The Radio Thread - All Things RF for All Purposes

Joined: August 14th, 2017, 10:03 pm

May 8th, 2018, 2:46 pm #1

OK, per Doc's request, I'll move this radio stuff to its own thread.  And here it is.  Complete with first relevant post.

Sunday I put a couple UHF connectors on a new span of LMR-240UF.  Sounds good, right?  Thirty feet of lovely low loss cable I can use almost anywhere.

Hooked it up to the VNA and wouldn't you know it, flaky as a bowl of rust.  Damn.  Should have added one connector and checked it before adding the second.  Now I have to decide which end I'll cut off.  If it's the good end then I've wasted two connectors. :P  Not going to mess around with ebay RF connectors anymore, going straight to Amphenol through Mouser.

So, yeah, Doc doesn't do much with radio, except maybe a consumer HT on the PB field.  But in the way of TWB, could you imagine a team with a net controller and everyone running around with APRS and some digital mode?  That's the ticket...
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Joined: October 8th, 2014, 2:05 pm

May 8th, 2018, 3:21 pm #2

PoisonOakMagnet wrote:Sunday I put a couple UHF connectors on a new span of LMR-240UF.  Sounds good, right?  Thirty feet of lovely low loss cable I can use almost anywhere.

Hooked it up to the VNA and wouldn't you know it, flaky as a bowl of rust.  Damn.  Should have added one connector and checked it before adding the second.  Now I have to decide which end I'll cut off.  If it's the good end then I've wasted two connectors. :P  Not going to mess around with ebay RF connectors anymore, going straight to Amphenol through Mouser.
I don't suppose your VNA also does time domain reflectometry? That's handy for finding shorts and opens in cables.

If it's a short in the cable an ohmmeter with good resolution at low resistance might give you a hint where the problem connector is. The one with the lowest shield-to-center resistance is probably (maybe?) the culprit.
So, yeah, Doc doesn't do much with radio, except maybe a consumer HT on the PB field.  But in the way of TWB, could you imagine a team with a net controller and everyone running around with APRS and some digital mode?  That's the ticket...
Until you get Roger out there with his laptop snooping your frequency and calling artillery strikes on your positions.
If it ain't broke, I'll fix it!
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Joined: July 28th, 2016, 7:48 pm

May 8th, 2018, 7:59 pm #3

You'll find this interesting.

https://www.rtl-sdr.com/

Using a usb3 to VGA adapter as a SDR transmitter.
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Joined: July 28th, 2016, 7:48 pm

May 8th, 2018, 8:04 pm #4

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Joined: January 11th, 2016, 8:57 pm

May 8th, 2018, 8:53 pm #5

If you want to play with a simple TDR, Google 'Simple TDR'. It'll get you circuits like this...



which, with a reasonable CRO will fire a short pulse down the cable, simultaneously triggering the trace, and let you look at the reflections from the cable to identify where the fault may be. Might save the cost of a connector or two.
Breakfast.com halted. Cereal port not ready.
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Joined: March 6th, 2018, 3:54 pm

May 9th, 2018, 11:51 am #6

Ah a fellow Ham! Greetings from Saginaw. -kc8wzm
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Joined: August 14th, 2017, 10:03 pm

May 11th, 2018, 4:35 am #7

Greetings from Capitola - K8SQB

Saginaw, Bay City and Midland are familiar old stomping grounds.  I went to school at Delta (Kornfield Kollege)

Used the VNA tonight to sort out a band connector on the cable, with a dummy load it was short work to locate the fault and replace, this time with a BNC from Amphenol.  Beats me why I try to save money buying connectors bulk from China.  End up tossing several anyway.  Just spend a few extra bucks and get them from Mouser....
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Joined: March 6th, 2018, 3:54 pm

May 11th, 2018, 1:20 pm #8

Our repeater (K8DAC) has an echo-link set up. Join us on the net Monday evenings at 9pm EDT. Saginaw has built up so much over the years that it isn't so much as much fields as it use to be.
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Joined: August 14th, 2017, 10:03 pm

May 18th, 2018, 1:01 pm #9

ZorronX wrote: Our repeater (K8DAC) has an echo-link set up. Join us on the net Monday evenings at 9pm EDT. Saginaw has built up so much over the years that it isn't so much as much fields as it use to be.
EchoLink: One of the 500 things I've yet to figure out (one of the others is there's more than 500 things)

Because 5 flimsy fibreglass fishing poles isn't enough a 40ft industrial grade pole is now on the way, which one fellow hoists a small quad up. Must be well reinforced to handle that load.
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