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Author Topic: N-type vs. SO-239 NO FIGHTING PLEASE! :-)  (Read 8459 times)
FREEMA22
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« on: May 23, 2010, 08:12:34 AM »

I am not looking to start a fight or debate, I just have a legitimate questions about these 2 types of connectors. I am considering putting up a more substantial antenna this summer, and they come in N-type or SO-239 flavors. From everything that I have read, it seems that the N-type is the best connector for VHF and UHF bands (HF is not a concern for me). BUT, my radio has a 239 connector on the back. Is there a point (other than weatherproofness) to use an N-type connector at the antenna if I am going to have reduced performance at the back of the rig itself? Maybe I missed something along the way.

Thanks for the input,
Mike
KC9JBY
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KE3WD
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« Reply #1 on: May 23, 2010, 08:15:39 AM »

So, use the N connectors everywhere else you have to use a connect and just "suffer" the slight degradation of signal that the one SO connect imparts at the back of the rig. 

Don't sweat the small stuff.


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N3OX
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« Reply #2 on: May 23, 2010, 09:04:04 AM »

I agree with "use N connectors everywhere else and don't worry about the back of the rig."

Either that or don't worry about it.

The reason why you're worried about starting a debate is because hams like to argue all day over whether or not a PL-259/SO-239 pair is going to cause some sort of VHF/UHF disaster, but they don't like to do a lot of research and put numbers to things.

The only measured response graph I've been able to find so far is a ham that actually measured the loss of two PL-259 to type N adapters joined with a SO-239 barrel connector.  

http://www.qsl.net/vk3jeg/pl259tst.html

That total thing plus cable mismatch loss in his test setup had a loss of 1.0dB at 432MHz.   That experiment seems to get quoted a bit  as proof of the disastrous results of using PL-259/SO-239 at UHF.  But he admitted the SO-239 barrel was of very poor quality, and I wonder if the N/PL-259  adapters were any better?    I think what he measured could probably be way worse than a pair of high quality PL-259 mating with the SO-239's on your radio and antenna.  Some cheap adapters have very questionable mechanical construction inside that would be hugely lossier than direct coax termination inside a decent connector.  The total length of stuff outside the coax is much longer in an adapter/adapter/adapter lashup , which affects the "impedance bump," and a PL-259 plug is very directly connected to the coax with short solid connections in a way that the innards of cheap adapters may not be.    So I'm just not sure I believe VK3JEG really did the definitive experiment on PL-259/SO-239's.  He measured three adapters in series, not a mating ordinary connector pair.  

That said, I use type N connectors here for my VHF/UHF antennas.  I have some reasons, listed in order from most to least important:

1) I had a dozen nice type N bulkheads so that was a good thing to mount through my grounding plate entrance panel
2) I have a really nice Bird coax switch with type N connectors
3) They're weatherproof.
4) They're low loss and constant impedance.

Go ahead and get the type N on the antenna..  Why not?  But you're never going to be able to tell the difference unless you're setting up a moonbounce setup for 432MHz and even then you might not.  K2RIW did a little testing too:

http://www.vhfsouth.org/tutorials/50-Ohms.htm

The fact is that the type N is really a superior VHF/UHF connector, but it's not so superior to justify the level of freaking out some hams do about it.  

73
Dan
« Last Edit: May 23, 2010, 09:07:49 AM by Dan » Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
K2DC
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« Reply #3 on: May 23, 2010, 10:48:43 AM »

Mike,

  There's no question that Type N connectors will outperform UHF connectors at VHF and UHF.  But unless you're prepared to open up the radio and replace the SO-239 with a Type N, don't sweat the single connection.   Just use a UHF-Type N adapter on the back of the rig and go with Type N connectors everywhere else.

I looked at the data that Dan, N3OX pointed to.  My first reaction was to question the data because the amount of noise in the plots at those levels is usually indicative of a relatively low quality measurement.  At the same time, I can't argue too hard with the results.  I've measured the insertion loss of Type N connectors many times using a similar method at around 0.016 dB at 1.3 GHz - not far from the data presented.

A UHF rig with an SO-239 output connector certainly isn't the best design, but it is what it is and unless you're prepared to modify the radio.  I use Type N everywhere except the back of the rig even at HF just because they are a much more robust design both electrically and mechanically.

GL & 73,

Don, K2DC

 
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KB1LKR
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« Reply #4 on: May 23, 2010, 11:19:44 AM »

Use an N connector at the antenna (since you have a choice) and the existing UHF (PL-259/SO-239 pair) at the radio. Either terminate your coax w/ one of each type (if you already have a coax w/ two of the same type connector just re-terminate one end) or use a female N to male (PL-259) UHF adapter at the radio w/ an N by N coax.
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N3OX
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« Reply #5 on: May 23, 2010, 11:25:02 AM »

At the same time, I can't argue too hard with the results.  I've measured the insertion loss of Type N connectors many times using a similar method at around 0.016 dB at 1.3 GHz - not far from the data presented.

Sure ... what I want to know is what the loss is at 144 or 432MHz  of a single decent quality PL-259, directly installed on a cable mating with the rig  or antenna SO-239 (also presumed to be decent quality).  K2RIW's test  from the second link is kind of illuminating, regarding running 700W through UHF connectors for 10 minutes... it's not a high precision measurement, but let's ponder it:

Quote from: K2RIW
After 10 minutes of 700 watts throughput power the UHF connectors were mildly warm. If I estimate that "mildly warm" represents a dissipation of 3 watts out of 700 watts, that's an estimated insertion loss of 0.019 dB for the pair of connectors.

If 1 paired UHF connector had 0.5dB loss at 432MHz, it would dissipate 76W of the applied 700W.   Think about soldering a PL-259 onto a cable.  If you put 76W into a PL-259/SO-239 pair for 10 minutes, you'll get a second degree burn if you grab it.  Even if it's well heatsinked to an amplifier chassis, it's very likely going to be more than "slightly warm."    If most of the dissipation is the center pin connection, it would solder itself to the SO-239 just like you can do in a few seconds with a 76W soldering iron.

Now, it could be that you are getting additional line loss from the mismatch caused by the "impedance bump."  That's the other thing people worry about, and since it's spread out in the coax it could be less obvious.  But we can look at that too.  VK1OD's transmission line calculator has an entry for 35 ohm coax, UT-141C-35.  

http://vk1od.net/calc/tl/tllc

We can use that as an impedance transformer to figure out how much a 35 ohm impedance bump (the oft-quoted PL-259 impedance) matters at 432MHz.  Let's put in a whole foot.

That transforms 50+j0 to 33-j12.  Let's see what that does to the rest of the run.  In a VNA measurement, say we have 1 foot of RG-58.  The matched line loss in 1 foot of RG-58 is 0.104dB according to Owen's calculator.  The loss when mismatched with 33-j12 is 0.128dB, a difference of 0.024dB.  So that's not where our power is going.

In an actual installation, maybe we have 50 feet of LMR400.   If we put our foot-long "impedance bump" right at the antenna, that results in 0.13dB additional line loss due to the mismatch and a 1.45:1 SWR back at the shack.  Not really a big deal.    And a PL-259 isn't a foot long, of course :-)   An inch of 35 ohm "bump" leads to a 1.2:1 SWR and about 0.045dB additional loss in 50 feet of LMR-400.

Quote
Just use a UHF-Type N adapter on the back of the rig and go with Type N connectors everywhere else.

I don't know if I'd risk the adapter, honestly.  VK3JEG presumably measured something. Maybe it was a mismatch loss between a 50 ohm source and slightly different impedance  (something that does NOT actually apply to a radio that will deliver full power into a range of impedances ) but I thought a network analyzer should account for that.  I can't see how you get a whole dB of loss from additional loss in the coax due to mismatch, and I can't see how you get it from the contact setup of a PL-259 ('cause they'd melt in K2RIW's test), so if that 1dB is measuring something, it may be measuring junk adapters.

So if there's something to VK3JEG's measurement to warn one off PL-259's, I'd worry most of all about getting a substandard UHF<->N adapter with a poor internal design.   That's probably not an adapter that's easy to get in "professional" quality like a BNC to N might be.   I've also heard Owen VK1OD warn people that PL-259's really have to be done up tight to make good electrical contact.

What I do here from the output of my FT-857D, and what I'd probably recommend to others who want to make a UHF to N transition is to get a high quality PL-259 and solder it onto one end of a short piece of good coax (or a long one, if you just want to do a run with no joints), and install a N connector on the other end.    And Mike: sorry for the long posts on a simple topic, but like you know, this is something that polarizes a lot of hams and it's good to figure out what's fact and legitimate concern and what's folklore and unfounded worry.  

I'd really like to hear from someone who melted a PL-259 to SO-239 junction (or maybe blew up an adapter) with a high power UHF amplifier.  Getting up near a kilowatt tends to expose excessive loss problems pretty easily Grin
« Last Edit: May 23, 2010, 11:28:18 AM by Dan » Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
AA4PB
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« Reply #6 on: May 23, 2010, 11:40:52 AM »

Use a type N at the antenna, since you have the option. Use a PL259 at the radio since modifying the radio is not a reasonable option.
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N3OX
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« Reply #7 on: May 23, 2010, 12:59:34 PM »

Then, he says "The final sets of comparison data is probably the most interesting to the VHF/UHF amateur being Forward Transmission or Insertion Loss known as S21 Parameter." The usual meaning of Transmission Loss is Pin/Pout. That is not the same as the definition of S21, and the difference is significant.

Thanks Owen.  I guess some VNA's can be asked to calculate the transmission loss but that wasn't done...  I didn't do a careful read of that page.

So, we're back to the situation where I've never seen an actual measurement of a PL-259 connector on VHF or UHF... just people fretting about impedance bumps and implausible loss per connector.  I wouldn't mind seeing a VHF/UHF reproduction of something like this photo by someone with a VNA who knows how to use it :

http://n3ox.net/files/Adapters.jpg

That was actually done on 160m in response to someone worrying about the RCA connectors on their preamp causing losses.  I don't even have a decent VHF/UHF wattmeter or slug.    

73
Dan
« Last Edit: May 23, 2010, 01:19:02 PM by Dan » Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
K0IZ
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« Reply #8 on: May 23, 2010, 05:19:59 PM »

There are some things in life that are just not worthy of much time and effort.  UHF vs N comes real close.   SInce the cost of an N is not much more than an UHF, and it IS better, just do it.  Then spend your time worrying about something else.
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W8JI
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« Reply #9 on: May 24, 2010, 12:32:17 AM »

...

So, we're back to the situation where I've never seen an actual measurement of a PL-259 connector on VHF or UHF... just people fretting about impedance bumps and implausible loss per connector.  I wouldn't mind seeing a VHF/UHF reproduction of something like this photo by someone with a VNA who knows how to use it :


I have seen estimates that the internals of a mated UHF pair of cable connectors has a geometry that suggests Zo is probably around 35 ohms.

If we consider a single connector pair, the effect of say 20mm length (assume 15° at 440MHz) of lossless 35ohm line with a 50+j0 load, the ReturnLoss is about 12dB (InsertionVSWR=1.7). MismatchLoss=0.28dB, but the figure is probably not directly applicable to most transmitters, it depends what power the transmitter delivers to the new load, including the effects of retuning where that is possible. (No mirrors needed!)
Owen

The impedance is down around 35-40 ohms, and the length of the bump is the length of the female connector's wide conducor area, about 1/2 inch or so. The male is no issue at all if installed correctly.

Some barrel connectors are a big problem, especially if long.

When I measure loss in connectors I have to use heating to estimate loss. The loss is too low to accurately measure with a network analyzer. The impedance bump is measurable, but that isn't acttual loss in the connector and it isn't signicant except when the female connector has a long area of mismatch.

By the way if you drill and fill the dielectric with holes around the large area of the female center pin, the bump goes away.

I use all UHF connectors here at HF up through six meters because they are more common, easier to install, and handle much more current and voltage. At UHF I use type-N for low power and type C, DIN, or EIA flanges for high power.
« Last Edit: May 24, 2010, 12:35:10 AM by Tom Rauch » Logged
KE3WD
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« Reply #10 on: May 24, 2010, 05:06:48 AM »

Lotta typin' goin' on over what amounts to about 1 dB...
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N3OX
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« Reply #11 on: May 24, 2010, 07:36:28 AM »

Lotta typin' goin' on over what amounts to about 1 dB...

For some people who do VHF/UHF, 1dB actually matters, and it's worthwhile for them to know  if a UHF connector will add 0.5dB (no) or 0.05dB (maybe) total system loss.

And for the rest of us, who might not care about 1dB, the 0.5dB/connector myth starts to worry people when you need to use more than a pair of connectors. 



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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
FREEMA22
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« Reply #12 on: May 24, 2010, 11:09:59 AM »

Guys, thanks for all of the responses. Although I agree that there will be some loss using a PL-239, I live in Metro Chicago, and there are LOTS of repeater sites that I can readily access on just a portable. Because of the density of sites, it may not make that big of a difference. Do you agree?

Mike F
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N3OX
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« Reply #13 on: May 24, 2010, 11:36:39 AM »

Although I agree that there will be some loss using a PL-239, I live in Metro Chicago, and there are LOTS of repeater sites that I can readily access on just a portable. Because of the density of sites, it may not make that big of a difference. Do you agree?

Absolutely, you have nothing to worry about, PL-259 or not.  Even if there were a dB or two loss, which there certainly won't be, you probably wouldn't notice it on FM at all, and certainly not on local repeaters.  (Hence KE3WD's comments that we're talking a lot about not much  Grin )  There's not a whole lot of copy difference between "very weak" and "very, very, very weak" FM signals ...

So practically speaking there's no point in even discussing connector losses for your particular situation: pick whichever ones are most convenient for your installation, like if you already have a PL-259 antenna and a run of decent coax, you might want to get the new antenna with a SO-239 just so you don't have to re-do a connector.  

I think even the guys who like weak signal SSB and might care about 1dB loss would never actually see that with a PL-259 instead of an N connector: both connector losses are tiny, possibly completely negligible up through 70cm.  If the weak signal SSB guys won't notice, you'll never notice, even on long haul weak FM simplex.

The reason why I went into detail and wanted to discuss it is because some of the weak signal SSB guys have a lot of worry and advice about connector losses that is unfounded even for them, not just in the FM context.  For your purposes, and probably for theirs, connector losses might as well be zero dB.

73
Dan
« Last Edit: May 24, 2010, 11:40:41 AM by Dan » Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
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