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6m Larcan Conversion

It's not my intent to gloat or brag, but what the heck. :) I can take other pictures to give ideas if it would help any. There is lots of other stuff in the cabinet that are useless. Controls to and from the TV exciter, filters, RF sample probes, etc are not much use any more.

Band change from 6M to 2M or 220MHz could be easy just by swapping out the module.

There is no shielding as such over the circuit board. I thought the basic design of the board made it somewhat self shielding. You wouldn't want fingers going nearby though. The enclosure has sliders to each side for the module and the plugs are on the back. I could take some RF level measurements if I ever get one working, or perhaps Garth would be willing to submit his amplifier to such testing.

I'm hoping to get a second similar transmitter. Both could be mounted in the same cabinet without much effort.




WA8ZYT said:
Wow! Nice! That would make a nice 2 meter KW amp! Our local university TV station has one of those running only 175 watts on Ch5 digital, (10-1) for weather and radar.

Still collecting parts for mine. Anyone got any photos of metal work to shield the circuit board?
Click to expand...
 
The strip line sections are actually small transmission lines. They should not radiate. The only connections the makes are on the rear panel and through two clips holding it into the chassis. The sides slide along plastic channels.

I'd like to take some actual measurements to find out for sure.
 
Has anyone tried the high band VHF Larcan modules? They should work nicely on the 220MHz band without any changes. Can they be modified for use on 2-meters? Are they worth scavenging for anything more than the MRF151 transistors? I see them on eBay and elsewhere, but not sure what they are being used for. Ideas?
 
Someone is trying to capitalize on the popularity of the modules as well as justify the price as compared to a mono band 6m or 2m amp in the same power class.Single band 1 Kw+ 2m or 6m amps are not cheap items. These Ebay guys are trying to justify the cost by the fact that a power supply for them can be had for about $30+ shipping and a little bit of work.
 
The response curve for the high band amplifiers shows gain at about 16dB from about 170MHz through to 230MHz making them perfect for 220MHz. It drops to about 10dB at 2 meters. Check the first page in this pdf.

http://members.rennlist.org/warren/1kwHBfreqResponse.pdf

Otherwise, the high band modules are identical with the same input and output connectors, same dimensions, etc to the low band version. Is there enough interest to make these worthwhile picking up other than to scavenge for parts or scrap for the aluminum heat sinks?
 
vo1ks said:
Let me know, still lots available.
Found a possible lead on another stash, possibly another 14 or 28 lo-lo modules.
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:drool: :thumbup: Sounds good! I would pick up another just to have on hand but bi-weekly truck payments are making me have second thoughts. :crying: I missed the Greenwood flea market earlier this month and was going to ask around but will keep my ears open if anyone else is looking. They may once spring rolls around again and brings more Es.


vo1ks said:
The response curve for the high band amplifiers shows gain at about 16dB from about 170MHz through to 230MHz making them perfect for 220MHz. It drops to about 10dB at 2 meters. Check the first page in this pdf.

http://members.rennlist.org/warren/1kwHBfreqResponse.pdf

Otherwise, the high band modules are identical with the same input and output connectors, same dimensions, etc to the low band version. Is there enough interest to make these worthwhile picking up other than to scavenge for parts or scrap for the aluminum heat sinks?
Click to expand...


Hey it's always nice to have spare parts on hand. :biggrin: What was the drive level on those units Warren? I suspect that with about 16 dB gain they must have been made for about 25 watts of drive? IIRC the lo-lo units were higher gain and worked great on 6m with about 10 watts of drive. It is generally much easier to raise the operating frequency on units designed like this but I have to wonder what it would take to lower it and push that gain curve into a more favourable position to cover 2m even if full output is not achieved. With 25 watts of drive and even just 500 watts out into a pair of stacked 13B2's one could do rather well I would think.
 
There was an extra stage of amplification prior to the high band amplifiers, so they do require more drive for full power output. Looking at my notes the high band units require about 4x the drive power. I don't know the maximum drive level the transistors will withstand. Simply pushing them harder isn't the solution to full rated output power.

Your high band amp is ready to pick up. Maybe you can pad things down a little and get it working better at 2 meters. There is a procedure to improve performance of the Lo-Lo modules at 6 meters that may assist with the high band units on 2 meters.
 
vo1ks said:
There was an extra stage of amplification prior to the high band amplifiers, so they do require more drive for full power output. Looking at my notes the high band units require about 4x the drive power. I don't know the maximum drive level the transistors will withstand. Simply pushing them harder isn't the solution to full rated output power.
Click to expand...

That sounds about right IIRC the Lo-Lo units required about 10 watts drive for full output and if these require 4x that or 40 watts that would make each transistor being driven by about 10 watts which is what the spec calls for to achieve full output at 250 + MHz. I just looked at the Macom spec sheet for the MRF-151G. Close enough.

Your high band amp is ready to pick up. Maybe you can pad things down a little and get it working better at 2 meters. There is a procedure to improve performance of the Lo-Lo modules at 6 meters that may assist with the high band units on 2 meters.
Click to expand...


COOL! Thanks. I worked last night and work again tonight but am off Mon thru Thurs. I go back Friday. Monday is a right off and one day will be screwed up due to a possible appointment the day of which has not been determined yet.I may be able to run out Tuesday night after I take my son to guitar lessons. I could drop him off in Windsor at 7:30pm and run out if the wife can pick him up on her way home from work. I will call first if do just to make sure you are home.
 
vo1ks said:
I don't know the maximum drive level the transistors will withstand. Simply pushing them harder isn't the solution to full rated output power.
Click to expand...


So what you are saying is that CBers have been doing it wrong all along? :whistle: That is the one thing I wish I could convince some folks of but unfortunately some think that more in equals more out and know nothing of IMD or gain compression etc.


There is a procedure to improve performance of the Lo-Lo modules at 6 meters that may assist with the high band units on 2 meters.
Click to expand...


Who would have thought lead configuration would have affected only the sync signal? :confused1: Strange. Thanks for the info Warren. I think I have a couple good winter projects to work on this year. I just got the basement cleared out somewhat with the new heat pump installed and have an area I plan to use as a work station as soon as I get the big old 36x72 inch solid oak desk moved over to use as a work place and some outlets installed. It should make a decent place to work.It has the added bonus of being located right under where the coaxial lines will go up into the shack so I will have easy access to antennas for testing etc.
 

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