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Author Topic: power supply or radio?  (Read 5010 times)
AI4WX
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Posts: 26




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« on: February 10, 2013, 06:43:01 PM »

I have a Yaesu 8900 that i took out of my car to use as my base station. When it was in my car, it worked fine. Now i have it set up inside with a radioshack 25amp power supply. When i transmit on 2 or 6m, it works fine. When i transmit on 70cm, it cuts off. The power supply remains on but you dont hear the fan running. how can i determine which is at fault?
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AD5X
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Posts: 1426




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« Reply #1 on: February 10, 2013, 07:05:08 PM »

Probably RF from the radio getting into the power supply.  I've seen this several times.  A ferrite snap-on core on the DC output and the AC input cables does a good job of eliminating the problem.

Phil - AD5X
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KF7GFL
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Posts: 44




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« Reply #2 on: February 12, 2013, 10:44:24 AM »

I think I have a similar problem with my Yaesu 857D. I have the Astron SS-30M power supply and it seems to power the radio fine. The moment I go to transmit on 2M, the power supply voltage cuts to 0 and stays there until I turn off the power supply and turn it back on again. As both the radio and power supply are brand new, I thought I had a defective power supply and was getting ready to ship it back to Gigaparts and have them replace it. I will give the ferrite snap-on's a shot and see if they work for me as well.

Matt - KF7GFL
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AA4PB
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« Reply #3 on: February 12, 2013, 12:46:37 PM »

How far away from the radio/power supply is your antenna?
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AA4HA
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Posts: 1378




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« Reply #4 on: February 12, 2013, 01:43:39 PM »

It could be that in certain operating modes or bands that the transmitter current is slightly higher than the output rating of the supply and the crowbar protection is kicking in.

Try lowering the power output of the radio in the bands in question and see what happens. If you have the ability to put an in-line ammeter to measure transmitter current I bet you would find that there is a current peak right that exceeds the supply rating right before the supply goes into shutdown mode.
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
KF7GFL
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Posts: 44




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« Reply #5 on: February 12, 2013, 04:31:53 PM »

AA4PB - My radio is only about 3 feet from a J-Pole antenna.

AA4HA - It is a 30 amp peak output power supply at 12 Volts. The moment I hit the transmit button, the voltage cuts to zero and stays there until I turn it off and on again. I watch the amp meter and it doesn't really move off of zero before the voltage drops. I have my transmit power turned all the way down to 5 watts and it still cuts out.

I gave Astron a call and they had me send them an e-mail. The guy I talked to seemed to know what the problem was and he was going to send me a fix via e-mail but I have yet to hear from them and that was yesterday. Everyone seems to love Astron power supplies and so I have a hard time believing I got a bad one. However, that could be the case.
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AI4WX
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Posts: 26




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« Reply #6 on: February 12, 2013, 09:47:09 PM »

i found an even easier way to fix this. Before, i had my radio sitting on top of the PS. i moved the radio about 3 ft away and it cured the problem. I've never set up a base station so this was def a learning experience for me.
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AA4PB
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« Reply #7 on: February 13, 2013, 05:32:16 AM »

You will probably solve the problem by moving the antenna much farther than 3-feet away from the equipment. At only 3 feet the antenna is probably coupling a lot of RF energy into the power supply cables.
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KF7GFL
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Posts: 44




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« Reply #8 on: February 13, 2013, 12:36:06 PM »

I was able to track down and solve my problem.

AI4WX - I had the radio and power supply right next to each other, but not stacked. I thought about stacking them but was actually more worried about heat and so I placed them in the same configuration that I would if I was to put them in a "go box".

AA4PB - I thought the antenna was a little close but ultimately that wasn't the problem.

The problem was how I had the antenna set up. About a year ago I created an emergency J-pole for 2 meters using twin ladder line. At the end of it, I have a loop of fishing twine that I can use to hang the antenna from a tree branch. It is nice because it rolls up and fits in a small bag and can be used with an HT as well as a mobile radio. As I was just playing with my new power supply and radio, I had things set up in my bedroom and just hung the J-pole from one of the pull strings from a ceiling fan.

It seemed pretty harmless to me until I thought about what was going on. Any time I would hit the transmit key on the radio, the signal was only a couple of inches from the ceiling fan coils. Half of the electrical system in my house was turning into an antenna and the power supply was picking it up. Naturally the power supply did the right thing and shut down.

In the end, no damage was done to either the radio or the power supply. I also learned a lesson that the antenna goes outside and the radio goes inside. Hopefully my antenna faux pas can serve as an example to anyone else experiencing problems with their switching power supply. I hope my solution can also help the original poster of the thread as he may have a similar issue.

Matt - KF7GFL
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AA4PB
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Posts: 12672




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« Reply #9 on: February 13, 2013, 12:44:42 PM »

I repaired a 2M transceiver for a friend a while back. He had a Radio Shack power supply that didn't have any over-voltage protection. It was a nice steel case so he slapped the 2M mag mount antenna on top of the power supply. He keyed the mike only once as the RF got into the power supply, caused it to output 25+ volts which promply trashed the PA module in the transceiver. A rather expensive lesson learned.

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