[TenTec] Rick's Scout and Low Dropout Reegulators

[Bwana Bob]

The schematic shows a 7805 regulator for the logic board. The minimum 
voltage for the 7805 is 7 V, so it should be OK.

The RX/control board uses an LM 2940, which is a low dropout regulator. 
However, it is prone to instability under certain conditions, according 
to the data sheet.  The regulated output to the RX/control is 10 V and 
the minimum input is 11.5 V, so a weak battery plus a little voltage 
drop in the power cable can spell trouble. Increasing the value of C22
  (33 µf. The data sheet specifies 22 µf minimum, with low ESR, and no 
maximum capacitance limit) may help.

It is also important to reduce voltage drop in the power cable and 
connector. Make sure that the power connector pins and sockets are clean 
and tight. Also, replace the spring-loaded in-line fuse holder with an 
automotive blade type.

I usually run my Scout at 30 W output and have had no problems running 
it on battery power. A 7 Ah gel battery will run it for a couple of 
hours. For longer duration, I use an automotive jump starting battery.  
I did have  a problem once with a corroded crimp connection on a power 
cable that caused a voltage drop which sent the Scout VFO drifting 
several kHz down the band.

I can try an experiment with a variable supply and listen with a 
separate receiver to see if the CW note gets chirpy at lower voltages.

                 73,

                 Bob WB2VUF

On 4/28/2015 12:44 PM, Rick - DJ0IP / NJ0IP wrote:
> Bob, I was a business manager, not an engineer.
>
> One of the things I learned how to do in business school was to use my
> resources and to delegate. (hi)
>
> I already have the designer of that radio looking into it for us and he is
> usually very good at solving problems like that.  He's as stubborn as me,
> but smarter.
>
> 73 - Rick, DJ0IP
> (Nr. Frankfurt am Main)
>
>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Katz Ajamas
> Sent: Tuesday, April 28, 2015 6:37 PM
> To: Discussion of Ten-Tec Equipment
> Subject: [TenTec] Rick's Scout and Low Dropout Reegulators
>
> Dear Rick,
>
> Have a look using the search term, "low drop out" regulator. Mouser and I'm
> sure the others have a wide selection. Specs are much better than the old
> three terminal jobs.
>
> 73, Bob ah7i/w4
>
>
>> ------------------------------
>>
>> Message: 8
>> Date: Tue, 28 Apr 2015 16:12:51 +0200
>> From: "Rick - DJ0IP / NJ0IP" <Rick at DJ0IP.de>
>> To: "'Discussion of Ten-Tec Equipment'" <tentec at contesting.com>
>> Subject: Re: [TenTec] OT: Anyone used LiFePo technology yet for
>>          portable        operations?
>> Message-ID: <011a01d081bd$6a6b18b0$3f414a10$@de>
>> Content-Type: text/plain;       charset="us-ascii"
>>
>> I just had an email with the OM who designed the Scout.
>> He is no longer with Ten-Tec, but I'm sure many of you know who he is.
>>
>> He agreed that a lower loss regulator would help and he promised to
>> take a look at it.
>> Perhaps he will suggest something.
>>
>> 73 - Rick, DJ0IP
>> (Nr. Frankfurt am Main)
>>
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