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#21 Riktar

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Posted 13 April 2020 - 09:28 PM

Thanks for the tips. If I go over the 100 foot mark by moving the antenna out of the attic and onto the roof I will definately look into the Heliax. For now I am going to stay with my 55 foot run into the attic. I originally planned on a 90 foot run using a 15 foot pipe next to the house but went with an attic mount solution to avoid outdoor elements and allow me to shrink my cable length needs. Was a good thing too. I had enough extra to cable to allow a couple of "whoopsies" with my initial attempts at using crimp connectors on the LMR400. 

 

Along the line of grounding: Since I am mounted on an attic rafter, I don't have any metal contacting the antenna at all. I don't suppose I could just run a ground line to the plumbing vent in the attic? Run a grounding line down to the basement and ground to the well pipe coming into the building? 

 

Thanks again for the advice!


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


#22 gman1971

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Posted 14 April 2020 - 02:19 AM

Well, attic and indoor certainly helps with SO239 and crimped cables rusting outdoors... but LMR400 in general is just too hyped. Honestly I would ditch it and get Heliax. You can find surplus heliax quite affordable.... but if you must have LMR400 at least use silver plated solderless N connectors like these:

https://www.ebay.com...872.m2749.l2649. I have a small 4 feet patch between the top arrester and the antenna, the N side is using such connector...  and the other side is using a 100% silver plated UHF connector, sold from the same guy. (since antenna is UHF...) next antenna will be N connector... and hopefully tri-metal too... we'll see.

 

Again, I strongly advice to ditch the SO239 as early as possible in your hobby endeavor. Otherwise you'll have to redo everything at a cost later...

 

As for grounding, sure, the metal mast I am using is mounted on the roof with no grounded metal nearby either so I ran a solid 10AWG copper wire to get it grounded directly to the rod at the electrical box. Ideally you'd want to ground yours to the outside ground rod too, and use the same cable for grounding all stuff... but any metal pipe that is grounded should work, just make sure its grounded, tho. I would still ground everything to the same ground wire if possible.

 

I've found out that the more I improved the grounding on the mast/antenna/radio the more it made cable lengths less important for SWR. When I had the antenna 100% ungrounded, then using different cable lengths gave vastly different SWR readings at the radio end, but once I started grounding it, the SWR differences between lengths became much smaller.

 

The explanation I've read for this is that verticals tend to have issues with feed line decoupling (I am using a TRAM 1450 vertical for GMRS) whereas higher quality antennas like the DB404 folded dipoles tend to not have this kind of issues due to how folded dipoles work.

 

Arresters, I think they are great for grounding the feedline, and I suggest using two, even for an attic setup like yours. One placed right under the antenna and another somewhere closer to the radio. I've had very good results with these Times Microwave LP-BTR-NFF, which are fairly inexpensive and use tri-metal instead of chrome plated connectors.

 

Lastly, I also recommend coiling two or three times the patch cable going from the top arrester to the antenna with around 8 inches diameter in each turn. That in conjunction with a sold ground should improve noise threshold quite a bit. Having the arresters at each end of the mast also made the installation really manageable, since now I can bring the antenna(s) down without having to remove or deal with the 20 feet Heliax anaconda feedline... :)

 

 

G.

 

Thanks for the tips. If I go over the 100 foot mark by moving the antenna out of the attic and onto the roof I will definately look into the Heliax. For now I am going to stay with my 55 foot run into the attic. I originally planned on a 90 foot run using a 15 foot pipe next to the house but went with an attic mount solution to avoid outdoor elements and allow me to shrink my cable length needs. Was a good thing too. I had enough extra to cable to allow a couple of "whoopsies" with my initial attempts at using crimp connectors on the LMR400. 

 

Along the line of grounding: Since I am mounted on an attic rafter, I don't have any metal contacting the antenna at all. I don't suppose I could just run a ground line to the plumbing vent in the attic? Run a grounding line down to the basement and ground to the well pipe coming into the building? 

 

Thanks again for the advice!



#23 Riktar

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Posted 14 April 2020 - 05:55 AM

I should have mentioned the antenna connection is a N type. As to the PL-259 connections the only one is the connection to the back of the Kenwood since I am trying to have only one line (In my case the LMR400) going from the antenna to the radio.

 

Now I am sure this is a real case of overthinking but would there be any benefit to removing the SO-239 on the radio and installing a Female N-connector so I could utilize Male N connections on both ends of the cable?

 

I will get on the grounding stuff this weekend. Shame I don't have the nerve to tackle the roof mounting. There are lightning arrestors up by the chimneys with cabling you could use to pull a tank with, going down to grounding rods on two of the corners of the house. Maybe the Son-in_law will be up this weekend.....  :rolleyes:   


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


#24 gman1971

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Posted 14 April 2020 - 05:05 PM

Very cool, yeah N connectors are great if only b/c they are sealed... which is great for outdoor installations. Also I think there are more options out there for higher end gear with N than SO239...

 

Unless you're super skilled in soldering this kind of stuff I wouldn't attempt replacing the SO-239 on the back of the radio...  and I've thought about it too. Just not worth the ris

 

All my Vertex Standard mobile radios use mini-UHF which are chrome plated and a pain in the rear to work with...etc... Had to make patch cables from mini UHF to N...  

 

The radio UHF connector is probably the least of the worries, as the radio usually is not sitting outside taking water... etc, the real problem arises when you start going down the UHF route b/c its what inexpensive gear comes with...  after some time you realize you have 10 devices that all use the UHF and changing course is just hard as heck.

 

I've had good luck using Deoxit to clean and lube the So239 connectors prior to connecting it...

 

G.

 

I should have mentioned the antenna connection is a N type. As to the PL-259 connections the only one is the connection to the back of the Kenwood since I am trying to have only one line (In my case the LMR400) going from the antenna to the radio.

 

Now I am sure this is a real case of overthinking but would there be any benefit to removing the SA-239 on the radio and installing a Female N-connector so I could utilize Male N connections on both ends of the cable?

 

I will get on the grounding stuff this weekend. Shame I don't have the nerve to tackle the roof mounting. There are lightning arrestors up by the chimneys with cabling you could use to pull a tank with, going down to grounding rods on two of the corners of the house. Maybe the Son-in_law will be up this weekend.....  :rolleyes:   



#25 Jones

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Posted 15 April 2020 - 10:57 AM

Just an insert note here for those new-to-the-hobby folks who are totally confused by the last few posts... "UHF" connectors, as they have been called for decades, are not really good for use on what we now know as the UHF band.  Back in the old days, UHF was considered pretty much anything over 30MHz.

 

Now, what's all this talk about SO and PL connectors?  The military designation "SO-239" is the female UHF connector.  The "PL-259" is the male UHF plug. These are the antenna connectors that have been used on CB radios since the 1960s, and still are today. You will also see reference to "SO-238" or "PL-258", which is a double female "Barrel" connector for hooking two coax cable together if both have PL-259 plugs. Those should be avoided at all cost on GMRS. If you need a longer coax, buy a longer coax, don't try to extend one.

 

Although UHF connectors are fine for CB, they just aren't as good on GMRS.  Constant impedance, and weather protected type N connectors are much preferred.


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#26 marcspaz

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Posted 15 April 2020 - 05:55 PM

Agreed... SMA would be my preferred connectors

#27 Riktar

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Posted 16 April 2020 - 06:23 AM

As someone who is new to this hobby (and sometimes confused by his own post's as well.. I noticed I incorrectly put down SA-239 in an above post when I do know from reading other posts it is an SO-239. Ugh, I try to use correct spelling and then do that...  :unsure:) I want to ask if I am going too far in the quest to keep my coax one long continuous cable from the antenna to the radio.

 

My antenna is in the attic of a 2 story home and the cable is fed down an unused chimney into the basement and back up to a first floor room where is exits out in the corner of the room and hooks directly into my radio. And it is a single piece of coax. The only break in the whole link is where I put a SWR meter in to check on the line and the antenna.0

 

 I am assuming that when people use a tower install or have an extreme length between the antenna and the radio it is not feasible to use one continous length of cable. But I have no idea what the standard would be for when it is practical to add addtional connectors for extending or stepping down the cable size to complete the installation.

 

IE: In my case, while it was a pain, I was able to wrangle the (approx) 60' feet of LMR400 all the way from the antenna to the radio in one continuous section. If I was ever inclined to try and get an antenna up on the 40 foot silo in my yard and into my house the path would be (again, approx) 200' feet long. Aside from the sheer bulk of handling one long piece of cable to do this AND considering that a run this long would mandate using something as heavy/large as heliax cable which (I am admittedly guessing here) is not as forgiving at being bent around multiple corners as LMR400 is as LMR400 is not as "bendable" as RG8x, etc, etc.

 

So I am trying to find some type of guidance as to minimize my losses while still making my cable run a practical one.

 

As a for instance: If I were to mount an antenna on the 40 foot silo in my yard would it be adviseable to run 1/2, 7/8, etc. Heliax from the silo down to the ground, form the widest 90 degree bend (6 inch radius? 9? 12?) under the ground (If not using burial grade the cable would be fed through some type pvc for protection) to the house where it would be stepped down to LMR400 as it got close to needing severe bends to get it to the room where the radio sits? And IF I wanted to avoid having cables just running through holes in the floor or wall, are there connectors that would minimze my losses while allowing more of an "attractive" install?

 

I have been searching for some type of writeup/article online but have not come across anything that I can apply to this endeavor. 


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


#28 gman1971

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Posted 16 April 2020 - 07:02 PM

Agreed... SMA would be my preferred connectors

 

Marc, did you really meant to say SMA? I think perhaps you meant to say N? Not sure how well SMA would work outdoors since its doesn't seem to be sealed and SMA might not work for anything larger than LMR240...

 

LOL, wrangling with a 20' run Heliax 1/2" is already a pain, I can't imagine dealing with a 7/8" longer than that... lol. 

 

However, for those who like running radio straight to the antenna, I did found out that I get far better S21 readings on the analyzer (the transmitted power, not the return loss) ) when using two grounds and 3 segments of cable between radio and antenna than with a single (ungrounded) piece of 1/2 Heliax straight to the antenna. What that means is that I see more RF being radiated through the antenna.

 

Also, when I had the single run of Heliax ungrounded I could never match 50 ohms impedance to the correct antenna length for the frequency. Now I have 50 ohms sharp and a solid -34 dB loss (~1.04 SWR) on a 5/8th wave vertical that reaches for miles... :)

 

I've always thought that more connectors was bad for reception, so I never bothered grounding things b/c I thought it will kill the radio signal, etc... But I can safely say I was wrong: what a good ground seems to do is lower the noise threshold and improve the radiation pattern.

 

G.



#29 marcspaz

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Posted 17 April 2020 - 07:23 AM

G.... it was a joke. LoL

I could be wrong, but I think the only SMA antenna mount is on an HT.
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#30 gman1971

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Posted 17 April 2020 - 12:42 PM

LOL...  you got me.

 

G.... it was a joke. LoL

I could be wrong, but I think the only SMA antenna mount is on an HT.


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