Suggest decent LMR-400?

Hi trying to find some decent LMR-400 coax about maybe 15 feet.
This will be for ADS-B and UAT.
I do not want KMR or RG58 Please.

I live in the U.S. btw.

I will be getting the Pro Stick and Pro Stick Plus and these antennas from Flightaware;

1090Mhz

978Mhz

I will be connecting everything to a Raspberry Pi 4B 8gig

Thank you in advance for any help given.

https://www.timesmicrowave.com/Resources/Distributors
You can buy the genuine Times Microwave LMR-400. I’m pretty sure if you contact them they’ll install the N male and SMA male connectors on the ends too.

While I’m a big fan of ‘overkill’, LMR-400 is very stiff and will add a lot of strain to the SMA/USB connectors unless you are very careful.

For only 5m, LMR-200 would give you 1dB performance drop, but would be much easier to work with.

3 Likes

I went and settled on this;

Im going to get 2.

Times Microwave LMR Coax Specs

 

 

 

RG6 Coax Specs

BELDEN TWIN SHIELD RG6

 

BELDEN QUAD SHIELD RG6

 

PASTERNACK QUAD SHIELD RG6

 

 

RG6 is the wrong impedance. 75 Ω as opposed to the correct 50 Ω.

If 75 ohm is wrong impedance, then why 75 ohm is almost exclusively used for TV, Satellite Dishes, and Cable TV?

Neither 75 ohm nor 50 ohm are wrong. They match the system for which they are used.

The voice communication systems were developed first and they adopted 50 ohm as their standard. The Amature Radio and Cell/Mobile phone being voice communication devices, they also adopted the already existing 50 ohm standard for themselves as it was easy and natural choice.

TV was developed independent of voice communication system. Initially the VHF chanels were used, and the VHF TV antennas had 300 ohm impedance. As a result the twin-lead ribbon used to connect TV antenna to TV Receiver was designed as 300 ohm line. The input impedance of TV sets was also designed to be 300 ohms.

Later with introduction of UHF TV channels, the antenna design was modified, and folded dipole with 75 ohm impedance and GHz suitable RG6 coax were developed with 75 ohm impedance. Newer TV receivers were also designed having 75 ohm impdance.

Since the DVB-T dongle is designed as a TV Receiver, its front end chip has an input impedance of 75 ohms :wink:. So connecting a 75 ohm RG6 coax to a Generic DVB-T provides a perfect impedance match.

When DVB-T dongles with integral LNA were introduced, the designers used a 50 okm input/output impedance RF Amplifier chip. This caused an internal impedance mismatch (50 ohm to 75 ohms) at interface of LNA chip and Tuner chip. However as LNA chip’s input impedance was 50 ohms, now it became suitable to connect a 50 ohm antenna coax.

 

Also 50 and 75 ohms are nominal values used as naming conventions. The actual impedances are 52 and 72 ohms. Even if they were actually 50 and 75, in a transmitting antenna and radio designed for 50 ohm coax, using 75 ohm RG6 would represent a 1.5:1 SWR which is quite good, representing only 3% (not dB) of power loss with 97% of the transmitted power reaching the antenna and being radiated (assuming the antenna itself is perfectly resonant at the operating frequency.) In the real world your SWR would probably be somewhere closer to 1.4:1 due to their only being a 20 ohm mismatch which is a 38% mismatch not a 50% mismatch.

In a receive-only system the slight amount of loss of using 75 ohm coax is insignificant compared to the attenuation of the length of coax. RG58 is 50 ohm coax but it’s only 33% efficient at 1100MHz so you would be better off using RG6 which is 50% efficient. Of course LMR400 is even better at 74% efficiency. The higher the efficiency the lower the signal strength attenuation over the coax.

Like antennas, transmission lines are compromises. You may be forced to use what you can get or what you already have, and none of them are perfect so you end up selecting the least bad. Also, like antennas, any coax is going to be better than no coax.

I will be definitely getting LMR-400.

Then you should get it from an authorized Times Microwave distributor or dealer to make sure you’re getting genuine coax and not a clone. Ham radio supply stores (DX Engineering, GigaParts) have it in bulk or by the foot but you’ll need to also buy crimp-on connectors and a crimper tool and coax stripper.

Although speaking of clones, I’ve had excellent results with pre-made cables I’ve bought from a store called “coolelectronics” in China. I don’t know if they have a presence on Ali or Bangood though, I’ve ordered mine from an online shopping site called Lazada that’s only in certain SE Asian countries. I’ve purchased several coax cables from them and they’re of excellent quality.

If you get Times Microwave brand I’d spring a few more bucks for their Ultraflex version. It may not be as stiff as regular LMR400 and has a tighter minimum turn radius making it easier to route the cable.

I really want to get it pre-made cause I don’t know how to crimp and don’t want to mess it up.

I live in the U.S.

I thought Ali Express was a bad place to go cause of fake stuff,clones,crappy made stuff.

I don’t want a clone.

https://www.amazon.com/gp/product/B013CY0IRU/ref=as_li_ss_tl?ie=UTF8&linkCode=sl1&tag=adsbexchange-20&linkId=ffcdd64c593acfb3d5d9dea42844175a&language=en_US&th=1

https://mpddigital.us/

2 choices above.

Another good coax cable assembler on the West coast is Pasternack. Used to deal with them in a former life. https://www.pasternack.com

1 Like

Pasternack is good.

Also try Air802. Good cables.

Ok im going to shoot for either the 15 or 25ft hopefully it works great.

That should work fine, especially for such a short coax run. LMR240 is what I use and it works well for me.

Ill be doing the 400 Series,my bad thought they had 15 ft in 400 Series lol.
So I guess I’ll be doing the 25ft 400 series.

FYI this will coax calculator be helpful in deciding which coax to buy: - Times Microwave

So how did it turn out?
Which did you get?

I was considering the LMR240 because of the cost, flexibility and of course jaymot’s recommendation :wink: