m (3ord harmonic of 20m). The best part is I don't have any RFI on my TV (which does have a high-pass filter and Amidon F240-K in place). The drawback is it seems to be about 2 S-units weaker of an antenna than the fan spider webby thingy in the attic (run through the tuner). I didn't compare it to the loop. If the SWR is good its worth a shot though, right?
Another idea is to use the spigot as a ground for a few types of antennas - hamsticks, a buddistick, etc, etc. Or, even a fan setup on the outside wall (painted the same color as the house to cammo it!).
I just wish I didn't have to jump through so many hoops. It really is a lot of work, but if I can get this to work without RFI problems and being able to put out a respectable signal it will all be worth it.
The first attic antenna I ever used was a 40m dipole zig-zagged around the attic space next to my room (second floor, one wall opens to an attic space). This never did well.
I used a screwdriver antenna mounted to my truck with about 150' of cable running to it for many years - this worked and I worked the world on it, but hooking it up and disconnecting it every time I came home or went back out was a real pain. I still have this option, and I run a lot of mobile HF these days with my FT-857D.
At some point in the past 3-4 years I stuck a 40m dipole in the attic above my room (along the peak of the roof - the best place inside to put it, or as much of it I could fit there). This is a decent antenna. I have made a ton of QSO's on it. However, the antenna covers one band and 40m usually has a high noise level - s5-s9 depending on conditions.
In my quest for a multi-band antenna I took a small piece of wire, very thin (not as thin as magnet wire, this is copper and insulated. I can't remember where I got it or what it was from), and tossed it up over the roof and tied it off to a tree on the other side of the property (mind you, the tree is only 10' high). Then I used part of the gutter system of the house as a counterpoise and loaded it up with a tuner. This worked, but caused some RFI - especially on 20m. I could turn things on and off when keying up that I probably never even found!
So I put up a loop antenna last year. This wraps around the entire attic space above my room - it covers the whole house, as much as the attic covers. I would say it is 200-250' long. I fed this with ladder line and ran it to my tuner. This antenna works pretty well on all bands since it uses the tuner, but it causes RFI - I notice it on my TV on 20m. However, I was using this antenna one day and my neighbor came over and complained about RFI on his TV. So now a whole new can of worms has been opened.
I also put up a 6m ground plane. This little antenna works great when the band opens. I have worked Nevada, Florida, out East to Maine, and most of the South/South East (EM land). It doesn't work as well as a beam antenna, but considering my circumstances it works pretty well.
Then, after the RFI issue with my neighbor I found it happens on 10m for sure. I didn't try any other bands other than 6 and 10. I think I was on 6m when I had the initial complaint and was only working 6 and 10 that day. After a high-pass filter and an Amidon F240-K ferrite core the RFI on 6 was gone but 10 was still there. So I put a ground plane antenna up, resonant for 10 meters. I think I was still getting in to the TV but I checked that before I left for my trip, which was over 3 weeks ago now. I will have to re-visit that one.
So, after some consulting with a friend of mine, Steve, on the RFI issue he suggested I try to get resonant antennas up. Having a resonant antenna with low SWR will go a long way to helping out on the RFI issue. The loop that I was using on all bands was being forced to radiate on non-resonant frequencies - which could be a leading cause of the problem. The antenna works, ham radio speaking, but causes other problems. Being in a compromised situation (the attic space for antennas) really makes this hard - it would be much easier to put a resonant antenna up outside such as a vertical, a set of dipoles, a fan dipole, or the best would be beam antennas on a tower! However, considering where I am - that can't happen.
So the creativity starts. After hearing a few of the odd-ball setups Steve has done in the past (fan dipoles, a vertical grounded to the water heater and run up through the second floor of an apartment, tiny magnet wire strung up in trees with a fishing sinker, etc) I thought the one that would be the easiest to do is a fan radiator grounded to some duct work in the attic. I had my 40m dipole up in the attic so I originally was going to do the fan dipole idea, however that is twice as much work as a set of 1/4 wave radiators. You take half of a fan dipole and run that off the duct work as a counterpoise (1/4 wave radiators on all bands connected to a single feed point).The duct work goes back in the house to all kinds of things, so there is no shortage of a counterpoise. I figured this would do the trick for sure.
I got to work on this (about 4 weeks ago now). I used an SO-239 chassis with the 4 bolt holes. I cut in to the rafter brace for the duct work (which was screwed in to the duct in two places - good electrical connection) for the SO-239 to fit and drilled holes for two bolts. Then I soldered a loop to the center pin (maybe 1/2") so I had room to solder on all of my radiators. Then I started fanning them out and tacking them in place wherever I put them.
Well, it isn't that easy. Apparently there is a lot of interaction between the wires where I strung them up. I have been having a lot of issues trying to tune the mess. One change here affects everything else there.
I had Steve come over yesterday and take a look at everything to see if he could come up with some ideas. After a trip to the attic he said my radiators were too close and to fan them out more. So that will be the next step to my project. I will have to get up there when it is cool enough to work (at night). The attic sure does get HOT!
That sounds easy enough, right? Well I am sure I will run in to some more problems on this one! It really is a mess of an antenna, but if I can get it to work that would be a big relief.
Just for the heck of it, Steve wanted to take a walk around the house to see if there were any other odd-ball things to consider. Sure enough, he found one - part of the gutter system (separated from everything else on the back side) has a downspout that runs a few inches from a spigot. The spigot is connected to the rest of the plumbing (all copper!) in the house = fabulous ground. The gutter system would make a nice radiator, fed against the plumbing, on some frequency.
So I gave this a shot. I got out another SO-239, some wire, a strip of braided ground strap, and a hose clamp and connected everything together. This setup makes an excellent antenna on 20m! It has a flat SWR across the whole band. It even resonates with about a 1.5:1 SWR on 60m (3ord harmonic of 20m). The best part is I don't have any RFI on my TV (which does have a high-pass filter and Amidon F240-K in place). The drawback is it seems to be about 2 S-units weaker of an antenna than the fan spider webby thingy in the attic (run through the tuner). I didn't compare it to the loop. If the SWR is good its worth a shot though, right?
Another idea is to use the spigot as a ground for a few types of antennas - hamsticks, a buddistick, etc, etc. Or, even a fan setup on the outside wall (painted the same color as the house to cammo it!).
I just wish I didn't have to jump through so many hoops. It really is a lot of work, but if I can get this to work without RFI problems and being able to put out a respectable signal it will all be worth it.
posted by Steve at
12:50 PM
1 Comments
