Coax cable

[Rawkee1]

I am running about 50' of LMR400 from two antennas. I am running two antennas with two separate cables. I plan on running the last twenty feet of LMR240 I need to snake through walls to reach the radios. How much loss will I have running fromLMR400 to LMR240 the rest of the way? What is the best connectors to use to connect the LMR400 to LMR240 BNC to BNC with the least loss?

 

[kb5udf]

Regarding the cable loss, your exact loss is depends on the frequencies involved. But, for example, my quick
review of loss charts suggests that if you are in the 150mhz region, swapping 20 feet of a 50 feet run, (ignoring loss from connectors), additional loss would be .5db or less.

I can't answer the second question, but have you considered one run of a more flexible cable, such as LMR400 ultraflex? That might simplify
matters and save you a small amount of loss.

 

[Rawkee1]

Regarding the cable loss, your exact loss is depends on the frequencies involved. But, for example, my quick
review of loss charts suggests that if you are in the 150mhz region, swapping 20 feet of a 50 feet run, (ignoring loss from connectors), additional loss would be .5db or less.

I can't answer the second question, but have you considered one run of a more flexible cable, such as LMR400 ultraflex? That might simplify
matters and save you a small amount of loss.

I would run the LMR400 all the way but it has to pass a barrier that the LMR240 will fit. Very tight quarters. I was looking for a low loss BNC double male to link the two coaxes or doesn't it matter?

 

[900mhz]

I would run the LMR400 all the way but it has to pass a barrier that the LMR240 will fit. Very tight quarters. I was looking for a low loss BNC double male to link the two coaxes or doesn't it matter?

Sounds like a point of failure. I have encountered this a few times before and have used the proper bits to drill a large enough hole up around 4 feet to pass 1/2 inch heliax. If you feel overwhelmed by this, contact a qualified electrician to do this.

 

[MTScannerNut]

I would use a surge/lightning arrester right before it enters your building and that also allows you to connect two pieces of coax. Of course, you would need to ground it properly.

 

[mmckenna]

I'd give the LMR-400 a shot, I've routed that through walls without issue. I've even run some LMR-600 in my own home. You may need to install a 90º connector at the end and connect that to a wall plate.

As always, it's wise to use a short jumper for more flexible cable to make the final connection to your radio, as that will keep the stress from the heavier cable damaging the antenna jack on your radio.

For the transition, it's usually best to use mating male to female connectors. That means one connection point. Using a "barrel" connector results in two connection points. While these connections don't add a bunch of loss, and probably not even noticeable to the hobbyist, it's easy to do if you are installing your own connectors, or ordering custom cables.

 

[a417]

You may need to install a 90º connector at the end and connect that to a wall plate.

This.

Too many people think that the inflexibility of -400 prevents you from using it in a wall, as they think that they can't make it around that last 90deg.

 

[Rawkee1]

You may laugh at what I’m about to say but I’ve had very good luck over the years using Rg59 cable. I have less than 75’ runs and I don’t see LMR240 making a whole lot of difference in reception. The Rg59 is a heck of a lot cheaper. I’m a little disappointed after buying the LMR240.

 

[mmckenna]

You may laugh at what I’m about to say but I’ve had very good luck over the years using Rg59 cable. I have less than 75’ runs and I don’t see LMR240 making a whole lot of difference in reception. The Rg59 is a heck of a lot cheaper. I’m a little disappointed after buying the LMR240.

Nope, not going to laugh.

If it works, it works. If you have a strong signal, good antenna, and a sensitive radio, you don't need to spend tons of money on coaxial cable. You just need to get enough signal out of the air and to the receiver with enough strength to give you a usable amount of recoverable signal. If RG-59 does the trick, then go for it. Ignore the haters. If everything you want to listen to is close and strong, do what works for you.

But if you are trying to listen to weak signal stuff, then you'll want something better.

 

[Rawkee1]

Thanks mm, I’ve also found that using the all band Discone antenna brought the signals in to an acceptable level. As I said in a post earlier I’m trying to tune an F23 to 160Mhz, but I don’t have the cut chart. The antenna was given to me and after seeing the length of it, I’m sorry I took it. Seem like a waste to tune it to the frequency area I’m interested in.

 

[mmckenna]

The antenna was given to me and after seeing the length of it, I’m sorry I took it. Seem like a waste to tune it to the frequency area I’m interested in.

Sell it to some ham and buy the antenna YOU want.

 

[Rawkee1]

What is a good quality antenna you’d suggest for uhf & vhf thats simple but yet good. I don’t mind paying as long as it works good. I read some of these threads and some listeners sink some serious money in coax, diplexers, amplifiers, ect. I’m kinda old school, and I’m amazed how technical and advanced monitoring has come. I guess I want an exceptional dual band antenna that I don’t have to tune.

 

[Ubbe]

but I don’t have the cut chart. The antenna was given to me and after seeing the length of it, I’m sorry I took it.

There's nothing that can be done to the laws of physics. An antenna has to be big to be efficient. It's probably tuned to 145MHz if it where already used by someone. Before cutting it, you where given the cut chart in a previous link and you can get it at Diamonds webpage, make reference listening and noting down signal levels from amateur repeaters in the 145MHz band, preferable distant and weak ones. If you can receive ATIS from an airport then also compare with that. Then swap with the F23 and compare to see the difference. If it's not enough to validate a change then sell it.

I would think that an Omni-X antenna would work a little better than a discone, especially on the higher 800MHz bands.

/Ubbe

 

[Rawkee1]

The antenna was bran new. It was never cut or tuned. I can't believe the height of the mast!

 

[Ubbe]

It comes cut to 145MHz from the factory and you can cut it shorter to raise its frequency. It doesn't weigh much, you can easily hold it in your left hand out of a window and control your scanner with your right hand to test, if the height above ground are not too different from the discone and the transmitters are on that side of the house. Or go up on the roof and do the same test there if you take your scanner with you.

/Ubbe