[SOLVED] HF AND V/UHF IMPEDANCES NETWORK MATCHING

[Stv]

HF AND V/UHF IMPEDANCES NETWORK MATCHING
Hi everyone

I'm new in Edaboard. Thanks for accepting me.

My question is about if it's possible (via a matching circuit) that different impedance elements on a transmitter network be well balanced with a minimum VSWR?

Circuits Case 1 (HF) and Case 2 (V/UHF) are emebedded.

I hope that my questions and drawing be so clear in order to get your help (with calculus and diagrams, please)

Thanks in advance

Stv

 

[volker@muehlhaus]

What is the purpose of your configuration, why do you use 100 Ohm cables for the 20m section in a 50 Ohm system? Just use 50 Ohm cables and you don't need matching networks.

 

[Stv]

Hi Volker,
Yours it's a logic question, of course.
A correct coaxial 50H's cable is expensive and I've found a good value for an old stock of RG62 type (@ 93H or 100H). It's strong with a good braid but with the inner "live" a bit different... That's the main reason. If you know if it's usable between 50 ohms lines with an adaptor and how, it'd be a solution. Thanks

 

[volker@muehlhaus]

You could use coax cable of ANY impedance if the cable length is a multiple of 1/2 wavlength, but that is not a solution for your wideband requirements. It would be VERY difficult to design transformers or matching networks for your targeted WIDEBAND frequency ranges, this will exceed the cost of 50 Ohm cable by a large amount.

You mention VHF/UHF in your document also, and cable loss matters at those frequencies.
RG62 is not really low loss: 10 dB loss @ 100 MHz per 100m

Example for an affordable with 50 Ohm and 5mm diameter, with approximately similar loss:
H155 would have 9.3 dB loss @ 100 MHz per 100m, cost is less than 2 EUR per meter

Of course, you can go for other 50 Ohm cables with lower loss at larger diameter.

 

[D.A.(Tony)Stewart]

Volker has already mentioned as I was going to say 500 MHz loss will be ~ 6 dB @ 500MHz /20m but negligible at 30 MHz.

The 100 ohm mismatch only adds 2 dB transmission loss peak every odd 1/4 wavelength, which is tolerable a< 30MHz at UHF would contribute to modulation noise if the BW is > a few MHz.

If it is low power 30 MHz, maybe tolerable if the cable is "free".

Baluns or transformers used to match impedances are rarely adequate more than 1 or 2 decades of BW. But you can roll your own since you seem to be on a DIY budget.

 

[BigBoss]

Have you ever checked that the cable can carry 100 W RF Power ?? It's worthy to note.

 

[Stv]

You could use coax cable of ANY impedance if the cable length is a multiple of 1/2 wavlength, but that is not a solution for your wideband requirements. It would be VERY difficult to design transformers or matching networks for your targeted WIDEBAND frequency ranges, this will exceed the cost of 50 Ohm cable by a large amount.

You mention VHF/UHF in your document also, and cable loss matters at those frequencies.
RG62 is not really low loss: 10 dB loss @ 100 MHz per 100m

Example for an affordable with 50 Ohm and 5mm diameter, with approximately similar loss:
H155 would have 9.3 dB loss @ 100 MHz per 100m, cost is less than 2 EUR per meter

Of course, you can go for other 50 Ohm cables with lower loss at larger diameter.

 

[Stv]

Hi Volker.
Thank you so much for your clear an convincent answers to my question.
Of course, I'll "Invest" a little more buying 50H coaxial wire in order to avoid mismatches and problems on both HF and V/UHF networks.
Appreciate!!!
Stv

 

[Stv]

Volker has already mentioned as I was going to say 500 MHz loss will be ~ 6 dB @ 500MHz /20m but negligible at 30 MHz.

The 100 ohm mismatch only adds 2 dB transmission loss peak every odd 1/4 wavelength, which is tolerable a< 30MHz at UHF would contribute to modulation noise if the BW is > a few MHz.

If it is low power 30 MHz, maybe tolerable if the cable is "free".

Baluns or transformers used to match impedances are rarely adequate more than 1 or 2 decades of BW. But you can roll your own since you seem to be on a DIY budget.

Hi Tony,
Thanks a lot for your information. Finally I've opted for buying 50H coaxial wire. I suppose it'll be for less problems
Appreciate
Stv

 

[Stv]

Have you ever checked that the cable can carry 100 W RF Power ?? It's worthy to note.

Hi

Have you ever checked that the cable can carry 100 W RF Power ?? It's worthy to note.

Hi Big Boss (and Volker and Tony),
As I've answered previously to Volker and Tony, finally I'll buy the right 50H coaxial cable. Some money more expensive than 93H one, but for sure less problems when some mismatch (or extra power) occurs.
Truly grateful!!!!
Stv