All my RX path questions

[mmckenna]

What is the diameter difference

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LMR-400 = 0.405"
LMR-600 = 0.590"

 

[Bonkk083]

LMR® Cables: Unmatched Flexibility and Minimal Loss for High-Performance Networks | Times Microwave Systems

Explore the power of LMR® Cables for high-performance networks. Experience minimal loss and maximum flexibility for optimal connectivity.

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LMR-400 = 0.405"
LMR-600 = 0.590"

DX engineering told me to use Hardline coax I don't think so

 

[buddrousa]

Here you go do not forget to buy the correct connectors.

Dx Ham Radio Supply - Heliax Coax Hard Line Coaxes

Heliax cables are ideal for applications that require the lowest loss and are great for use on repeaters

www.dxhamradiosupply.com

 

[Bonkk083]

Here you go do not forget to buy the correct connectors.

Dx Ham Radio Supply - Heliax Coax Hard Line Coaxes

Heliax cables are ideal for applications that require the lowest loss and are great for use on repeaters

www.dxhamradiosupply.com

Does the coax take away db from the antenna are just from the antenna to scanner

 

[prcguy]

Does the coax take away db from the antenna are just from the antenna to scanner

It’s loss between the antenna and radio and coax loss will be similar to reducing antenna gain.

 

[AB5ID]

the tower is 36 miles just 851-860 MHz

Are you primarily interested in listening just this one tower? Is there a clear path from your antenna to the tower? You could end up spending more than necessary if that's the case.

 

[Bonkk083]

Are you primarily interested in listening just this one tower? Is there a clear path from your antenna to the tower? You could end up spending more than necessary if that's the case.

By Scadacore I have but that's just a guess if a omni can reach that far I would go with it if not I would go with a yagi

 

[mmckenna]

DX engineering told me to use Hardline coax I don't think so

No, don't use hardline.
It's expensive.
It has a large minimum bend radius.
It is very difficult to install in a residential environment.
If the person installing it for you doesn't know how to work with it, they'll kink it and it'll be trash.
Installing connectors is not easy unless you have done it before.
It's way overkill for 50 feet for scanner use.
Did I mention it's expensive?


No matter which one you choose, you need to use a short jumper of smaller/more flexible coax to connect to your radio. Connecting LMR-400, 600 or hardline/Heliax directly to your scanner is going to break the antenna jack off. Use a short jumper of RG-58 between your scanner and the end of the coax.

 

[Bonkk083]

No, don't use hardline.
It's expensive.
It has a large minimum bend radius.
It is very difficult to install in a residential environment.
If the person installing it for you doesn't know how to work with it, they'll kink it and it'll be trash.
Installing connectors is not easy unless you have done it before.
It's way overkill for 50 feet for scanner use.
Did I mention it's expensive?


No matter which one you choose, you need to use a short jumper of smaller/more flexible coax to connect to your radio. Connecting LMR-400, 600 or hardline/Heliax directly to your scanner is going to break the antenna jack off. Use a short jumper of RG-58 between your scanner and the end of the coax.

I was thinking that Hardline was too much

 

[G7RUX]

I'm planning on is 50' and for as a antenna I'm not sure what to get it's between a 11 dbi omni or a 13-15 dbi yagi the tower is 36 miles just 851-860 MHz

Ok, in that case I would say LMR400 at an absolute minimum but 600 or perhaps the smaller heliax types would be better if you can do that; it’s not cheap but well worth it in the long run.
With that I would suggest a masthead preamp with modest gain and a decent band pass filter would be a good move too.
The antenna and feeder are extremely important parts of any radio system so doing your best there will give excellent resu.

 

[paulears]

The idea is to have the losses balanced against the gains - Lots of people make the mistake of 'improving' the antenna they have on a pole on the house, but installing a tall tower in the garden, but forget the extra distance means cable losses. It's not uncommon for the tower to be worse. This is when people move to mega expensive hardline - because they have to. Having a high antenna and your local geography gives more signal before you even add antenna gain - so losing 50% in the cable can often be lived with. it sounds a lot, but is often quite normal. Going up 10ft can make a lot of difference sometimes, with hardly any extra loss. Other times, it makes no difference - that damn building across the road is still in the way!

 

[Ubbe]

If only receiving then the most economic solution are to use an amplifier at the antenna and you can then use cheap RG6 coax and get better performance than any super expensive hardline you can buy as coax and connector loss and any other type of loss like a splitter will be compensated for. If using a low noise amp it will also increase the sensitivity of the scanner.

The negative aspect will be if you have a powerful local transmitter that could overload the amplifier. But that could then also happen to your scanner.

/Ubbe

 

[G7RUX]

expensive

If only receiving then the most economic solution are to use an amplifier at the antenna and you can then use cheap RG6 coax and get better performance than any super expensive hardline you can buy as coax and connector loss and any other type of loss like a splitter will be compensated for. If using a low noise amp it will also increase the sensitivity of the scanner.

The negative aspect will be if you have a powerful local transmitter that could overload the amplifier. But that could then also happen to your scanner.

/Ubbe

Well, in general I would agree but would like to caution that doing this can lead to more noise than is necessary; keep the losses down as much as is sensible and avoid needing lots of preamp gain to keep the system noise figure down.

 

[buddrousa]

Ubbe has always made the point in his using preamps LOW NOISE and JUST ENOUGH GAIN for the desired effect. As posted in your Quote about the effects of a PREAMP in GAIN and STRONG signals near by.

 

[G7RUX]

Ubbe has always made the point in his using preamps LOW NOISE and JUST ENOUGH GAIN for the desired effect. As posted in your Quote about the effects of a PREAMP in GAIN and STRONG signals near by.

Oh absolutely so. The point is that lossy coax cannot be compensated for with preamp gain without adding extra noise and this can be avoided by reducing the system loss in the first place.

The issue with low gain preamps is that they are often achieved by using a fixed gain block with attenuation rather than a purpose designed amplifier for the required gain, with the latter being more expensive.

All that said, for general scanning use it’s a perfectly sensible approach so long as one doesn’t try to use preamp gain to compensate for unnecessarily poor performance coax; use the best coax you reasonably can as a starter and go from there.

 

[G7RUX]

In the short term it’s not likely to cause any serious performance issues but in the longer term the OP may well want to start using the setup for other things. Hence my suggestion to do the best you reasonably can in the first instance; “do it right and do it once” is a good motto.

 

[prcguy]

Oh absolutely so. The point is that lossy coax cannot be compensated for with preamp gain without adding extra noise and this can be avoided by reducing the system loss in the first place.

The issue with low gain preamps is that they are often achieved by using a fixed gain block with attenuation rather than a purpose designed amplifier for the required gain, with the latter being more expensive.

All that said, for general scanning use it’s a perfectly sensible approach so long as one doesn’t try to use preamp gain to compensate for unnecessarily poor performance coax; use the best coax you reasonably can as a starter and go from there.

When properly done a preamp at the antenna will improve reception compared to the receiver being right at the antenna due to the improvement in system noise figure. A typical scanner has a noise figure in the 5dB range Which is determined by filter loss before any LNA plus mixer conversion loss, etc. If there is no problem with signal overload, placing a .5dB noise figure preamp with minimal gain in front of the scanner will make the entire system noise figure about .5dB. That is a significant improvement for weak signal reception.

 

[AB5ID]

By Scadacore I have but that's just a guess if a omni can reach that far I would go with it if not I would go with a yagi

Can you hear the tower at all with the built in antenna, maybe standing outside on ladder? Listen to the control channel with the squelch open to verify.

 

[G7RUX]

When properly done a preamp at the antenna will improve reception compared to the receiver being right at the antenna due to the improvement in system noise figure. A typical scanner has a noise figure in the 5dB range Which is determined by filter loss before any LNA plus mixer conversion loss, etc. If there is no problem with signal overload, placing a .5dB noise figure preamp with minimal gain in front of the scanner will make the entire system noise figure about .5dB. That is a significant improvement for weak signal reception.

Absolutely so and I wouldn’t disagree. My comment was more aimed at using a preamp to compensate for poor performance coax.

 

[AB5ID]

Ok, in that case I would say LMR400 at an absolute minimum but 600 or perhaps the smaller heliax types would be better if you can do that; it’s not cheap but well worth it in the long run.

LMR400 to LMR600 is only 0.8dB difference at this frequency and length.