Newbie with hand built 10m dipole
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| Feb 18th 2014, 13:46 | |
K1BBBTotal Topics: 0 Total Posts: 0 |
Hi, I'm a complete newbie and attempted building my own dipole last night. I have a like-new Icom 761 I bought from a friend, and by all appearances, it appears to function like new. The dipole I built, is rather crude, using solid copper wire connected to a PL239 adapter. Fed by a 50ohm 50foot PL239 coax cable. The soldering I did was terrible, and I believe I need to buy some higher quality solder and redo the work. But, in my excitement to get started, I did the best I could. It's very cold outside and we have about 3 foot of snow in the back yard. I had about a 4 foot pole I put the antenna on, and it looks a bit like an inverted V, with the wire draped down across the snow. I attempted to tune my 761 per the manual, but at the last step, it tells me to turn two small dials under a panel till all 4 LED lights go out. Two were still on. I played around with this, trying it over and over, but achieving the same results. The manual says this could be due to high SWR, which I wouldn't be surprised at considering my construction skills. But, the step that tells me to check the SWR by setting the mode to RTTY and pressing the transmit button for a few seconds, appears to show either very low SWR, or maybe the needle is pegged all the way to the left? Which seems like the opposite of high SWR to me? Despite all of this, I decided to set my autotuner to "preset" and adjusted the dials as such per the manual. I then ran through the 10m band a few times, and to my surprise I heard a voice! I continued to listen in, and found that the two gentlemen were relatively close to me, as I heard conversation about local events and locations. I was very excited to at least hear something. It however was late at night, and my wife was wanting me to come to bed. I decided to scan through the band a couple more times, just to see what I could find. Rather than finding completely new conversations, I heard the same conversation 3 separate times at different frequencies. Which seemed disheartening. I attempted to do an online search with some key words, but couldn't find anything related to this. I am hoping that someone here has an explanation. Again, this crude dipole was simply something to do, and only temporary, as I have a Carolina Windam that I will be putting up in the spring, once the snow has melted. Thanks! Matthew - KC9ZFI |
| Feb 18th 2014, 16:15 | |
W1VTSuper Moderator Total Topics: 0 Total Posts: 0 |
You may need a bigger soldering iron--you need a lot of heat to properly solder PL-259 connectors. I use a 100 watt iron. You also need to get the antenna up higher to reduce the ground losses from it being so low. The761 has a very crude automatic antenna tuner. If the SWR meter needle doesn't move,and it is all the way to the left, that is a low SWR, assuming that on transmit, the meter moves to the right. For an accurate reading, the meter needs to move all the way to the right. A strong local signal can overload the radio so you hear it several places on the dial. For just listening, you may be better off with10 or 15 ft of wire attached to the center conductor of a PL-259 that you screw into the antenna jack of the radio. You can actually hear better without the coax due to the high input impedance of the IC-761's receiver when you are running this sort of antenna. Zack Lau ARRL Senior Lab Engineer |
| Feb 18th 2014, 16:37 | |
K1BBBTotal Topics: 0 Total Posts: 0 |
Zack, Thank you for your reply, it was very informative. I might have the wrong size iron, as it's only a 20/40watt unit. But I also believe I have cheap solder, so I'll look at both of those. I'll see about throwing my antenna up in one of the trees I have out back, I should be able to get it up about 10 or 12 feet that way. Is it possible to receive signals from other bands, because a signal is so close? Say, the guy who was transmitting loudly last night was a neighbor on 2m (pure speculation), is it possible I was hearing that? Lastly, the SWR meeter on my 761 starts off about in the middle, and then when I transmit on RTTY per the instructions in the manual, it moves to the left. I'm not currently infront of the radio, but I believe the SWR rating goes down as it goes to the left, which I think might be opposite of what you were indicating in your post. Which might mean I'm good on SWR? Do you know what it means if it's fully pegged to the left? Here is a picture of the meter on the front of a 761 (not mine) http://www.universal-radio.com/used/UU03met.jpg Thanks again! -Matthew, KC9ZFI |
| Feb 18th 2014, 16:49 | |
W1VTSuper Moderator Total Topics: 0 Total Posts: 0 |
Getting it up higher will help--I have mine at 42 ft and it works really well. The usual recommendation is to get it up at least a half wavelength, which is 16 ft, but 12 ft is way better than what you have now. It is possible, but very rare to have an HF radio overloaded by 2M. More common is harmonic distortion, in which you hear a 40M signal on 20, 15, and 10 meters. You can also have intermodulation distortion, in which a station will splatter up and down an amateur band. The radio meter starts out midway because it is reading received signal strength. All the way to the left on the meter is 1. Midway is 3. A very high reading is to the right. Zack Lau W1VT ARRL Senior Lab Engineer |
| Feb 18th 2014, 16:55 | |
K1BBBTotal Topics: 0 Total Posts: 0 |
Again, this information is fantastic, thank you. If I understand you correctly, my SWR should be fine, and I really just need to get my antenna up high. I'll do this tonight and let you all know the results. -Matthew, KC9ZFI |
| Feb 19th 2014, 13:25 | |
K1BBBTotal Topics: 0 Total Posts: 0 |
I have to say, last night was very exciting. I got my antenna placed in a tree about 12 to 15 feet up, and got on the air around 6PM EST. I live in Northern Indiana mind you. The first contact I heard on 10m, was in Central Indiana, and I thought to myself "ok, that's not bad considering the condition of your antenna," but, the next one I heard was from Montana! He was talking with Japan and Sweden (but I couldn't hear the other side). Scanning through the band I found some strong signals from California as well, and was able to listen in on that for quite a while. This all died down around 8:30PM. I'm assuming that's when the band closed down? Can you tell me what times I will normally be able to hear or make contacts on 10m? Thanks again Zack! |
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