I actually like your presentation. It made me aware of connector quality. From now on I will check the one I have. Thank you for taking the time to put this troubleshooting video online. 73 de Fred HB9HWF
(I realise this is along time ago now) It's possible you had the same problem I once did about 30 years ago. There are 75 ohm and there are 50 ohm BNC connectors. Though the centre pin diameters are about the same on the main shank , they look a little different - IIRC the 75 connectors have a "sharper" pin at the tip, though the nominal diameter is the same after the tapered tip. (people _think_ they are different but I have a feeling the main shaft diameter is the same - I think, anwways) Anyways, what can happen is that if you use 75 Ohm BNC males in 50 ohm BMC females, the narrower end of the tip sometimes doesn't make perfect contact especially if the female is old and the centre receptacle has been flared out through longterm usage. Many terminators from the days of late 1970s and 1980s coax ethernet used cheaper (in those days) 75 ohm plugs even if they used a 50 ohm resistor. So this problem occured more in the 80s and 90s. Now, when you test it with a ohmeter, it reads fine probing the BNC male to male directly. It ALSO tends to read fine if you fit a BNC to N or BNC to PL259 or SO239 adapter too. Why? Because when we probe the adaptor's pin, we tend to push it slightly sideways and the very slight movement transfers through to the problem BNC plug in a seesaw motion, unless the adaptor is extremely high quality. This means it reads OK at DC, because the slight sideways movement makes the circuit. However, at VLF-HF and into low VHF, there's an open circuit (in fact it's a tiny capacitance so will read high SWR at lower frequencies) . At UHF, there will be enough pF there to have relatively low reactance. So you may not notice much loss or high VSWR at 400 to 2GHz, but at HF or MF it's pretty bad. Even if all connectors are 50 ohm, you could still have an old or widened female centre receptacle. To see if that's the problem - using a good eye magnifier use a sewing needle to bend one of the leaves of the female centre receptacle in towards the centre to tighten it up - if that solves the problem you either have poor new connectors or old worn ones. They don't last forever in the lab especially if you homebrew a lot and these days everyone uses 50 ohm modules much more than they used to 30 years ago so coax connectors get a lot of wear. This can cause arcing and RF plasma in the connector with high enough power. My first clue was mysterious ozone smell coming from the BNC connector when I was doing a high power PA test into a dummy load on HF. The same cable was fine into the same load even running 1KW pulsed at 1or 2 GHz (radar testing)
I actually like your presentation. It made me aware of connector quality. From now on I will check the one I have. Thank you for taking the time to put this troubleshooting video online. 73 de Fred HB9HWF
(I realise this is along time ago now)
It's possible you had the same problem I once did about 30 years ago.
There are 75 ohm and there are 50 ohm BNC connectors. Though the centre pin diameters are about the same on the main shank , they look a little different - IIRC the 75 connectors have a "sharper" pin at the tip, though the nominal diameter is the same after the tapered tip. (people _think_ they are different but I have a feeling the main shaft diameter is the same - I think, anwways)
Anyways, what can happen is that if you use 75 Ohm BNC males in 50 ohm BMC females, the narrower end of the tip sometimes doesn't make perfect contact especially if the female is old and the centre receptacle has been flared out through longterm usage. Many terminators from the days of late 1970s and 1980s coax ethernet used cheaper (in those days) 75 ohm plugs even if they used a 50 ohm resistor. So this problem occured more in the 80s and 90s.
Now, when you test it with a ohmeter, it reads fine probing the BNC male to male directly. It ALSO tends to read fine if you fit a BNC to N or BNC to PL259 or SO239 adapter too.
Why? Because when we probe the adaptor's pin, we tend to push it slightly sideways and the very slight movement transfers through to the problem BNC plug in a seesaw motion, unless the adaptor is extremely high quality. This means it reads OK at DC, because the slight sideways movement makes the circuit.
However, at VLF-HF and into low VHF, there's an open circuit (in fact it's a tiny capacitance so will read high SWR at lower frequencies) . At UHF, there will be enough pF there to have relatively low reactance. So you may not notice much loss or high VSWR at 400 to 2GHz, but at HF or MF it's pretty bad.
Even if all connectors are 50 ohm, you could still have an old or widened female centre receptacle. To see if that's the problem - using a good eye magnifier use a sewing needle to bend one of the leaves of the female centre receptacle in towards the centre to tighten it up - if that solves the problem you either have poor new connectors or old worn ones. They don't last forever in the lab especially if you homebrew a lot and these days everyone uses 50 ohm modules much more than they used to 30 years ago so coax connectors get a lot of wear.
This can cause arcing and RF plasma in the connector with high enough power. My first clue was mysterious ozone smell coming from the BNC connector when I was doing a high power PA test into a dummy load on HF.
The same cable was fine into the same load even running 1KW pulsed at 1or 2 GHz (radar testing)