MRK "special" bandsplit value. With caveat

Post by **willbartlett** » Mon Oct 11, 2004 1:15 pm

OK, After risking divorce with the amount of time I've spent with my MRK this last week, I have made some headway with the special bandsplit resistor value.

I believe what I have found is a true Hack, as it is not a permanent solution.

I removed the 4.7Kohm resistor (r142) and soldered in a variable potentiometer. Using a value of anywhere between 5.5 and 3.0Kohm allows the radio to be brogrammd as 150-174, and any value between 2.5 and 1.5Kohm allows it to be programmed as a 136-160 mhz radio. Using a value of 5.5-6.8Kohm allows the radio to be programmed as a special bandsplit radio. Now this is a bit misleading, as the radio will not lock the VCO above 5.5 Kohm, but if you program at say 5.7Kohm and then return the resistance to any value in the vhf range, the radio will lock and operate between 146-170 mhz. I did not do a very thorough test of sensitivity or power out, as I was trying to get most of this done during my 2 year olds nap yesterday.

My suggestion would be to build up a personality with special bandsplit values and program the radio by paralleling a 10Kohm resistor across the band sense pins going to the logic board and remove the resistor to return the radio to it's original configuration to operate.

I know it's a kludge and probably not very useful for most of us, but I thought I'd put my info out there.

DISCLAIMER: Untill you can confirm that the radio is operating WITHIN spec by having it's alignment confirmed by a professional, I STRONGLY discourage anyone from doing this to a radio where your safety or the safety of anyone else might be put in jeopardy. Do not do this to your work radio. I did this to mine because I am by nature a tinkerer and my radio is used exclusively for ham use. BE SMART!!!!

Will

rescue161 · Post by **rescue161** » Thu Oct 14, 2004 6:38 am

I wonder if the values are the same for the Orion. What software are you using?

Post by **willbartlett** » Thu Oct 14, 2004 7:59 am

Sorry, All this was done using edacs 3, conv1.

Will

Luis1972 · Post by **Luis1972** » Mon Oct 18, 2004 11:28 am

Would this mod also work on the uhf mrk II (403 -430)? Also where do you find this r 142, i can't locate on the board..

I would like to use it on the ham bands .....

Thanks

Lou

Post by **willbartlett** » Mon Oct 18, 2004 3:06 pm

Well, I'm not sure. I don't have a uhf MRK-II to check with. If I remember correctly, I believe the UHF band sense resistors were somewhere 10 and 22 Kohm. The variable resistor I had only went to 10k. I did notice below 1k, it would show as a 398-430 radio. So the other bandsplits are probably sprinkled through the whole range. Anyone have a 400-430 rf section they want to donate to the cause? I'll buy one if the price is right.

R142 is the only resistor on the bottom row of chip devices at the bottom of the rf board, if viewed from the back of the radio. It's the first device on the right cluster of chips going from left to right. I believe all the other caps are for decoupling on the control lines going from the controller to the rf deck through the pin header.

Will