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Every once in a while we like to do some bench testing for continued education and try and break people of some poor habits and thinking. Figured Id share.

We pulled three cable kits off the shelf and threw some mini-UHF connectors on them. Left them at the 17' length and stretched them out so they were not anything resembling a coil. (choke)

Laird mb8- stranded RG58 with brass NMO mount. (mini-U had nickle center pin)
Larson NMOKHFUD- solid center RG58 with 100% braid coverage and stainless steel NMO mount. (mini-U had nickle center pin)
Laird mb8x- solid center RG8x with brass NMO mount. (mini-U had brass center pin)

The test setup utilized an IFR 1200, roof mount adapter with female SO259 adapted to BNC male for NMO mount. Mini U to N connector for other side. (yes there is some loss there) quick and dirty but this is how many systems are installed. You know, quick and dirty.

We did the best we could to come up with a signal standard across the test. So not entirely scientific. We tested all three cables at each of the listed frequencies and noted how much loss we sustained. Remember that this is closer to real world in many cases. Many installers cannot bring themselves to cut the cable kits down to size. Instead they choose to coil them up and create neat little RF chokes (not all cables are 100% shielded and besides its considered bad practice in most arenas).

Remember-
3dB is half your signal. If you have 3dB of loss through your antenna system then your receive will 3dB down as well. (a fact that is forgotten on many) A 30 watt radio will only get 15 watts to the antenna. If your antenna is not matched well then the loss numbers will go up. (note for the sales departments- This is a great way to sell more infrastructure though.)

10dB is 10x your signal. Pay for 30 watts get 3 watts to the antenna. Nice eh? same goes for receive.

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"A well regulated breakfast, being necessary to the healthy start of the day, the right of the people to keep and eat food shall not be infringed."

Good material. Another favorite in the unnecessary loss department is using "large center button" lowband NMO mounts with 800/900 meg antennas that use a thin center pin.

Taking it a step further is the Comtelco CEZM-00 mount which addresses the impedance mismatch where the coax connects to the mount. These have excellent characteristics for 700/800/900mhz and especially at 1.2/2.4ghz where everything else on the market has so much loss that they are essentially unusable.



True with the exception of HF where it is actually considered to be a good thing. It acts as a common-mode choke which keeps all the stray RF from your mismatched mobile antenna from getting back into your radio and making it sound like crap and/or act strange.

Thanks Rich!


I just got the same reply from my counterpart who has roughly 100 Kenworths with lowband installs. Im just learning lowband let alone HF compared to some of you guys. My start was with a 900 radio system in the late 80's. Then on to mobile cellular installs in the Los Angeles area. More recently our 900 conventional system on the Olympic peninsula worked well until the noise floor at 896 went through the roof. Even working well though you can pass a forest and watch the signal sink >20dB.

Ive got a couple of other kits that I want to test as well that are better designed for the higher spectrum with the smaller button. Ill post the results.

The Larsen kit above comes with a large removable button. If removed you need an antenna with a very small center pin to engage the contact. Not something Ive seen on to many available antenna's.

One thing that still has me bewildered... How many techs still forget to factor in cable loss when reading reflected power on a watt meter especially at higher frequencies. I watched a tech install an 800 SMR antenna on a 900 system because the antenna matched according to his calculations.

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"A well regulated breakfast, being necessary to the healthy start of the day, the right of the people to keep and eat food shall not be infringed."

Great post, thanks!

"""One thing that still has me bewildered... How many techs still forget to factor in cable loss when reading reflected power on a watt meter especially at higher frequencies. I watched a tech install an 800 SMR antenna on a 900 system because the antenna matched according to his calculations."""

With 17dB of "Insertion" loss no antenna at the mount would still give a decent SWR (32dB return loss!!!!!) So that coax becomes a not-too-shabby dummy load ;)

What surprises me is that the industry hasn't developed a coax-to-antenna and through the automotive sheetmetal system that ACTUALLY WORKS at frequencies above 700 Mhz... Your tests bear out the necessity as the "motorola" mount system works OK through UHF... At 700Mhz and above, not so much............

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That is how the people at DARPA think. they take things and use them in unconventional ways, to see what happens.

I use LMR240 in my mobile installs, for the most part. NMO mounts soldered/pinned...

About $5 for the mount, and .50 cents a foot (last time I bought a roll)

You can have custom lengths without scrap, and higher performance, usually less expensive than the mount/cable combo from the big names.

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Oh! Come and see the violence inherent in the system! Help, help, I'm being repressed!

I just bought two kits with LMR240 for this test and might have time tomorrow. The only real difference is the button size when comparing to the Larson kit. The cable type is identical in design to the naked eye.

I will eventually be using one of them for a 2.4ghz wireless mic so that will be part of the test results as well.

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"A well regulated breakfast, being necessary to the healthy start of the day, the right of the people to keep and eat food shall not be infringed."

Factor in time to solder every one. And the extra time it takes to route a larger, more stiff cable. Now how much?

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Interoperability is an attitude, not a technology.

Considering RG8X isn't a real standard, which means Company A RG8x might have 2x the loss of company B RG8X...

Not to mention the availability of LMR240-UF, which is ultraflex..

LMR240 is only a hair bigger than 58, with half the losses, and considerably better shielding (for those worried about RFI/magnetic induction)

Takes me 3-4 minutes to solder an NMO mount on there properly, then test for leaks and proper flux capacitance.

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Oh! Come and see the violence inherent in the system! Help, help, I'm being repressed!

If you have to worry about a dB or 2 of performance, your radio system sucks.

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I generate Board Warnings

Thanks for posting those John. Its something I was trying to get around to. Ive been slammed and haven't gotten back to this...

We do not solder mounts on either. Nothing beats the manufacturers solder jig. Nothing! And we get to impatient and want to move the mount too soon before it cools so policy was made. We have a couple of very good guys when it comes to solder so not from inexperience. But if we let them then the new guy wants to as well, blah blah. I do carry the mounts myself and will add them in the case of a bus or similar vehicle where the cable was run during manufacturer however.

Your charts show a stark contrast to what Ive found and this is much of the point.

1 or 2 dB- yup! I can point to a system that was put in with absolutely no reserve and I as well as many others feel the system needs to be torn out and done over. They are easily 10-20dB away from achieving their coverage needs and thats before you consider the mobile installs.

But 15dB loss on a mobile goes both ways.
1. You will never see much of the reflected power from an improperly tuned antenna.
2. You will need to be closer to the transmitting source than the guy with only say- 9dB loss to hear the system your monitoring at the same levels as that guy.

Besides my attempt to keep some sort of standard while I was testing (which Im sure failed badly) the things it did show is that there are many ways an installer can screw up in both the actual installation and the design of the install. At the higher frequencies you are never going to see the same low loss numbers that you would get if you were building for VHF. But it seems to me people have just stopped trying.

We measured 17dB of loss in the antenna install of a vehicle that will be on a public safety 700mc system very shortly. The install was done by a big M darling shop and performs worse (on receive) than the portable tested against in the driveway of said agency. Since all the installs are done the same way I have to believe we will see the same loss numbers across the board if we were to test.

I saw this the first time in my early days installing our 900mc mobiles back almost 30 years ago. The stuff put in by the radio shop that sold us the system performed worse than the units put in by myself with the help of a retired tech. They used big button kits and coiled the excess. We used small button kits and cut to length. Pretty simple really.

Im going to compare some receive numbers by looking at various control channels and weather radio RX and will post soon. There is a method to my madness and if nothing else- good discussion.

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"A well regulated breakfast, being necessary to the healthy start of the day, the right of the people to keep and eat food shall not be infringed."

Great info guys!

Being part of an agency that will be moving to the new 700 system soon I'm very concerned about the coverage in my area and being able to communicate with dispatch and others. After looking at some of the install work that was done I'm sure it will probably contribute to any issues my agency will have in our upcoming migration, if and when that happens.

In fringe areas, especially with digital signals, it could be the difference between hearing and being heard, and.. *boooooonnnnnnnnnnnnnnnkkkkkkkk*

Most pre-soldered mounts run you around $25, and are 17'... I'll toss in a discount because you're buying a ton of them, so let's say $20 a piece.

In reality, you're probably only gonna use about 10' of that, the other 7' is trash..


So, $20 - 1-2db loss
or

10 ft @ .50 cents per foot = $5
NMO mount =$5


So, $20 vs $10

Even if you hired a guy at $20 an hour, whose job is SOLELY to solder those cables, and he did one every 5 minutes, that's 12 an hour....that adds roughly $1.66 per cable...

So, $11.66 per cable vs $20

So, better signal, at almost HALF the cost... and no waste...

It's a no brainer.

ETA: The cost savings and loss calculations look even BETTER when going for longer lengths..oddball applications like school buses, or command posts....

58 is just so..blah...

Now, if I was pushing LMR400 in a mobile install for a standard sedan sized vehicle, then yeah, I'd expect some flak...

But LMR240UF just makes sense...

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Oh! Come and see the violence inherent in the system! Help, help, I'm being repressed!

$20?

Yikes I wish true radio techs came that cheap!

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"A well regulated breakfast, being necessary to the healthy start of the day, the right of the people to keep and eat food shall not be infringed."

Doesn't have to be a tech if all he's gonna do is solder cable.

They're called *gasp* technical assemblers..

:-p


I'm sure someone could even rig up a jig so it's all but impossible to screw up....



Shit, on the ODOT install, the STATE supervisor who was responsible for signing off on all the work, DEMANDED that we NOT cut the cable...and also demanded that we 'wrap it in a circle, as tight as reasonably possible'... :facepalm:

So, we had some rigs that would've had a 6' cable run, but had 11' of coiled wire sitting next to the XGM....

We had guys with EE's telling them WHY you don't wanna coil up the wire, and the guy just didn't care... 'we're paying for all the wire, so we're gonna use all of it'......

:nono:

_________________
Oh! Come and see the violence inherent in the system! Help, help, I'm being repressed!