Unlock the RIT on the HTX-100
I've had a lot of fun working DX from my car with this rig. It is
one of the easiest to modify, if you want to unlock the RIT.
One of the major drawbacks with a rig of this class (HR-2510,HR-2600,
HTX-100) is the tuning. There are usually 4 step sizes used when
tuning to the desired frequency. (500 kHz, 10 kHz, 1 kHz and 100 cycles).
The 500 kHz step is rarely used. Its main purpose is to move you from
one part of 10 meters to another. For example, if you are in the CW
portion of the band and want to move to the SSB end, this switch is
handy. The 10 kHz step tuning can be used when looking for contacts but
you skip over most of the band. The 1 kHz step isn't too bad,
but if the other station is 1/2 kHz off frequency, you'll have to switch
over to the 1 hundred cycle tuning. Even then, the station may be 50
cycles off from you. I always found myself using the 10kHz step to find a
section of the band with activity, then switching to the 1kHz step to pick
out a 'loud one' then switching again to the 100 cycle tuning to fine tune
the person in. Often times I still could not get the station in just right,
and there just isn't any other way to get any closer to their frequency!
Sure, you can use the rig's RIT contol to tune your receiver right on, but
then your transmit frequency is still off a bit since it doesn't move with
the RIT control!
What's the answer? A simple modification to allow the transmit frequency
to move in sync with the receiver frequency when using the RIT control.
This mod takes only a few minutes, is reversable (in case you change your
mind later) and really makes the radio a pleasure to use afterwards.
There are only 2 parts to this conversion. You'll need a 6 inch piece of
wire and a 10k variable resistor. Any 10k pot should work fine.
Preparing The Radio:
To begin the conversion, first place the radio on a flat SOFT surface
(the cases of these rigs seem to scratch easily) with the speaker side
down, and place the rig so the front is facing you.
Remove the top 4 cover screws and the top cover. Locate the radio's lamp
light, and follow the white leads down to the green circuit board. Notice
that one of the lamp's leads is connected to a point on the board marked
as +8. Now look on the circuit board to the right of the +8 point. You
should see a white jumper plug. In front of this and slightly to the left
is a printed circuit board trace line. It is a straight line with a solder
point on each end. If you have a volt meter take a voltage reading from
this trace against the chassis ground. It should read near 7 volts. Mark
down this number.
Next, disconnect the power from the radio. Take the 10k variable resistor
and solder the center tap lead of the resistor to the board at the +8 solder
point. Next take the 6 inch wire and solder it to either of the two remaining
leads of the variable resistor. Use a sharp tool to break the straight line
trace that you had just found. Cut it in the middle of the line if possible.
Then solder the free end of the 6 inch wire to the end of the trace closest
to the front of the radio. The existing end solder point works nicely for
this. This trace line originally provided voltage only during receive. Since
the 8 volt source that we are now tapped into is there during both receive
and transmit, the control will change frequency in both cases now.
Testing Your Work:
Connect the antenna and power but do not replace the cover yet. Now you have
to reset the radio back on frequency. To do this, you can use a frequency
counter, or a local ham. Set the RIT (now RIT/XIT) to the center OFF position
and adjust the 10k resistor to set the radio on the correct frequency. Have
your ham friend transmit on a pre-determined frequency while you set the
resistor to tune them in. Another method would be to use the voltage reading
that you took earlier, you can just check the center tap of the resistor now
and set the pot to the original voltage and you will be close to the correct
frequency. Once back on frequency replace the cover, screws, antenna and
power. At this point, let me inject a word of warning, your frequency
display WILL NOT CHANGE as you use this new RIT/XIT. So be careful around
the band edges, don't get too close or you may actually be out of band!
Now You're ready to see how much easier the rig is to operate. With the RIT unlocked, I
generally just leave the step size set to the 1kHz position, tune close to a "loud one'" and then just
use the RIT/XIT for the final touch up. You get about 1 1/2 kHzs on each side of the control's
center. It's great! Have fun and I'll see you on 10 meters!
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