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 Post subject: Re: TROUBLE
PostPosted: Mon Feb 11, 2013 8:32 am 
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Joined: Fri Aug 03, 2012 5:35 pm
Posts: 36
Yes, I can recompile. I've got the free compilers.


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 Post subject: Re: TROUBLE
PostPosted: Tue Feb 12, 2013 10:18 am 
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Joined: Mon Jul 23, 2012 6:25 am
Posts: 1143
OK in the DSP code main.c try adding:

spiData[0] &= 0x0fff;

right before

SPI1BUF = spiData[0] | 0x7000; // write the data out to the SPI peripheral

and

aoutBuff[0] &= 0x0fff;

right before

SPI1BUF = aoutBuff[0] | 0xd000; // write the data out to the SPI peripheral

This should prevent the data from crossing channels.


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 Post subject: Re: TROUBLE
PostPosted: Tue Feb 12, 2013 9:45 pm 
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Joined: Fri Aug 03, 2012 5:35 pm
Posts: 36
OK Jim. I modified the DSP code. It doesn't make any difference at all.

However, I've had some revelations.

First, as for DACA, of course it doesn't rise above 2.04 V. "SPI1BUF = spiData[0] | 0x7000" sets the DACA GA bit high; gain is 1X; its Vmax is 2.04V !!!!!!!
I could change the code to "SPI1BUF = spiData[0] | 0x5000" to set DACA's GA low. That would set gain to 2X and allow its Vmax to go to VDD. Would that be appropriate?

Second, as for DACB, I've realized that the magic setting of RF Gain, above which DACB's output is drastically reduced, corresponds exactly with a change in the display. Below the "magic setting" the display indicates a series of squares while keying in CW mode. Above the "magic setting" the squares are replaced by a line of dashes. According to the "LCD IO Cheatsheet.pdf," a line of dashes indicates an SWR trip. I'll bet the PIC18 responds by drastically reducing the DSP_TXD level !!!!!! While testing without the off-board PA attached, to simulate a low SWR, should I short pin 1 of J2 to ground and pull pin 2 of J2 up to 5VD? Or vice-versa?


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 Post subject: Re: TROUBLE
PostPosted: Wed Feb 13, 2013 7:03 am 
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Joined: Mon Jul 23, 2012 6:25 am
Posts: 1143
Yes, try the 0x5000 value.

I hadn't remembered the SWR shutdown feature, yes try grounding the RFL input. It's not an actual SWR shutdown but a high reflected power shutdown.

Jim


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 Post subject: Re: TROUBLE
PostPosted: Mon Feb 18, 2013 10:04 pm 
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Joined: Fri Aug 03, 2012 5:35 pm
Posts: 36
OK, the DSPic code modification fixes the DACB problem. And temporarily grounding the RFL input circumvents the SWR shutdown feature and allows testing the transmitter when the off-board PA is not connected.

Now, key down in CW mode, I'm getting strong DACA, 1st IF, and 2nd IF signals. And I'm getting a strong RF out of MX-1.

In 6 meter mode, I'm getting strong RF through the 6 meter bandpass filter. However, in 10 meter mode there's still something wrong with the 10/12 meter bandpass filter. Key down CW in 10 meter mode, I measure the following:
190 mV rms output at MX-1 pin 1;
104 mV rms at the junction of L9 and L4;
40 mV at the junction of L8 and L3; and
20 mV at C45.

I've rebuilt the 10/12 meter bandpass filter 3 times now, with two different batches of the recommended parts, and most recently with different brand substitutes. All 3 configurations give virtually the same results--unacceptable attenuation through the filter.

This filter is responsible for the missing gain in receive mode, too, which was noted in the AGC thread of this forum.

Were there any last minute changes in the 10/12 meter bandpass filter that I missed?
Do you have any suggestions?

(as always thanks)


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 Post subject: Re: TROUBLE
PostPosted: Tue Feb 19, 2013 11:52 am 
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Joined: Tue Oct 02, 2012 4:58 pm
Posts: 38
I am experiencing this same attenuation in the 12/10 MHz filter with a good signal leaving the mixer but hardly any by the time it gets to C45. My receiver's S meter also doesn't respond to even strong signals unless it is like a 60 db over 9 generated by a near by transmitter.. A 20 db over S9 signal on my commercial receiver results in nothing on the S meter display although the signal is very "copyable" on the DSP-610. The only way to get the S meter to change is turn down the RF gain and then the receiver sensitivity is lost. It looks like the filter has a LOT of loss. I haven't rebuilt it with other components but have checked the ones there and they seem to be as specified in the schematic.


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 Post subject: Re: TROUBLE
PostPosted: Wed Feb 20, 2013 7:01 am 
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Joined: Mon Jul 23, 2012 6:25 am
Posts: 1143
I went back and checked the simulation and the inductors are (L8 and L9) are given as 390 nH not 150 nH. So I plugged 150 nH in the simulation which results in a loss of about 30 dB at 10/12M. So it look like a mistake in the schematic/BOM. Should be 390nH for L8 and L9.

Jim.


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 Post subject: Re: TROUBLE
PostPosted: Fri Feb 22, 2013 4:20 pm 
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Joined: Fri Aug 03, 2012 5:35 pm
Posts: 36
Eric:

Thanks for your reply. I thought I was the only one with this problem.

Jim:

I just replaced L8 and L9 with 390 nH parts (Newark P/N 20T1119). YES, that makes a big difference. Now the receiver has much more RF sensitivity. Typical 10 meter afternoon noise pegged the S meter; so I had to reprogram the DSPic with the original baseline code. Now the S meter works correctly.

Transmitting in CW mode, with the SWR shutdown feature disabled, I'm getting about 50 mV rms on 10 meters.

So, the bottom line is replace L8 and L9 and keep the original DSPic baseline code.

Thanks for your help Jim and Eric. This weekend I'll try to get the off-board PA up and working.


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 Post subject: Re: TROUBLE
PostPosted: Sat Feb 23, 2013 5:56 pm 
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Joined: Fri Aug 03, 2012 5:35 pm
Posts: 36
I set the bias to Q10 to 100 ma with TX keyed in SSB mode with no audio.

However, I'm not getting anywhere near 1/2 watt from the main board (only about 39 mW).

Key down, on 10 meters, in CW mode, into a 50 ohm load, with SWR shutdown feature disabled, with VR1 set to maximum, I measure the following:
Input into U7 at C129 = 36 mV rms;
Output from U7 at pin 3 = 158 mV rms; and
TX_OUT from Q10 at C2A = 1.4 V rms.

Jim, I think you said the PA chain requires about 20 mV rms of drive at J17.So, apparently I'm missing a lot of gain in the PA chain. I calculate gain through U7 is about 6.4 dB; and gain through Q10 is about 9.5 dB. Does either, of both, of these seem unusually small?

(Thanks)


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 Post subject: Re: TROUBLE
PostPosted: Sat Feb 23, 2013 9:53 pm 
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Joined: Tue Oct 02, 2012 4:58 pm
Posts: 38
Oh my what a difference having the correct value inductors make! I am now getting about 15 watts out on 10 and 12 meters but only about 1 watt on 6 meters so I still have something amiss in that leg of the circuit. So far I haven't seen any adverse affects caused by the transmitter to the digital portion of the radio and I will be very content with 10 to 15 watts of clean power. Jim, before I waste any more time trying to figure out why the 6 meter output is low, can you confirm the capacitors in that filter are supposed to be 68pf and 82pf? I can get a little more output by squeezing L5, L6 and L7 basically reducing their length. I am soooo close to having this totally working! :D Thanks for all your help on this project! 73's, Eric


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