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40M HAM rig with internal frequencies of 3MHz and 10MHz

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obrien135

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When building a 40M HAM rig with internal frequencies of 3MHz and 10MHz, what kind of cable should I use to connect the oscillator circuit boards to the main board (with the IF amps and mixers) and the output to the chassis mount connector and such? I've seen a type of small coax that isi used to connect signals between bpards and even across tha same board, but I don't know what to call it by name.

George

Added after 1 hours 12 minutes:

This is me again. Maybe it's shielded twisted pair I'm thinking of. Would that work?
 

Re: cable question

For joining RF circuits, I would use a coax cable as suggested above.
But make sure of the correct impedance and match it to the circuits involved. Try searching wikipedia for co-axial cable. there you will find the full range of RG cables, diameters and impedances. I would use RG58U for 50Ω circuits, or RG174 / RG178 if losses are not important. RG179 are good for 75Ω circuits too.
 

Re: cable question 3MHz - 10MHz

If I use RG-174 and the impedance isn't 50 ohms, would that be a problem? The impedance is matched between source and load, but for the transmission line I was using twisted pair and to be honest, I was ignorant of it's impedance. Not all of the sources and loads are 50 ohms. RG-174 is 50 ohm cable right?
 

cable question 3MHz - 10MHz

Hi,
Yes, its a 50Ohm & Twisted pair(Wire Wrap) is a ca. 100Ohm cable.
If you did ignored the higher impedance of your twistedpairs, maybe it will be less problematic with a 50Ohm coaxial, even if its not properly matched/terminated...
K.
 

Re: cable question 3MHz - 10MHz

I noticed on another chart of specs for coax cable that the RG-174 cable has a maximum frequency for 100% skin depth for solid conductor copper of 107kHz. Am I right to assume that 100% skin depth is not necessarily a requirement and that the cable will work alright at 10MHz? None of the other types of cables had a rating for that spec as high as 3MHz either. Does that spec matter that much, and if so how can I find some cable with a high enough rating? My two oscillators are 3MHz and 10MHz.
 

cable question 3MHz - 10MHz

Hi,
Dont worry! :)
You can use this cable up to such 100MHz too, so is 10 MHz really absolute not a problem...
With the cited Skin depth of 107KHz is some thing surly wrong!
**broken link removed**
K.
 

Re: cable question 3MHz - 10MHz

If I was to terminate the oscillator boards with 50 ohms, and change the transformer turns ratios on the receiving board, would I be OK to terminate the receiving board with 50 ohm resisters also, on the transformer primaries, or would that cause the load current to double?
 

cable question 3MHz - 10MHz

Hi,
do you mean a serial termination/or output impedance of oscillator as 50 Ohm realized and feeded with a coax to RX and on this point is terminated with 50 Ohm?
These is for me a 50 Ohm source, and is only one time terminated (but makes a half of signal amplitude).
Double terminating is if your system has two loads/coaxial cables; where both are 50 Ohm terminated, also the residual load is really a 25 Ohm equivalent... These can have same amplitude as by one time termination_if the source can drive with double power.
K.
 

Re: cable question 3MHz - 10MHz

I probably had the wrong idea, but I have a 2700 ohm output impedance on the oscillator (Zo from output to ground looking back into the output). And the coax is 50 ohms.. And the relected impedance seen at the primary of the transformer which is on the receiving end is 50 ohms. I guess, based on what you are saying, I wouldn't have to put a 50 ohm resister on the transformer primary, because that would make the input impedance of the receiving circuit 25 ohms, which I don't want. Is that correct?
 

hi sir.. even i want to design a ham radio with suitable range.. actually i have no idea about the range and the components required. so can u help me with that..pls
 

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