Ugh... SWR issues and more Updated: fixed. Thank you KN4KL!

Just installed my first mobile today (Kenwood TM-281A). It worked fine for the first few minutes. Then the trouble started. Every time I would key up on high power, the radio would rapidly turn off, then back on. It stayed on fine during reception, and on low power tx. Everyone could hear me strong and clear.

I checked the SWR with a radio shack SWR meter.... off the charts.... like, as high as the meter goes, so more than 3:1

Rechecked all connections, no problems there. Rechecked antenna length, antenna mount, NMO solder connection, power supply wiring at battery, etc. All fine.

Checked SWR again... still high.

Decided to recut and reinsert the coax into the PL259 (solder less) at the transceiver end of the antenna cable. Now it only picks up stuff if i jiggle the cable. Not sure if it's a crappy cut on the coax, a crappy solder less pl259, or something wrong with the connection on the radio.

I'm going to try to get help tomorrow, but if anyone has any constructive tips or things i haven't thought of, please feel free to speak your mind. I'm kinda ticked off at myself right now for what seems like botching this install.

Edit: It was a bad connector (soderless PL-259), AND crappy wiring job on my part (crappy splice job). Ed, or KN4KL, really helped me out, and showed me some basics on soldering and wiring, and totally fixed both problems. Thanks again Ed!

Do you have a digital VOM or continuity tester. I'd bet there is a short between your center and shield.

Dump the solderless connector and replace it with a real PL-259 and do it right.

Yeah, wish i had just done the real one to begin with but Radio Suck didn't have any with the adapter for RG58... only the ones made for RG8.

Short between the center and shield of the antenna cable at the connector?

I think you've just isolated the problem to the solder less PL-259 at the radio. I never knew they existed and would avoid such an animal at all cost. Well except for good quility crimp ones, is that what you have?

Earlier today I got an email from a Ham that I sold an IC-751A to a while back, and he was receiving fine but it would shut down on transmit after he had moved some things around. Turned out to be bad ends on coax there too.

Yeah I called Kenwood and I asked "hey man, is there an auto shutoff feature to protect the finals if the SWR gets too high?" And he maintained that there was NOT.... BUUUTTT, it seems like that is exactly what was happening, especially if there was a short, because that would basically be like transmitting without an antenna right? It would reflect everything back to the radio (correct?).

I will get the real PL259 tomorrow if i can find a Radio Shack that has one. It's slim pickings around here, with no Amateur radio friendly stores within 150 miles of my location.

The braid of the coax is shorting against the center conductor. Its very common with those stupid solderless connectors. I would bet that someplace in your area you can find a real PL-259 connector. If you can't PM me and I will send you one with the adapter.

I just installed the same model in my pickup a couple of days ago.

I used the 54.?" (or however fucking long it is) magnetic mounted rooftop mount recommenced by the kind gentleman at HRO ($30) and I seem to be GTG.

I also have a 2M/440 and much shorter magnetic moung with an SMA connector on the end I bought for mobile HT use. HRO sold me an adapter and I am going to try the shorter antenna out for size as it is stealthier and won't bang around with low lying bushes, McDonalds overhrad things, etc.

I am basing this on results as I have no SWR meter for either of these but I do know they were specifically cut to length for the 2M band.

My first simplex QSO was a guy several miles away crossing a bridge. Repeaters all over this AO are a snap.


Pic

Yeah, I did the NMO mount thing (boy that took some balls to drill through the roof of my truck), with a Larsen NMO150B which is a 5/8 wave. When the rig was working, I was hitting repeaters I had never heard before just by scanning around, but then my problems arose.

The antenna was cut for 144, but it had the cut chart, so i cut it down to 146 since that is the center of the band.

Don't be surprised if the PL-259 meters dead short even if the connector is installed properly. Some antennas are base loaded with a tapped coil for matching purposes so it will show dead short even when it's OK. If you remove the antenna from the mount, there should be no continuity between the center and shield.

If you are in the tidewater I can lend a hand if needed.

which part of VA

Couple things . .

1. Look for an electronics/TV/cable/telephone supply store, instead of a radio place . . a place the local independent cable installers and small businesses are getting parts . . our small town100+ miles out of the nearest big city has one that has a couple good coax choices and a limited variety of both cheap and quality connectors, including the amphenol solder version with adapter (pretty much the best to get).

2. If the whip cut ended up too short (you'll be able to tell when you get close and measure both ends of the band), you could get a spring and cut more conservatively when adjusting for the spring length.

Warning, Radio Shack has some plated PL-259s that are almost impossible to solder. They are just crap. Buy some good quality PL-259s and learn how to install them.

Watch and learn:

How to install PL-259s

http://www.youtube.com/watch?v=7m4fhs__kAI PL-259 Installation Made Easy and FUNny 1 of 2

http://www.youtube.com/watch?v=xX6zOGP0RY4 PL-259 Installation Made Easy and FUNny 2 of 2

http://www.youtube.com/watch?v=PzXXjzmA-IE PL-259 on RG-8X

http://www.youtube.com/watch?v=n1nabA6yMoI PL-259 on RG-213

http://www.youtube.com/watch?v=_jlPcBVg45E PL-259 installation pt 1

http://www.youtube.com/watch?v=agkP9YMR3Kc PL-259 installation pt 2

radio shack doesnt have a VHF SWR meter last i knew. if you are using there CB SWR meter there is your problem with the high SWR. what length is your antenna? where did you get your power from for the radio? where is the ground going for the radio?

If you try the old CB trick of getting power from the cigarette lighter socket, your radio will turn off due to insufficient current/voltage during transmit. Your 2m rig requires a lot more juice than the cig socket can supply. Make sure you are wired with 10 ga (at least) wire directly to the battery. If the voltage drops below about 11 v it will cut off.

And yes, a CB SWR meter won't do for 2m.

It may not be particularly accurate on 2m, but if it's showing an uberhigh SWR, this is not a good sign.

Go by a two way radio shop and have them crimp a UHF connector on your coax, probably cost you $5-$10.

Or buy a crimp tool for $25 or so and you can do it yourself.

You could easily have a combination of high SWR and voltage drop going on with the installation.

14ga wire size is sufficient for shorter runs for mobiles in the 50w class, if you're running one of those 75w rigs you should run 12ga.

The radio is 65W on high power, and 25W on low power.

Yes, I was using the CB SWR meter, but I figured that was okay.

I am learning to solder, and will try to find a real PL-259 today.

I routed the power cables directly from the battery terminals, through the firewall, under the dash, and to my radio.

I have a a DC line noise filter in line with the power cables.

take out the filter and see what happens. as others have asked, where are you in Va, i am willing to bet one of us are close enough to lend a hand. another thing to do, use a DMM and check the voltage at the connector at the radio. use the meter on the hot and ground in the plug, also, check the voltage at the battery. they should be pretty close.

The filter could be causing a voltage drop under high current (transmit) conditions. The radio will turn off if that happens, then turn back on when you release PTT.

Forget Radio Shack.

Agreed. If it's a CB filter or something it is likely not capable of the kind of amperage load that a 65w radio will put on it.

Few FM radio installations in a modern vehicle will need a noise filter on the DC power line.

+1. Most modern radios won't turn of if transmitting with high SWR.
OP, your output power may drop down to protect the finals but the radio should not just turn off. Check your power wiring. Make sure your wiring is properly sized and all connections are tight (as described by A_Free_Man). Run both positive and negative leads (properly fused) directly to the battery.

What kind of antenna & mount are you using? Could be common mode current.

My SWR meter says to check when the radio is on LOW power. Try that as well.

COol! You is up an runnin'.

Congrats on getting your station up and running!

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