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antenna and cable questions for a home base setup


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#1 Riktar

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Posted 21 March 2020 - 06:01 PM

 So I bought a Midland MXT400 and some Midland talkies for the property I manage. It makes the wife feel better about being able to reach me when I am wotking on the property since the cell service out here is horrendous. Anywho, on to my setup:

 

Midland GXT1000VP4 twin pack of walkie talkies from the local Walmart. They do a reasonable job of providing total coverage to the house on the 225 acre property I manage.

 

Midland GXT115 mobile. Bought a couple of these. One for my car and one for a base unit at the house. I am still using the included antenna for the car but will be upgrading that soon. The one I am using for the house is where I have the question(s).

 

I picked up a Harvest BC200 450-470Mhz UHF 6.5dBi 200W Pre-Tuned GMRS Base Antenna and have it mounted on a 15 foot (approximate) pole next to the house which is a 2 story. The pole was already there with nothing else on it and the thought of scaling my EXTREMELY steep pitched roof to get the antenna on the top of it was more than I wanted to consider. so the antenna is on this pole right next to the house for now. Also, I had some RG-8x cable (about 50 feet approx) which I used to make a quick connection to the base unit and proceded to measure the SWR with a Nissei RS-50 digital meter I borrowed from my brother. I was VERY dissappointed to find my "pretuned" antenna was reading 1:4 for SWR. 

 

So finally, here come my questions:

 

Can I make adjustments to the cable length to affect the Swr? And speaking of cable: The ultimate length I am going to need is somewhere around 85 - 90 feet. Being that long is it of measureable benefit to get LMR400? How "bendable" is LMR400? Part of the run will be MUCH easier if I can make a couple 90 degree turns that would be kinda sharp.

 

Thanks for any advice!


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#2 marcspaz

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Posted 21 March 2020 - 06:21 PM

With centimeter radio and cheap cable, the cable length is not going to change anything even remotely close to noticeable... likely not even measurable. 

 

Also, anything under 3:1, you won't have any risk of damage.  Anything 2:1 or better is good.  Anything 1.5:1 is really good.  getting a 1:1 match usually means the antenna is not resonant at your target frequency.  You should be very pleased with 1.4:1.  Normally I target about 1.75:1 at the antenna feed point and then use an LC network to maximize output power to the antenna. 

 

Get that antenna 40+ feet in the air and you will dramatically increase your coverage and performance in the covered areas. 


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#3 Riktar

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Posted 21 March 2020 - 06:52 PM

Thanks for the reply and the explanation! 

 

That is so wild that you mention 40+ feet. There is a 40 foot silo in back of my house! It would require over 100 feet of cable to get from the top down to the ground back and into my house.

 

So far I am satisfied with what I have: The wife can reach me anywhere I go on the property with the walkies and we have about a 7 mile range between the house/base and the mobile. And that is with the included antenna for the MXT115. I am hopeful that upgrading that will get me out another mile or 2.

 

So if I understand correctly, I am ok with my setup but try and get as much elevation on the base antenna for extended range.

 

If I work up the nerve to scale the rung ladder on the silo I will shimmey the antenna up there and report back on how much farther I can get out.

 

Thanks again! 

 

EDIT: Just thought up another question: I need to add another 35ish feet to my setup to get the base radio out of the kitchen and into my computer room/office. Better to do it with a single run of cable or could I just add to the existing RG-8X cable by way of adding another length (screwed together by way of a PL259 Jack to Jack Coupler) of RG-8X?


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#4 marcspaz

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Posted 21 March 2020 - 07:12 PM

So if I understand correctly, I am ok with my setup but try and get as much elevation on the base antenna for extended range.

 

Yes, that is correct. There is a saying in the LOS radio world that "height is might".  The higher you go on each end, the better the performance and range gets. 

 

The ground absorbs UHF waves and the rest heads out to space about 15% (distance wise) past the visual horizon.  So, the higher you go, the less terrain is in the way, the more land surface area is exposed because you are pushing the horizon line out further as you go up.

 

An example would be, at 5 feet above all obstacles (about where an HT is while standing) gives you about 5 miles of radio horizon.  15 feet gives you about 9 miles to the horizon.  However, 40 feet gives you 14 miles.  The truth is, if nothing is in the way, and you get one station up in the air 3,000 feet (on the side of a mountain for instance) and the other radio was at sea level, you could get 125 miles with the proper power levels.  With the power we are restricted to, you can get 65-70 miles with enough elevation.
 

 

 


If I work up the nerve to scale the rung ladder on the silo I will shimmey the antenna up there and report back on how much farther I can get out.

Sounds good!  Looking forward to hearing back.


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#5 Jones

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Posted 21 March 2020 - 11:18 PM

If you are planning on eventually running 100 feet, you WILL need better coax cable.  RG-8x is NOT RG-8u.  8x is the small coax used for CB radio.  Even the best grade of 8x has over 9 dB of loss at 462MHz at 100 feet.  For the low-cost/best performance per dollar ratio, go with LMR-400.

 

NOTE: I do not EVER recommend LMR-400 for repeater use, but for simple base station operation, it works great.


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#6 marcspaz

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Posted 22 March 2020 - 02:18 AM

EDIT: Just thought up another question: I need to add another 35ish feet to my setup to get the base radio out of the kitchen and into my computer room/office. Better to do it with a single run of cable or could I just add to the existing RG-8X cable by way of adding another length (screwed together by way of a PL259 Jack to Jack Coupler) of RG-8X?

 

Just saw the edit... do not splice lines together with barrel connectors.  You are going to suffer losses as it is, with a run that long.  Adding extra connections will just make it worse.

 

As Jones mentions, LMR-400 would be good for the run, but make sure its one long run.


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#7 kipandlee

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Posted 22 March 2020 - 07:55 AM

Jones     marcspaz

how much difference would LDF4-50A make than  LMR-400



#8 Jones

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Posted 22 March 2020 - 11:18 AM

If you can afford it, use the LDF4-50A.  Perhaps even LDF5-50A if your run is longer than 100 feet.

 

At 460MHz at 100 feet, RG-8x has a loss of 9.4 dB. LMR 400 has a loss of 2.7 dB. LDF4 has a loss of 1.4 dB. LDF5 has a loss of 0.82 dB.

 

If you are using LDF Heliax, it is just fine to use a short jumper at the end for flexibility going into your radio.

 

Also, keep in mind your cost vs. return on investment ratio.  How far do you really need to talk?

 

Personally, I use LDF4-50A, but I'm only running about 80 feet.


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#9 marcspaz

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Posted 22 March 2020 - 11:20 AM

Jones     marcspaz

how much difference would LDF4-50A make than  LMR-400

 

 

 

Attenuation of LDF4-50a is about 1.4db at 467 MHz.  LMR-400 is about 2.7db.


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#10 Riktar

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Posted 22 March 2020 - 12:54 PM

Thanks for all the info! I ordered the LMR400 cable. Should be here later this week. I will order enough to get the antenna a touch higher. 

 

Getting enough to put it on the silo is another thing. Looking over what would be involved, it's not just a matter of me working up the nerve to climb and mount it. It's trying to figure out how to get it trenched under 25 feet of asphalt that is between the silo and my house. 

 

But I definitely do need to get it higher. I can clearly hear other stations broadcasting but they can't hear me at all. And the closest repeater is (roughly) 11 miles away so my 6-7 mile range is not going to cut it. Especially with all the hills and valleys between myself and the repeater..


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#11 JohnE

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Posted 22 March 2020 - 02:00 PM

just a note to the 400 cable vs LDF

these are completely different types of cable to deal w//

400 is a nice flexible fairly user friendly cable. LDF4 on the other hand for a novice is not going to end well. it is fairly rigid  bend it too much and its done, have seen that 100x over. putting on the connectors is pretty strait forward depending on what you buy. you will need to have some practice to get a feel for it.

wouldn't even bother w/LDF5  that is a 7/8 cable that requires specialized tool to put connectors on.

  as to your height, 2 story cape style house in the end should give you 30' of height to tip, roughly.

look at this as I have finally added new pics

 

https://forums.mygmr...pes-and-losses/


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#12 Riktar

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Posted 22 March 2020 - 05:49 PM

Thanks for the additional info on cabling. Once the LMR400 gets here I will look at how much added height I can get without the having to engineer additional bracing. And I will do the measurement from the tip of the antenna to see just how high I can go.

 

There is an installer who advertises as doing satelite installs as well as tower installs for TV, etc. I think I am going to give him a call and see what he wants to scale my roof and move the antenna up there.


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#13 quarterwave

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Posted 22 March 2020 - 06:41 PM

For thought...if you need to run that much coax, it would be worth it to buy something like a Motorola Desktrac with tone remote capability. Mount the radio in the attic or silo and run a short coax to the antenna, then a CAT5 from the radio to a tone remote. Now you have Base Station! 


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#14 Lscott

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Posted 23 March 2020 - 12:30 PM

If you want the better coax, hard-line, its going to cost you. The site below does sell 1/2" and 7/8" hard-line. It seems they are able to install the connectors too. I'm sure there are other places you can get the cable, likely at around the same cost.

 

http://www.davisrf.com/heliax.php


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#15 JohnE

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Posted 23 March 2020 - 12:39 PM

at 50' 400 would be good

    100' 1/2 super or hard line

in excess of 150' 7/8 

after that you get into the really big stuff 1-5/8, 2-1/4 and waveguide.


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#16 Riktar

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Posted 27 March 2020 - 07:41 PM

My 90 feet of LMR400 arrived earlier today. My swr is about the same but my power output (40w capable) has jumped from 24 to almost 37 according to the meter.

 

I can now hit pretty much all the repeaters in the area and I now can cover the better part of 15 miles, terrain changes and elevation notwithstanding. This is great since not only can the Mrs. get ahold of me anywhere on the property but running into town is now covered as well!

 

Thanks everybody for all the suggestions and info!


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#17 marcspaz

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Posted 27 March 2020 - 07:46 PM

Good to hear!


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#18 Riktar

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Posted 29 March 2020 - 09:13 PM

I have been reading some other posts on this forum about attic mounting the antenna instead of going the outside route. 

 

In my case if I mounted the antenna in the attic (and I do have enough clearance to mount the antenna without touching the rafters or the joists) I would gain about 8 - 10 feet in height. Right now my antenna is on a 16 foot pole so the top/tip of the antenna is about 20 feet off the ground. So while the attic wouldn't get me to 40 feet, it would elevate the top of the antenna to about 28 feet. Would the height increase offset having to push through the osb sheets and the asphault shingles?

 

I would not have to sweat lightning strikes in the attic and I could reduce my cable length to less than 40 feet compared to the 90 foot length I currently have. 

 

Along the lines of cable length: I understand that I am benefitting from having LMR400 cable instead of the RG8X I was using but would it syill make much of a difference if I reduced the overall length of the cable by 50 feet? It's not so much about being cheap, it is about ease of snaking the cable down through the walls. I live in a 1890 farm house that utilized ballon construction so it's a straight shot down the outside wall from attic to first floor. And that LMR400 cable is pretty darn stiff compared to the RG8x stuff. 

 

Hey, what if I could reduce the cable length to 15 feet? The reason I ask is I could just take over the spare bedroom on the second floor and have a really short run from the attic. And it was also isolate me from the wife who will not have to remind me to turn down the radio while she is watching tv.

 

Anyway, just had the thought. I did do a quick toss of a spare Browning mobile antenna on a magnetic base (Dont tell the wife about her copper cookware... SHHHH) on a 16 inch pan and ran the cord through the attic access hatch to one of the mobiles. And surprise, surprise, I can still hit the repeater 30 miles away. 

 

And well, it just got me thinking....

 

Then again, I would have to lean out from my roof to get the antenna off that 16 foot pole.

 

Geez I hate heights. And yes, 16 feet seems like a bit of a height at my age.  ;)


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