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  #1 (permalink)  
Old 06-12-2014, 9:14 PM
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Default Connect Antenna Directly to 2M Radio???

OK, I'm still pretty inexperienced at this and I have a question. I just bought a new 2M radio (Yaesu FT-2900R) for my jeep. It will be a while before I can install it. I would like to be able to set the radio on a work bench and connect the radio to a car battery and start learning how to use the functions and store the repeaters I have, but I'm afraid I might accidentally key the mic without and antenna attached (I don't have a dummy load).

My question is, can I screw a PL-239 90 degree elbow into the coax connection on the back of the radio and the them attach a 2M mobile antenna directly to the other side of the PL-239 elbow (no coax) just to protect the radio while I'm learning to use it?

I have about wore out my Google finger looking for this info.

Thanks for any help,
Howard
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Old 06-12-2014, 9:22 PM
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Originally Posted by hw999 View Post
OK, I'm still pretty inexperienced at this and I have a question. I just bought a new 2M radio (Yaesu FT-2900R) for my jeep. It will be a while before I can install it. I would like to be able to set the radio on a work bench and connect the radio to a car battery and start learning how to use the functions and store the repeaters I have, but I'm afraid I might accidentally key the mic without and antenna attached (I don't have a dummy load).

My question is, can I screw a PL-239 90 degree elbow into the coax connection on the back of the radio and the them attach a 2M mobile antenna directly to the other side of the PL-239 elbow (no coax) just to protect the radio while I'm learning to use it?

I have about wore out my Google finger looking for this info.

Thanks for any help,
Howard
Howard -
I believe it wouldn't really offer any protection.
I wouldn't risk my new radio.
Short of a dummy load, an inexpensive mag mount quarter wave
on a file cabinet or a large appliance is cheap insurance,
plus it's useful in the future.

Good luck.
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Old 06-12-2014, 9:28 PM
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Originally Posted by mikepdx View Post
...an inexpensive mag mount quarter wave
on a file cabinet or a large appliance is cheap insurance, plus useful in the future.
If that would work, I can do that. I actually thought about a mag mount antenna, but did not know if what I stuck it on had to be grounded to the radio. I hate to spend $42 on a dummy load that I will likely never use again.

Thanks,
Howard
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Old 06-12-2014, 9:34 PM
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If you're only worried about ACCIDENTALLY transmitting, the antenna on the back would work fine. It will present a load, though crummy, and you would most likely not hurt the radio if you accidentally bipped the mic and transmitted for a short time.

I don't understand all this concern over ACCIDENTALLY transmitting (you're not the first to ask the question), it's pretty hard to do so.
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Old 06-12-2014, 9:37 PM
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Quote:
Originally Posted by hw999 View Post
If that would work, I can do that. I actually thought about a mag mount antenna, but did not know if what I stuck it on had to be grounded to the radio. I hate to spend $42 on a dummy load that I will likely never use again.

Thanks,
Howard
The mag mount does not have to have a physical connection to the artificial ground plane.
The mag mount is inductively coupled to it.
So, the radio is "RF grounded" via the magnet base to the file cabinet (or whatever).

Much luck. Have fun.
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Last edited by mikepdx; 06-12-2014 at 9:50 PM..
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Old 06-12-2014, 10:41 PM
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Disconnect the microphone. While some radios can be triggered to TX without a mic, it's probably going to reduce the chances of it happening.

Also, accidentally keying up the radio without an antenna isn't going to instantly destroy the final amp. The damage comes from heat, and it takes a bit for the heat to build up enough.

Other thing you could do is to run it off a small enough power supply that won't supply enough power to actually TX with the radio. A 1 or 2 amp power supply is enough to power the radio, program it and receive, but if you tried to TX, the power supply would be overloaded and the radio would "bonk". Or, remove the stock 15 or 20 amp fuse that is probably in the radio power lead, and replace it with a 1 or 2 amp fuse. Accidentally TX'ing will pop the fuse and you'll be safe.
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Old 06-12-2014, 11:04 PM
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Thanks folks for all the help. Some of the functions I wanted to try/learn are on the mic, so I need it plugged in. Apparently the PTT button on the mic that comes with the radio is very easy to accidentally push. Several of the reviews/videos I've watch on this particular radio said they accidentally keyed the mic. Just want to be extra careful and not burn something up before I get it in the jeep.

Thanks again for the help,
Howard
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Old 06-13-2014, 12:06 PM
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Nice starter radio. Most 2m antennas don't need a ground to work. Also turn your 2900 down to 5 watts. If you have a SWR meter check it. It everything is ok you can run your 2900 now and have fun. I still use a antenna indoors during T-storms to see what's going on. When storm is over I switch back to outside antenna. And I know that a surge can take out my radio. But I should not get hurt. .
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Old 06-13-2014, 2:02 PM
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Default Even without an antenna brief transmitting likely OK

I can't imagine that if you accidentally pressed the PTT key for a second or two without a load on the output that anything would happen to the final output transistor. Just turn the power down to the lowest setting as suggested. If the output had a non inductive dead short on it, it probably still would not harm it if transmitting for a brief second or two on low power, but don't test that assumption. Power output would probably fold back to the lowest level anyway, even if it were not set. Prolonged transmitting with an improper load will damage the output eventually.

Connect that mag mount antenna and set to low power and don't worry. Set the mag mount on any large metallic object to get a ground plane and it may be usable to transmit a QSO. An SWR meter will confirm if the ground plane is adequate. Invest in even an inexpensive SWR meter and not a dummy load and check your antennas and feed lines for every installation and at periodic intervals to insure everything is OK. Antennas and feed lines can get damaged. Any decent SWR meter will show that.
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Old 06-13-2014, 2:15 PM
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Is there a TX inhibit available, in the radio's menus?

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Old 06-13-2014, 3:03 PM
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Page 18 of the FT-2900 manual describes how to lock the radio. There are seven different ways to lock the radio, including one just for the PTT switch.
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Old 06-13-2014, 3:42 PM
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Old radio restorer's trick. Put a 12v lamp in series with the power supply lead from the battery. It will pass sufficient current to run the radio on receive but will drop all the voltage if you try to draw transmit current through it.
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Old 06-13-2014, 4:01 PM
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A mag mount is capacitively coupled to whatever and the size of the mag mount base determines how much capacitance and now much coupling. That's why mag mounts usually work fine for VHF/UHF but for HF there is not enough capacitive coupling to the ground plane.

Anyway, a 19" whip sticking out of the back of a 2m radio will work just fine and its probably a better match to the radio than other antennas on the market. I would keep the transmit power at a reasonable level like under 10w, otherwise you can get RF into the mic cable and above that you venture into unsafe RF exposure levels if the power is higher and you get closer than a foot or two.
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Quote:
Originally Posted by mikepdx View Post
The mag mount does not have to have a physical connection to the artificial ground plane.
The mag mount is inductively coupled to it.
So, the radio is "RF grounded" via the magnet base to the file cabinet (or whatever).

Much luck. Have fun.
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Old 06-13-2014, 4:22 PM
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Quote:
Originally Posted by majoco View Post
Old radio restorer's trick. Put a 12v lamp in series with the power supply lead from the battery. It will pass sufficient current to run the radio on receive but will drop all the voltage if you try to draw transmit current through it.
I like that idea and the 1 or 2 amp fuse idea. Simple, cheap and 100% foolproof/idiotproof..

Some of the functions I wanted to learn actually require me to push the PTT button. Hey folks, I'm a real novice at this and I'm just trying not to mess my new radio up. I do know enough about it to know that transmitting without an antenna is bad news and this radio is 75W on high.

Thanks again for all the responses.
Howard
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Old 06-13-2014, 4:53 PM
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Interesting thread. I have a transceiver in my auto. Yesterday I decided to try out a new automatic car wash, fearing damage to the left rear quarter panel MOT NMO antenna, I stopped in the drive, used a wrench to unscrew the antenna, screwed on a black plastic 'rain cap' and drove through the car wash. I forgot to turn off the radio and as I drove away I noted it seemed to work as usual, receiving the local 800 MHz analog system at full quieting, the rain cap keep out the water but not the RF. It has been working quite normally today. Oh, yes this is all on the LOW power setting. It looks very stealthy.
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Old 06-13-2014, 5:19 PM
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Quote:
Originally Posted by lep View Post
Interesting thread. I have a transceiver in my auto. Yesterday I decided to try out a new automatic car wash, fearing damage to the left rear quarter panel MOT NMO antenna, I stopped in the drive, used a wrench to unscrew the antenna, screwed on a black plastic 'rain cap' and drove through the car wash. I forgot to turn off the radio and as I drove away I noted it seemed to work as usual, receiving the local 800 MHz analog system at full quieting, the rain cap keep out the water but not the RF. It has been working quite normally today. Oh, yes this is all on the LOW power setting. It looks very stealthy.
Although I'm in a hilly rural area, there's no difference whether I have
an antenna on my 800 scanner or not.
I guess we're both lucky to be in high signal areas.
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Old 06-13-2014, 9:55 PM
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I have a 2M radio sitting on top of the hutch on the radio desk. It has a 90 degree adapter on the antenna jack. A banana plug with 19" of tinned copper wire soldered into it is pushed into the adapter. A piece of 24 gauge solid hook up wire was stripped on one end for about three inches and wrapped around the adapter, trimmed to 19 inches, and allowed to hang off the back of the hutch. This is my back up radio for when storms are in the area and I have to disconnect the outside antenna. This setup has been used many times over the years to check into the local weather net on a repeater about 12 straight line miles away with good signal reports running 5 watts. No damage has befallen the radio.
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Old 06-14-2014, 3:30 AM
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Quote:
Originally Posted by hw999 View Post
I like that idea and the 1 or 2 amp fuse idea. Simple, cheap and 100% foolproof/idiotproof..

Some of the functions I wanted to learn actually require me to push the PTT button. Hey folks, I'm a real novice at this and I'm just trying not to mess my new radio up. I do know enough about it to know that transmitting without an antenna is bad news and this radio is 75W on high.

Thanks again for all the responses.
Howard
As already mentioned, brief transmissions without the antenna should not cause damage. Older radios, think tubes, required the proper impedance connected, or the finals would be destroyed. Using the lowest transmission power is a good idea, like has been mentioned.

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Old 06-14-2014, 3:56 PM
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Quote:
Originally Posted by hw999 View Post
...I hate to spend $42 on a dummy load that I will likely never use again.
EVERY amateur station should have a dummy load handy. It's just one of those must-have station accessories.
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Old 06-14-2014, 7:56 PM
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You are really overthinking this. You WILL NOT damage the PA with an ACCIDENTAL key up. Hell, I have had radios come into the shop with a complaint that dispatch has been reporting them scratchy for weeks and find that they have pulled an old speaker mic (antenna mount style) and never moved the antenna from the radio to the mic (in effect their only antenna is the mic cord). Pull the mic and throw it on the monitor and it is 100% fine. Bottom line is that PAs in modern radios take a lot of abuse and it generally takes a long time with lots of transmissions to cause damage.


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