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Re: a simple spur fix
How did you arrive at 47pF and 5uH for 12mhz?
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freq = 1/(2*pi*sqrt(L*C)) = 1/(2*pi*sqrt(47e-12 * 5e-6)) =?10382123 Hz Though that 30mhz LPF is a fairly complicated network to hang an LC trap on, there may be more going on here.? The 12mhz trap my not be needed if you reduce the loading on the si5351 clocks since this would reduce crosstalk between clocks within the si5351. ? Table 3, "DC Characteristics", in the si5351 datasheet says the output impedance is 50 ohms. My best guess is that this means there is effectively a series 50 ohm resistor between the? CMOS driver and the output pin.? If you then put a 50 ohm external load to ground on it and? the driver is trying to drive high to 3v, then the expected current would be 3v/(50+50ohms) = 30ma. But the output driver is limited to 8ma, so that output will be current starved. And with three clocks all working hard as they possibly can, the crosstalk is pretty bad on the si5351. So we want an external load that's more than 50 ohms on the si5351 clock pin, but we want the mixer to see a 50 ohm source impedance to avoid reflections. A pi network resistive attenuator is not a good choice. I suggest each si5351 clock pin drive a series DC blocking cap and a series 100 ohm resistor into the mixer port.? Assuming the si5351 has not hit its 8ma current limit, the mixer will see a source impedance of 50 ohms (internal to the si5351) plus that 100 ohm resistor, so 150 ohms. Add a 75 ohm resistor from mixer port to ground, that in parallel with 150 ohms makes it a 50 ohm source impedance for the mixer. Jerry, KE7ER it? On Fri, Nov 9, 2018 at 05:53 PM, Ashhar Farhan wrote:
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Re: a simple spur fix
allison and others, the traps are capable of adding a notch of -20 db. so even if you don't hit the bottom precisely, a 10 db reduction is all that is necessary to clean it up to the required level. these are meant to be fixes that work with existing boards : from v1 onwards. i tried to choose a method that was easy to do. we will need a different post mix if amp design going forward yes the traps are for 90 mhz and 12 mhz. the 10 mhz insensitivity is something i will look into today, I havent experienced it. perhaps we should move the trap to tx filters for the 21 mhz to 28 mhz band? the 12 mhz is filtered for the lower bands in any case. the other place to apply the 12 mhz trap would be the local oscillator output? - f On Sat, 10 Nov 2018, 05:48 Mike Woods <mhwoods@... wrote:
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Re: a simple spur fix
¿ªÔÆÌåÓýMy guess is that the two intended
filter frequencies are:? 90Mhz (second harmonic of 45MHz 1st LO)
and 12MHz (2nd LO).? The parts represent the right values for a
filter at 90MHz, but it seems that 30M band would be wiped out by
the second of the mods (which somebody has already observed).??
12MHz should be being wiped out instead, so I suspect a typo.
Perhaps? either a 35pF capacitor and the 5?H inductor as stated or a 3.8?H inductor and the 47pF capacitor as stated being about right for getting the filter resonant just on the low side of 12MHz.? Mike ZL1AXG On 10/11/18 9:49 AM, Brian L. Davis wrote: 10pf series with .3uhy - resonant about 91 MHz
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Re: a simple spur fix
Allison,
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I'm not 100% sure what his LC traps are doing, but they may not have to move around. My best guess is that the one at TP13 (tuned to around 90mhz) just removes the 2'd harmonic of the 45mhz IF that gets created by those 2n3904's running flat out.? It doesn't have to move. Example:? Transmitting at 21mhz, clk2 is at 45+21=66mhz. If any 2*45=90mhz energy is present, it mixes with the 66mhz clk1 at D1,D2 to create a 90-66 = 24mhz spur. Farhan suggests the second LC trap is to suppress the 12mhz BFO energy due to crosstalk between clk0 and clk2. Though we have a report that this also sucks out 10mhz reception, so either that particular example is tuned differently than Farhan's, or that's an awfully wide trap, or I don't know what's going on there.?? If these mods are easily reproducible for acceptable results, good enough by me. We'll see. Jerry On Fri, Nov 9, 2018 at 02:45 PM, ajparent1/KB1GMX wrote:
Your doing what I tried back in June/July time frame, it failed then. |
Re: a simple spur fix
Good!? Sounds like it's working!? ;-)
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I for one am willing to give up 30m on what is mostly an SSB rig. If you were planning to operate CW on 30m, you could put a couple pins and a jumper in series with that C+L.? So with the jumper out, the mod is undone. Transmitting CW we don't have trouble with spurs, since the BFO and clk1 are both shut down. The only RF floating about the rig is clk2 at the transmit frequency. Jerry, KE7ER On Fri, Nov 9, 2018 at 03:03 PM, barry halterman wrote: I installed the series trap across C202 in the LPF and it reduced the 30 meter sensitivity drastically. |
Re: a simple spur fix
I installed the series trap across C202 in the LPF and it reduced the 30 meter sensitivity drastically. On Fri, Nov 9, 2018, 5:46 PM ajparent1/KB1GMX <kb1gmx@... wrote: Farhan, |
Re: uBITX AGC - Adafruit TPA2016, A Success!
#ubitx
¿ªÔÆÌåÓýI don't know. Check the T_DO and T_CS pins on the test set and see if one of the connected to the same input pin on the Teensy as the encoder SW. On Nov 8, 2018, at 1:23 PM, John Scherer <jrsphoto@...> wrote:
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Re: Transmit Problem
Hi Wayne,
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Shielding can be added to the interior of those "attractive plastic boxes". I made my own steel box from new steel. But I have used the aluminum foil lining inside wood or plastic boxes, The heavier foil pans that are sold for baking or the ones frozen meals come in are much sturdier than the paper thin foil sold for wrapping food. 73, Bill KU8H On 11/9/18 5:20 PM, Lawrence Galea wrote:
Have you tried putting the amplifier on the back panel? --
bark less - wag more |
Re: a simple spur fix
Farhan,
Your doing what I tried back in June/July time frame, it failed then. Reason first series traps good enough to suck out the spur at a given frequency are narrow enough? to be only a spot frequency fix.? The 2IF-LO spur for 28mhz BAND is between 17 to 16 mhz for 10M alone.? So you need a series trap that can not do a band. The other issue is the power amp.? At 80M and 10W out the gain is about 60db but as you go up, at 20M the gain is down to ~56db, and at 10M the gain is maybe ~52DB.? ?So at the spur frequency you have more gain available than the desired output frequency and the differential gain is enough to put that spur as shown at -45db at more like -37db below 2W. The fix has to be more comprehensive.? Also it must be field verifiable or factory set to allow for 1 or 5% parts. The 45mhz section needs: ? 45mhz filter inductors shielded or better that section relocated. ? Amplifier distortion clean up. ? Swap the 45mhz port and LO ports as IF ports are most sensitive to mismatch. A thought to look into... ? Replace the TIA amp at 45mhz with a more common resistive feedback amp (typical 2n5109 amp) ? with 20db gain.? Here is the hint:? Often when that amp is shown due to the fact that changes at either ? port impact the opposing port they often have a 6db pad at the output.? However for the TX case that ? same pad can be at the input and it insures the 45mhz filter will have a good match for the network ? and the transistor with its input impedance stable will have output stability going to the mixer. Allison |
Re: Transmit Problem
Have you tried putting the amplifier on the back panel? On Fri, Nov 9, 2018 at 5:59 AM Wayne Leake <wayneleake@...> wrote:
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Re: DIGITAL FREQUENCY READOUT
I WANT TO BUY? "The Raduino board with Si5351, Arduino Nano. Fully tested AND PROGRAMMED." I DON'T NEED THE LCD READOUT.
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HOW MUCH AND WHERE CAN I ORDER? WILLIAM On 11/9/2018 1:32 PM, MONEYSMITH wrote:
THANK YOU |
Re: DIGITAL FREQUENCY READOUT
THANK YOU
On 11/9/2018 1:21 PM, Vince Vielhaber wrote: The crystal is on the green board under the display.? Unplug the display and you'll see it.--- This email has been checked for viruses by AVG. |
Re: DIGITAL FREQUENCY READOUT
Vince Vielhaber
The crystal is on the green board under the display. Unplug the display and you'll see it.
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Vince. On 11/09/2018 03:26 PM, MONEYSMITH wrote:
THIS BOARD HAS A MEGA328P CHIP. I HAVE NO INFORMATION ON THE BOARD. --
K8ZW |
Re: a simple spur fix
Timothy Fidler
Yup.? it is correct.? The easiest way to get the units right is? L in uH , C in uF and result will be in Mhz? ie recip of sqrt of micro x micro .
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But remember when you are working at VHF with 5 percent capacitors and air wound coils,? even Tiny errors or tolerances? will put you off by 100s of KHz.? Ditto temperature effects on components. ? Timothy E. Fidler : Engineer BE Mech(1) Auckland , NDT specialist AINDT UT /RT3 , MT2 CB #2885,?
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Re: a simple spur fix
¿ªÔÆÌåÓýAshhar: ? You give the number of turns necessary, and the core IDs, but what is the gauge of wire used??? ? David A Posthuma, WD8PUO 1 (616) 283-7703 ? From: [email protected] <[email protected]> On Behalf Of Ashhar Farhan ? so, there is one spur fix that is now consistently working for me. among rhe solutions, i was looking for one that would be easy to apply. first, the distortion in the 45 mhz amp is creating harmonic distortion. so a 0.3uh in series with a 10 pf is used across TP13 (output of the 45 MHz IF amp going to the front end mixer). 8 turns on T30-6 gives you 300nh. second, there is a cross talk inside the Si5351 where the 12 mhz from the bfo leaks into the local oscillator. A 5uh in series with a 47 pf across C202 of the LPF will suppress it. 35 turns on T30-6 gives you 5uh. - f ? |
Re: DIGITAL FREQUENCY READOUT
The Si5351 is on the back side of the board in the first picture, between the display and the board that the ATmeg board plugs into.? The board with the plug is the Raduino board. On Fri, Nov 9, 2018 at 2:27 PM MONEYSMITH <w4nfr@...> wrote:
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Re: DIGITAL FREQUENCY READOUT
¿ªÔÆÌåÓýTHIS BOARD HAS A MEGA328P CHIP. I HAVE NO INFORMATION ON THE BOARD. I FOUND NO SI5351A CHIP? PHOTOS ATTACHED. W4NFR On 11/9/2018 11:42 AM, Arv Evans wrote:
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