In a message dated 00-12-10 11:58:17 EST, you write:
<< Sounds to me as if the Scout has a 7810 or LM340-10 regulator for the VFO.
That regulator needs about 2.5 volts headroom input to output to maintain
regulation. Very likely the TO-92 version 78L10.
I have no Scout and no scout manual to see.
Perhaps that regulator could be replaced by a LM2937ET-10 or LM2940-10 or a
series resistor and a TL431 family programmable zener diode. The LM29xx
family works with down to
0.6 volts drop, the TL431 would work lower though a bit less efficiently
than the series regulator. The TL431 programmable zener diode is a far better
regulator than any plain zener diode.
73, Jerry, K0CQ > >
The Scout uses the LM-2940 in the T0-220 package of to develop a nominal
10 vdc regulated power for the entire radio. The LM-2940 is located on
connector 5 of the Receiver Control Board P/N 81644 .
The PTO is only one of several circuits that draws from this internal 10 vdc
bus.
The Scout manual specifies minimum operating voltage of 12 volts.
Perhaps the low voltage problem is brought on by the confluence of all the
voltage drops in cabling and connectors ( both external and internal )
enroute to the LM-2940.
I have always been rather unimpressed at the chinzy power connectors used
in TT transceivers. I have measured 0.5 volts drop across my Scout
connector ( key down at 50 Watts out ), and another 0.6 v drop across the
fuse. Thats a 1.1 Volt drop before the power even gets to the radio !
A bit excessive don't you think ?
Connectors and fuses really do have finite resistance that can devour
marginal voltage reserves.
It might be prudent to measure the DC voltage across the pins of the Scout
power connector just inside the back panel of the Scout (during key down 50
watt Transmit conditions) to observe just how much of the already low battery
voltage has been further reduced by the connections.
73,
- Phil KF6ZZ
--
FAQ on WWW: http://www.contesting.com/FAQ/tentec
Submissions: tentec@contesting.com
Administrative requests: tentec-REQUEST@contesting.com
Problems: owner-tentec@contesting.com
|