Base Antenna Issues

[gortex2]

From Post here - HERE

 

@Flameout said - "The cablelowering it and all of a sudden I could pick up the repeater. I just had lots of noise, especially compared to the mag mount Nagoya about 3' off the ground. I really wouldn't mind buying another antenna if I knew it would work. Too bad there isn't a store that rents them is 50' of ABR Industries RG 8/U and the SWR is great (but then again, it is also great using a dummy load) I had the antenna up about 20' but experimenting one day, I was"

@WROZ250 gave you some good info. For a base radio I'd use the best you can find. You said you are using 50'. Do you really need that much cable ? 

I would use the least amount as possible. I'll be honest I would not even entertain 50' of LMR myself but know not everyone can afford LDF cable. I would say if you can get down to 25' of cable you may find a much better experience. I will also suggest watching ebay for LDF. I have seen 50' chunks for around $100. You need to search and it may take some time but LDF is online and can be had reasonable. 

 

[Flameout]

I ended up running that Wireman LL400, which according to that coax calculator, is almost identical in specs to my LMR-400 and I am, at least for now, receiving the repeater using the Comet 712EFC.  I think it's time I learned more about coax!  I looked on that calculator for LDF cable and didn't see it there? Is there a specific name for that cable? I can definitely shorten the run. I was saying 50' because that is just the length of cable I have. It is probably about 35-40' total run.

[gortex2]

LDF4-50A is standard 1/2" Hardline

LDF4-50A

AVA-50 is the 7/8" Hardline. Anything over 100' I run that. To be honest all my repeaters have 7/8" and some are only 50' up the tower. 

AVA-50

[JohnE]

I posted this a few yrs ago.

https://forums.mygmrs.com/topic/252-cable-types-and-losses

 

[WyoJoe]

3 minutes ago, JohnE said:

I posted this a few yrs ago

https://forums.mygmrs.com/topic/252-cable-types-and-losses

 

John,

I've seen that post before and it definitely contains some great info. It helped me to realize that RG- series cable isn't sufficient for runs of even a moderate length (~30 to 50 feet) unless you are willing to accept the significant losses.

That's really what it boils down to: how much loss (for both Rx and Tx) are you willing to accept in your feedline?

Obviously, there will be some losses regardless of what you use. They can be minimized by keeping your runs as short as possible, and using the best feedline for your situation. Your information helps us to make informed decisions about what feedline works best from a cost vs. performance perspective.

[gman1971]

Loss in the feedline is inevitable, nothing you can do about that.

Realizing that some loss in the feedline won't have much impact on range is the hardest thing to understand. A 2 dB loss in the feedline won't affect range if the antenna system is optimal, ie, placed high enough and the antenna is not a dummy load. When you add any filtering, you'll quickly incur in a 2 dB loss in the feedline. Again, some filtering might reduce a couple dB from your signal, but will remove 80 dB or more from all the unwanted trash... which will improve receiver performance.

Then there is always the choice of using a tower mounted LNA preamp... which will handily overcome the feedline losses on receive.... but you'll probably need another TX PA to make up for too much loss on the feedline.

G.

[JohnE]

my over all loss at my remote site is ~2.5db. here is the  breakdown, Pa into a celwave bp/br duplexer -.8, Connecticut microwave isolator -.4, 5' FSJ4 (1/2" superflex), polyphaser mounted on a ground bar and 95' of LDF5 50A -.8.
It was initially tested w/100W PA that gave me ~75W at the antenna port. once the antenna was up it was checked w/site master and showed an SWR of 1.35 and a return loss IIRC was ~16. power reading was 75W FWD/1.5W REF.

There is also a DEI LNA on the Rx side w/3db pad.

[gman1971]

10 minutes ago, JohnE said:

my over all loss at my remote site is ~2.5db. here is the  breakdown, Pa into a celwave bp/br duplexer -.8, Connecticut microwave isolator -.4, 5' FSJ4 (1/2" superflex), polyphaser mounted on a ground bar and 95' of LDF5 50A -.8.
It was initially tested w/100W PA that gave me ~75W at the antenna port. once the antenna was up it was checked w/site master and showed an SWR of 1.35 and a return loss IIRC was ~16. power reading was 75W FWD/1.5W REF.

There is also a DEI LNA on the Rx side w/3db pad.

Nice.

Whats the LNA gain? 

[JohnE]

17dB w/0.5 noise figure. forgot to mention there is a pre selector in front of the LNA w/1dB insertion loss. duplexer is 0.9 loss. the net gain w/cable and insertion losses is ~11.5dB. its a little hot.

[gman1971]

7 hours ago, JohnE said:

17dB w/0.5 noise figure. forgot to mention there is a pre selector in front of the LNA w/1dB insertion loss. duplexer is 0.9 loss. the net gain w/cable and insertion losses is ~11.5dB. its a little hot.

not bad, what is the IP3? 

My LNA has an 11dB pad after it... but I also have a much shorter run so the net gain on mine is about ~8dB.

[JohnE]

there was no IP3 spec

here is the current spec sheet for it.  mine is 12 or 15 yrs old and has a different configuration when he was still in NJ. 
http://01895fa.netsolhost.com/PDF/l-lna.PDF

I really miss Chip from Angle linear he made some great stuff but he retired a few yrs ago

wow his spec page is still up

http://www.anglelinear.com/gaasfet/phemt.pdf

[gman1971]

Very nice, the one I am using is this one:

https://www.minicircuits.com/pdfs/ZX60-P103LN+.pdf

It has a very high IP3 and it works very well even in very high noise sites.

G.

[JohnE]

yeah Mini makes some nice stuff. have a RLB from them for my tracking gen