Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
Amplifier internal coax runs.




 
The AM Forum
January 28, 2023, 12:42:52 PM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: Amplifier internal coax runs.  (Read 553 times)
0 Members and 1 Guest are viewing this topic.
KD1SH
Member

Offline Offline

Posts: 475



« on: January 19, 2023, 03:00:22 PM »

Making great progress on my 8877/YU-158 two-holer restoration, and now getting into some internal RF wiring. Spaces are tight and bend radius becomes an issue. To comfortably use RG-8 or 213 I'd need to do some drilling and blasting. Anyone use LMR-240 or similar for internal RF connections in big amps? The specs I'm finding are a bit confusing: Times Microwave says: "Power Handling (DWV) 1500". Yet "DWV" usually means Dielectric Withstanding Voltage - hardly a measurement of power. And then they say: "Peak Power KW 5.6".
I intend the run the amp at legal output on the air, but I'd like to be able to test those tubes into an appropriate dummy load at something at least close to their maximum capabilities, to find out where they're at, condition-wise. Those two tubes would probably make somewhere around 4KW PEP. I'd think that the issue with very sort runs of coax would be more one of peak voltage rather than total power in watts.
Logged
KD6VXI
Contributing
Member
*
Offline Offline

Posts: 2533


Making AM GREAT Again!


« Reply #1 on: January 19, 2023, 06:36:11 PM »

LMR240 is garbage for what you are looking at.

That 5kw figure?  Peak pulse.  Not a high duty cycle.

LMR400 I've used at 10 grand avg //10 meters//....  The Amphenol right angle gave up before the LMR did.  Old school Amphenol soldered ends.

I've run a pair of 3000 on LMR600.  The figures above where a single tube.  Being beat on, but done.

I say this so you can kind of extrapolate num era for your own use.

LMR400 would be fine unless you plan on really laying into the amp.  The true rating vs frequency of LMR240 is attached.  A single 8877 will turn it into mush.  It's rg8x.

There is RG400 and other small bend radii coass available, just have to break out the pocketbook.

I've also made a psuedo strip line before.  Used a calculator I found online to space a copper bar I had.  Used it from Ctune to the vac relay.  The calculator said its dimensions spaced xxx mm from the ground plane (chassis) would be 50 ohms.

I did it, it worked, and was a PITA to get all the spacing, etc right.




But, if I can get a piece of 1 5/8 heliax into an rf deck, you got this 😁

--Shane
WP2ASS / ex KD6VXI


* Screenshot_20230119_192944_Foxit PDF Editor.jpg (471.86 KB, 2400x1080 - viewed 32 times.)
Logged
KD1SH
Member

Offline Offline

Posts: 475



« Reply #2 on: January 19, 2023, 07:00:18 PM »

Thanks, Shane - I know you're a QRO guy so I was figuring you'd answer this. I'll probably go with LMR400; I'll just have to hog out some more metal to make room. I was trying to avoid that because I hate to subject the Jennings vac-variables to a ton of metal-mutilating vibration, (heavy gauge steel) and removing them would be a pain. Otherwise I'd just have at it with my air-chisel. Pneumatic die-grinder should get in there okay, with less impact vibration.

LMR240 is garbage for what you are looking at.

That 5kw figure?  Peak pulse.  Not a high duty cycle.

LMR400 I've used at 10 grand avg //10 meters//....  The Amphenol right angle gave up before the LMR did.  Old school Amphenol soldered ends.

I've run a pair of 3000 on LMR600.  The figures above where a single tube.  Being beat on, but done.

I say this so you can kind of extrapolate num era for your own use.

LMR400 would be fine unless you plan on really laying into the amp.  The true rating vs frequency of LMR240 is attached.  A single 8877 will turn it into mush.  It's rg8x.

There is RG400 and other small bend radii coass available, just have to break out the pocketbook.

I've also made a psuedo strip line before.  Used a calculator I found online to space a copper bar I had.  Used it from Ctune to the vac relay.  The calculator said its dimensions spaced xxx mm from the ground plane (chassis) would be 50 ohms.

I did it, it worked, and was a PITA to get all the spacing, etc right.




But, if I can get a piece of 1 5/8 heliax into an rf deck, you got this 😁

--Shane
WP2ASS / ex KD6VXI
Logged
K9MB
Member

Offline Offline

Posts: 274


« Reply #3 on: January 19, 2023, 07:43:32 PM »

I am working on a 2x 4-1000a amp. Certainly not as powerful as a pair of 8877s , but my plan is to use RG303 for input circuits and RG-400 for output runs in the chassis.
RG 400 will handle 2kw up to 10 meters and RG303 is not far behind.
RG-303 is smaller and more flexible but either will work I think.
73, Mike

Logged
W1ITT
Member

Offline Offline

Posts: 533


« Reply #4 on: January 19, 2023, 07:48:26 PM »

One thing I have done to save space on in-chassis coax runs is to skin the jacket off the cable.  It ain't gonna be raining in there.
73 de Norm W1ITT
Logged
KD1SH
Member

Offline Offline

Posts: 475



« Reply #5 on: January 19, 2023, 07:57:17 PM »

Good idea.

One thing I have done to save space on in-chassis coax runs is to skin the jacket off the cable.  It ain't gonna be raining in there.
73 de Norm W1ITT
Logged
W7TFO
WTF-OVER in 7 land Dennis
Contributing
Member
*
Offline Offline

Posts: 2451


IN A TRIODE NO ONE CAN HEAR YOUR SCREEN


WWW
« Reply #6 on: January 19, 2023, 10:11:33 PM »

Harris Broadcast used up to 20' of solid-dielectric RG-8 to connect the 50kW PSU to the amplifier cabinet, carrying 10kV @ 5A 24/7 in their HT-series FM transmitters.  Never seen that part fail.

73DG
Logged

Just pacing the Farady cage...
K9MB
Member

Offline Offline

Posts: 274


« Reply #7 on: January 20, 2023, 10:30:26 AM »

Harris Broadcast used up to 20' of solid-dielectric RG-8 to connect the 50kW PSU to the amplifier cabinet, carrying 10kV @ 5A 24/7 in their HT-series FM transmitters.  Never seen that part fail.

73DG

Wow! I have never seen anything like that much power in an RG-8 cable either.
If it was known that it would fail at a predictable time, I would travel there, pop popcorn and get a 6 pack and watch it from 50 yards away. 😉😂😂😂

Seriously, I have long wondered why RG-8 is rated at 4kV when polyethylene that thick should handle twice that much. Connectors have to be the limitation and keeping the curves long and no kinks…
Logged
W7TFO
WTF-OVER in 7 land Dennis
Contributing
Member
*
Offline Offline

Posts: 2451


IN A TRIODE NO ONE CAN HEAR YOUR SCREEN


WWW
« Reply #8 on: January 20, 2023, 10:45:35 AM »

They used no connectors, rather stripped coax and lugs screwed to porcelain standoffs.

73DG
Logged

Just pacing the Farady cage...
K9MB
Member

Offline Offline

Posts: 274


« Reply #9 on: January 20, 2023, 11:18:03 AM »

They used no connectors, rather stripped coax and lugs screwed to porcelain standoffs.

73DG

Sounds perfect. I just checked- polyethylene has a voltage rating of 20kv/mm.
That makes that RG-8 a super insulated cable, even though they only rate it at 4kv.
Great stuff sitting in every ham shack, right?
I will be using Rg-213, which is almost the same thing for my 4500volt cable from ps to amp.
I still like Rg-400 and Rg-303 for short RF runs. Rg-400 Good for several kw at HF. MB.


Logged
W7TFO
WTF-OVER in 7 land Dennis
Contributing
Member
*
Offline Offline

Posts: 2451


IN A TRIODE NO ONE CAN HEAR YOUR SCREEN


WWW
« Reply #10 on: January 20, 2023, 12:24:51 PM »

Yep, 8 & 213 are the best small coax in my book because of the connectability.

I've had many failures with the LMR stuff, even with factory-applied connectors that just pull right off with little encouragement.

A properly applied type N or UHF on RG8 will stay there thru a lot of abuse.

The best I've seen are the DIN 7-16 jobs.  Rugged, watertight, economical, and easy to use. (If one has the room for them).

73DG

Logged

Just pacing the Farady cage...
W2JBL
Member

Offline Offline

Posts: 669


« Reply #11 on: January 20, 2023, 08:03:12 PM »

I use RG-142 and RG-303 for all my station jumpers, and internal cabling in the 4-1000 amp here. The 4-1000 does close to 3 KW, and I also run a Johnson Desk KW (no desk) that does 1200 carrier and 6KW PEP. No issues with cable melting/arc over etc. We used LMR-400 at Motorola with good results as long as we used good connectors. That said LMR-400 would be difficult to use for internal wiring without connectors. The center conductor is copper clad aluminum and can't be easily soldered. The foil under the braid wicks the heat away from it if you try to solder it. It's crimp connectors only. There is a pretty long list of stuff the Johnson KW has torched but never any of my RG-142 cables.
Logged
K9MB
Member

Offline Offline

Posts: 274


« Reply #12 on: January 21, 2023, 10:03:39 AM »

I use RG-142 and RG-303 for all my station jumpers, and internal cabling in the 4-1000 amp here. The 4-1000 does close to 3 KW, and I also run a Johnson Desk KW (no desk) that does 1200 carrier and 6KW PEP. No issues with cable melting/arc over etc. We used LMR-400 at Motorola with good results as long as we used good connectors. That said LMR-400 would be difficult to use for internal wiring without connectors. The center conductor is copper clad aluminum and can't be easily soldered. The foil under the braid wicks the heat away from it if you try to solder it. It's crimp connectors only. There is a pretty long list of stuff the Johnson KW has torched but never any of my RG-142 cables.

Rg-142 is almost the same as rg-400. The center conductor is plated steel and the rg-400 is plated copper, so slightly higher loss for lower frequencies, though a few feet will not be measurable difference.
I also like the 400 better for choke baluns because it is noticeably more flexible.
Rg-303 is amazing for it’s size. Very flexible and handles a lot of power for drivers, and it can be used for regulated screen voltage feed or whatever.
Logged
W3SLK
Member

Offline Offline

Posts: 2533

Just another member member.


« Reply #13 on: January 21, 2023, 10:16:45 AM »

W2DU(SK) stated (Reflections III) that he tested RG-303 to 9KW up 10Mhz and 3.5KW at 50Mhz! Now that is impressive!
Logged

Mike(y)/W3SLK
Invisible airwaves crackle with life, bright antenna bristle with the energy. Emotional feedback, on timeless wavelength, bearing a gift beyond lights, almost free.... Spirit of Radio/Rush
KD6VXI
Contributing
Member
*
Offline Offline

Posts: 2533


Making AM GREAT Again!


« Reply #14 on: January 22, 2023, 12:01:21 PM »

CBers have been using rg303 at higher levels than that.

It was the go to coass years ago.  Because, SHINY!!


--Shane
Logged
WD5JKO
Member

Offline Offline

Posts: 1977


WD5JKO


« Reply #15 on: January 22, 2023, 12:26:24 PM »

This thread reminded me to go check my junk box.

I have a commercially made PL259 to PL259 cable that is 16.5 feet long. It contains equal lengths RGU-303 (50 ohm) and RGU-302 (75 ohm) coax in parallel. There is a label at one end that says, "40M-3 Matching Section". Does that make 30 ohm coax?

I also have several pieces of RG-400 at various lengths...

Looks like I have a gold mine!

Jim
Wd5JKO
Logged
K9MB
Member

Offline Offline

Posts: 274


« Reply #16 on: January 22, 2023, 01:10:08 PM »

This thread reminded me to go check my junk box.

I have a commercially made PL259 to PL259 cable that is 16.5 feet long. It contains equal lengths RGU-303 (50 ohm) and RGU-302 (75 ohm) coax in parallel. There is a label at one end that says, "40M-3 Matching Section". Does that make 30 ohm coax?

I also have several pieces of RG-400 at various lengths...

Looks like I have a gold mine!


Jim
Wd5JKO

Well, the rg303 and rg302 both have a 0.69 velocity factor, so hooking them in parallel should gove you the 30 ohm impedance you mention.
As far as a matching section, 16.5 feet is a quarter wave at about 10.9mHz, so it will be capacitive at 40 meters, I think. It will, however cause an impedance transformation, though reactive and not resistive.
If you used it as a simple Q section at 10.9mHz, it would match a 18 ohm load to a 50 ohm cable.
Just guessing though…😉 73, Mike
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone © 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.055 seconds with 19 queries.