G5RV Loads 10M when Ice Covered!!! - elmers Forum at eHam.net

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eHam.net Forum : elmers : G5RV Loads 10M when Ice Covered!!!

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G5RV Loads 10M when Ice Covered!!!	Reply
by NG1I on January 13, 2005	Mail this to a friend!
Hello, I have the full sized G5RV that doesn't do 10M but I just it tuned on ten meters but only when ice covered after two ice storms. During these times I have managed to get it loaded up 3:1 SWR with 70 watts output. I managed to get MA QTH (my home state ----80 miles east of me) and today NM with 45 watts! Can anyone explain this? Also as anyone ever removed the balun and it "tv" lead line from the 102' ant and replaced it with ladder line right at the center insulator? If done, would you experience any internal RF shack problems if I use up to 600W? Only 4" of ladder line would protrude from the window to the tuner up against it. Just a thought.....or a useless post? I can take it. Frank NG1I

RE: G5RV Loads 10M when Ice Covered!!!	Reply
by K0BG on January 13, 2005	Mail this to a friend!
A G5RV is a fair antenna for 80, 40, and 20 meters. On any other band, it requires an antenna tuner, and losses can be VERY high. You very well might have loaded 10 meters with it (ice or no ice), but the system losses would have been nearly 100%. Alan, KØBG www.k0bg.com

RE: G5RV Loads 10M when Ice Covered!!!	Reply
by WA6BFH on January 13, 2005	Mail this to a friend!
If you really want to see or learn what is happening with the antenna, draw it out to scale, perhaps 1 cm equals 1 foot etc. You of course only need to do this for half of the antenna. Now, draw out the voltage and current distribution for each band. The easiest way to do this would be to make one drawing, and several xerox copies. After you have done this, you will literally see the 'transformed impedance' as it hits or crosses the feedpoint of the antenna. You may then also want to go through this same procedure from the feedpoint, down the feedline, into the shack.

RE: G5RV Loads 10M when Ice Covered!!!	Reply
by N4HRA on January 13, 2005	Mail this to a friend!
I added a SGC ATU to my G5RV and now tunes all ham bands Lew

RE: G5RV Loads 10M when Ice Covered!!!	Reply
by WB6BYU on January 13, 2005	Mail this to a friend!
Ice loading changes the velocity factor of the antenna wire, thereby changing the electrical length. If your antenna doesn't load on 10m, it probably is because the impedance presented to the tuner at the end of the feedline is out of the range that the tuner can match on that band. Changing the (effective) length of the antenna changes the impedance at the tuner. If you read the comments of Lou Varney, G5RV himself, you will see that he recommends feeding the antenna with open wire line to a balanced ATU ("aerial tuning unit") as being more efficient. The coax cable feed is simply for the convenience of being able to use coax cable. And, if you are going to use balanced line all the way, there is no magic in the specific antenna length unless you want a 3/4 wave antenna pattern on 20m. I encourage you to read further on the G5RV. Here are some links that may be of interest: http://www.qsl.net/aa3ps/g5rv.html http://www.cebik.com/g5rv.html

RE: G5RV Loads 10M when Ice Covered!!!	Reply
by WB2WIK on January 13, 2005	Mail this to a friend!
That you couldn't load on 10m before and you can now only indicates detuning from the ice, as Dale said. However, whether the antenna will "load" on 10m (or anywhere other than 20m, its real design frequency) or not depends on several variables to begin with. You just didn't get lucky originally. I've had G5RV's (102' original design model) that loaded on 10m just fine, without doing anything to them; I got luckier with my feedline length, or maybe just used a better tuner that had wider matching range than yours does. Feeding the antenna with 450 Ohm ladder line all the way to the shack is a great idea, and as Dale said, the actual way that G5RV himself used his own antennas! Doesn't matter if you have 4" of line in the shack, or 40 feet in the shack. If the line is balanced and the load is balanced (and they normally are, or pretty close), the line won't radiate and nothing bad will happen. I have a QSL card for my QSO with Louis, G5RV, back in 1974. It has a photograph on the front of the card, showing his antenna, which was actually a 204' long doublet fed all the way with ladder line. His card doesn't mention any other antennas, so I think this was the "real G5RV antenna!" WB2WIK/6

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