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Old 03-22-2013, 10:01 PM   #1
SoCalRVer
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Unhappy Mounting 2M antenna on ladder

New to Ham Radio and this forum. I have a small class C MH and previously had a CB antenna mounted atop the ladder. Gave up on CB and went to Ham 2 months ago. Replaced the CB antenna with a short 18" Comet dual band antenna with a spring. This is actually shorter than the CB antenna. Total height is 11' 8". Problem is the match on the radio is 2.0 to 1 and although I have no problem reaching the local repeater, I have better luck on the ARC simplex checkin with my HT. I get nothing with the FT1900 at high pwer. The MH is parked in the driveway facing the house. I did try an NGP antenna, but it brought my height to 14" and no spring.
So it does appear to be operating correctly with the repeater but just doesn't work well on simplex. Everyone tells me there's no ground. If so, how come it works with the repeater? Watts reading on the SWR meter shows appropriate power level readings, just 2.0 to 1 on match.
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Old 03-23-2013, 11:13 AM   #2
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The apparent lack of a ground may have two effects: (1) a generally weak signal, and (2) a signal that goes mostly somewhere other than toward the horizon, which is where the other guy's antenna is (the one on the repeater or on the other ham's handheld when you're working simplex). But I would think that in most cases the ladder would be a pretty good ground at two meters. Two to one isn't a terribly bad SWR; many commercial two-meter antennas aren't resonant at the correct frequency anyway, unless you tune them carefully, and have poor SWR right out of the box even with a perfect ground.

Or, possibly, everything's working well. If the repeater can hear you, and another ham on simplex can't, it's usually because the repeater's antenna is high up and in the clear. That's why repeaters exist -- if repeaters couldn't hear (and be heard) better than individual stations, no one would bother building repeaters and everyone would work simplex.

Me, I don't like short antennas (shorter than I am) on ladders. Climbing down, I've been stabbed by such an antenna when I wasn't super-careful, and even when I was super-careful. Usually you get stabbed when starting down the ladder, and usually you get stabbed in the face. Scary. If the stab doesn't injure you, the consequent fall probably will.

And welcome to ORR and to the hobby!
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Old 03-23-2013, 01:33 PM   #3
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As Carl stated, welcome to the hobby and to ORR.net.

Many ladders on RV's are not electrically grounded. That may (or may not) be an issue. And as Carl stated, if the repeater can hear you, you are probably OK. With the line of sight nature of VHF/UHF simplex can be a bit "iffy" which makes it interesting.

One of the biggest challenges to the RVing ham is getting a mobile antenna set up on the RV. Portable is pretty simple, but mobile is something else!

Again, welcome to ORR.net. Unlike some forums, we enjoy having newbies on our boards!
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Old 03-23-2013, 04:57 PM   #4
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Well depending where you added the spring you may have detuned the antenna. Unless it is a 1/2 wave antenna you'll need some type of ground plane and guessing your roof is fiberglass it maybe necessary to add radials or some type of ground plane. Years ago a friend got me on the roof of his RV to show me some thing on his roof it was a 10" saw blade stuck to the roof and aluminum tape in a 6'X6' cross the antenna was long gone but the ground plane was still there. Repeater antennas have a pretty fair amount of gain and are usually sitting on a hill to begin with (the line of sight thing). All though your antenna reads 2:1 that does not necessarily mean it will radiate well a dummy load is a perfect match but is a very poor antenna.
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Old 03-24-2013, 12:53 AM   #5
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Default Mounting 2M antenna on ladder

I ran a test in my driveway with the SWR meter and was getting 2.0:1 to 2.25:1 as I increased from 5 to 50 watts. I then drove out to an open area and the match dropped considerably down to 1.5:1 to 1.8:1. So the structures around my driveway are the problem.
I will have to checkout a roof top antenna for my house along with a power supply so I can checkin with the local ARC on simplex freq.
I also put back my CB antenna and radio and it lowered my match even further down to 1.3:1 to 1.7:1. Antenna are about 15 " apart on opposite rungs atop the rear ladder. Will try listening to both with high squelch and turn the other off prior to using them. Hope this works and doesn't cause problems.
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Old 03-24-2013, 07:39 AM   #6
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If you stand next to an antenna and check the SWR it will have an effect on your readings so yes other things around the antenna will slew the readings if you want to have fun with your SWR meter try it at a transmitter site. What are you using for a mount for the VHF/UHF antenna? And what are you using to test your SWR?
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Old 03-24-2013, 09:56 AM   #7
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Default Mounting 2M antenna on ladder

The antenna is a Comet HS-05 18" mounted on a mirror mount. The antenna has a spring built into it and it attaches to the SO-239 The mount was drilled out so the double female S)-239 barrel connector would pass thru it with a flat nut on each end. RG8x coax was used, about 34 feet and the SWR meter is a MFJ-862.
My match changes by increasing as the power level is increased. This increase is about .5:1. Should the match stay the same?
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Old 03-24-2013, 10:46 AM   #8
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The SWR should be the same no matter what the power level.
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Old 03-24-2013, 11:41 AM   #9
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So what does that mean when the SWR meter rises with power?
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Old 03-24-2013, 01:26 PM   #10
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Well, I'd say it must be one of two things: (1) inexpensive SWR meter; (2) operator error.

The SWR is a a measure of the fraction of the power going up the transmission line toward the antenna that is reflected back down the transmission line by a mismatch at the antenna. It depends on two things: (1) the [complex] characteristic impedance of the transmission line, which in the case of commercially manufactured coaxial cable will be quite constant; and (2) the [compex] impedance of the load (the antenna), which likewise is independent of power level. The reflection, and thus the SWR, depends on nothing else.

If you ran so much power that you damaged the cable or the antenna, the SWR would change; but then it wouldn't change back when you reduced the power.

So, that leaves the instrument or the operator. I'm betting on the instrument, which may perhaps be not quite linear with power changes. Many (nearly all) inexpensive SWR gauges use diodes to rectify the RF for measurement. Since diodes have a nearly constant forward drop, this means that the meter is less sensitive at low power levels than at high levels. This makes for a large error at low levels and a smaller error at high levels. Thus the SWR measurement is usually less accurate (lower!) at low levels than at high levels; you ought to trust the high-power reading more than you trust the low-power reading. Also note that the SWR error from the diode forward drop will always result in an artifically low SWR reading at lower levels.

So I'd say that your actual SWR is nearer to 2.5 than to 2.0. That's a little high for good performance at 144 MHz with 35 feet of coax.
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Old 03-24-2013, 06:57 PM   #11
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You got some issues, are you using this with an HT? or do you have adaptors from the SMA to PL259 going to the RG8X? I am beginning to think you are reading the SWR of an 18" jumper. Again what is the antenna? The HS-05 is just a jumper from SO239 to SMA. That jumper is a little light of a 1/4 wave on 2 meters.
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Old 03-24-2013, 06:58 PM   #12
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Reran the coax to shorten it. Cut off 30 inches. I did get the match down to 1.2:1 on low power and 1.5 on high. I was moving to coax around in the cab and noticed the signal strength fluctuating from nothing to half on the bars. I left it in a postion where I had the most bars. The coax is in an auto wire covedr along with the black and red power wires. Could this be my problem having them straped together?
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Old 03-24-2013, 08:12 PM   #13
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Quote:
Originally Posted by SoCalRVer View Post
I was moving to coax around in the cab and noticed the signal strength fluctuating from nothing to half on the bars.
No, strapping them together wouldn't cause that, or have any effect at all. Sounds to me as if the connectors are not making contact, or are shorting intermittently.

Alternatively, if the connectors are not properly installed, you could be receiving on the outer surface of the outer conductor (and not with the antenna). That could cause received signal strength to vary when you wiggle, or even touch, the cables.

Have you continuity-tested and short-tested the cables while wiggling them?

Changing the length of a 34-foot cable by a foot wouldn't make a measurable difference, by the way.
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Old 03-24-2013, 09:34 PM   #14
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Sorry, that should be a Comet Ss-460sb antenna and the radio is a Yaesu FT1900. I have the power coming directly off the house batteries instead of the engine battery. The house batteries are being charged all the time from the shoreline power.
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Old 03-25-2013, 07:35 AM   #15
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I think you have answered your own question with the coax and or the connections. All though RG8X being 35' feet long is not a huge loss the shorter the better in the VHF/UHF bands as cables become rather lossey at higher freqs. Comet makes a pretty good antenna but no better then the feed line going to it.
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Old 03-25-2013, 08:21 AM   #16
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One thing I see in this thread is confusion over two terms

Ground

And Ground plane

They are NOT the same thing.
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Old 03-25-2013, 09:13 AM   #17
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Quite correct. An imperfect ground will likely affect the impedance (and thus the SWR); an imperfect ground plane, on the other hand, will affect mostly the radiation pattern. Either can also reduce the efficiency of the antenna system.

But I haven't noticed anything that implies confusion of the two.
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Old 03-25-2013, 04:12 PM   #18
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Definately need to check the pl259 at the radio and maybe try using a patch cable from the SWR meter and wiggle.
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Old 03-25-2013, 04:47 PM   #19
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I think at this point I would go looking for an ohm meter and work on the cable. Make sure you have some thing close to zero ohms both at the center conductor and the braid at both ends and infinite resistance between the center and the braid first. Can you get your hands on a known good coax long enough to go from the radio to the antenna even if you have to stick it out the window? If this is a home made cable many times I have seen guys cut the braid too long and short it to the center pin when they push it into the 259.
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Old 03-25-2013, 11:10 PM   #20
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Went out to the MH tonight and tested the pl259. That's the problem. Wiggling the coax at the back of the connector and it makes the needle on the SWR meter jump along with the signal strength. When I played around with it, I got a match of 1.2:1 on low power, High power jumps up to 1.5:1. I must be doing something wrong when I install the PL259. Either the shield wires aren't getting soldered or the small center wires at the tip aren't. Watched Youtube video on how to do it. Do you need to cut the shield wires as I have done? Can you bend back extra wires back into the tip?
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