As had been noted by some clever hams here before when I posted the plots from my OCFD vs G5RV...



The SWR really doesn't rise between resonance points like it should in that plot...because the losses to the antenna are very high...close to 250ft of a mix of RG8X and RG213.

Similar for the G5RV.

Today I changed to 200ft of LMR400 instead and here is the new plot.  Red is the OCFD, orange is the G5RV.



So we can see the SWR has shot up, and the tuner is definitely doing more work now...but this is a good thing as losses to the antenna have been reduced.

I saw S reading differences of between half and a whole S unit vs the G5RV.

I will try lengthening the antenna a bit to see if I can get some of those dips in better places...glad I left the extra wire on!

Next I need to get to work on the tower.

Good to see the improvement!



Quick question: How exactly did you measure the antenna?  I get weird readings (very high SWR compared to my IC-7200's meter) on mine using this MFJ analyzer I picked up, and I don't know if the analyzer is wonky or if there is something else going on.  Jup mentioned connecting the coax shield to earth ground to get a more accurate reading, and I haven't tried that yet because the shack is on the 2nd floor of the house with no good earth ground.  No other analyzer or HF antenna to compare.

I used an AIM4170 analyzer.

The coax to the antenna from the analyzer includes a 5ft RG8X jumper, lightning protection device, 100ft of LMR400, lightning protection device, 100ft of LMR400.

So my coax is grounded at 2 locations.  Before anyone jumps, both ground rods are connected with #8.

Taking my test(s) tomorrow.  My balun arived today for the OCFD in this forum.  I've been studying rather than posting Newb questions here, however, I look through the forum daily, and since the topic came up--I need some coax.  It seems that LMR400 is proprietary, so there is only the one (main) supplier, but many companies build cables.  


Any you recommend?  Amazon will send from Times Microwave, and google brings up the antenna farm, and many others.  

Also is there a "better" style of lighting protector or types to avoid outright?  I'm doing my build in a vacuum and trying to avoid reinventing the wheel.

Thanks!!

I use 400MAX from DX Engineering.  It's a LMR400 copy that is very good.

Another supplier, who  I  have not used but many people swear by, is  The Wireman. They have a very good reputation.

Good luck on the tests!

Best lightning protection is the one where you unplug the power supplies from the wall AC outlets, and
disconnect antenna coax from the radios.

The $5-8 lightning arrestors are nothing more than shield grounds. Look for one of the units that uses a gas arc chamber.

 
Yep - nothing will stop a direct strike except a complete lack of connection.

Any lightning protection is better than none.

Better lightning protection is better than crappy lightning protection.

Disconnecting the cable is a good idea.

I went one step further...all of my antenna connections have multiple lightning protection devices that use a replaceable arc-gap...and I also bought a few of these and soldered jumpers across them on the SO side.  I push them onto the window panel connectors after I disconnect the cables from the panel to the radios.

I mean...why tease mean ole mister lightning with a spark-gap?

Lots of antenna sites take direct lightning strikes all the time and are not disconnected.

I watched visually an amateur repeater antenna take several direct strikes while talking to someone on the repeater.

I've seen several antennas that the tips looked like moonscape, or a completely shot up steel target or something.

Lightning protection is good protection equipment, tons of grounding to give the energy somewhere else to go, obsessive attention to detail and sometimes a little bit of luck.

As far as LMR400 I'll repeat my usual caution, that I don't recommend it for most of the common amateur uses. Actual LMR400 has a copper clad aluminum center conductor which does not take repeated flexing - it should be installed, put in position (with attention to the minimum bend radius) and fastened down. Strongly advise not to feed a dipole where the cable will be swaying in the wind or something like that with true LMR400. There are LMR400 clones that are solid copper center conductor, those are safer, or the variants with stranded center conductors.

Thanks for the warning, hadn't considered that.

The stuff I got was not LMR400, but similarly spec'd as far as loss.  I have another length of it to go to the tower and will take a good look at the ends to see what the center conductor is.  If it is copper-clad aluminium I will probably cut the length of RG213 I have to exactly match the run from outer ground rod to the feedpoint.

Then I can use the other end of the RG213 as the flexible feed from the LMR400 end at the top of the tower to the A-4S.

Definitely never use LMR400 to a rotated antenna. There are flexible variant types with similar loss characteristics.

Thanks for the help.  I passed my General tonight--see my post in the can't fail thread.  I think I'll stay with RG8 for now and upgrade later.  I'm sure, like AR mags, you can't have too many lengths of coax laying around.

For the slight cost increase, buy LMR SuperFlex.  It's got a stranded core vs. the solid core.

It's actually called "Ultraflex", LMR-400-UF. I've used it very successfully on a number of jobs for work, with thousands of cable assemblies deployed. Highly recommended!

Confirmed, the cable I have has cu-clad al center conductor.  I will redo the section to feedpoint in RG213 as soon as time allows.

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With the way LMR400 is touted, I would not have thought of this detail either. Thanks for pointing it out.
 

Any opinions on the Wireman equivalents of 400, ultraflex, etc? They have the bonus (for me) of coming to local ham events now & again. :-)

Dunno.

The guy I got my lengths off on ebay is out of them now.  $35/100ft for LMR400 was a deal though!  Testing indicates it is the same stuff.

I was ordering as you were posting  Next time I'll know!

I prefer the Wireman #106 versus Ultraflex. The center conductor is much finer stranding so a more flexible cable with less migration. I've also seem some issues with braids breaking at connectors on Ultraflex, the jacket is so wimpy that it doesn't provide any support for the braid. Had better luck with clamp type connectors than crimps for ultraflex.

That's one nice thing about this LMR400 knock-off I got, the jacket is very tough...tougher than my hardline.

LMR400 and most copies are polyethelene jacketed, same as what heliax/hardline type cables generally have.