My OCF Dipole and the 30m Miracle

 
As modern radio operators, we take a lot for granted.  It's my understanding that back in the old days a ham might have several dipoles that might each work on 1 or 2 bands.  Now we have good multiband antennas like the off-center-fed dipoles.  I use an OCF dipole made locally in Georgia called a Maxcon OCF-3K80.  This antenna claims "Operating bands 10, 12, 17, 20, 40 & 80 meters without a tuner."  Let me tell you, it works FB just as advertised.  I've also used the Maxcon OCF-3K80 on 6m, 15m, 30m and on even 60m with fairly good results using just the built-in tuner on my rig.  

Unlike a lot of folks, I like to use LMR400 equivalent feedline even on HF especially to reduce noise (in and out of the coax) and to prevent loss since I'm feeding my OCF dipole with 100+ft of coax.  I do use the Maxcon line isolator choke to isolate the antenna from the feedline.  I'm not sure this is working exactly as it should...

Maxcon OCF-3K80

When I first got setup at my new QTH with my OCF dipole, I was able to use it on all advertised bands plus 6m, 15m, and 30m with the tuner.  I could not use it on 60m as I could at my previous QTH.  At that location, I was feeding the antenna with 150ft of LMR400.  So I assume the line isolator isn't fully isolating the antenna from the feedline and therefor the longer length of feedline was allowing the radio tuner to see a different resonance.  

Yesterday, I added a barrel connector and 15ft of LMR400 to the 100ft already feeding my OCF dipole.  After a little cable management, I tested and found that it no longer was able to tune 30m.  I removed the 15ft coax extension and tested and was still not able to tune 30m.  Quite frustrated, I went to bed. This morning, still bothered, I went to check again.  I pressed the tune button on my FTDX-101D...just a beep and it gave up.  I pressed it again...and it tuned it flat.  What the hell?  All I can figure is that it's a miracle my rig's tuner is able to tune this OCF dipole flat on 30m.  Looking at the antenna on an analyzer shows no discernible dip for 30m and the SWR is about 5.4:1 on the entire 30m band.  That is beyond an internal tuners capabilities.  Somehow, my rig's tuner apparently can do it but slight adjustments to the antenna (or feedline by extension) might push it out of the tuners capabilities.  Apparently even the time of day, moisture in the air, or other unknown variables can also prevent it from tuning (such as last night it wouldn't tune and this morning it would).  The weird part is that when the rig does tune it, it will memorize this tuning and so the antenna is usable on 30m until another adjustment is done that might need a retuning.  

I was rather frustrated with losing 30m.  Even though this antenna doesn't advertise 30m capabilities, it works quite well and I've worked some good DX with it.  I only use FT8 on 30m, so I really didn't want build a 30m dipole for this one band considering I can pretty much work all the other bands except 160m with the Maxcon.  Spoiled little modern operator.  In any case, I'm hoping that I can once again extend my coax and clean up the cable management without losing 30m.  Here's hoping I hold my mouth right.

UPDATE 2/7/2023

I found that again, I couldn't not get my tuner to retune and the SWR was just a bit high on 30m.  After moving (separating) my coax feedlines for HF and VHF antennas, I was once again able to tune 30m flat.  The latest theory is that the VHF feedline right beside the HF feedline was somehow coupling and presenting as additional "length" on my OCF dipole.  All is ok for now...except the wheels are turning for additional antennas.

73 de K4LST sk