Vhf coax, if it aint broke...?

[Ketchgould]

Thanks all. Going to record and wire. Switching from rg8 to 400 as well. Led masthead replacement too.

[The Garbone]

240 or 400? I was leaning towards 2 runs of 240 to install AIS on the spreader.

[El Rubio]

Originally Posted by The Garbone

240 or 400? I was leaning towards 2 runs of 240 to install AIS on the spreader.

On a C27 or C30, I would go for the 240 myself. Many here disagree and insist on having the absolute lowest cable loss without truly considering what a dB, or fraction thereof, really means in real world operations.

[s/v Jedi]

Originally Posted by El Rubio

On a C27 or C30, I would go for the 240 myself. Many here disagree and insist on having the absolute lowest cable loss without truly considering what a dB, or fraction thereof, really means in real world operations.

Trying to sneak through with the cheaper options again, aren't you?! This was discussed before and the consensus was that you were wrong and low loss cable wins every time (for receiving as well as transmitting during bad conditions)

LMR400 beats LMR240 in every way except price.

[El Rubio]

Facts don't have to sneak. LMR240 is SMALLER. If space is limited, or running multiple leads, it's low loss for its size is a good selection.

[transmitterdan]

Originally Posted by s/v Jedi

Trying to sneak through with the cheaper options again, aren't you?! This was discussed before and the consensus was that you were wrong and low loss cable wins every time (for receiving as well as transmitting during bad conditions) LMR400 beats LMR240 in every way except price.

Sorry, but that's not what the math says. A fraction of a dB is not a big deal. Other considerations such as cost and weight are as important. Often times loss in signal happens in the connectors if done poorly. Good connectors properly installed are much more important that the type of cable.

In the other threads where this was debated one proponent of low loss cable had mistakenly set his radio at over 13db below full power and was able to make long distance comms work.

In blind testing few people can tell the difference 3dB makes. At 10dB most can tell the difference. No human can discern 1dB in a blind test.

[s/v Jedi]

The game of words. You are right, a fraction of a dB (that would be 0.1dB) is not an issue. But that has zilch to do with installation on a boat, where we are not talking about a fraction of a dB.

[Celestialsailor]

Originally Posted by Roy M

And while you're at it, pull out every piece of electrical wiring in the mast, and probably the fixtures. From your statement regarding the age of the boat and the frequency of removal of the mast, you probably have some surprises waiting for you. When the mast is down, it's relatively easy to do this work. When it's up, it's a real bear. Also, pull out the sheaves and grease the axles, check each and every fastener to see if it simply snaps off with reasonable torque. It's better to fix this stuff now before it costs a heck of a lot more later.

Double ditto

[socaldmax]

The published specs for LMR240 and 400 are for perfect world lab conditions.

Throw the cumulative effects of less than perfect connections, high power, salt, rain, age, cable loss, the expense of removing the mast...

and one could easily be looking at 3dB losses in a couple of years, which is 50% loss. I'd err on the side of better quality cable if at all possible. You can get a 75' length of LMR400 for under $100.

[madsb]

After reading this thread I tried playing a bit around with Welcome to Times Microwave | Coaxial Cable - Attenuation & Power Handling Calculator which suggests that the difference between LMR-240 and LMR-400 would be around 0.7 dB (0.8 vs. 1.5 dB) given a transmission frequency of 150 MHz and a run length of 45 feet.

[El Rubio]

Originally Posted by socaldmax

The published specs for LMR240 and 400 are for perfect world lab conditions. Throw the cumulative effects of less than perfect connections, high power, salt, rain, age, cable loss, the expense of removing the mast... and one could easily be looking at 3dB losses in a couple of years, which is 50% loss. I'd err on the side of better quality cable if at all possible. You can get a 75' length of LMR400 for under $100.

I disagree mostly. These cables, like most, are designed for the conditions you described. Standard Times Microwave ( LMR)cables are designed to withstand 20 years of UV exposure. I work with these cables regularly and they are no less durable than anything else in their class. Suggesting the cable will quickly degrade when exposed to elements can't be based on actual cable performance; but possibly other components like improperly terminated connectors, or physical damage which would be the same for any. Cable type. Specifically, the LMR240 is just as impervious to weather and elements as LMR400. If those have an effect over years, it isn't going to manifest itself as a small loss either. LMR240 is rated for >600watts at VHF frequencies. High power will not be an issue. You might also be able to fish the smaller cable down a mast without stepping it.

The point of agreeing with the poster's selection of 240 instead of 400 is in the fact that he said he was running two runs. Two runs of 240 are just slightly larger than a single run of LMR400. LMR240 runs about $0.20 per foot cheaper than LMR400. The savings is minuscule, but that isn't the main point. Size and flexibility combined with decent attenuation should also be considered.

Madsb makes the point that the difference in loss is minimal. Lmr400 is better performing cable, but not by much at vhf and not if it doesn't fit. Would you consider Lmr600, lmr900, fsj50, etc, because all of those are better performing than Lmr400? I'd guess probably not, because of size, flexibility, cost, and the fact that the performance gains are minimal and undetectable in actual operations.

[socaldmax]

Originally Posted by El Rubio

I disagree mostly. These cables, like most, are designed for the conditions you described. Standard Times Microwave ( LMR)cables are designed to withstand 20 years of UV exposure. I work with these cables regularly and they are no less durable than anything else in their class. Suggesting the cable will quickly degrade when exposed to elements can't be based on actual cable performance; but possibly other components like improperly terminated connectors, or physical damage which would be the same for any. Cable type. Specifically, the LMR240 is just as impervious to weather and elements as LMR400. If those have an effect over years, it isn't going to manifest itself as a small loss either. LMR240 is rated for >600watts at VHF frequencies. High power will not be an issue. You might also be able to fish the smaller cable down a mast without stepping it.

The point of agreeing with the poster's selection of 240 instead of 400 is in the fact that he said he was running two runs. Two runs of 240 are just slightly larger than a single run of LMR400. LMR240 runs about $0.20 per foot cheaper than LMR400. The savings is minuscule, but that isn't the main point. Size and flexibility combined with decent attenuation should also be considered.

Madsb makes the point that the difference in loss is minimal. Lmr400 is better performing cable, but not by much at vhf and not if it doesn't fit. Would you consider Lmr600, lmr900, fsj50, etc, because all of those are better performing than Lmr400? I'd guess probably not, because of size, flexibility, cost, and the fact that the performance gains are minimal and undetectable in actual operations.

What we're doing here is essentially quibbling over lines in the sand. One person thinks LMR400 is worth it, another thinks LMR240 will work just fine...

and yet another will think that RG8 is all that one needs. The evidence of that is how much RG8 is currently out there? Probably quite a bit.

We all need to use some common sense. If LMR400 won't fit, then possibly LMR240 or something even thinner might be better, or perhaps the answer is to make a larger channel. It all depends on what one feels is acceptable.

I sell race radios to the Baja racing/offroading crowd. I'm the newest competitor in this field, and all of my better established competition have no electronics background, they simply slap a sticker onto the product and resell it at 100% profit. They sell a 50 watt radio with an off the shelf 1/2 wave antenna. I sell a 75 watt radio with a properly mounted 5/8 wave antenna on a ground plane, tuned to midband.

At first glance, the difference between my rig and the competition might look like an extra 50% more power. But in reality, the difference is my rig clearly transmits and receives 4x to 6x farther than theirs, depending on terrain. That's not a minor difference when your vehicle is broken 25 mi from camp, that's the difference between wondering why no one can hear you and being able to clearly communicate with someone who can bring tools and parts. We routinely get 65-85 mi between vehicle and base camp, while all of my competitors struggle to get past 15-20 mi.

Sure I could have cut corners like my competition, but the entire reason I got into the field was because I was dissatisfied with the horrendous performance of the $600 radio/antenna kit that I bought, and I knew I could do at least twice as good for half the price. My personal philosophy is once you start cutting corners, why not cut a few more? Pretty soon that nice, perfectly straight and square box you intended on building looks a lot like a circle.

But again, that's just where I draw my line in the sand, and everyone draws theirs in a different location, whether it's a cost/benefit ratio, ease of installation, what will or won't fit, etc. I'm certainly glad my competition cut a lot of corners and sells overpriced, underperforming radios, or I wouldn't be making any money in that particular little niche.

[socaldmax]

Originally Posted by madsb

After reading this thread I tried playing a bit around with Welcome to Times Microwave | Coaxial Cable - Attenuation & Power Handling Calculator which suggests that the difference between LMR-240 and LMR-400 would be around 0.7 dB (0.8 vs. 1.5 dB) given a transmission frequency of 150 MHz and a run length of 45 feet.

Since antenna height is your friend, I would opt to mount the antenna at the top of the mast, if there is any room up there. Let's say the avg mast height is 60-65 ft. We need to add a bit to get to the radio, so I'd say at least 75 ft of cable, possibly 85ft.

Using the chart you linked to, under perfect conditions, total calculated loss would be 1.3dB to 1.5dB, assuming there are no imperfections in the section of cable you bought.

Doesn't sound like much, does it? 1dB of cable loss is 25% power loss.

An 85ft section of LMR240 with 2 connectors is calculated to have a combined loss of 2.8dB. Depending on who attached the connectors, brand, etc, one could easily get another .2dB of loss, for a total of 3dB of loss at 150MHz. Again, doesn't sound like much.

3dB is 50% power loss. Assuming a perfectly tuned antenna (highly unlikely if someone bought an off the shelf antenna) and a 50 watt radio, max. output power is only going to be 25 watts. Jeez, now that the power numbers are inserted into the equation, I hate to lose 50% of anything - receive sensitivity, transmit power, income, internet speed, fuel economy.

Now throw in an untuned antenna (perhaps tuned to 144MHz instead of 150MHz or higher) and your VSWR could be pretty high, limiting output power and receive sensitivity even further.

[socaldmax]

One more (possibly minor) issue is the dielectric material. I just looked it up, and LMR240 and 400 both use PF, polyethylene foam for their dielectric material. While it significantly decreases losses over solid PE dielectric, it is supposedly capable of absorbing moisture from the environment, according to wikipedia.

I don't know how much moisture it actually would absorb in a properly terminated/sealed application onboard ship, but a wild guess would tell me it might not be too much of an issue or Times microwave wouldn't be using it as a dielectric, or they'd be warning people not to use it in a tropical rain forest or in a marine environment.

[s/v Jedi]

The calculations are easy. LMR240 will only pass half the signal for both receive and transmit. That is why I wrote before that we're not talking about a couple of tenths of dB, because LMR400 only has half the losses, i.e. 1.5dB vs 3dB means a 1.5dB difference. With LMR400 you cut the losses by half for very little extra cost.