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mr. pips

Parallel resonance

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Help!

For a Maxim 2235 amplifier output end, I like to make a L//C parallel resonance 'harmonic trap'...

For high impedance @ 915 MHz Maxim give a 10 nH/3.3pF combination as a good design.

Now I like to make such thing for 868 MHz.

Can someone help me to find a nice combination or knows the formula to calculate it?

I did try to find it on the net but I really don't understand noting about that hocus pocus.

Thanks,

Rienk

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The exact placement of those low value components along the impedance controlled strip line will have an affect on the results. If it was me, I would stick with the filter values they recommended for 915Mhz (if necessary, just move them along the strip line to achieve the best results for your 868Mhz app). If your RF measurements suggest the values aren't optimal, then simple component subs will help you optimize (but I expect the current values will be fine as a harmonic filter).

These sort of projects require a spectrum or network analyzer to dial them in. Don't forget that the board layout is very critical. If you use the layout and circuit board material that they recommend in their app notes, you can avoid some trial and error mistakes. :)

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Thanks!

I will follow your advice.

Meanwhile I did find a dummies calculator for at least calculating the impedance of a given L//C.

It proofed you are more than right. With that L//C combination the imp -AT-868 is even 3 times bigger than @ 915!

So when the components are coming I'm ready to make a lot of mistakes..

When it will be not a complete failure, I will post some results here.

Rienk

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use this:

fflc-f.gif

or simply download RF SIM 99

it is free and will let you calculate and simulate simple RF circuits.

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wow that amp part is not easy to use, have you access to:

spectrum analyzer ? network analyzer ?

and have extensive experiance with RF design ?

How do you plan to prove the power and gain is right ?

and your macthings are right ?

and your harmonics are within acceptable levels ?

how much power do have ?

and how much do you need ?

there exist much more smart devices for gaining up 1GHz from mW to W

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Thomas,

Thanks for your interest. The formula you mentioned did blow my brain and calculator because the many zero's.

Now your questions...

no

no

no

no

no

no

1 dbm

I was hoping, even with a bad design, from the potential 30 dbm of this chip, a 6dbm would be a realistic result. Please don't tell me I will end up with 0.1 dbm!

I like to have a 10km range with a recalculated goof proof tx antenna.

But for another application a 2km range would also be nice.

I like smart stuff, Can you give me a clue?

Thanks,

Rienk

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Please don't tell me I will end up with 0.1 dbm!

Not only that, but you might also be sending 20dBm of unwanted noise, polluting other bands ;)

With both no knowledge and no equipment, I'd just buy something that is ready-made and tested.

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Help!

For a Maxim 2235 amplifier output end, I like to make a L//C parallel resonance 'harmonic trap'...

For high impedance @ 915 MHz Maxim give a 10 nH/3.3pF combination as a good design.

Now I like to make such thing for 868 MHz.

Can someone help me to find a nice combination or knows the formula to calculate it?

I did try to find it on the net but I really don't understand noting about that hocus pocus.

Thanks,

Rienk

Rienk,

Can you give me a little more insight into what you need? Are you trying to filter out a spur or attempting to notch out amplifier noise to allow better operation with a collocated receiver?

Mike

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It seems he's just wanting to design input and output bandpass filters matching his operating frequency to put around his amplifier chip.

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yes I know Kilrah, but to make a design that work you need access to equipment,

see the datasheet they say you need coils and caps with atleast Q>100 and that is a 1GHz

with tiny smd coils that is impossible, and with homemade FR4 boards it all end up will too unaccurate striplines

so you will get a 10dB returnloss or worse on all ports even if lucky.

Purchase a ready made amplifier or Tx module with the power avail as needed = much better and much cheaper result.

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I know that and actually backed that point. I was answering to Old Man Mike who was asking about the purpose.

Edited by Kilrah

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Thanks guys!

With your comments I'm about giving up on this project! Yeh, really thank you. Too bad because this Maxim is intresting.

Kilrah: I forgot about polluting other bands, stupid! Do you expect the non correct placement of a single capacitor in the output line to give a lot of pollution?

Thomas: can you give more info on those smarter devices for gaining up?

Old man: Kilrah did explain exactly what I was aiming at..

Rienk

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Do you expect the non correct placement of a single capacitor in the output line to give a lot of pollution?

Yes. As Mr. RC-CAM said earlier, at these frequencies the shape, size, placement,... of your PCB traces will generate parasitic caps/inductances that might actually exceed the small component values you quoted from Maxim in the first post. With a good design you might actually not need any "physical" component to make your filter, just a clever PCB design could suffice in generating it using its parasitic properties.

That might be a bit exxagerated, but it's to show that if you want to get it right you need to be able to calculate all the unwanted effects, include them in the design, and verify them once the thing is manufactured.

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Thanks, Kilrah.

Now that makes me really stop this project :(

But still I'm desperatly looking for an amplifier.

I did some more searching on the web, but didn't find something usefull...

Can anyone help me with a name? Thomas, are you still there?

Rienk

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Can anyone help me with a name?

I would suggest you look at the Linx Technologies broadband PA modules to see if they have something you like. They are sold by Digikey and cost under $15.

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Thanks Mr Rc-cam'

That looks very good to me.

What would be range....

868 MHz/18 dbm/50 mW/(improved) goof proof TX antenna/small dipole rxantenna....

And now the things what put me down :( :

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Sorry pushed wrong button.

What is depressing me

At Digi-Key:

one Linx bba-519-A $15

S&H to Europe $37

Tax(aboutimpossibletoavoid) $10

TOTAL $62

Can you beleve that?!?!

I did email some other shops (they not have it in their catalog) to get it for a 'normal' price.

Waiting for their reply now...

Rienk

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What would be range....

That is sort of asking how much a hen weighs. :) It depends. Range will vary with Rx sensitivity and other variables. But for the sake of throwing a number at you: Assuming an ideal environment, reasonable Rx performance, proper installation of EVERYTHING, fixed line-of-sight use, etc., you may see a 5+ mile range. In practice, especially with mobile applications, the reliable range will be much lower.

... goof proof TX antenna/small dipole rx antenna....

I'm not sure what you are creating or how it will be used. But the usual installation would put the dipole on the mobile Tx and the patch aerial on the fixed position Rx.

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Thanks,

That's a nice rooster!

I'm intending to use it for an uplink. That's why it's the other way around.

So I'm waiting now for a price from Linx themselves...

Rienk

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if you cant verify the performance with: spectrum analyzer / network analyzer / power meter ?

dont design your own amp, simply purchase one !

we at IF have now our own multipurpose amplifier boards and cases in milled aluminium with SMA connectors,

the board alone will be fine for size and cost and weight sawing in planes,

the board alone with no heatsink added I think it can handle 200-300mW and have 20-30dB gain

we can easyly match such an amp board for your desired frequency, we have amp devices on stock for 40-3600MHz.

so we can actually help you, but at the moment I am 100% loaded with other of our projects, sorry.

that is why I say it is smarter faster and cheaper to simply purchase a transmitter with the right power the first time :-)

but I dont know if your video TX is a homemade device ? you want to boost up ?

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Say Thomas.... What do you think of useing MMIC chips like the Mar 6 family n the Gc range for amplifiers.Should be fairly easy to set up on a board along with a stripline antenna.

Edited by W3FJW-Ron

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yes MMIC is the way to go !

I would simply use a quarter wave wire antenna, they can be made with out any measure equipment.

use a x 0.9 shorten factor from the wavelength in vacum, due to it is a wire.

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Thanks Thomas. When I get my motorhome squared away and my workbench set up, I'll give it a try. I have some of those MMICs in storeage somewhere.

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Freescale, WJ, Minicircuits, Skyworks,

they have many types with the gain and output power you need,

the P1DB is the figure you need for output power,

it is the output power where the gain is dropped 1dB

DONT use the device at any more output power, it will generate tons of harmonics,

and intermodulation due to non lineary behaviour,

remember our modulation is ultra wide and analog, we need lineary performance,

yes it is FM modulation, but with multicarriers at different levels and different modulation index.

Edited by ThomasScherrer

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Thanks Thomas, also from me!

Finally my Linx BBA is on it's way :D !(for a normal price :D )

So first I like to see results from that Linx...

And be back here for more advice form you guys....

Rienk

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