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Author Topic: New ham needs help!: 2m Mobile TX (or lack thereof  (Read 705 times)
KD7NEW
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« on: May 09, 2003, 03:41:13 PM »

I'm sure this is a very easily solved problem (or one that is self-created) so excuse my ignorance. I've been out of the hobby for a bit (Just finished a deployment w/ USS ABRAHAM LINCOLN).

I just bought a IC-V8000 for my '89 Taurus. It is running through a Valor VAA002 20 in. (1/4 wave) steel whip on a mag mount right behind my rear windshield (centered).

My problem: Where most can hit local repeaters cleanly w/ 5w, I can't open them with 75w! I know the PL tones and freqs are correct, since I can access them in places closer geographically to the repeater itself. I can RX just fine, as far as I can tell. Also, when I can transmit, those on the repeater say I am "Over-modulating" or my signal is very unreadable. Everything is hooked up correctly with the rig itself, so I have NO IDEA why my signal is so bad and why I can't get into repeaters from ideal locations.

ANY HELP WOULD BE GREATLY APPRECIATED!!!!!!

Aaron KD7NEW
USS ABRAHAM LINCOLN (CVN-72)
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K7IHC
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« Reply #1 on: May 10, 2003, 03:11:25 AM »

It would be helpful if you had a good SWR/wattmeter to check the power output and SWR of your setup.  I use a Diamond SX-600, and it is very handy.  You may have a problem with your transmitter, especially if it has been modded for extended transmit capabilities.  The unit may have excessive deviation or some similar problem.  See if you can find someone with a communications service monitor that could hook it (IC-V8000) up and check it out.
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N7PTM
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« Reply #2 on: May 10, 2003, 11:12:38 PM »

This antenna is physically adjustable for SWR. Is it adjusted right?  Get an SWR/field strength meter and check it out.  Sounds like it's out of adjustment.

Or as a quick check, does your radio have an SWR display?  When you TX @ full power what does it show?

On my Icom 706 HF rig (and some others), there's a radio safety feature called "SWR foldback" meaning if your SWR is too high, the radio automatically cuts back the TX power. It may say it's on high power, but it may not be putting out nearly that much power due to a too-high SWR.  

That said, another way to look at your problem is through the rig's power meter - if it's not at full power when you TX on the "high power" setting, then your SWR is too high & the radio is automatically compensating.
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N8EMR
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« Reply #3 on: May 12, 2003, 08:03:54 AM »

As noted I would check out the radio and antenna system. I would also re-evaluate my antenna system. You picked up a high power mobile radio and then stick it on a 1/4 antenna. Find an antenna with some gain to further enhance your system.
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KB0NLY
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« Reply #4 on: May 16, 2003, 02:34:36 AM »

Assuming that there is nothing wrong with the radio, why not go for a better antenna?  A 1/4 wave wouldnt do me any good where i live, a wet noodle would probably work better.  A 5/8 wave antenna is the minimum that i will put on a 2m rig, even though they only have roughly 3db gain, its still better than nothing, and a lot better than shelling out $70-$100 for some fancy antenna that offers more gain, or is a dual band antenna.

If you have a NMO mount antenna base, im guessing that it might be a mag mount on the trunk, buy yourself a Larsen NMO-150C and screw it on.  That's a nice durable 5/8 wave with 3db gain.  I have two of them in use now, and a spare that i have yet to use, but you never know with low branches etc, the whip wouldnt break but the base could always suffer damage no matter what brand of antenna or how much you paid for it.  Another suggestion, if you are using a mag mount antenna, get out the drill and make a hole if you will have the vehicle for any length of time.  Use a good quality 3/8 inch through hole NMO mount, drill the 3/8 inch hole in the center of the trunk deck, or even better in the center of the roof, and it will be a lot more reliable, and the grounding will be better at the mount than a mag mount could offer.  The only drawback is if you have a fiberglass body on the car, but that doesnt sound like a problem for you.

If your wondering about how to get access to the roof pull down the dome light, drill the hole up through the roof, install the NMO mount, and snake the coax under the headliner and over to one side and down under some trim.


73,

Scott, KB0NLY

www.qsl.net/kb0nly

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KB0NLY
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« Reply #5 on: May 16, 2003, 02:39:56 AM »

Also, before the flames start rolling, drilling a NMO mount into a car is no big deal.  I have bought vehicles, installed antennas, and then sold them years later.  I just remove the NMO mount, pop in a rubber body plug, available from Antenna Specialists or a local auto body shop, and drill the mounts into the next vehicle.

If you have ever seen a retired police or fire vehicle you will see those black circles on the trunk or roof, thats the body plugs filling in the 3/4 holes that the Motorola NMO through hole mounts use.  Seems to me that they are starting to make the switch over to the easier 3/8 mounts, after all why drill a 3/4 hole when it can be 3/8.

73,

Scott, KB0NLY

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NN5KS
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« Reply #6 on: May 28, 2003, 01:10:09 AM »

The part about your post that stood out for me is this:

> Also, when I can transmit, those on the repeater
> say I am "Over-modulating" or my signal is very
> unreadable

While I won't belittle the idea of a horribly mismatched t/r and antenna, this part may be indicative of a problem with the radio itself.

First and foremost: beg or borrow an SWR meter from a fellow ham and check that the t/r and the antenna are matched. Then check the power output of the radio.

Next, have someone monitor your signal from a handi or another radio from about a half-mile away.  See if your signal is unreadable or noisy.  At that distance, the rig should provide clean voice with full-quieting.

Of course, If you know of a ham or benchtech with access to a communications monitor, so much the better.  Have it checked for PLL lock, Freq stability, over-mod or weak output.

If it is noisy then recommend get it replaced/fixed.  Since it is new, you should be able to exchange it.

Good luck.
NN5KS
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