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Realigning and Spectrum

 

I noticed that my BIT40v3 was well shy of the top of the band.
On the spectrum analyzer, I noticed two other peaks about 18KHz
on each side. They seem to be a bit higher than I'd expect,
but I'm a relative newbie on what's allowable.

I have a snapshot of the spectrum at:


First, is there a problem with my board or is that within limits?
I remember when I was setting up an SDR other signals were down by
47 or 48 dBm.

Second, does this mean I should adjust the trimmer to move the max
operating frequency to 7.3 MHz minus about 20 KHz?

I few minutes later I noticed that the other signals had pushed out about
6.5 KHz more:


The only change I've made to the RF side of things is replacing the resistors
to reduce drift.

- John
W1JDS
 

John,

there seems to be an strong 18 KHz moduation on the transmitted signal. i have a home-built spectrum analyzer that I have used to see the output spectrum. There was a strong spur in the output just below 5 MHz. It is well below 43 dbc that the FCC mandates. The other was the second harmonic at 14 MHz, again below the -43 dbc level.

I ran the scan again, just now, to be doubly sure. I set my resolution bandwidth to 1 KHz and ran the scan at 100 KHz span with a 2 tone, 50 mv audio injected into. I did notice a number of distortion products, but nothing 18 KHz away. The crystal filter took them al out.

The 18 KHz modulation could only be coming from the circuit after the crystal filter. try running this from clean battery to see if this persists. i would suspect, given the 18khz murmer, it is from an smps.

- f


On Fri, Dec 9, 2016 at 9:30 AM, John Sutter jds@... [BITX20] <BITX20@...> wrote:
?

I noticed that my BIT40v3 was well shy of the top of the band.
On the spectrum analyzer, I noticed two other peaks about 18KHz
on each side. They seem to be a bit higher than I'd expect,
but I'm a relative newbie on what's allowable.

I have a snapshot of the spectrum at:


First, is there a problem with my board or is that within limits?
I remember when I was setting up an SDR other signals were down by
47 or 48 dBm.

Second, does this mean I should adjust the trimmer to move the max
operating frequency to 7.3 MHz minus about 20 KHz?

I few minutes later I noticed that the other signals had pushed out about
6.5 KHz more:


The only change I've made to the RF side of things is replacing the
resistors
to reduce drift.

- John
W1JDS
 

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I'm running this off one of the cheap Chinese 12V Li-Po battery packs I bought a few years ago.
I'll try it on 12V of alkaline cells tomorrow.

Thanks,

- John

On 12/8/2016 9:46 PM, Ashhar Farhan farhanbox@... [BITX20] wrote:

?
John,

there seems to be an strong 18 KHz moduation on the transmitted signal. i have a home-built spectrum analyzer that I have used to see the output spectrum. There was a strong spur in the output just below 5 MHz. It is well below 43 dbc that the FCC mandates. The other was the second harmonic at 14 MHz, again below the -43 dbc level.

I ran the scan again, just now, to be doubly sure. I set my resolution bandwidth to 1 KHz and ran the scan at 100 KHz span with a 2 tone, 50 mv audio injected into. I did notice a number of distortion products, but nothing 18 KHz away. The crystal filter took them al out.

The 18 KHz modulation could only be coming from the circuit after the crystal filter. try running this from clean battery to see if this persists. i would suspect, given the 18khz murmer, it is from an smps.

- f


On Fri, Dec 9, 2016 at 9:30 AM, John Sutter jds@... [BITX20] <BITX20@...> wrote:
?

I noticed that my BIT40v3 was well shy of the top of the band.
On the spectrum analyzer, I noticed two other peaks about 18KHz
on each side. They seem to be a bit higher than I'd expect,
but I'm a relative newbie on what's allowable.

I have a snapshot of the spectrum at:


First, is there a problem with my board or is that within limits?
I remember when I was setting up an SDR other signals were down by
47 or 48 dBm.

Second, does this mean I should adjust the trimmer to move the max
operating frequency to 7.3 MHz minus about 20 KHz?

I few minutes later I noticed that the other signals had pushed out about
6.5 KHz more:


The only change I've made to the RF side of things is replacing the
resistors
to reduce drift.

- John
W1JDS
Sudanthiram N
 

Can any one help me ,how can I work with bitx40 v3.Now I am QRV in San mode with approx.5 watts. Since I am a cw lover I asked this question


On Dec 9, 2016 11:36 AM, "John Sutter jds@... [BITX20]" <BITX20@...> wrote:
?

I'm running this off one of the cheap Chinese 12V Li-Po battery packs I bought a few years ago.
I'll try it on 12V of alkaline cells tomorrow.

Thanks,

- John

On 12/8/2016 9:46 PM, Ashhar Farhan farhanbox@... [BITX20] wrote:
?
John,

there seems to be an strong 18 KHz moduation on the transmitted signal. i have a home-built spectrum analyzer that I have used to see the output spectrum. There was a strong spur in the output just below 5 MHz. It is well below 43 dbc that the FCC mandates. The other was the second harmonic at 14 MHz, again below the -43 dbc level.

I ran the scan again, just now, to be doubly sure. I set my resolution bandwidth to 1 KHz and ran the scan at 100 KHz span with a 2 tone, 50 mv audio injected into. I did notice a number of distortion products, but nothing 18 KHz away. The crystal filter took them al out.

The 18 KHz modulation could only be coming from the circuit after the crystal filter. try running this from clean battery to see if this persists. i would suspect, given the 18khz murmer, it is from an smps.

- f


On Fri, Dec 9, 2016 at 9:30 AM, John Sutter jds@... [BITX20] <BITX20@...> wrote:
?

I noticed that my BIT40v3 was well shy of the top of the band.
On the spectrum analyzer, I noticed two other peaks about 18KHz
on each side. They seem to be a bit higher than I'd expect,
but I'm a relative newbie on what's allowable.

I have a snapshot of the spectrum at:


First, is there a problem with my board or is that within limits?
I remember when I was setting up an SDR other signals were down by
47 or 48 dBm.

Second, does this mean I should adjust the trimmer to move the max
operating frequency to 7.3 MHz minus about 20 KHz?

I few minutes later I noticed that the other signals had pushed out about
6.5 KHz more:


The only change I've made to the RF side of things is replacing the
resistors
to reduce drift.

- John
W1JDS
 

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There must be a 18KHz source around my desk somewhere that's coupling in
somehow.?? False alarm on that one (probably).

As for alignment, I adjusted C93 but was only able to reach 7.257 MHz.
I tried different values for C95:
??? 100 pF 7.095 MHz
??????? 0 pF 7.033 MHz
????? 10 pF 7.139 MHz
????? 25 pF 7.257 MHz (original part)
????? 35 pF 7.35*? MHz (10 pF piggy backed on original part)
????????????????????????? ? * Estimated max frequency, forgot to write it down
Now I'm covering 7.12 -> 7.3 MHz.

I installed a larger heatsink cut from a Pentium 3 heatsink.? Was lucky there was a
hole in just the right spot and just the right size to self-thread using the original screw!.

In January I'll add
? A QRP-Labs VFO, though I'll add a LPF.
? AGC
? A speaker
? Separate PA power with a selection switch and probably a relay

I think I'm good for a while, though I should probably try to make a contact or two
before I go too far.

Thanks,

- John


On 12/8/2016 10:06 PM, John Sutter jds@... [BITX20] wrote:

?

I'm running this off one of the cheap Chinese 12V Li-Po battery packs I bought a few years ago.
I'll try it on 12V of alkaline cells tomorrow.

Thanks,

- John

On 12/8/2016 9:46 PM, Ashhar Farhan farhanbox@... [BITX20] wrote:
?
John,

there seems to be an strong 18 KHz moduation on the transmitted signal. i have a home-built spectrum analyzer that I have used to see the output spectrum. There was a strong spur in the output just below 5 MHz. It is well below 43 dbc that the FCC mandates. The other was the second harmonic at 14 MHz, again below the -43 dbc level.

I ran the scan again, just now, to be doubly sure. I set my resolution bandwidth to 1 KHz and ran the scan at 100 KHz span with a 2 tone, 50 mv audio injected into. I did notice a number of distortion products, but nothing 18 KHz away. The crystal filter took them al out.

The 18 KHz modulation could only be coming from the circuit after the crystal filter. try running this from clean battery to see if this persists. i would suspect, given the 18khz murmer, it is from an smps.

- f
 

Very nice. This looks like an easy way to put the VFO in the U.S. SSB band.

I'll bet the 18 KHz is from a CFL or LED light bulb.

My board came without C95 installed. The schematic shows 47 pF, but I am sure this is adjusted by the makers to achieve the proper VFO according to their criteria. I should think that starting with a 33 pF cap would be good to begin with for U.S. rigs. That should give a coverage of about 7.120 to 7.270 MHz. Mind you, the VFO still will drift a lot...

john
AD5YE


On Saturday, December 10, 2016 1:13 AM, "John Sutter jds@... [BITX20]" wrote:

?
There must be a 18KHz source around my desk somewhere that's coupling insomehow.?? False alarm on that one (probably).
As for alignment, I adjusted C93 but was only able to reach 7.257 MHz.
I tried different values for C95:
??? 100 pF 7.095 MHz
??????? 0 pF 7.033 MHz
????? 10 pF 7.139 MHz
????? 25 pF 7.257 MHz (original part)
????? 35 pF 7.35*? MHz (10 pF piggy backed on original part)
????????????????????????? ? * Estimated max frequency, forgot to write it down
Now I'm covering 7.12 -> 7.3 MHz.

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