Coax jumper for use with PS

JJ4SDR
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Coax jumper for use with PS

Postby JJ4SDR » Fri Sep 16, 2022 2:52 am

Any recommendations for reliable source for the coaxial jumper to use Pure Signal? Many out there, but would want the very best quality. BNC one end and SMA male on the other (amp end).

Cheers,
Juha
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w-u-2-o
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Re: Coax jumper for use with PS

Postby w-u-2-o » Fri Sep 16, 2022 12:11 pm

This is a non-critical application. <50MHz, low power level, short distance. Any 50 Ohm impedance coax cable that isn't total garbage or actually broken will work. I'd buy whatever looked best off of Amazon (and often do ;) )

https://www.amazon.com/s?k=sma+to+bnc+cable

The best part about Amazon is that if some reason it was junk just send it back and get a different one.

However, it is fair to say that there is a lot of junk on Amazon and I've certainly received my fair share. If price is no object, then buy from Pasternack or L-com, both top of the line, professional sources for RF cables, connectors and other goodies. Their catalogs are extensive, and if that's not good enough they will literally make whatever you want (for a price!)

https://www.pasternack.com/rf-cables-category.aspx
https://www.l-com.com/
JJ4SDR
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Re: Coax jumper for use with PS

Postby JJ4SDR » Fri Sep 16, 2022 8:19 pm

Hi Scott,

Looked at Pasternack as well.

Low power level indeed, but in my case, the jumper will need to be about 5 feet in length. I would prefer something like 1 foot, but that isn't doable today. Curious if ferrite snap-ons may be necessary? Well, I presume I try it without first as they me completely redundant.

Best!
Juha
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w-u-2-o
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Re: Coax jumper for use with PS

Postby w-u-2-o » Fri Sep 16, 2022 9:44 pm

You are way over-analyzing this...
K1LSB
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Re: Coax jumper for use with PS

Postby K1LSB » Fri Sep 16, 2022 9:54 pm

There is one specific requirement I have for my PS jumper, and that is excellent shielding. I don't want any RF at all getting into the jumper and influencing the PS feedback (I sometimes feed 1KW into my dipole which is only 35 feet above my shack).

LMR coax (240 or 400) has an advertised shielding of >90 dB so that's what I use.

But that's just me.

Mark
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Re: Coax jumper for use with PS

Postby JJ4SDR » Sat Sep 17, 2022 2:16 am

Hi Mark,

Those are the thoughts that I was entertaining, and, yes, that may amount to "over-analyzing." :lol:

Best!
Juha
PC: 8 Core i7-10700 CPU @ 2.90GHz, NVMe SK Hynix 512 GB SSD, 32GB RAM
Windows 10 Home, Version 22H2
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K1LSB
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Re: Coax jumper for use with PS

Postby K1LSB » Sat Sep 17, 2022 11:55 am

I attribute my own over-analyzing to a particularly sinister manifestation of what my doctor calls CDO. He says it's similar to OCD but the letters are in alphabetical order.. :D

Mark
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Re: Coax jumper for use with PS

Postby AG5CK » Sat Sep 17, 2022 12:58 pm

I don't know where to find top shelf sma cables but it isn't critical. The ones I bought from Amazon seem to be good quality. Read the reviews.

My puresignal jumper consists of around 60 feet of lmr400, an antenna switch to select the amp amplifier and some Amazon sma cables at each end.
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w-u-2-o
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Re: Coax jumper for use with PS

Postby w-u-2-o » Sat Sep 17, 2022 1:02 pm

If you want to get crazy:

https://www.pasternack.com/sma-male-bnc-male-pe-p195-cable-assembly-pe33989-60-p.aspx

Triple shielded!

But it'll probably be a lot less expensive to pick up a BNC-BNC LMR240 assembly off of Amazon and add a BNC to SMA adapter.
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w9ac
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Re: Coax jumper for use with PS

Postby w9ac » Sat Sep 17, 2022 6:47 pm

For RF sampling and 10 MHz external reference, I use preassembled BNC-to-SMA RG-316 cables. Teflon dielectric, FEP jacket, silver-plated inner conductor and shield. Have a look at eBay item number: 141559843103. The four-foot cable length is only USD $12 with free shipping from California. Or, this from Amazon:

https://tinyurl.com/27r54d9n

There's no need for a larger cable size. Short-length attenuation is minimal below 50 MHz, and more importantly, attenuation change within the sampled passband is negligible.

Paul, W9AC
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w-u-2-o
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Re: Coax jumper for use with PS

Postby w-u-2-o » Sat Sep 17, 2022 7:11 pm

That's what I use, also, Paul. But Juha is worried about shielding effectiveness and LMR240 performs substantially better in that respect than RG316.
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w9ac
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Re: Coax jumper for use with PS

Postby w9ac » Sat Sep 17, 2022 8:41 pm

I've long been suspicious of Times' spec of >90 dB shielding effectiveness from their LMR series of cables. That spec is nonsense as it doesn't convey effectiveness as a function of frequency. There's no way Times can justify >90 dB effectiveness across a broad RF spectrum, especially at HF.

At HF, braiding is substantially more effective than a foil. Cables with a braid + foil are a good compromise for shielding effectiveness when used across a large RF spectrum. But if I was really concerned about getting the most PureSignal shielding effectiveness below 50 MHz, I would use multi-braid cable. RG-316 is offered in a dual-braid version like this:

https://tinyurl.com/mry3er4a

That said, I typically see -60 dBc to -70 dBc IMD products from my legal-limit amps with PS engaged. An 80m center-fed Zepp with balanced open feeders is about 50 ft above the shack. At least at this location, I doubt any further performance improvement can be attained with a double-braid sampling cable.

Paul, W9AC
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w-u-2-o
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Re: Coax jumper for use with PS

Postby w-u-2-o » Sat Sep 17, 2022 10:12 pm

That double braid is good stuff:

http://suddendocs.samtec.com/testreports/shielding-effectiveness-report_rf316_web_shd.pdf

That eBay link is an outstanding find. Assuming the cable is built well and they are really using the RG316-D. They are so cheap I'd buy an extra piece or two just to cut up and inspect for material and workmanship.
K4IBC
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Re: Coax jumper for use with PS

Postby K4IBC » Sun Sep 18, 2022 8:26 pm

Even RG400 would be a good option. Easier for me to have one common type of coax in the shack rather than different sizes and all the different connectors associated with it.
JJ4SDR
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Re: Coax jumper for use with PS

Postby JJ4SDR » Sun Sep 18, 2022 11:55 pm

I ended up getting Military-grade RG174/U rated 50 Ohm coax with 90% braid coverage (Amazon), hoping that it will fit the bill. If not, I will look at alternatives.

Juha
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w9ac
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Re: Coax jumper for use with PS

Postby w9ac » Sun Sep 18, 2022 11:58 pm

K4IBC wrote:Even RG400 would be a good option. Easier for me to have one common type of coax in the shack rather than different sizes and all the different connectors associated with it.

I use RG400 for all shack RF transmission cabling and RG316 for small-signal applications like PureSignal sampling and GPSDO distribution. That way, I'm less apt to grab the wrong cable and blow out the GPSDO or sample output coupling port by accidentally transmitting into it. So, RG400 for high power, RG316 for low power.

Another consideration is that due to the higher bending tension of RG400, it can sometimes place undue stress on the mating SMA jack, especially if it's only mounted onto the PC board without chassis hardware. The SMA jacks on the Hermes Lite 2 transceiver is one example.

Paul, W9AC

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