GMRS Base Station

[tibadoex]

Need some feedback on this setup: Wanting to setup a GMRS base station. Was going for the Midland MXT400 and a Browning 450-470MHz Omni Base Antenna. Connecting the two with 100ft of RG8x Coax.

 

[K7MFC]

This MXT400 is a decent radio, but a tad overpriced when compared to a second hand commercial rig like a Kenwood TK-8180. Also, the Midland does not do split tones for repeaters - different CTCSS/DCS tones on transmit and receive. This is a pretty big drawback for some GMRS users.

 

[N5XPM]

Others may be better acquainted with the specific radio and antenna, but using lower-loss antenna coax will improve both your transmit and receive experience substantially.
Something like 9913 or LMR 400 is much better according to this chart: Coaxial Cable Attenuation Chart This calculator may help you estimate the total signal loss: Coax Calculator
Ordering with pre-installed connectors is good if you don't install them often (especially on the high one) and vapor block to seal outdoor connectors is important as well. Routing, drip-loops and grounding are important as well and searching RR and google should help locate discussion on those as well.

 

[mmckenna]

Connecting the two with 100ft of RG8x Coax.

100 feet of RG-8X isn't a very good choice.
40 watts out of the radio will suffer a LOT of loss over that length of cable. Of the 40 watts you put in, less than 6 watts will make it to the antenna. That is 8.4dB of loss. Same works on the receive side, you'll lose a lot of your received signal due to coax losses.

Two options:
Greatly reduce the amount of cable between your radio and antenna.
If that is not an option,
Use a higher grade cable. LMR-400, LMR-600 or 1/2 inch Heliax for a 100 foot run. That'll give your transmitted and received signal a chance. Problem is, those are going to be more expensive and harder to install.

 

[CaptDan]

100 feet of RG-8X isn't a very good choice.
40 watts out of the radio will suffer a LOT of loss over that length of cable. Of the 40 watts you put in, less than 6 watts will make it to the antenna. That is 8.4dB of loss. Same works on the receive side, you'll lose a lot of your received signal due to coax losses.

Two options:
Greatly reduce the amount of cable between your radio and antenna.
If that is not an option,
Use a higher grade cable. LMR-400, LMR-600 or 1/2 inch Heliax for a 100 foot run. That'll give your transmitted and received signal a chance. Problem is, those are going to be more expensive and harder to install.

just a question - would it do any good to use 2 different cables ? I am getting ready to do an outside antenna. When building we had conduit installed that goes out thru the concrete floor, under the footings and will come up alongside where a antenna structure will be. So in order to get the cable(s) thru the conduit would it make any sense to use something like 8x from the radios, out the conduit then switch to something better for 50 - 75 feet up to the antenna ?

If is a completely stupid idea - feel free to say so

 

[mmckenna]

just a question - would it do any good to use 2 different cables ? I am getting ready to do an outside antenna. When building we had conduit installed that goes out thru the concrete floor, under the footings and will come up alongside where a antenna structure will be. So in order to get the cable(s) thru the conduit would it make any sense to use something like 8x from the radios, out the conduit then switch to something better for 50 - 75 feet up to the antenna ?

If is a completely stupid idea - feel free to say so

That is a reasonable solution if it's a short run.
Issues I'd be concerned about:
1. Any conduit below grade -WILL- collect water. You need to be sure the coax will handle that. Filled/direct bury rated cable can solve that issue, but there can be fire code issues running some of those cables indoors for too far a distance.

2. RG-8x is a pretty low grade cable. Doesn't make sense to use it in any sort of commercial application. There are -much- better cables.

3. Consider the added losses of the connections you'll be adding. Coax connectors are not lossless connections.

If the conduit is undersized, that's a design issue. RG-8x is "radio shack grade" cable, not really that good for much else than cb radio use. Not suitable for long runs at higher frequencies. If you have put the effort into conduit and a 50 to 75 foot antenna support, don't cripple the system with low grade coax. Something like LMR-240 is a similar size and has better performance.

 

[alcahuete]

Shocked that nobody has mentioned the antenna yet. If that's the one I'm thinking (that is around a foot or so tall), you're not going to be impressed. I have the Laird (non-Chinese knock off) and it's great for very local stuff, but it's by no means a performance antenna.

 

[CaptDan]

That is a reasonable solution if it's a short run.
Issues I'd be concerned about:
1. Any conduit below grade -WILL- collect water. You need to be sure the coax will handle that. Filled/direct bury rated cable can solve that issue, but there can be fire code issues running some of those cables indoors for too far a distance.

2. RG-8x is a pretty low grade cable. Doesn't make sense to use it in any sort of commercial application. There are -much- better cables.

3. Consider the added losses of the connections you'll be adding. Coax connectors are not lossless connections.

If the conduit is undersized, that's a design issue. RG-8x is "radio shack grade" cable, not really that good for much else than cb radio use. Not suitable for long runs at higher frequencies. If you have put the effort into conduit and a 50 to 75 foot antenna support, don't cripple the system with low grade coax. Something like LMR-240 is a similar size and has better performance.

Conduit was a necessity for access to the location - room is secure, solid concrete all the way around - so conduit was installed thru the floor, underground and underneath the building's footing and back up above grade outside the wall. Conduits are 2 inch pvc and were planned properly - just as in any project one in place and operational always something to add on. Total conduit length is only about 10 - 12 feet. In my case and considering adding some additional antennas for scanner, maybe even a CB antenna just for fun, a WiFi antenna, perhaps a dedicated antenna for MURS

 

[mmckenna]

Conduits are 2 inch pvc

If it's electrical PVC with sweep 90º's, fitting a few LMR400 runs in there shouldn't be an issue. Just pull them all in at once.

I've got a run of 2" pvc with a run of 7/8" heliax in it at a parking garage. Only difference is we had the bends done on site with a hot box and the turns are very wide.

 

[tibadoex]

Thanks for the replies. In regards to the antenna, what about these two: FG4607 Antenex Laird or the Comet CA-712EFC . Out of these two: is either one better than the other. My personal preference, I prefer the Laird style. Not sure if the Laird one is a Chinese knock off or not. I take it the higher the gain the better?

 

[mmckenna]

Comet is amateur/hobby grade stuff. Would probably work just fine for what you are doing.

The Laird is a commercial antenna with a reputable background in commercial type applications. Since a lot of the cost with installing antennas like this is in the labor (yeah, I know, you'll do it yourself, but there are risks), usually putting up a good antenna that will last a long time is a good plan. Putting up some Chinese junk antenna and then having to replace it in a few years isn't what you want.

The type of antenna you need really depends on the exact application. Antennas will be shown as having a certain amount of 'gain'. Gain is relative to how they design the antenna to focus the radiated power. Antennas with higher gain direct more of the radiated power towards the horizon (or just slightly below in what is called "down tilt".
Throwing more of your radiated power out at the horizon can give you better performance farther away from the antenna. Read that as "more range".
But that can also backfire. Focusing power at the horizon can be detrimental to coverage if your antenna is on a very high hill, or if you are located down in a valley. Blasting power over everyones head, or into the side of the hill, isn't always the best approach. There are times when lower gain antennas will out perform higher gain antennas. Lower gain antennas will allow more energy to be directed above and below the horizon.

So, depending on where you are, picking the right antenna can make a big difference.
Looking at the terrain around Gladys, VA shows low rolling hills. A high gain antenna like the Laird might be a good choice if you can get it up high enough to see over the local terrain. Lower gain antenna might not be a good solution.

So, I'd probably agree with you on the Laird. Good antenna that will last a long time. Feed it with the best coaxial cable you can budget for, get it up high, and make sure you properly seal the outdoor connections well.

 

[bill4long]

Was going for the Midland MXT400 and a Browning 450-470MHz Omni Base Antenna. Connecting the two with 100ft of RG8x Coax.

I would use LMR-600 if you can. If you can afford it, use Heliax. And that Browning antenna is unity gain. Since you're going to all the trouble, get something with 6dbd (8dbi) gain at least. That will make your 40w radiate as 160w ERP. That Comet would be sufficient.

 

[WA3ATV]

I am also planning on installing a GMRS base station. Regarding selecting a radio, it is my understanding that commercial radios that are FCC Type Accepted under Part 90 (land mobile) are not necessarily type accepted for use in the GMRS service (Part 95.) First of all, is that understanding correct? Second of all, if it is correct, does anyone have a comprehensive list of base and/or mobile (not hand-held) radios that are type accepted for Part 95?

 

[alcahuete]

You are correct in your understanding. There are a bunch of Kenwoods and older Vertex radios that are certified both Part 90 and Part 95. Here is a decent list in this thread: Part 95 GMRS radio list

However, the FCC seems to generally takes a relaxed stance on using Part 90 radios on GMRS, and really don't care one way or the other, since Part 90 radios obviously meet rigorous technical requirements.

 

[WA3ATV]

Thanks alcahuete. I'll check that list out. I agree. As a practical matter, the FCC isn't going to knock on my door and demand to see the Type Acceptance sticker on any of my radios. Heck, you could probably operate a ham radio out-of-band and no one would know or even care. In this case I actually want a stand-alone radio for the GMRS work so I might as well dot the I's and cross the T's.

Thanks again,
Dan

 

[mmckenna]

Most of the older TK series Kenwood radios have Part 95. You should have no problem finding a used or even new/old stock TK-8180 online.
The TK-8180 Type 1 will cover GMRS. It's 450-520, some have reported success in programming them into the 70cm repeater band.


The programming software (KPG-89) is very easy to learn and a lot cheaper than Motorola. Same with programming cables.

TK-8180 Type 1, 30 watts, 450-520MHz FCC ID K4437313110

FCC - OET TCB Form 731 Grant of Equipment Authorization

TK-8180H Type 1, 45 watts, 450-512MHz, FCC ID K4437313210

https://apps.fcc.gov/oetcf/tcb/reports/Tcb731GrantForm.cfm?mode=COPY&RequestTimeout=500&tcb_code=&application_id=2htwbvTNWxlzdajKZ5ggAw%3D%3D&fcc_id=K4437313210

The TK-8180 Type 2's are 400-470MHz, however they do NOT have Part 95 certification.

The TK-x180 series radios (TK-3180 is the UHF handheld version) were only recently discontinued. They share the same chassis and accessories as the NX-x00 series NXDN radios, and those are still being sold new. That means there are a ton of accessories out there on the used market.

 

[Bailey1213]

I used a Midland MXT115 (15watt) with the tiny stock antenna on a steel pizza pan mounted to the top of my fireplace chimney and had no problem hitting a repeater about 75 miles away. Granted the repeater is on a small mountain top in North Georgia but still. I am now running a used Motorola CDM1550 40 watt with 50 ft of RG58 to a Tram 1485 antenna with 5db gain attached to a 10 ft pole mounted to the fireplace chimney (30ft total in the air) Total cost right at $250. Base to mobile almost 30 mile radius and I sound much better on the repeaters. The little Midlands are great but limiting as they are narrow band only.

 

[mmckenna]

with 50 ft of RG58

If it's working, that's good.
I will point out that 50 feet of RG-58 on GMRS frequencies isn't helping you.
With that coax, you are losing about 4.5dB of your signal just to cable losses. That means your 40 watt radio is getting about 15 watts to the antenna.
And that works both ways, more than half of your received signal is lost even before it reaches your radio.

If your budget will allow, upgrade that coaxial cable and you'll see even more of an improvement in performance.

to a Tram 1485 antenna

I'll also point out that this antenna is a dual band amateur radio antenna. On the UHF side it's designed to work in the 430-450MHz range. That's impacting your performance also. Again, if it's working for you and you are happy, no problem, but make sure you check the SWR.

 

[Bailey1213]

The antenna is tuneable which i have done and i am running a 1.12 swr

 

[Bailey1213]

Your right about the cable i really need to upgrade