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Accomplished DX-er
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Registered: 10-2009
Location: Abertillery
Posts: 454
Karma: 9 (+9/-0)
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MFJ-1026 Blowing the lamp fuse..


If you have a MFJ-1026 then you may have noticed that on times there is a light inside the unit ? this is the lamp fuse, its just a 'bulb' and its purpose is to protect the 'Noise antenna ' circuit from high levels of static or strong RF by going open circuit ( blowing ) thus disconnecting the noise antenna from the RF amplifier.

Now on times ive noticed the lamp fuse inside my unit lit up like a christmas tree depending on how much power im using, at 400 watts its very brite, just to say that the seperation between the main tx/rx antenna and the antenna i use for picking up the noise is seperated by about 20 feet so its quite close really, anyway today i was using the radio and the lamp fuse blew, and what a potch it is to replace it, you have to remove the case and de-solder the lamp fuse and install another one, but this could go almost instanly IF the same conditions that blew it still exist.

So my thoughts on this was, why not use a relay to switch the noise antenna out of circuit on TX and at the same time short the input to the noise antenna to ground, this should remove the problem of the lamp fuse blowing as its been removed and a relay has been installed in its place ... here are some photos i took of my MFJ, the relay i used is a [sign in to see URL] type and the coil is for 12 volts, one side of the relay is the switch for the noise antenna , the other side is to operate two LED's one for TX the other for RX, here it is all assembled but rough looking, I shall etch a board for the relay and i shall install a single dual colour led for RX/TX rather than drill two holes for the leds.

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Mark

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http://www.youtube.com/MrMadjones

http://gw0wvl.webs.com/
8/Nov/2011, 9:13 am Link to this post Send Email to madmark1   Send PM to madmark1 Blog
 
Hot Fusion Profile
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Registered: 03-2008
Location: South West England
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Re: MFJ-1026 Blowing the lamp fuse..


A useful mod there.

You say you have removed the lamp entirely - does the relay switch fast enough to protect the rest of the circuitry from the milisecond burst of RF it would get before the relay has a chance to switch?

Could back-to-back Zeners and a series resistance add extra protection in that event?

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Andy - FB107
11/Nov/2011, 5:57 pm Link to this post Send Email to Hot Fusion   Send PM to Hot Fusion
 
madmark1 Profile
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Accomplished DX-er
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Registered: 10-2009
Location: Abertillery
Posts: 454
Karma: 9 (+9/-0)
Reply | Quote
Re: MFJ-1026 Blowing the lamp fuse..


I tried back to back diodes and the lamp fuse still blew.

I use hard switching, the Radio, amp, and mfj are switched via a footswitch. I also run full legal power of 400 watts on nearly all bands and as yet ive had no problems at all, by now the original lamp fuse would have blown a couple of times.


Mark

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http://www.youtube.com/MrMadjones

http://gw0wvl.webs.com/
15/Nov/2011, 7:28 pm Link to this post Send Email to madmark1   Send PM to madmark1 Blog
 


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