Pages: 1 [2]   Go Down

Author Topic: LMR-400 For Repeater  (Read 12624 times)

K9KJM

  • Member
  • Posts: 2415
RE: LMR-400 For Repeater
« Reply #15 on: December 17, 2009, 01:37:31 AM »

Don't use LMR for duplexer jumpers.

Replace them with either RG-400, RG-142, or 1/4 inch
superflex jumpers.

If your duplexer was properly tuned on a tracking generator, these jumpers may be compromising your isolation.

OH?     Just why not use TIMES LMR series for duplexer jumpers?
I would like to see any documented cases of it causing a problem.
(Real Times manufactured, Not some "clone")
Many years ago there were a few documented problems with the foil shield type coax (I think it was some Belden 9913) After internal exposure to moisture, And a number of people "ASSumed" that might apply to all foil shield coax types......

And just what is "RG 400"   I thought that was simply a description of coax type, Kind of like saying "RG 8" 

There are lots of dual shield coax that can also work well for duplex operation. True mil-spec RG 214 etc.
Logged

KS4VT

  • Member
  • Posts: 166
RE: LMR-400 For Repeater
« Reply #16 on: December 26, 2009, 03:16:26 PM »

I like to use 1/4 superflex myself.  It is very easy to work with and has 100% shielding.  If you want to maintain the use of PL259 connectors you can use the RG59 reducer with a standard connector and install just like RG58, but with a much more solid connection and performance.

I have 2 VHF 100 watt Motorola Quantars set up this way with 4 cavity TX/RX duplexers and experience no desense issues.

Mark KS4VT
Logged

KI6DYR

  • Member
  • Posts: 227
RE: LMR-400 For Repeater
« Reply #17 on: December 26, 2009, 08:08:30 PM »

Of course LMR and hard line have lower loss than Super-flex but they all work.

I don't really have a choice on SO-239's in the shack. The 6-cavity duplexer (WaCom) uses SO-239 tee's.

The issue has resolved itself, at least for now. I have a suspicion that a neighbor with a new tower and an odd paired repeater one block away may have been the real issue. He was denied coordination and I assumed he was off the air. But his 4 bay exposed dipole is pointed right at me. My LMR is still under snow on the roof, so I don't think condensation is the cause.

I could be wrong. It has happened before. Ask my wife. She knows everything. <grin>
Logged

KS4VT

  • Member
  • Posts: 166
RE: LMR-400 For Repeater
« Reply #18 on: December 30, 2009, 04:49:09 PM »

When your only talking a few feet, like between a duplexer and repeater, you will never see the differences in loss between superflex and RG type cable.
Logged

K5MBV

  • Member
  • Posts: 265
RE: LMR-400 For Repeater
« Reply #19 on: December 30, 2009, 09:58:31 PM »

As I understand it, SO239 connectors aren't recommended
for operation on VHF and above. I hear that even some
N connectors that haven't been swept and tested to
frequency don't perform well. In fact very poorly.

I don't think this is an old wives tale, since I have a
friend that operates all bands to 24 GHz. He always tests
his connectors before using and finds many that are unuseable at 144 MHz.

73 Ken  K5MBV
Logged

KI6DYR

  • Member
  • Posts: 227
RE: LMR-400 For Repeater
« Reply #20 on: December 30, 2009, 10:53:53 PM »

The WaCom WP-642 6-cavity BrBp duplexer has Amphenol SO-239 T's from start to finish. I doubt that it is practical to even invest time in researching a N connector upgrade or making new interconnect cables. Although there may or may not be evidence to support PL-259's or SO-239's as high as 144MHz, in 30 years of playing with radios I have yet to see one even at 500MHz that had an N connector. I'm sure that one exists, but I haven't found it yet :)

Since the intermod, interference, or whatever stopped shortly after beginning this thread I don't think that its a connector issue. With that said, even the TKR repeater has a N connector and a BNC on the receive (that alone is a mistake.)
Logged

PY2HR

  • Member
  • Posts: 20
Re: RE: LMR-400 For Repeater
« Reply #21 on: May 23, 2021, 03:19:03 PM »

Hello Dear, what is a double cavity pass filter?
73"
PY2HR Moises C.

The cold temps and thermal change I was referring to is actually all "outside," where the feedline and antenna are.

Condensation forms in the antenna connector, and if that connector is really well sealed, it has no way to escape so it can stay in there a long time, even after the sun comes out to warm things up a bit.

Pressurized line and connectors take care of the whole problem, if this is actually the problem.

One way to find out would be to climb up and disconnect the transmission line from the antenna and see if the connector is wet inside.  If it is, use compressed air to blow it out so it's completely dry, do the same thing with the connector on the antenna, and then re-connect and see if it makes a difference in the noise/desense/etc.
Logged

N0GV

  • Posts: 627
    • HomeURL
Re: LMR-400 For Repeater
« Reply #22 on: May 23, 2021, 06:52:27 PM »

LMR 400 has a Cu coated Al center conductor. This can, and does, have corrosion issues, particularly when the Cu is "nicked" when stripping the dielectric from it. With repeated heating and cooling will get water into the cable, it won't matter if it is upside down or right side up if it is not sealed hermetically. The antenna feed can also wick water into the cable in a 239/259 combo as the SO 239 is NOT hermetic.

That all said, if the cable has been up for a number of years and has been problem free, next time you have an issue break out a spectrum analyzer and take a look at what else is going on in the neighborhood. More often than not it is some moron's GD garage door opener somehow emitting at 1/3 of the spec'd frequency.... 433/3 = 144.3 MHz and if the LO is, like usual, running at 1/5 or 1/3 of the spec'd frequency it will be a noise source. LED drivers are also notorious for generating noise at obscene frequencies (don't ask me how I know this) as are fluorescent lamp electronic ballasts. In fact the FL ballasts can be absolutely impossible to filter/choke/strangle etc. as the RF is in the discharge plasma!

If a spectrum analyzer is too expensive (they make a cheap one for $50 these days!) tune an all mode rig slowly through the spectrum on cw and note the problem frequencies then correlate them with repeaters etc. and any unknowns. Make an effort to demodulate (AM/SSB/CW/FM/PSK/DMR/D-STAR/SYSTEM FUSION etc.) and locate. If there are any "mysteries" left after that run them down and localize the culprit.

Pretty sure it is your buddy down the block but I'd not convict him without real evidence....

Grover
Logged
Pages: 1 [2]   Go Up