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Ran into some unexpected problems when connecting to the BNC output of the V2 sBitx and using a (cheap) adapter to SO239 -- SWR was infinite at times!? ?Careful examination seemed to indicate not just one, but two problems
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1) cheap adapter didn't have nice "fingers" to grasp the center prong of a PL259 -- you could feel that it wasn't being grasped as you slid it in, when I did it carefully.? ?Work with a pointy screwdriver to bend the fingers more inward helped somewhat
2) the adapter tended to have problems when "rotated" also -- looked like the connection between BNC and SO239 side wasn't perfect.? ?
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Example of the type problem #1
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These two problems together made this difficult at times.? ?Better SO239 have better-grasping fingers, often with a bit of space around them so a curve or something can be built into them (I think).? ?
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I ended up taking a spare coax jumper and crimping a nice BNC male connector on one end to make a permanent adapter cable for this unit, and that worked quite well once constructed.
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Gordon KX4Z
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Good point Gordon.
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Many years of industry work puts BNC as handy and convenient but potentially?
susceptible to various failures and adapters are a sore point.
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For one high use project and my own use I have a bunch of BNC male to SO239
(female end of PL259)?3ft cables (using LMR240).? Puts less strain on the
unit/radio and assures a good connection.?
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Also testing on a an Agilent VNA they were much more consistent
than random adapters.
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--
Allison
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Please use the forum, offline and private will go to bit bucket.
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Can you give us a link to the cable-SO239 that you prefer???
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Thanks!
Gordon KX4Z
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I always use BNC to UHF and SMA to BNC cables. I think that the smaller connector hardware is not designed to handle the load of larger cables. In particular I'm cautious with circuit board mounted connectors that have no solid mechanical connection to a case.
--
73
??? Bob? KD8CGH
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Another issue to beware of:? BNC (and N) connectors have 50 ohm and 75 ohm variation.?
The shell dimensions are the same, but the 75 ohm center pin is thinner.?
To help distinguish them in the dark, the 75 ohm center pin SHOULD be pointed, while the 50 ohm pin SHOULD have a blunt rounded end.?
You need to measure the pin diameter to truly know.?
A 50 ohm plug will ruin a 75 ohm receptacle, while a 75 ohm plug will make intermittent contact with a 50 ohm receptacle.?
 ? ?
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50 or 75 ohm variant BNC connectors my be used on the adapters you buy from ebay, AliExpress or Temu.
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N0YWB:
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Are you very sure there is a standard for the difference in pin diameter between the 50 and 75 ohm versions?
If you notice, there can be a difference in the dielectric as part of their efforts to hit 75 ohms, while the 50 ohm seems the one that works to 4GHz.? ?I examined multiple web sites and manufacturers all said their products were interchangeable mechanically between 50 and 75, but they tended NOT to have the technical spec on the pin diameter.
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I found ONE manufacturer who did have very detailed pin specifications -- and there is no mention that it differs between 50 and 75 ohm versions:? Look at dimensions N and D on page 68: ?
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There might be variation between manufacturers, perhaps more so than between different impedances, as the impedance change seems to be handled by the adjustments in dielectric.
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Perhaps you have found dimensions that show a difference?
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Gordon KX4Z
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May be SO239 connectors on the sBitx would solve the issue? I would definitely buy the sBitx version with PL connector if it existed. I already had problems with adapters and it was painful until finding the issue.
- Rafael
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On 1/21/25 4:50 PM, Gordon Gibby KX4Z via groups.io wrote: N0YWB:
Are you very sure there is a standard for the difference in pin diameter between the 50 and 75 ohm versions?
If you notice, there can be a difference in the dielectric as part of their efforts to hit 75 ohms, while the 50 ohm seems the one that works to 4GHz.? ?I examined multiple web sites and manufacturers all said their products were interchangeable mechanically between 50 and 75, but they tended NOT to have the technical spec on the pin diameter.
I found ONE manufacturer who did have very detailed pin specifications -- and there is no mention that it differs between 50 and 75 ohm versions:? Look at dimensions N and D on page 68:
There might be variation between manufacturers, perhaps more so than between different impedances, as the impedance change seems to be handled by the adjustments in dielectric.
Perhaps you have found dimensions that show a difference?
Gordon KX4Z
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Rafael,
I have found several over the years where the center pin was not wide enough to make a proper connection. This is regards to BNC connectors and their adapters.giving alot of intermittant problems. Most i have found was involving the teflon filled connectors. Mostly BNC connections and fittings on my own end ws the culprits.
You can look at them and if they have the dark hard body filling,which is?molded phenolic insulator they seem to consistantly have good connections. versus the ones with the plastic teflon filling, with my own experience..The larger wire cables seem to have a better success in preventing center pin twist too.? Just my take of it all.
?I throw the ones away with the plastic teflon so239 fittings.teflon fillings? ,likewise same for pl259 connectors. Hence the teflon disasters like to twist at the center conductor and if using smaller diameter feedline the pin twists, breaks the center conductor but still maintains connection to drive you nuts trying to find an intemittant. If in doubt i throw these teflon? out.?
As for BNC for rigs, nice for test equipment or micro watt powered rigs,but i prefer the old fashioned pl259 to so239 connection. Its the first piece that gets changed when buying a used or new radio. all my ubitx units have so239 connectors on the cabinets. ripped out the BNC. just my own preference.
73 David ac9xh
On Tuesday, January 21, 2025 at 01:00:31 PM EST, Rafael Diniz <rafael@...> wrote:
May be SO239 connectors on the sBitx would solve the issue? I would
definitely buy the sBitx version with PL connector if it existed. I
already had problems with adapters and it was painful until finding the
issue.
- Rafael
On 1/21/25 4:50 PM, Gordon Gibby KX4Z via groups.io wrote:
> N0YWB:
> Are you very sure there is a standard for the difference in pin
> diameter between the 50 and 75 ohm versions?
> If you notice, there can be a difference in the dielectric as part of
> their efforts to hit 75 ohms, while the 50 ohm seems the one that
> works to 4GHz.? ?I examined multiple web sites and manufacturers all
> said their products were interchangeable mechanically between 50 and
> 75, but they tended NOT to have the technical spec on the pin diameter.
> I found ONE manufacturer who did have very detailed pin specifications
> -- and there is no mention that it differs between 50 and 75 ohm
> versions:? Look at dimensions N and D on page 68:
>
> There might be variation between manufacturers, perhaps more so than
> between different impedances, as the impedance change seems to be
> handled by the adjustments in dielectric.
> Perhaps you have found dimensions that show a difference?
> Gordon KX4Z
>
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The characteristic impedance of any coaxial transmission line is highly dependent on the "ratio" of the diameter of the shielding conductor to the diameter of the inner conductor.
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Since the outer part of a BNC connector has fixed dimensions, it is only possible to change the characteristic impedance by varying the thickness of the inner conductor.
Dielectric properties ( the relative dielectric constant & the relative permeability ) matter more for the Velocity factor than for the impedance.
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/ Niels - OZ9NS
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Niels ,
good physics, . this is why i dont use BNC connectors.
73 David ac9xh
On Wednesday, January 22, 2025 at 09:08:33 PM EST, Smeden <niels@...> wrote:
The characteristic impedance of any coaxial transmission line is highly dependent on the "ratio" of the diameter of the shielding conductor to the diameter of the inner conductor.
?
Since the outer part of a BNC connector has fixed dimensions, it is only possible to change the characteristic impedance by varying the thickness of the inner conductor.
Dielectric properties ( the relative dielectric constant & the relative permeability ) matter more for the Velocity factor than for the impedance.
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/ Niels - OZ9NS
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Niels,
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I used to calculate the velocity factor dealing with my transmission lines when i was young and working in an engineering enviroment, .
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I gave that up for more general calcs for my lines and antennas. In fact i only use one cable for all my equipment. rg-6u quad shield.
I cut the factory fitting off and put on a twist on f fitting and then f to pl259 adapter.I spend more for the good fittings over the junk. amphenol has great products in my own opinion.
I use this setup from 160m up thru 1ghz for my equipment. for the frequencies above 2 meters i use a rtl-sdr setup with the rg-6u quad shield cable.
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I really dont worry about 50 or 75 ohm my cable is 75 ohm impedance. i use it on all applications with the pl259/so239
all equipment containing BNC has the BNC removed .I use it on all my ubitxs, and other QRP transceivers. only thing ive had problems with is the doggone BNC fittings. So as a laxy ham, i rip em out. they are only used on my scopes, signal generators and such.?
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73
David
ac9xh
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Formulae for coaxial cable from Pasternak:
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On Jan 22, 2025, at 21:08, Smeden via groups.io <niels@...> wrote:
? The characteristic impedance of any coaxial transmission line is highly dependent on the "ratio" of the diameter of the shielding conductor to the diameter of the inner conductor.
?
Since the outer part of a BNC connector has fixed dimensions, it is only possible to change the characteristic impedance by varying the thickness of the inner conductor.
Dielectric properties ( the relative dielectric constant & the relative permeability ) matter more for the Velocity factor than for the impedance.
?
/ Niels - OZ9NS
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Of course, the IEC 1 69–8 specification costs money to buy.?
I was surprised in most drawings to see limited information about the male pin. ?Apparently the specification requires that any type be intermateable with others. ?
there more information is given about the potential for male pin size differences, as follows:
“See interface dimensions shown on next page. Applicable to Females only: oversize pin .055 inch (1.4 mm) max. dia.,.080 inch (2.03 mm) deep; insertion force 2 lbs. (8.9 N) max. with .054 inch (1.37 mm) min. dia. pin; withdrawal force 2.00 oz (.556 N) min. with .052 inch (1.32 mm) max. dia. pin.”
but still, this isn’t the real standard. This is just one manufacturers presentation. It suggest pins anywhere from .052 inch to . 055 inch.I don’t have the time or money to purchase the real standard.
Gordon kx4z?
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On Jan 23, 2025, at 02:29, Gordon Gibby KX4Z via groups.io <docvacuumtubes@...> wrote:
? Formulae for coaxial cable from Pasternak:
Gordon kx4z? On Jan 22, 2025, at 21:08, Smeden via groups.io <niels@...> wrote:
? The characteristic impedance of any coaxial transmission line is highly dependent on the "ratio" of the diameter of the shielding conductor to the diameter of the inner conductor.
?
Since the outer part of a BNC connector has fixed dimensions, it is only possible to change the characteristic impedance by varying the thickness of the inner conductor.
Dielectric properties ( the relative dielectric constant & the relative permeability ) matter more for the Velocity factor than for the impedance.
?
/ Niels - OZ9NS
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I was wrong in claiming that the outer conductor of the male BNC connector always has the same diameter for the 2 types. :o)
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For the 75ohm version, the diameter of both inner and outer conductor are different in the male BNC !
Physical compatibility is somewhat ensured since the outer conductor material is made thinner.
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The difference in the center-pin is ~0,3mm, but they should be compatible. At least a 75ohm BNC Male -> 50ohm BNC Female.
However, I wouldn't recommend you use a 50ohm BNC male -> 75ohm BNC Female.
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This is possibly why some 75ohm "quality" BNC connectors are also made with a 1.6mm center pin. ( Although this deviates from the standard. )
example:
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The full explanation and some pictures can be seen here:
-----------
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That said. You don't have to look far on ebay/aliexpress to find "non-standard" 75ohm hybrid versions ( Lets call them Frankenstein-BNC's ), where the difference is only a thinner inner conductor. :(
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Lets just stay away from these cheap unbranded versions. :D
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This tech note is consistent with my understanding about mechanical mating capability (male/female), dielectric differences and center pin diameter difference in the coax crimp area.?
you can use the embedded link in the note to bring-up pictures.
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Up to the mid 1970s the center pin diameter was different.
IEC 169-8 in 1978 defined interchangeability.
The diameter of the center pin in current production BNC plugs is 1.32-1.37mm (0.052-0.054”),
the same for both 75 ohm (MIL-STD-348B 9Feb2009), and 50 ohm (MIL-STD-348 20 April 1988).?
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I became painfully aware of the issue when I bought a compression N plug for LMR-400 at the local parts store before Field Day.?
After set-up, I measured bad SWR on my 75 meter station.?
Sweeping peaks and nulls with my antenna analyzer, and knowing the VF of LMR-400 indicated my discontinuity was at the new N connector near the antenna.
Prying on the connection suddenly made the SWR good.??
Evidently that connector had been in the store inventory a long time.?
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Thanks, Gary. The difference in the pins is basically only in the CRIMP area. ? The specification gives only 3 thousandths of an inch variation in the pin ?mating area. ?That is just about or slightly greater than the thickness of a piece of paper. ? ?I don’t think that’s going to make much difference and that would indicate that mating is safe either way.
I’m certain that there could be manufacturers producing products that do not follow the standard however
Gordon kx4z?
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Show quoted text
On Jan 23, 2025, at 11:31, N0YWB via groups.io <n0ywb1@...> wrote:
?
Up to the mid 1970s the center pin diameter was different.
IEC 169-8 in 1978 defined interchangeability.
The diameter of the center pin in current production BNC plugs is 1.32-1.37mm (0.052-0.054”),
the same for both 75 ohm (MIL-STD-348B 9Feb2009), and 50 ohm (MIL-STD-348 20 April 1988).?
?
I became painfully aware of the issue when I bought a compression N plug for LMR-400 at the local parts store before Field Day.?
After set-up, I measured bad SWR on my 75 meter station.?
Sweeping peaks and nulls with my antenna analyzer, and knowing the VF of LMR-400 indicated my discontinuity was at the new N connector near the antenna.
Prying on the connection suddenly made the SWR good.??
Evidently that connector had been in the store inventory a long time.?
?
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Thanks N0ywb! ?That historical insight is fascinating
toggle quoted message
Show quoted text
On Jan 23, 2025, at 11:31, N0YWB via groups.io <n0ywb1@...> wrote:
?
Up to the mid 1970s the center pin diameter was different.
IEC 169-8 in 1978 defined interchangeability.
The diameter of the center pin in current production BNC plugs is 1.32-1.37mm (0.052-0.054”),
the same for both 75 ohm (MIL-STD-348B 9Feb2009), and 50 ohm (MIL-STD-348 20 April 1988).?
?
I became painfully aware of the issue when I bought a compression N plug for LMR-400 at the local parts store before Field Day.?
After set-up, I measured bad SWR on my 75 meter station.?
Sweeping peaks and nulls with my antenna analyzer, and knowing the VF of LMR-400 indicated my discontinuity was at the new N connector near the antenna.
Prying on the connection suddenly made the SWR good.??
Evidently that connector had been in the store inventory a long time.?
?
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Niels,
I agree fully. Unfortunately we have to spend more money but the old saying is "you get what you spend" HI HI
I found out early in ham journey that alot of companies ,even reputable ones , will sell a junk product just to make a sale. I refuse to buy the junk fittings. cable ends, chassis connections, and adapters.
Great post Niels!!!!!!
73 David ac9xh
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Bob Benedict, KD8CGH
N0YWB
Smeden