Vhf coax, if it aint broke...?

[El Rubio]

Originally Posted by socaldmax

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.

What i'm suggesting isn't "cutting corners" it's selecting an appropriate product that will perform, in real world communications, just as well. If these were indeed lines in the sand, you wouldn't be able to see two lines because they would be so close.

It sounds like you have a real leg-up on your competition. There are many pages here that describe poor performance, usually caused by real corners being cut, such as connectors smashed with pliers, or not weather sealed. If your competitors used the same antennas, you would hardly, if at all, be able to distinguish between the 50 and 75 watt radios. There's a lot of factors that come into play, such as your description would indicate about a 4dB improvement over your typical competitors. This is also discounting the possible installation issues. 65-85 miles is good, is base camp on a mountain?

[socaldmax]

Originally Posted by El Rubio

What i'm suggesting isn't "cutting corners" it's selecting an appropriate product that will perform, in real world communications, just as well. If these were indeed lines in the sand, you wouldn't be able to see two lines because they would be so close.

It sounds like you have a real leg-up on your competition. There are many pages here that describe poor performance, usually caused by real corners being cut, such as connectors smashed with pliers, or not weather sealed. If your competitors used the same antennas, you would hardly, if at all, be able to distinguish between the 50 and 75 watt radios. There's a lot of factors that come into play, such as your description would indicate about a 4dB improvement over your typical competitors. This is also discounting the possible installation issues. 65-85 miles is good, is base camp on a mountain?

I don't think the difference between 25% loss and 50% loss is that close, as long as the better cable could physically fit I would choose it.

IRT the base camp question, in one instance it was 2 75 watt radios mounted in vehicles, one on a hilltop and the other instance it was a 50 watt radio in a vehicle communicating to my base camp 75 watt radio with a double stacked dipole tuned to 154 MHz mounted on a pole with a height of about 35'. There were some hills in between, so we were a bit surprised at the range we achieved that time.

[The Garbone]

Here is the thing I am considering in LMR240 over 400. On my old RG8 they had it running thru the deck in the mast step and turning a 90 and exiting out the compression post and running across the overhead in the head. They did not use conduit and was nicely sealed they also ran a multi conductor cable for the mast lighting and instrumentation. They did a good job of running it but sealed the base of the mast step and put connectors on all the cables were the exited the deck prior to stepping the mast.

My thought is to replace these cables with a flexible conduit stubbed 3" above the step that I can run 2 coax and a pair of 3-conductor wires for my mast lighting. I will prewire the mast and coil the extra 30ft of coax and 10 feet of wires with a 90 fitting already fed over it at the base of the mast. As we step the mast I can push all the wires down the conduit to a helper below, push on and sealing the 90degree fitting and then use some elephant snot to seal the hole with the cables. (conduit can be sealed to the deck when installed) Hopefully the entire operation can be managed without adding 15 minutes to the stepping operation in which I will be paying for the lift truck and $70 an hour for the its operator and for a rigger.

I hope to have no cuts in the coax between the antennas and radios no excess electrical connections above the deck. My guess it not having a junction in the coax at the deck almost makes up for using 240 over 400.

Oh, here is an good picture of 30 years poo built up in my mast, and no the rg8 was not functional as they PO had a whip tied on the transom.

[transmitterdan]

Originally Posted by 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.

Not exactly. The difference in loss has to be 3dB to say the difference is 1/2 power.

[s/v Jedi]

Originally Posted by transmitterdan

Not exactly. The difference in loss has to be 3dB to say the difference is 1/2 power.

So, half of 3dB is not 1.5dB? Edit: I did write "half the loss", not "half the power"

[El Rubio]

Originally Posted by socaldmax

I don't think the difference between 25% loss and 50% loss is that close, as long as the better cable could physically fit I would choose it.

IRT the base camp question, in one instance it was 2 75 watt radios mounted in vehicles, one on a hilltop and the other instance it was a 50 watt radio in a vehicle communicating to my base camp 75 watt radio with a double stacked dipole tuned to 154 MHz mounted on a pole with a height of about 35'. There were some hills in between, so we were a bit surprised at the range we achieved that time.

I'm talking about the difference perceived by the receiving station. Lets say your 75 watt rig has a medium power switch that cuts it to 50 watts. The other vehicle would not likely be able to tell when you were on 50 or 75. This is my point regarding the two cables. The difference between using one over the other will be imperceivable at these frequencies and lengths.

It sounds like your long distance conversations were possibly tropo ducting at the elevations you described. In that case, you may have been able to converse on just a few watts even. I was on a local 2m repeater a couple of years ago and it was a particularly noisy night rf -wise. Our repeater was open with no pl and would get keyed by the output of a repeater on the input frequency. That distant repeater was about 350 miles away. I had recently picked up an old Icom IC-260 2m SSB/FM 10w radio. I had built a moxon antenna and had it on a test pole in the yard about 15 feet off the ground. It was the only horizontally polarized antenna I had. I switched that rig on, tuned to the ssb calling freq of 144.2 and called CQ. I picked up a ham 59 in Jacksonville. I'm in New Orleans, about 500 miles west. I was using 10 watts at first, but switched over to 1 watt just to see. I was still able to make armchair contact as they say at one watt. The moxon, if you're not familiar is basically a two element yagi with the radiator and reflector elements bent towards each other. It makes the antenna a little smaller, has similar gain to a two element yagi, but the front to back rejection of a 3 element yagi. I don't operate much ssb above 10 meters. Tropo is not very common here at or below sea level. It's exciting when you make contacts like that so I can appreciate your Baja DX.

[transmitterdan]

Originally Posted by s/v Jedi

So, half of 3dB is not 1.5dB? Edit: I did write "half the loss", not "half the power"

Not in power. 1.5dB is 71% and 3dB is 50%.

[transmitterdan]

The difference in 45 feet of LMR240 and LMR400 is 15% in power. In signal strength it's only 8% less. No human can tell the difference so don't beat yourself up over it. Connector loss is the same for both cables. Weather resistance is the same. In either case if you don't weather seal the connector at the mast head it will eventually cause problems.

Marine VHF radios are massively over powered for the range required. Most communications in open water could be done with only 10% of the normal 25W power. Range is dominated by antenna height and a few tenths of a dB in cable loss is insignificant.

[El Rubio]

Originally Posted by The Garbone

Here is the thing I am considering in LMR240 over 400. On my old RG8 they had it running thru the deck in the mast step and turning a 90 and exiting out the compression post and running across the overhead in the head. They did not use conduit and was nicely sealed they also ran a multi conductor cable for the mast lighting and instrumentation. They did a good job of running it but sealed the base of the mast step and put connectors on all the cables were the exited the deck prior to stepping the mast.

My thought is to replace these cables with a flexible conduit stubbed 3" above the step that I can run 2 coax and a pair of 3-conductor wires for my mast lighting. I will prewire the mast and coil the extra 30ft of coax and 10 feet of wires with a 90 fitting already fed over it at the base of the mast. As we step the mast I can push all the wires down the conduit to a helper below, push on and sealing the 90degree fitting and then use some elephant snot to seal the hole with the cables. (conduit can be sealed to the deck when installed) Hopefully the entire operation can be managed without adding 15 minutes to the stepping operation in which I will be paying for the lift truck and $70 an hour for the its operator and for a rigger.

I hope to have no cuts in the coax between the antennas and radios no excess electrical connections above the deck. My guess it not having a junction in the coax at the deck almost makes up for using 240 over 400.

Oh, here is an good picture of 30 years poo built up in my mast, and no the rg8 was not functional as they PO had a whip tied on the transom.

Elephant Snot???
I clicked the link to your blog. I too have a '78 C30 and am interested in what mods others have done. My boat was well cared for by previous owners and still rather new to me. If you would like any pics or layout of anything, just pm me. What is elephant snot?

[The Garbone]

Also affectionately know as monkey ****. I figured that the 90 at the top will help water from wicking down the cables.

We basically bought our boat for the price of the lead keel. A lot of work as I will be replacing every wire and connection in her. The goal is to keep the entire project under $10k minus our labor hours of course.

[El Rubio]

You must have some connection to the phone company. I have seen that stuff on telco ckts and they all called it Monkey Sh!t. I would install a rubber grommet at the mast head and adjust the cables to make a drip loop to keep water from running down the cables. You might consider getting some butyl from Maine Sail and rebedding all of the deck hardware, especially the chainplates since you have the mast down. Maine Sail also has a how to article on his site explaining how to "pot" holes in a cored deck to prevent core damage even if there's a leak.

[The Garbone]

I have plenty of butyl, just not to that stage yet.

I planned on doing the epoxy sealing of the core when I drill out for the conduit. The plan is to use proper bedding and only the monkey **** when sealing the cable in the duct itself. Good advice.

Besides the drip loop at the top I planned on a lightening loop at the bottom. Rumor is lightening does not like to go back up so a 360 loop before the going in a lateral direction will cause it to jump out an of the coax and possibly save the gear. I actually think that the theory is complete horsepoo but that was the practice a few years back when I was doing wireless installs so that is what I plan to do. I have seen enough smoked gear to know the lightening is going to do what it wants.

Maine Sails hall of Fail is some great stuff..