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 Post subject: Re: TROUBLE
PostPosted: Mon Feb 25, 2013 6:55 am 
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Joined: Mon Jul 23, 2012 6:25 am
Posts: 1142
Yes 68 and 82pf are correct, according to the model. I'm glad to hear that everything is working.


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 Post subject: Re: TROUBLE
PostPosted: Mon Feb 25, 2013 7:39 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: Mon Feb 25, 2013 10:19 pm 
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Joined: Mon Jul 23, 2012 6:25 am
Posts: 1142
9.5 dB sounds about right for Q10 but U7 should have more than 20 dB gain. Check the DC operating conditions is there 5V at pin3 of U7? Are you fairly sure that you bypass the unused transistor amp stage?

See what you get if you open up C130.

Jim.


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 Post subject: Re: TROUBLE
PostPosted: Sun Mar 03, 2013 9:04 pm 
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Joined: Fri Aug 03, 2012 5:35 pm
Posts: 36
I making progress.

First, I've realized that the gain calculations in my last post were incorrect. They reflect voltage gain. Power gain = voltage gain squared.

So, in terms of power gain, U7's gain is 12.8 dB; Q10's gain is 19 dB.

Unfortunately, as previously noted, a total of 31.8 db is still falls about 11dB short of making 0.5 watts at TX_OUT to the Off-Board PA (OBPA).

But, I know where the missing gain went!!! A whole amplifier stage was omitted from the OBPA schematic. So, I pulled off the jumper wire and installed the MPSH10 (Q11) amp stage.

Now, with VR1 maxed, in CW mode, on 10 meters, I get about 0.25 watts at TX_OUT. That's enough to make about 40 watts out from the OPBA to a dummy load (about 30 watts on 12 meters). (I haven't tested 6 meters yet.)

So, I'm up and running on CW. Unfortunately, I'm not getting any modulation in SSB mode. I'll work on that next weekend.

Next time you revise the OBPA schematic, I suggest you add the MPSH10 (Q11) amp stage, as shown in the original DSP-610 schematic.

(As always Jim, thanks. This has been, and continues to be, a very fun and interesting project.)


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 Post subject: Re: TROUBLE
PostPosted: Sun Mar 10, 2013 11:51 am 
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Joined: Fri Aug 03, 2012 5:35 pm
Posts: 36
First, I fixed the SSB modulation problem with a piece of electrical tape. The heatsink was shorted against the mic terminals.

Second, I fixed the low RF drive problem by changing R49 from 100 ohms to 56 ohms (per Jim's suggestion). That significantly increased gain from the LO2, which in turn increased IF and RF levels all the way up the TX chain, Now I don't have any problem making enough RF on 10 or 12 meters to drive the OBPA to 50 watts.

So now I'm working SSB on 10 and 12 meters, and getting consistently good signal reports.

But the IF/mixer chain still doesn't make enough RF on 6 meters to drive the OPBA. At J17, RF power output is 20 dB lower on 6 meters than on 10/12 meters.

Jim and Eric: Have you thought of any way to get more RF through the 6-meter bandpass filter?

(As usual, thanks in advance.)


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 Post subject: Re: TROUBLE
PostPosted: Mon Mar 11, 2013 2:54 pm 
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Joined: Tue Oct 02, 2012 4:58 pm
Posts: 38
Marc,
I am experiencing the same problem with the 6M exciter chain not having enough gain to drive the PA to any output to speak of. At one point I was getting about 1 watt out but then I decided to clean any flux off the board and after that I wasn't getting anything to speak of, would barely move the needle on my watt meter. I guess it liked the flux. lol I am loosing a lot thru the filter chain and get my most output when I have the coils of L5, 6 and 7 squeezed closer together. I asked Jim if the component values for the 6M filter were correct and he replied they were. I work a bunch of stations on 10 and 12 meters in Europe, South America and the Caribbean during the phone contest a got many unsolicited good audio reports so that portion of the radio is working well now. I am building the "all on 1 board" version and keeping the power level at 20 watts I am not having any problems with RF getting into the control sections of the radio. I am happy with 20 watts output especially with the wonderful audio reports I am getting. Now I am stuck again with the 6M transmitter not working like you are. The problem seems VERY similar to the filter issue we had with the 10/12M as the symptoms seem identical. Wish I could be more help but is seems we are now both in the same boat. Let me know if you find the secret to bringing this alive and I will do the same!
Thanks and 73's,
Eric


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 Post subject: Re: TROUBLE
PostPosted: Sat Mar 16, 2013 9:02 pm 
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Joined: Mon Jul 23, 2012 6:25 am
Posts: 1142
Hi Guys,

I've been on spring break but I glad to hear that things are working. You can thank Bob Allison at the ARRL lab for the TX audio. The first version just used the 2.2 kHz filter and when he listened to it he said that it didn'e have enough lows, so I modified the code to have a separate TX only filter and gave it some more low end.

I have found a free for non-comercial use program that generates the coefficients for various FIR filters if you want to change the filter characteristics.

http://www.cumbriadesigns.co.uk/DSP.htm

How much power are you getting from the OBPA on 50? The most I've seen from a HR50 is 37 - 39 Watts.

Jim.


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 Post subject: Re: TROUBLE
PostPosted: Sun Mar 17, 2013 7:29 am 
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Joined: Tue Oct 02, 2012 4:58 pm
Posts: 38
Jim,
I am not getting enough signal thru the 6M filter consisting of C46 and L5 to C52 and L7 to fire the PA. This filter seems to have too much loss for the PA to get enough signal to work. I notice the crystal filter is also loosing about half the signal value also but it does that on 10/12 meters also so that isn't the problem. On 6M I get about 100mv of RF out of SBL-1 but hardly anything to C49. I am not sure why all the signal loss.
Thanks,
Eric


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 Post subject: Re: TROUBLE
PostPosted: Fri Mar 22, 2013 7:15 pm 
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Joined: Fri Aug 03, 2012 5:35 pm
Posts: 36
Eric and Jim:

I don't think the 6M bandpass filter (L5, L6, L7) is the problem, as least not in my case.

I've established that the 6M bandpass filter works absolutely correctly. I've injected clean 51-MHz RF from my signal generator through it; and the loss is very small (< 0.5 dB)!

Key down in CW mode, on 6M, I'm getting 64 mV (peak-to-peak) on pin1 of the SBL-1. After the 6M bandpass filter I measure about 20 mV (P-P) at C49.

I don't have a spectrum analyzer, but I expect that output from the SBL-1 contains frequencies including IF, LO, LO + IF, and LO - IF. So, the relatively large signal losses prove that the 6M bandpass filter is doing its job by attenuating signals that are outside of the 6M band.

BUT I HAVE MADE A BREAKTHROUGH!!!

Jim: Please check this. I think L20 and L21 are reversed!

According to the spec sheet, L20 (P/N BLM21BB600SN1D) is expected to have impedence ranging from about 30 to 40 ohms at frequencies ranging from 12M to 6M. That's not very effective for isolating U7's RF output from its power supply.

On the other hand L21 (P/N BLM21BD182SN1D) is expected to have impedence ranging from about 500 to 1000 ohms at frequencies ranging from 12M to 6M. Wouldn't L21 be a better RF choke for U7 than L20?

I reversed L20 and L21. Now I get LOTS of RF drive on 12M, 10M, and 6M.

Unfortunately, drastically different settings are required at VR1 for each band. However, with appropriate peaking of VR1, the off-board PA (OBPA) will produce about 48 or 49 Watts on 12M and 10M.

(I've still got a bug in the 6M OBPA circuit; so I'm getting 0 Watts out on 6M. But it's an OBPA problem; I'm getting plenty of 6M drive now.)

--Marc


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 Post subject: Re: TROUBLE
PostPosted: Sat Mar 23, 2013 4:42 pm 
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Joined: Tue Oct 02, 2012 4:58 pm
Posts: 38
Marc,
YOU are the man! I swapped L20 and L21 like you suggested and now I have at least 20 watts out on all 3 bands. When I have L5, L6 and L7 squeezed pretty tightly together or putting my finger on the board near this section SW1, SW2 and the associated components, I can significantly change the output so I have some parasitic oscillation going on or something. It seems VERY sensitive to how these coils are configured for changing the power out. Squeezing them just a little can change the output from 5 watts to 20 watts. I am very happy to now have a working radio on all 3 bands. I like you see a variation in the setting of VR1 on all 3 bands but have chosen a position that gets me around 5 watts out on low and 20 watts on high with a little less on 6M. I can get more out on 6 but then the low setting for the other 2 bands is about 15-20 watts instead of 5. In actuality I am happy with a tribander that can transmit and receive at least some power. I am thinking of playing a little more with it to make it stable and then calling it good. Thanks so much for your help with L20 and 21 as I never thought to look there! That was certainly the cure for me for no power out on 6M. I now just have to investigate what makes it so sensitive or at least find a setting that is stable and leave well enough alone! :D
Thanks again and 73's,
Eric


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