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#1 Riktar

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Posted 04 April 2020 - 07:43 AM

Both of my "commercial"  premade antenna cables (LMR400 - 90ft and 15ft) show a reflected power reading of 0.23 and 0.05 respectively on my Nissei RS-50 meter. The forward power is 24 watts and the swr is 1.15 between the 2.

 

I tried my hand at crimping a PL-259 connector on another cable to make a "custom" length. And since I am still waiting on the stripping tool for this I went online and used the example(s) of a box knife to prep the cable. What a pain that is. I hope the stripping tool gets here soon!

 

Anyway, after doing this and hooking up the meter I am show a minor deviation on the forward power but the reflected power has jumped to 1.68. My SWR has also increased to 1.56.

 

While connector installation looks proper on the cable I am wondering why the increase in reflected power? Could I have done a poor job on soldering the tip of the connector to finalize the connection to the center conductor? 


The more I know, the less I understand
All the things I thought I figured out, I have to learn again. - Don Henley


#2 berkinet

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Posted 04 April 2020 - 07:54 AM

Was the original connector also a PL–259?

Everything we hear is an opinion, not a fact. Everything we see is a perspective, not the truth.

-- Marcus Aurelius


#3 Riktar

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Posted 04 April 2020 - 08:15 AM

In a manner of speaking. I suppose I should elaborate:

 

Both of the commercially made cables are MPD Digital cables that have PL-259 connectors on both ends. The cable I am modifying is a 100 foot LMR400 cable with male N connectors on both ends. Aside from shortening the cable to 35 feet for a better fit, I wanted to install the PL-259 connector to avoid having to use an adapter on my Kenwood 8180 which utilizes the PL-259 connector for cable attachment. The antenna I wanted to try and use has a female N connector so I thought adding the PL-259 connector on the LMR400 would allow me to avoid having to use adapters to connect the antenna to the radio. 


The more I know, the less I understand
All the things I thought I figured out, I have to learn again. - Don Henley


#4 Riktar

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Posted 04 April 2020 - 08:17 AM

Sorry for all the edits to the above post.


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All the things I thought I figured out, I have to learn again. - Don Henley


#5 WRAK968

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Posted 04 April 2020 - 09:39 AM

You likely would have done better using a N female to PL259, MPD digital cables basically have a lifetime guarantee, but if you cut them you lose that :(

LMR400 also crimps a bit differently. You need to have the proper connectors and tools to make sure the crimp is correct with as little loss as possible. My experience is that your better off with soldier/crimp combinations when it comes to LMR cables. You have to make sure the cable is cut cleanly (Using a pair of shears is not advised) and accurately (1/16" of an inch off with your shielding can cause a lot of issues with reflected power) A lot of people will claim the loss is from the PL259 connection added in, but personally I haven't seen much effect unless you have multiple PL259 connectors in a long run of coax, and even then, I think the length of coax has more to do with loss than the connectors do.

Lastly, its very difficult to get a perfect 1:1 in SWR and 0 reflected power. II tell people that if they are less than 1.3:1 SWR they shouldn't continue tweaking their system as its easy to lose ground just as you have.


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#6 Riktar

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Posted 04 April 2020 - 12:49 PM

The solder/crimp terminals (and the crimp tool) I have are for LMR400.

 

And, well, nuts on pooching the lifetime warranty. Then again, I mis-measured terribly and 100 feet was way more than I needed so I figured I would cut off the excess and experimaent with the shorter 35 foot long piece.

 

Once I get the stripping/prep cutter tool I will give this another go on the "short" section. Hey, at the end of the day there will be a value (to me anyway) in learning about this process.

 

For now my big concern is the increase in reflected power. Could a reading as high as mine cause damage to the radio?


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All the things I thought I figured out, I have to learn again. - Don Henley


#7 Riktar

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Posted 04 April 2020 - 01:13 PM

Just tried another crimp. Pretinned the end of the conducter before putting the crimp/solder on this time. MUCH better results. 

 

I am comparing my 35 foot "practice" piece to a 90 foot premade MPD Digital LMR400 with PL-259 connectors that is also a bit long for what I need but anyway....

 

Now my reflected power is more in line. The premade piece is showing 0.53 with and SWR reading of 1.45 and my practice piece is showing 0.48 and SWR is at 1.40

 

Maybe the tinning helped? Maybe the 2nd time I had practice? In any event I am going to leave well enough alone since trying to wotk with LMR 400 is REALLY fricking hard without the proper stripping/prep tool. At least for someone with my experience level.

 

Thank you all for the replies and info!


The more I know, the less I understand
All the things I thought I figured out, I have to learn again. - Don Henley


#8 WRAK968

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Posted 04 April 2020 - 01:14 PM

The solder/crimp terminals (and the crimp tool) I have are for LMR400.

 

And, well, nuts on pooching the lifetime warranty. Then again, I mis-measured terribly and 100 feet was way more than I needed so I figured I would cut off the excess and experimaent with the shorter 35 foot long piece.

 

Once I get the stripping/prep cutter tool I will give this another go on the "short" section. Hey, at the end of the day there will be a value (to me anyway) in learning about this process.

 

For now my big concern is the increase in reflected power. Could a reading as high as mine cause damage to the radio?

We all have to learn at some point so I hope you understand I wasn't meaning anything negative. :)

Almost all commercial radios can handle up to a 3:1 SWR, though I would only run a radio with that high SWR in short bursts or in low power with a fan to help cool the heat-sinks. Below 2:1 and the radio will be fine though you may see a reduction in range which is why people strive for a 1-1.5:1 ratio.



#9 WRAK968

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Posted 04 April 2020 - 01:16 PM

Just tried another crimp. Pretinned the end of the conducter before putting the crimp/solder on this time. MUCH better results. 

 

I am comparing my 35 foot "practice" piece to a 90 foot premade MPD Digital LMR400 with PL-259 connectors that is also a bit long for what I need but anyway....

 

Now my reflected power is more in line. The premade piece is showing 0.53 with and SWR reading of 1.45 and my practice piece is showing 0.48 and SWR is at 1.40

 

Maybe the tinning helped? Maybe the 2nd time I had practice? In any event I am going to leave well enough alone since trying to wotk with LMR 400 is REALLY fricking hard without the proper stripping/prep tool. At least for someone with my experience level.

 

Thank you all for the replies and info!

Glad to hear your experience is helping :) With the right tools it becomes very easy. I am curious, which tools did you order for stripping and crimping?



#10 Riktar

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Posted 04 April 2020 - 03:14 PM

The crimping too (and included PL-259 ends came from Amazon:

 

https://www.amazon.c...0?ie=UTF8&psc=1

 

It does a reasonable job:

 

IExq8c2.jpg

 

The stripping/prep cutter I am still waiting on:

 

https://www.amazon.c...0?ie=UTF8&psc=1

 

And while I am waiting (and upon reflecting how "cheap" this stripping/prep too) I am pondering ordering this:

 

https://www.amazon.c...,aps,182&sr=8-1

 

Now if this was the only time I would be doing this than I would not consider this. But after wrestling with the LMR400 last night and considering my brother and my daughter want to get a home base setup similar to what I am putting together. Maybe I would be well served to buy this. 

 

Buy quality and you only cry once sort of thing.


The more I know, the less I understand
All the things I thought I figured out, I have to learn again. - Don Henley


#11 Lscott

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Posted 05 April 2020 - 03:47 AM

The cable I am modifying is a 100 foot LMR400 cable with male N connectors on both ends. Aside from shortening the cable to 35 feet for a better fit, I wanted to install the PL-259 connector to avoid having to use an adapter on my Kenwood 8180 which utilizes the PL-259 connector for cable attachment.

I think you have two things going on here.

 

1. The connector you installed, PL-259, is not a constant impedance type like the type "N" which will contribute to the higher SWR reading. The connectors calculate out, based on some dimensions on a few I've looked at, of around 25 to 40 ohms. It also depends on what the dialectic material used happens to be as well. The length, connector, of the miss match section also matters but in this case its rather small. This results in an impedance "bump" and a cause for some reflected power. If the radio uses an SO-259 socket there isn't much you can do about that.

 

2. When you cut the cable length from 100 feet to 35 feet you reduced the losses in the cable. However that applies to not only the forward power but also the reflected power. The formula for calculating SWR based on the power reading is:

 

SWR = (1 + sqrt(Pref / Pfwd)) / (1 - sqrt(Pref / Pfwd))

 

Where:

 

sqrt() - square root function

Pfwd - Forward power

Pref - Reflected power

 

How this works to increase the SWR reading as measured at the radio end of the cable is as follows. With lower forward losses the reflected power from any antenna mismatch will be higher because the power to the antenna has increased. Additionally the reflected power is attenuated less as well. Both work to increase the ratio (Pref / Pfwd) in the above formula. Remember you're measuring the forward power at the radio end and that hasn't changed. Thus the numerator becomes larger while the denominator smaller in the above formula. The final result is the number calculated becomes larger, the SWR.

 

I suspect the cable length change has more to do with the increase in SWR than the connector in this case. So as others have pointed out most radios work OK with an SWR up to 2:1, at least that's what I've seen in the spec's for the ones I looked at, without issues. An SWR around 1.5:1 or so is fine. You won't gain much by trying to lower it.


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#12 Riktar

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Posted 05 April 2020 - 03:44 PM

Thank you for the replay and the info! I will try and digest that and use it going forward.

 

 While I said I wan't going to try any more PL-259 installs on the LMR400 I decided ti do one more this morning. My reflective power is now down to 0.42 and the SWR is holding at 1.37 so I am going to leave well enough alone.

 

 As to your explanation (and again, thank you) about the impedence mismatch between the N connector and the PL-259: Since my Kenwood does use the SO-239 and the antenna has the N, would it be better to just use an n to 259 adapter/connector? From the information I have gotten from others about minimizing the amount of added items between the antenna and the radio I figured that replacing the N connector with a PL-259 would eliminate the need for an extra connector. Or in the case of having 2 different types of connecters, it doesn't make enough difference adding an adapter in vs changing one adapter for another?

 

 And for future purchases and/or installs: Avoid getting an antenna with an N connector and sticjk with SO239?


The more I know, the less I understand
All the things I thought I figured out, I have to learn again. - Don Henley


#13 Riktar

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Posted 05 April 2020 - 03:49 PM

One other question then: Other people have stated the DB404 antenna is the pinnacle of performance for a base setup. I have not seen and listing for one with a SO-239 connector. How would a person handle the difference between the 2 types of connector in that scenario?


The more I know, the less I understand
All the things I thought I figured out, I have to learn again. - Don Henley


#14 Jones

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Posted 05 April 2020 - 04:38 PM

The mismatch is not between the connectors. Always use type "N" connectors when possible, but if your antenna is type "N" and the radio is SO-239, then using a cable with type "N" on the antenna side, and a PL-259 on the radio side is the way to go. Try to never use adapters in any kind of permanent installation.

 

The impedance bump is on the PL-259, not on the "N" connector, which is an impedance balanced connector.  {By the way, there are 2 different types of "N" connectors out there, depending on whether you are using 50 Ohm or 75 Ohm transmission line (cable).}

 

To clarify your previous question, "...if the radio has an SO-239, should you also get an antenna with an SO-239 so they match?" ...the answer is NO. Always use "N" connectors for UHF when available, but if SO/PL is what the device has, use it.  Having different connectors on each end of the feedline is not the problem, and having a slight mismatch on one end is better than having a slight mismatch on both ends.


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#15 Riktar

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Posted 05 April 2020 - 04:57 PM

Thanks for the info!

 

 This forum (and the members of it) are great!!


The more I know, the less I understand
All the things I thought I figured out, I have to learn again. - Don Henley


#16 Solly

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Posted 11 April 2020 - 04:48 PM

The Microwave Times is what I use at work every day. The cheaper one will work also, but I was more prone to mistakes with it. Always test the conductivity and be sure there is no cross conductivity, prior to installing your coax.   



#17 Riktar

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Posted 11 April 2020 - 05:19 PM

The Microwave Times is what I use at work every day. The cheaper one will work also, but I was more prone to mistakes with it. Always test the conductivity and be sure there is no cross conductivity, prior to installing your coax.   

Oh you betcha! I have my VOM ready after every crimp/solder/twist.etc. Standing by to verify a good connection!


The more I know, the less I understand
All the things I thought I figured out, I have to learn again. - Don Henley


#18 n4gix

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Posted 13 April 2020 - 01:58 PM

If you think that $99 tool is expensive, check out the price for a stripping/prep tool for 1/2" heliax. I got 640' of Andrews FSJ4-50B for free a few months ago. It's just sitting my garage waiting for nicer weather... :D

CommScope Automated Tool for FSJ4-50B - $153.42 (includes shipping)
https://www.amazon.c...6803654&sr=8-22

 

EDIT: I just ordered it since I just noticed that I had a $25 worth of rewards points on my Amazon Visa card... B)



#19 Riktar

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Posted 13 April 2020 - 04:49 PM

If you think that $99 tool is expensive, check out the price for a stripping/prep tool for 1/2" heliax. I got 640' of Andrews FSJ4-50B for free a few months ago. It's just sitting my garage waiting for nicer weather... :D

CommScope Automated Tool for FSJ4-50B - $153.42 (includes shipping)
https://www.amazon.c...6803654&sr=8-22

 

EDIT: I just ordered it since I just noticed that I had a $25 worth of rewards points on my Amazon Visa card... B)

I guess it's all relative. IE: If I was suddenly blessed with getting as much 1/2 inch as you did,  adding a $150+ dollars to the equation would be a no brainer.

 

Congrats on scoring the cable!


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All the things I thought I figured out, I have to learn again. - Don Henley


#20 gman1971

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Posted 13 April 2020 - 05:16 PM

Lets not sugar coat this and get to the point:

I've had horrible experience using MPD made LMR400 cables. First off, these cables were a PIM galore, riddled with high SWR and noise, and windy day? forget to hear anything but noise due to the cables swinging in the wind.. In addition, the crimping always failed too. Connectors are chrome plated cheap garbage, even though they claim silver, they are NOT silver. The crimping is not weatherproof either, they are not using anything to help weatherproofing at all, its just a regular POS shrink tubing... nada. So, when sitting outside the outer jacket will rust and the already crappy LMR400 PIM-galore performance will turn into utter trash with sky high SWRs.

For a 100 feet run, please, save yourself all the headaches and buy Heliax, 1/2" should be a good start; seriously, don't bother with LMR garbage. I can hear it... "here comes another heliax snob..." yes yes, I've heard that before, but let say I owned a ton of LMR400 too, I always thought it was the best thing since sliced bread...., I thought it was great... ha... ha... ha.... until I tried Heliax and chrome-less connectors... never ever ever in a million years will use LMR for anything longer than a 3-4 feet patch, and silver plated connectors or tri-metal ONLY.

In addition to that, I will reiterate what everyone here has already stated: use N connectors, preferably Commscope tri-metal ones for the long Heliax runs; the cheapo chrome plated ones suck at impedance as I've found out. If you want performance, be prepared to spend $$$, unless you live atop Mount Everest... :)

Yes, its hard to swap the UHF thingy, but I've recently done it, and it was well worth it, and once you have the setup running you'll love it: no more sealing connectors, ever, no more creeping SWR after a couple of thunderstorms... no more hearing the NOAA due to PIM garbage LMR400 swaying in the wind... etc..

G.

EDIT: Oh, don't forget to ground PROPERLY the antenna/mast/radio to the same ground rod. Massive improvement when I did this in noise floor threshold reduction...




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