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6m Larcan Conversion

Yup thats the one there i was speaking about

I have a further question, dont know if anyone is versed on it

i calculated a 6db attnator would bring down my 100 watt output to a max of 15 for the amp input, just incase i ever forget to turn the power down.

well after running the math, i would be dissipating well into 70 watts of heat in the resistor and a suitable non wire wound is quite expensive at that wattage.

So, im left with 2 options

No attenuator, turn the thing down and pray for NO smoke

3db attenuator which should help somewhat and maybe give margin error

Or i suppose i could sample the input signal with a detector diode and set it up to trip the swr circuit and turn the amp off on over drive, but i haven't looked into the complexity of this yet.

and upon further investigation i could build a 6d with caddock resistors rather reasonably
 
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A 6dB attenuator would reduce 100 watts to 25 watts.
I'd suggest a commercially built coaxial attenuator (Bird, Coaxial Dynamics, etc) so that the return loss / VSWR would be acceptable. Getting the proper resistor values at that power level and maintaining a good match could be a challenge otherwise.

The amplifier has a RF input sample built in. I don't know where the line goes or what it does though. I'll have to pull out the diagrams to find out. You can see it in the lower right section of the circuit board.
http://members.rennlist.com/warren/larcan3.JPG
 
My idea was to provide a fixed DC voltage whenever the amp is turned on and feed that back to the radio's ALC input. That way if the radio was at 100 watts it would be limited in power output as soon as the amp was powered up. Experimentation will tell me if it will work well. Some rigs seem to have a full power spike at key up before settling back when the power is adjusted from the menu but with a fixed external ALC voltage this issue seems to go away. I believe my FT-857 is one of those radios. :crying:
 
Consider worst case and how you could make something fail, then redesign to prevent it from happening. If the fixed DC were to disappear for whatever the reason you could easily over drive the input. AGC response time may not be adequate either. At $150 per FET (x4) it would be an expensive lesson. Having a passive attenuator permanently installed inline would greatly improve safety.

A 6dB pad would limit the smoke escaping and likely give the radio a better AGC range to work within. It would also provide a 12dB better input match for the transmitter.
Item # 100-A Series, 100 Watt, Bi-Directional Attenuators on Bird Technologies Group
 
I see your point but I think it is senseless to run the exciter wide open and then dump at least 3/4 of the power away before amplifying it again. I don't know........maybe the attenuator or maybe the fixed ALC voltage scheme. Both have advantages and disadvantages I suppose. I Have a 6 dB Bird attenuator but I think it may only be a 20 watt unit.
 
The original reason i chose 6db for the roughly 75% reduction was the fact that i dont believe my 847 gives me a full 100 watts on 6m, so a little headroom would be nice.

But i have read people have had issues with their transceivers emitting DC at key up (specifically the 847 was mentioned) among others, and that is why i felt it wouldn't be adequate to just turn down the power.

id rather dump 3/4 of my power, than 3/4 of a grand on FET's and getting the damn things here, we pay 45% duty on electronics, hence why my amp was delivered to my chosen location.
 
If you go to the Goggle 6m Larcan group., there is most all the info you need.
Some have had grief trying and many have had sucess.
Don't drive with more than about 8 to 10 watts.
In a well converted unit the gain is well more than 20db at 1000 watts + out..
Should use a bandpass filter as well.
Good luck..
 
Well, my Larcan has made it to its first destination on its way to me, and pics indicate it was very well packaged by warren, thanks a lot, and Garth for informing me about them, there appears to be some defacing done to the board, i didn't notice at first as i was hauling a full load while looking at the pic on bbm, however warren indicated it appears graffiti is on the board, i will have to check and am requesting better pics from my girlfriend. Although i do believe Garth is to blame here;):)



Uploaded with ImageShack.us
 
avistar23 said:
Well, my Larcan has made it to its first destination on its way to me, and pics indicate it was very well packaged by warren, thanks a lot, and Garth for informing me about them, there appears to be some defacing done to the board, i didn't notice at first as i was hauling a full load while looking at the pic on bbm, however warren indicated it appears graffiti is on the board, i will have to check and am requesting better pics from my girlfriend. Although i do believe Garth is to blame here;):)



Uploaded with ImageShack.us
Click to expand...


Nope, don't think so. :whistle:
 
lol ill leave it till i see it in person, let me know if you guys come across any good deals on relays, ive seen a few, but im still looking, or any other deal i should know about, its hard ordering stuff shipping it a different place, lots of back n forth etc.
 

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