[DSP-10] Voltage readings and more

[Don AE5K]

Hi Mike,

I have the pdf files of the original articles and have extracted the 
schematics from them.  but thank you.  It is referenced on Bob's DSP-10 
page near top and the link is to the TIS of ARRL which has it for all to 
see, not just members.  The large sheet with the top markings/parts 
placement would be nice to have the original file to be able to enlarge 
a portion of it.  The printing is kind of small.  I also noticed it must 
have been from a previous version of the pcb as there are slight 
difference between it and what my board is.  Example the orientation of 
U4 and U5 are turned (rotated) slightly.

I'm so exhausted from this and other things today so will start when 
fresh in the morning to see if I can localize the gain and intermittent 
gain problem to one stage.  One thing I'm not sure of is what I should 
be reading on the meter.  Since the circuit is supposedly (maybe) 50 
ohms impedance for the mmic's and the meter also starts out with a 50 
ohm load at its input, am I correct in thinking I should be reading half 
power? (or possibly 1/4 the power?)  At any rate, I guess I can see if I 
have a poor amp stage without know actual power.

The KA7EXM meter is quite similar, but more sophisticated, to the one 
W7PUA and W7ZOI? published earlier.  He uses a PIC to do some nice 
things in it.  Yes, it goes to the -70 dBm area...it uses a AD8307 chip, 
LM324 amps and the PIC with LCD display, some math curve fitting, etc..  
Max power in is +7 dBm.  With the 40 db tap in circuit I don't have to 
worry about exceeding that when connected to the DSP-10 output.

Of course, I'll let everyone know my results.

Don AE5K

On 04/13/2013 08:26 PM, kd7ts wrote:
> On Sat, 13 Apr 2013 15:32:01 -0700, Don AE5K <donj at ae5k.us> wrote:
>
>> Am I wrong in my assumptions?
>
> Hi Don,
>
> I think this will work to see what is needed.
>
> The 3 part article is online somewhere, but I have local copies in PDF 
> format. They expand very nicely on the monitor. I can send as 
> attachment in mail or post them and send you a link, if you like.
>
> The second installment has a block diagram that says the 3 transmit 
> stages togerther are 40 DB gain. Working from that, backwards says we 
> have about -23 dbm from the D1 pin switch. This should be easily seen 
> on the KA7EXM meter. I'm guessing it goes to -70 dbm or so.
>
> These are approximates
>
> input -23 dbm 12 -15 mV
> mar6  20 dbg
> -3
> mar4  8 dbg
> +5
> 2n5109 12 dbg
> output =  +17 dbm
> 3 stages together  total 40 dbg
>
> This was all in the article .. just repetitive except the D1:A2 
> measurement
>
> press the Home key to put the
> transceiver into transmit. With the key up,
> you should measure the following voltages:
>
> D1-A2    RF Filter TR diode    0.73 V
> U4 pin 3    1st transmit amplifier    3.6 V
> U5 pin 3    2nd transmit amplifier    4.6 V
> Q2 emitterPower-amplifier emitter 1.2 V
> Q2 base    Power-amplifier base    1.9 V
>
> Nothing different here than you reported.
>
> The alignment is pretty simple, and is done in receive.
>
> Next, peak crystal-filter coils L12 and L13 for maximum signal. The 
> signal-level
> indication can be helpful for these adjustments. Select a repeater 
> frequency as close as possible to 147 MHz and peak the RF filter coils 
> L1, L2, L8, L9, L10 and L11 at that frequency.
>
> I didn't see anything, or recall that there is anything to peak for 
> transmit. All these setting do affect transmit, though.
>
> Let me know about the PDF files.
>
> Mike KD7TS
>
>
>
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