Is your 2510 slow on agc??? does it take 3 frames at 1200b for the
rx to come up to sensitivity?? do you want to make the rit a rtit (rxtxit)
then maybe these mods will help you, they also may apply for the newer 
versions of this radio, you who have the 2600 may be able to use them.
mod 1.
 speed up agc, this is easy, just pull out the transistor q111 and you have
fast agc, if you need to select slow agc then put a switch from the collector
to emitter and pull the collector pad to ground for slow agc 
mod 2.
 make the tx and rx both responde to the rit control and reduce the amount
of frequency change for the control.
this one requires that you locate the rit control and remove the following:
r 802  a 1k resistor in series with the rit pot
the rx 8v line that goes to high side of pot, remove and put aside, you
will need it for power to nb switch and rf gain control.
now remove the subassembly b801 pb-120 and remove r802. cut pc land between
high side of vr802 and r 801 you will now solder the rx 8v line to the
freed side of r 801.

the 1k resistor, r 802 will be replaced with a 100k resistor, and a line
will be taken from the 8v side of ic 107 the 8v regulator to a resistor
network that will give aproximately 52k (you will need to experiment to
get a value such that you rit pot will give you readout frequency when
the feducial line is pointed at center)
lift one side of diode d150, this will free the pot vr111 from the line
that feeds the varactor on the pll board. you may use the pot in conjunction
with a 50k resistor (47k) to set the rit pot to center position, by putting
it in series with the 50k resistor and adjusting. this combinations will
give aproximately +-300hz either side of readout freq.
the best way to use the pot vr111 for this is to lift a jumper that runs
to the land on the high side of the pot and solder the 50k resistor to this
land. run a wire from the other side of the resistor to +8v (make sure it
is not tx or rx 8v since that is switched on or off depending on what state
radio is in tx or rx)
 
having done these mods you will have a radio with a fast agc and a rtit control
that will give the narrow changes needed for packet. the radio will be quite
stable. now to see about putting a g3ruh modem on the varactor of the radio
hmmm anyone for 4800b or 9600b on 10m (you gringos get a sta and lets try
it, could be interesting!!)

For this bit of work, i also got in the bargain a rx to tx time of abt 20ms
i can send frames with a txd of 3 on my tnc-2 clone and the local switch
will receive it just fine. there is enough front porch for all the radios
which run open squelch or direct from the detector to copy the 1st frame
out of the box!! (all our switch and bbs radios run 2211 modems connected
direct to the disc or detector here in costa rica, thereby getting rid of
a lot of problems of switches and bbs not copying the users.)
if you have any mods for the 2510 or i think the radio shack 10m radio is
of the same insides, please send them, lets put a lot of these boxes on 
packet and scare some of that cb and other illegal operations off 10m now!
ciao and enjoy de chuck ti3djt@ti0paq.cri.na


              FREQUENCY MODIFICATION: PRESIDENT/UNIDEN HR-2510:

The 10-meter mobile amateur transceiver will transmit and receive from 26.000
MHz to 29.9999 MHz when the following modifications are performed:

1) Locate the CPU: IC 315 (UC-1201).

2) Pin 34 and 35 are together grounded (see the bottom - solder side). Cut the
PCB Pattern to disconnect the pins 34 and 35 from ground. Now, both pins are
free from ground and floating.

3) To activate 26.000 to 27.999 MHz (pin 35) and 29.7 to 29.999 MHz (pin 34),
just add 10 K ohms, 1/4W resistor between the pattern of pin 34 and 35 to the
pattern of DC+5V line.

NOTE: The display will indicate the EXACT 40 CB CHANNELS (Yes sir!) when "G"
band is selected.

                    ---------------------------------------

POWER OUTPUT MODIFICATION: HR-2510 and Realistic HTX-100.

Transmitter power output of these rigs can be increased up to 100 Watt (SSB),
when an easy modification/tune up is done.  Complete details can be found in
73 AMATEUR RADIO, september 1989, p. 48

Daniel VE2BAP @ VE2CSC.PQ.CAN.NA

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