DAS26miles
San Fernando Valley, California
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Joined: 10/11/2003
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If you have read my other topics on the NGP antenna, you know I just wasn't getting out beyond a mile. I had my best match mounting the NGP antenna on my awning stop bracket and ran the coax down the side. I was able to get a match of channel 1- 1.7:1 Channel 20 1.1:1 and channel 40- 1.8:1.
I ordered a ground plane Firestik II with coax, and it arrived today. I tried the new antenna where I had the NGP, on my awning bracket. I tried grounding it every which way and the match was high. All were 2.5 to 3.5.
I moved the mount to my rear ladder which is probably made of some anoidized metal, maybe aluminum. I mounted it down about a foot from the top. I ran a ground (2- 14gauge wires wound together) to my hitch. I tested it and got a match of 2.5:1 on channel 1 and 1.7:1 on channel 40. I moved the antenna higher on the ladder and the match came down. I tuned the antenna by turning the knob on top and got the best match of 2.0:1 on channels 1 and 40, and 1.5:1 on channel 20. I tried to get radio checks on all channels with no luck. I can hear some chatter on a few channels, but can't talk with them.
My my MH is in my driveway facing my house and the freeway is about 3/4 of a mile off the rear of the MH. So I will have to take the MH out tomorrow and do a real good antenna match check in a parking lot with no obstructions. Is this match of 2.0 to 1.5:1 OK or should I go back to the NGP?
I realize that I will hear very little chatter from behind and almost all from in front of the MH.
2004 Class C Winnebago Minnie 22E
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plascell
Lynchburg, VA
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Joined: 01/13/2002
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Been reading some of your posts -
It is unfortunate that a perfect match of 1:1 doesn't mean the antenna will radiate or receive well. A dummy load is 1:1, but radiation is nil.
The maximum radiation occurs from the current lobe (not voltage) in the antenna. In a 1/2 wave dipole or 1/4 wave whip with full size radials the current lobe is at the feed point. Any changes in physical size and the required "matching" to keep reflected power from the transmitter, will likely change the location and level of the current lobe.
A simple experiment might be to make a dipole for 27 MHz (ft = 468/MHz) and place the feed point at the bottom corner or upper corner at the back of the RV. Try to keep the center coax lead connection to the vertical wire, and run the shield side horizontal as a single radiator. Tape the antenna to the outside and give it a try. This will work only with fiberglass RV.
Good luck with your experiments.
Pete W4WWQ DX70 IC-2800 Smartire X-10 camera
2006 Chevy 3500 CC LB 4WD DRW Duramax auto-6
2003 Cardinal 29WB LX EU3000is Roto-Choks 300W from www.amsolar.com
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DAS26miles
San Fernando Valley, California
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plascell- that's way over my head?? I went out this morning and did some more testing. Seems the more grounding wiring(s) U attached to the mount, the worse the match bacame. The best match I could get was Ch1 1.7:1, ch 19 1.6:1 and Ch40 2.1:1. Shortneing the tip caused ch1 and 19 to rise, but Ch40 stayed the same. Since I don't use but channels 13-19, does it really matter if the match on the very uppper channels is just over 2?
I was able to get a trucker about 2 miles away from my driveway. Remeber, the MH facing the house not the freeway. So I am getting out 2 miles to the rear. I should get out much farther to the front, I hope.
I still need to get better grounding wire today and take the MH out to a clear area for the best test.
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DAS26miles
San Fernando Valley, California
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Went to the hardware store and bought 10 gauge wire for the ground. I replaced the 2 wires I had used and secured the new wire to the mount and the frame. Got a high match of 2.5 to 3.5. I don't understand why when I get a better ground, that my swr reading goes up higher. I just can't seem to get this new antenna to work. I got a better match just using the ladder as the ground and I don't think it's grounded. Perhaps I should try grounding the antenna to the awning gutters. Seems the lower I go on the MH to ground it the worse it gets.
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lhuff
Marietta, GA USA
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Joined: 06/18/2002
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Does the packaging tell you what portion of a wavelength the antenna is (guessing 1/4 wavelength? In general, ground plane antennas require a "ground plane". This is the other half of the antenna or counterpoise. If you have a fiberglass motor home, try cutting a 108" piece of wire and fastening it to the metal part of the mounting bracket for the antenna. Let it hang beside the motor home. Check your VSWR on any channel. Snip a couple of inches from the free end of the wire you added and check it again. If it went down, the wire your added (counterpoise) is coming closer to the frequency (channel) you're checking and vice versa.
Now the problem. In electrically shortened antennas, the bandwidth is much narrower than with full length antennas. That means you tune for the middle of the band and accept the the edges or tune to the channel you will use the most and accept the rest. The closer to 1/4 wavelength the antenna physically is, given everything else stays the same, the lower the VSWR across the entire band (assumes 1/4 wavelength ground plane). The counterpoise, in real life, is the mounting bracket, ladder, metal in the motor home, and anything else in the area that effects radio waves. So, moving your antenna around will effect the VSWR because the counterpoise (remember it's the other half of your antenna) changes.
Now for the good news. High VSWR readings (3.0 to 1 or more) will effect how well you "get our", but not much. I like to get my best reading to 1.5 to 1, but in real life, 2.0 to 1 or even 3.0 to 1 will do little to how well you are heard, and almost zilch in how well you hear. The main concern is the effect of the "reflected" voltage on your transmitter final, and at 5 watts, that worry is minimal and modern radios usually protect themselves against this kind of damage.
A little more bad news. If you're having problems hearing and transmitting, make sure you don't have a loose connection in your coax. I believe you have more problems than VSWR. I would start by looking for an open center conductor then shield on the antenna end.
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DAS26miles
San Fernando Valley, California
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It's a 5/8 wave Firestik. I had to add 12 feet of coax to the Firestik coax I bought to reach the radio. Plus I have to use the spring off the NGP kit, cause it's 12'8" high. is there something about having 3 foot sections of ground wire?
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DAS26miles
San Fernando Valley, California
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Finally got the swr readings down below 2.0:1 Channel 1 is 1.8:1, channel 19 is 1.4:1 and channel 40 is 1.7:1. I had to run 2- 10 gauge ground wires, 1 to each awning gutter where they are screwed into the gutter. So I have the ground plane after all. I did a radio check and got a trucker about 3 miles from home. So that is a good increase. Will try it on the road next week. Too hot outside to do anything more.
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YC 1
Yuba City Calif.
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Joined: 01/11/2005
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As mentioned if you are working with the same piece of coax there is a good chance of having a bad connection on either end or just a bad piece of coax. You would also want to be several feet away from any trees, house, laddar, or human body while making the checks. For example at those frequencies we have to pull vehicles out onto our parking lot to get a good measurement.
Question ? Did you put your own connectors on the coax ? If so be sure to use an ohmeter on your coax jumper to check for an open or short. Easy to do. Measure from the center conductor to the shield and look for it to be open. {Disconnect from antenna for this}. Then short out one end and check the other end to see if you can see the short.
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lhuff
Marietta, GA USA
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Your ground wire (from mount to ground) should be as short as possible. Longer pieces start to act as part of the antenna and "out of resonance/frequency" pieces will adversely effect performance (and SWR which is less important). YC_1 is right on about your next steps and how to correctly check VSWR. Three miles on channel 19 sounds like things are getting better.
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DAS26miles
San Fernando Valley, California
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Joined: 10/11/2003
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I got the Firestik coax with lugs on one end and the plug on the other. I did add a 12 foot peice of coax which has a plug on one end and I put a plug on the other end. So only that one plug is new and is OK.
So when I made an 8 foot ground wire running down the back of the MH it was causing that resonace I guess and giving me higher SWR readings. I tried using only 1 wire attached to the awning gutter and got a high swr reading. But it's working fine now with a 2 foot section to the right gutter and a 6 foot section goingto the left gutter. Just checked it again and can't believe everything is under 1.8:1. So as the DW gets home, I will take it over to a parking lot and check it again.
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