President Lincoln IF filter

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President Lincoln IF filter

Postby 31 » Sat Mar 25, 2017 6:35 am

GF,
I'm aware of all the cap changes to help in the audio response. I know most hardcore DXers will try to increase selectivity by narrowing the IF filter. Looking at the schematic, the 455Khz 2nd IF is only used for SSB. Am I wrong at thinking the AM is only limited in bandwidth by the 10.695 Mhz FT-102? I dont operate on SSB , my only mode is AM. I have swapped all my personal radios for a wider 2nd IF normally at 9Khz for a 6Khz usable BW. Is there any problems getting a wider 10.695 filter? I'm aware of the adjacent channel bleed over possibility but I like to listen on the wide side. Also have the AM carrier pot on the front panel and do notice that if set to high, it'll back swing. The variable deadkey mod online, lifts R175 and routes it to the SWR Pot on the front for a variable deadkey. Is the R175 and essentially VR107(AM carrier pot) defeating each other if used that way/
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Re: President Lincoln IF filter

Postby Goldfinger » Sat Mar 25, 2017 1:57 pm

I'm not sure about wider 10.695 filters.

No, VR107 is in a different part of the circuit so it would be independent of the R174 mod.

The R174 variable power mod works great as it lets the radio swing to full power from any dead key. The problem with turning the dead key down with VR107 is that you lose peak power when you do. Turn it down to 1 watt dead key and PEP drops down to 8-9 watts. A 2510 will swing 30-40PEP from a 10 watt dead key. Lincolns with a linear pill, 25-35PEP

What I do is set VR107 so the radio dead keys 10 watts before I modify it. Then once you do the R174 mod, it will go from 0-10 watts dead key and swing full power at all levels.
This mod adjusts the gain of IC106. It is the transmit mixer/low-level AM modulator IC.
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Re: President Lincoln IF filter

Postby 31 » Sat Mar 25, 2017 3:56 pm

Cool thanks! I've done the mod before , just not on a Lincoln . Reading the service manual , I don't get why the AM detection wouldn't come after the 2nd IF at 455khz but I guess they like the single conversion better ? I'll change the 455 kHz anyways and see if it does any better for the AM.

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