Getting Back Up And Running
I have been in hibernation with the radios at the house. I haven't been very active at all (on HF anyway). The big reason is the noise level here. On 40 meters I have S8-S9 noise. If I knock my preamp off it still only drops to S5. It really is quite annoying.
The other reason I haven't been on HF much is because of my antenna options. I can't put up any visible outside antennas. That severely limits my options. I used to use my screwdriver antenna on the truck. However, that was a pain in the butt to connect and disconnect every time I left/came home. So I stopped doing that.
The first installed antenna I tried was a 40m dipole in the attic. This got me on 40m, but the noise level is just hideous. I can get out with it, but the problem is being able to hear the stations coming back to my calls. If the noise level is S9 and the station calling is S5 it is darn near impossible to even detect that they are there in the first place. An S5 signal is a great signal by most standards. It really is discouraging to be putting out a bigger signal (which, by the way, can't be much anyways) than what you can hear - also known as being an Alligator (a term typically applied to the guys running huge amps with poor antennas).
Because of the noise issue I pretty much stopped trying HF at the house. I put an FT-857D in the truck for mobile use, so that is where I have stayed. Since I got that rig nearly 100% of my HF QSO's have been mobile or portable (in other words - not at this QTH).
I was talking to a friend of mine on a local repeater last week and he made the suggestion of trying a loop antenna instead as they are supposed to be "quieter" antennas. I thought about it for a bit and decided to give it a shot. I had the supplies to do it - I bought a 500' roll of 7-strand 18 gauge bare copper wire a few months ago for a portable antenna project I never got around to and I had some 450 ohm ladder line in the garage (a feed line from a G5RV-style antenna).
I went to work on it Friday afternoon. The first priority was routing the ladder line. It is not like coax in that it is very sensitive to it's environment. There is a magnetic field that develops around the cable that acts as a shield, as compared to coaxial cable that has a physical conductor shield. The magnetic field on the ladder line is affected by anything conductive or remotely conductive. In short, this means the line can't touch anything! In practice this is much easier said than done. Since my antenna from the start is a huge compromise I didn't worry about the feedline. I just ran it straight down through the drywall from the attic, right behind the tuner.
Next I ran the wire. There was no rhyme or reason behind how I ran it, I just tried to enclose as much area as possible. I didn't measure anything. I took the spool of wire up with me and started where the feed point was to be and unrolled the spool as I went. I used 3/4" brad nails to attach the wire (with a half hitch type loop) directly to the wood rafters. I only put in an anchor where the line changed directions. All said and done I think I put up 100 to 150' of wire. Again - I didn't measure it, I just unrolled the spool and tied it up where I did.
The feed point is up at the peak of the roof. I wanted to get it as high as I could because the feed point has the highest amount of energy of any part of the antenna = more radiation. The higher this point is the better. The loop is soldered directly to the feedline for a low resistance bond (I like to solder everything, even crimp-on connectors). More on the feed point in a bit.
After hooking up the antenna I tried it out. I am able to load it up on all bands through my tuner - 160m all the way to 6m! I wrote a post a long time ago about the use of tuners and what exactly it is they do. In short, "tuners" aren't really tuners. They are impedance matchers. They match whatever impedance is presented to them (within their capable range) to 50 ohms - what all of our radios are. They do NOT tune the antenna itself - only the impedance match between the radio and antenna. The match from the tuner to the antenna is still bad.
So if there is always going to be a bad match to my antenna, no matter how well I have the impedance matched through the tuner, what good am I doing? If I was using coaxial cable I would have a nice attic heating element. The rest of the world wouldn't even notice I was there - nearly all the energy from my transmitter would be lost in heat, not radiation. With ladder line on the other hand, this is not a problem. There is still some signal loss, but ladder line (inherently balanced) is nearly impervious to impedance mismatches. Even when presented with a bad match ladder line still gets your power to the antenna where it can radiate. This principle is why my loop has become my favorite antenna - I can run any band I want, although a compromise and not very efficient in the real world. It works and I can make contacts on it - that is what counts!
The antenna didn't come without some tweaking. When I first put it in I couldn't run much power. Anything over 50 watts usually would result in the impedance going haywire. After some investigation, the tuner was fine. I have arc'ed tuners before and this was not a case of zapping the bugs in the tuner. I talked with a friend of mine, Phil WD8QWR, and he suggested I check the feed point for arcing instead. Apparently the feed point is where the highest voltage is in this type of setup (as opposed to a dipole where the voltage is the lowest at the feed point while the current is highest). The more power I ran in to the antenna the higher the voltage would get - until it jumped to something conductive.
So, I got back up in the attic this afternoon and checked out the feed point. There was no sign of arcing. No melted insulation (on the ladder line), no black spots on the antenna, rafters, or staple plate. Even so, I figured I would move it around just for the heck of it. I used some nylon zip ties and moved the feed point a couple inches away from the wood and staple plate.
Success! Now the impedance stays rock-solid all through the bands... until 160m. I am surprised the antenna loads up on 160 from the start, given that the antenna is SO small for that band. If I short the feed line at the longwire port on the tuner and load it against a counterpoise it will load up on 160 with much better results.
So for now I am back up and running! The shack is still a mess, but all the radios and accessories are back on the desk and hooked up. I have made a few QSO's so far - nearly all CW. It really feels good to get back in the swing of things! I have been wanting to get my CW speed up but I have not used it much for many months so I am a bit rusty. Just since I have put my station back together with the new loop I have worked out the rust in my code and I'm at about 15wpm.
The other reason I haven't been on HF much is because of my antenna options. I can't put up any visible outside antennas. That severely limits my options. I used to use my screwdriver antenna on the truck. However, that was a pain in the butt to connect and disconnect every time I left/came home. So I stopped doing that.
The first installed antenna I tried was a 40m dipole in the attic. This got me on 40m, but the noise level is just hideous. I can get out with it, but the problem is being able to hear the stations coming back to my calls. If the noise level is S9 and the station calling is S5 it is darn near impossible to even detect that they are there in the first place. An S5 signal is a great signal by most standards. It really is discouraging to be putting out a bigger signal (which, by the way, can't be much anyways) than what you can hear - also known as being an Alligator (a term typically applied to the guys running huge amps with poor antennas).
Because of the noise issue I pretty much stopped trying HF at the house. I put an FT-857D in the truck for mobile use, so that is where I have stayed. Since I got that rig nearly 100% of my HF QSO's have been mobile or portable (in other words - not at this QTH).
I was talking to a friend of mine on a local repeater last week and he made the suggestion of trying a loop antenna instead as they are supposed to be "quieter" antennas. I thought about it for a bit and decided to give it a shot. I had the supplies to do it - I bought a 500' roll of 7-strand 18 gauge bare copper wire a few months ago for a portable antenna project I never got around to and I had some 450 ohm ladder line in the garage (a feed line from a G5RV-style antenna).
I went to work on it Friday afternoon. The first priority was routing the ladder line. It is not like coax in that it is very sensitive to it's environment. There is a magnetic field that develops around the cable that acts as a shield, as compared to coaxial cable that has a physical conductor shield. The magnetic field on the ladder line is affected by anything conductive or remotely conductive. In short, this means the line can't touch anything! In practice this is much easier said than done. Since my antenna from the start is a huge compromise I didn't worry about the feedline. I just ran it straight down through the drywall from the attic, right behind the tuner.
Next I ran the wire. There was no rhyme or reason behind how I ran it, I just tried to enclose as much area as possible. I didn't measure anything. I took the spool of wire up with me and started where the feed point was to be and unrolled the spool as I went. I used 3/4" brad nails to attach the wire (with a half hitch type loop) directly to the wood rafters. I only put in an anchor where the line changed directions. All said and done I think I put up 100 to 150' of wire. Again - I didn't measure it, I just unrolled the spool and tied it up where I did.
The feed point is up at the peak of the roof. I wanted to get it as high as I could because the feed point has the highest amount of energy of any part of the antenna = more radiation. The higher this point is the better. The loop is soldered directly to the feedline for a low resistance bond (I like to solder everything, even crimp-on connectors). More on the feed point in a bit.
After hooking up the antenna I tried it out. I am able to load it up on all bands through my tuner - 160m all the way to 6m! I wrote a post a long time ago about the use of tuners and what exactly it is they do. In short, "tuners" aren't really tuners. They are impedance matchers. They match whatever impedance is presented to them (within their capable range) to 50 ohms - what all of our radios are. They do NOT tune the antenna itself - only the impedance match between the radio and antenna. The match from the tuner to the antenna is still bad.
So if there is always going to be a bad match to my antenna, no matter how well I have the impedance matched through the tuner, what good am I doing? If I was using coaxial cable I would have a nice attic heating element. The rest of the world wouldn't even notice I was there - nearly all the energy from my transmitter would be lost in heat, not radiation. With ladder line on the other hand, this is not a problem. There is still some signal loss, but ladder line (inherently balanced) is nearly impervious to impedance mismatches. Even when presented with a bad match ladder line still gets your power to the antenna where it can radiate. This principle is why my loop has become my favorite antenna - I can run any band I want, although a compromise and not very efficient in the real world. It works and I can make contacts on it - that is what counts!
The antenna didn't come without some tweaking. When I first put it in I couldn't run much power. Anything over 50 watts usually would result in the impedance going haywire. After some investigation, the tuner was fine. I have arc'ed tuners before and this was not a case of zapping the bugs in the tuner. I talked with a friend of mine, Phil WD8QWR, and he suggested I check the feed point for arcing instead. Apparently the feed point is where the highest voltage is in this type of setup (as opposed to a dipole where the voltage is the lowest at the feed point while the current is highest). The more power I ran in to the antenna the higher the voltage would get - until it jumped to something conductive.
So, I got back up in the attic this afternoon and checked out the feed point. There was no sign of arcing. No melted insulation (on the ladder line), no black spots on the antenna, rafters, or staple plate. Even so, I figured I would move it around just for the heck of it. I used some nylon zip ties and moved the feed point a couple inches away from the wood and staple plate.
Success! Now the impedance stays rock-solid all through the bands... until 160m. I am surprised the antenna loads up on 160 from the start, given that the antenna is SO small for that band. If I short the feed line at the longwire port on the tuner and load it against a counterpoise it will load up on 160 with much better results.
So for now I am back up and running! The shack is still a mess, but all the radios and accessories are back on the desk and hooked up. I have made a few QSO's so far - nearly all CW. It really feels good to get back in the swing of things! I have been wanting to get my CW speed up but I have not used it much for many months so I am a bit rusty. Just since I have put my station back together with the new loop I have worked out the rust in my code and I'm at about 15wpm.
posted by Steve at
7:58 PM
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