Realistic DX-100L (model20-9228 - RTT/ONL/X0031)
By ON6MU www.qsl.net/on6mu

DX-100L MODS (de ON6MU)
Place take caution when performing these modifications.
I can not be held responsible for any damage or loss of waranty leading from opening your receiver and performing any modifications.
Use them at your own risk.

Improved audio quality	The lower audio frequencies are not well present. You can improve the audio quality by adding some thin foam on the back (remove front panel) of the speaker and glue some on the inside of the cover. There is lots of space at the speaker side of the cover. Replace C61 (22 nF) with 220nF
Improved BFO SSB detection	The BFO signal to receive SSB signals is somewhat on the low side. IT works but you need to tune (with an ATU or ATT) the SSB-signal to almost no signal S1 to be able to tune to SSB signals and understand what they are saying HI. By increasing the BFO output we can improve the detection of SSB signals. Folow the little black coax cable that comes from the BFO knob. Replacing C41 with a capacitor of 330pF worked fine in my set, but Bill G4KKI reported capacitor of 100pF to be ideal in his DX-100, so experimenting is probably needed.
Improved VFO drift stability fig.03	A very effective way to improve the frequency drift is extra cooling of Q9. I've found that Q9 gets hot after some time which tend to change the voltages as it heats up causing extra VFO drift. Mount an extra larger heatsink on the transistor and don't forget to put some thermal grease on it (fig.03).
Connect a Frequency Counter fig.04	You can connect a frequency counter to the DX100! The frequency read-out is about 455kc off but gives you a perfect readout of the tuned frequency. You could (as I did) modify a "low budget" frequency counter to give the correct readout. You need: 20 cm of shielded cable 6,8 pF capacitor 47 Ohm carbon 1/4watt resistor a RCA female plug Solder in serie the resistor and capacitor to the receiver (look at fig.04)
Connect a 50 Ohm coaxial Antenna fig.06	By default the DX-100L comes with a telecopic antenna and a 300 Ohm external antenna connector (fig.06). Those antenna connections goes to the preamp via a coil L1. Connect the centre part of the coax before L1 and decouple it with a 2n2 capacitor and connect the braid to the chassis of the receiver (fig.06). Finally place parallel on the SO239 a 1k 1/4 watt carbon resistor. SO239 backside
fig.05	You need: 1 kOhm carbon resitor 2,2 nF capacitor 20 cm of 50 Ohm coax SO-239 chassis UHF connector (female counterpart of the PL259) This is how I lead the 50Ohm antenna connection and the frequency counter connection to the outside world (fig.05). Lots of space to mount the extra connectors there.
fig.06

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