Adding VFO to Midland 13-898B

[Justin B.]

I have a nice Midland 13-898B and the only thing wrong with it (besides FUBAR clock) is it's 23 channel. I decided it would be nice to have all 40 channels+ so I dug out a DDS VFO I built a few years back for a different project and decided to give it a go.

It was pretty straightforward once I decided which crystal spot to hijack. Here's the quick and easy...

I decided to use X106 - 23.580 MHz - which covers channels 20- 23. I removed the wire to that crystal from the channel selector switch and soldered a .oo1 uf cap to the terminal, attached the center lead of a piece of RG-174 and ran it underneath to the rear of the chassis. Do no ground the shield at the channel selector end, only at the other end to prevent a ground loop.





I didn't want to drill a hole in the chassis so I decided the "REC" jack would probably never be used so removed the wire from it and wired the other end of the coax to that RCA jack.



Plug in the VFO, set channel to 23, and crank in the modified X106 frequency for whatever channel you want. This VFO is controlled with an Arduino Nano so I will probably write some new code to switch between VFO/Freq mode and channel mode. But for now I just made a chart listing what freq to dial in for the desired channels.





Hope this might help somebody out as I got no replies to a thread I started asking how to do it. I would think this should apply to most synthesized radios..

Have fun!

 

[nomadradio]

Our answer to the ground loop problem is to connect a .001uf disc cap from the coax shield to the circuit board ground near the synthesizer circuit. This grounds the braid for the RF circuit, and blocks any DC-ground loop issues.

Very cool! Which DDS did you use? The 985x or the 5351?

73

 

[Justin B.]

I built this several years ago but looking at my notes it's an AD9850. I'm toying with the idea of cutting the front panel to fit a display and removing the FUBAR clock if I can't find another or a replacement motor. So far no luck on that...

Thanks for the cap tip, never thought about it that way just remembered a lot of my boat-anchors use the "ground one end" method... I really wasn't sure if coax would be a good idea due to possible added capacitance but it seems to work OK.

73,

 

[TM86]

I have one of these that the clock and meter were fubar when I got them. The equivalent AM only model clock and meter fit perfectly.

Didn't think about putting a DDS VFO in it, though.