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So here is one that I have been pondering over in my mind... These mosfets (erf2030) by ekl that seem to becoming fairly popular latly have interested me since they came out a while back.
This is my thoughts on the subject.... In most circumstances fets are used in an exact oposet way than how they are used in a cb. In a standard cb the final runs off of low voltage and high current....... pretty much the exact oposet way that fets are used in most circuits--- alot of the time fets are used with a high voltage low current situation.
Although they do work with low volts high amps, there seems to be a problem with the need for alot of drive on the fet to get any power out. Like in a standard Cobra 29... usually the outcome of a final switch to FETS is a lower carrier high modulation outcome--- and the stuggle seems to be getting carrier power out of these--
I'm sure everyone has alot of different mods for these for bringing the carrier up some--
My idea is to run the fet like many others are.... higher voltage lower current
Basically stepping up the voltage after the driver, rematching the input impediance and taking the current draw/volt draw off the audio IC and adding it from another source ect ect.
The main idea is to try running the erf 2030 and final rf amp circuit of a cobra 29 off higher volts lower current like how alot of fets are used. I am very curious as to what the carrier/ modulation output would be.
This is just an idea I've been playing around with in my head for a bit ...I'm curious if anyone else has any thoughts or idea about using these fets this way

The thought is ok, but woukd entail some major redesign, as well as major new design. In the FET mods that I've done (cobra 29's primarily), I see carrier levels of around 5 to 6 watts, with my Wavenode system regularly recording 40 to 45 watt peaks. I've had customers come back after having the EFT mod done and tell me they walked on guys running amps. The only things I do differently from the cbtricks procedure is use higher cap values, change the driver base input resistor to 4.7 or 3.9 ohms, and add a 33pf cap to the spot where the 1k resistor is removed (i forget the number right now, its near the antenna socket by the SWR bridge circuit). Oh, I usually replace that 1k with about 15k so there's still bleed-off for any static electricity that might be building up.

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My little search came up with this. It is not mine, I haven't tried it, and I can't remember the source, but I would love to hear from someone who has tried it:

"I do have some new info for you on the Cobra 29 / Uniden mod. The existing Cobra 29 mod is very popular, but the only complaint I have ever heard about this mod is that the dead-key is low with the ERF-2030 (approx. 3-4 watts with the current mod).

We have come up with a couple of additional steps to the current Cobra 29 mod that increases the dead-key to approx. 8 watts without affecting the peak power.

To get the higher carrier, do the current mod and then do the following 3 additional steps:

1) Add a 4.7K ohm resistor (1/4 watt) from the positive side of C116 to the gate of the ERF-2030 (this is the left-most leg when looking at the face of the ERF-2030).

2) Remove the capacitor at C62, and replace it with a 390pF capacitor. Also, make sure that there are no additional capacitors tacked on the solder side of the PCB (sometimes Cobra adds additional capacitance at this part to get everything to tune-up correctly). If there is an additional capacitor on the solder side at C62, then remove it.

3) Remove diode at D8, and replace it with a jumper. Or, just add a jumper wire across D8.

We have had good success with these additional steps and it gives everyone the carrier level that they are looking for."

5 or 6 watts clean is pretty good... I've got around that number but I had to volt the predriver which I really don''t care to do.. unfortunatly I didn't have long to play with it. I did get in some more fets and I'm going to check out what I can get.

To run the fet off of high volts low current would certainly be a total rework of the rf amp section ( voltage supply ect ect), but its one of those thing I would like to try just to see what these things can actually yeild.
My thinking is that more carrier power and perhaps swing can be achieved from running the fet off high volts low current.

DTB.... thanks for the reply. Any thoughts or ideas you have for my project let me know.
Thanks again



[quote="DTB Radio"]The thought is ok, but woukd entail some major redesign, as well as major new design. In the FET mods that I've done (cobra 29's primarily), I see carrier levels of around 5 to 6 watts, with my Wavenode system regularly recording 40 to 45 watt peaks.

Like I said, it isn't my mod, but it was what I found in a search for higher carrier. Thanks for the feedback. Step three is bad then. How about the first two steps? Are they a good way to get the wanted carrier?

Thats one thing that I don't care to do in any am radio...... jumper the anti spiking diode. its not worth it for the 1 watt gain (or so). I have done it in scap radios that I was playing around with.... but if I ever did that in a customers radio, the head tech at the shop would more than likly consider shooting me LOL.
:shock:

Thats a new one I havent heard... I guess you mean R55 ( I think thats the one) or R54.... anyhow I know what you talking about.... replace the resistor with a cap-- cool I try to remember that one
Thanks for the reply

I personally don't remove that resistor, just change it to a higher value (about 15k-22k). It is R55, by the way.

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I have had a Uniden for 3 years with the spike diode jumpered.
Even ran it at 16v. What is the problem?

The only problem I've ever encountered is with Cobra 29's. On some 29's, with that diode jumped, strong receive signals at high volume settings can begin to garble severely, and sound like harsh squealing.

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