SINUS B1 PROJECT

[XXL]

Right iv finally got something happening with it. its oscillating, but at 133mhz. Turns out my bf199 were fake pieces of crap. if I touch the trimmer that iv added to c6 I get around 52-55mhz. but its looking like the 133mhz is stronger so my meter is picking that up instead. That's air band territory and 133/2 is 66.5mhz so don't know wtf is going on.

Also the resistor pot on RP2 is doing nothing. i can only change the frequency with c9 trimmer.

[sinus trouble]

Turns out my bf199 were fake pieces of crap.

Hooray!

Seriously! I am genuinely pleased that you have made some progress! You will get it working eventually, Just takes a bit of patience!

With the current schematic, My TX works at a frequency of 53.2Mhz to 58.3Mhz by adjusting the TUNE potentiometer!

I dont know what test equipment you have? You can verify that each side of the oscillator is in the range of around 25 to 30Mhz?

Because you made your own PCB? You may need to fiddle with the LC tank circuit a bit? I dont see no reason why it should not work?

The harmonics can be pretty strong on this TX because there is no output filter! A low pass filter would sort this out if you wish!

Harmonics are further reduced if you mount it in a case!

[Albert H]

Right iv finally got something happening with it. its oscillating, but at 133mhz. Turns out my bf199 were fake pieces of crap. if I touch the trimmer that iv added to c6 I get around 52-55mhz. but its looking like the 133mhz is stronger so my meter is picking that up instead. That's air band territory and 133/2 is 66.5mhz so don't know wtf is going on.

You'll probably find that your oscillator IS running at 55MHz - your counter is seeing the harmonic at twice the oscillator frequency!

[XXL]

Atm the harmonic seems to be stronger than the main signal though which is worrying. Surly it should be weaker than the main frequency?

[sinus trouble]

Another way the further reduce harmonics is to balance the oscillator!

The oscillator needs to be as symmetrical as possible! Try to adjust the oscillator coils in a uniform manner! This will improve cancellation of the frequencies you do not want!

I need to build a low pass filter for mine but havent had the time? I will get round to it eventually!

[Albert H]

Atm the harmonic seems to be stronger than the main signal though which is worrying. Surly it should be weaker than the main frequency?

It might be, but some counters lock to the highest frequency they "see".

[sinus trouble]

Atm the harmonic seems to be stronger than the main signal though which is worrying. Surly it should be weaker than the main frequency?

It might be, but some counters lock to the highest frequency they "see".

Thats a good point Albert!

[sinus trouble]

I have been simulating some Low Pass Filters for Band 1

I chose the 'Traditional' 7 pole Chebyshev in LT Spice! I will show the results!

These are just theoretical and would probably work? However they have not been tested in a 'Real Life' Situation!

[sinus trouble]

This is the first filter! As can be seen, It starts to roll off @ 88Mhz which is desirable! However, the response in the Band 1 region is a bit wobbly?

B1 LPF.PNG

[sinus trouble]

Here is the second version!

This filter starts to roll off a bit earlier, @ around 84Mhz! Also the response in the Band1 region is a lot smoother!

CaptureB1 LPF 2.PNG

[sinus trouble]

Just to add! The coils have no specific dimensions! An online Inductance calculator can easily be used to accommodate your needs!

As long as they are close to the values shown? You can make them whatever size you want?

[XXL]

Atm the harmonic seems to be stronger than the main signal though which is worrying. Surly it should be weaker than the main frequency?

It might be, but some counters lock to the highest frequency they "see".

No my counter definitely picks up the strongest signal because when I touch c6 on the oscillator with a metal screwdriver, it reads around 53mhz. The screwdriver is acting is an Ariel.

[sinus trouble]

Another possibility could be?

If you are using short lengths of coax or patch leads to connect to your dummy or SWR meter etc...

These could be radiating the harmonics instead of the fundamental?

Try to connect a 47 Ohm resistor direct to the output of the PCB!

[sinus trouble]

A problem with 'non connected' frequency counters (which i am guessing you have) As Albert eluded to is that they will lock on to random fields of energy!

That is why expensive spectrum analysers have expensive couplers to measure what is actually present in the signal with a high degree of accuracy!

Yes there are harmonics present! But they may not be as high as you think!

[sinus trouble]

So i built a prototype Low Pass Filter for my Band 1 TX

The Prototype was a simple copper clad construction! The coil dimensions are 4 turns, 10mm diameter with an approximate length of 8mm!

After testing the coils, The values fell short of the expected 120uH i was aiming for? However there was no serious issues with SWR or power losses

I suspect the roll off could be tightened to target those harmonics with a bit of adjustment!

A work in progress! Picture below!

[sinus trouble]

B1 LPF Test1.png

[sinus trouble]

B1 LPF Close.png

[sinus trouble]

Considering there are so many factors to get my head round here? Overall, there was a significant improvement in harmonic suppression!

[XXL]

Nice work! I might give it a go but iv given up on it atm. I'm trying your band 1 RX instead. I tried a different design but it didn't work so I'm going to try yours instead. I was wondering what the "SIG" pad is for in the middle ?

[jvok]

Sinus, do you have gerbers available for these boards yet? I see you have pcbs from jlc but couldn't find a link for gerbers