Base Holy Wideband!!

[Greg T]

Finally had some decent weather so I could climb up and change out my feed line and make a new choke. I'm only running about 50' or so and decided to use Times Microwave LMR-240. So, I installed the choke about 1 foot from the SO-239 on the antenna and then used little stand-offs to keep the coax away from the mast and tower all the way down. Buried about 6' of it between the house and the shed (where the antenna lives).
I also made new random jumpers between the radio and amp, amp and meter, meter and low pass filter. I could not believe what I was seeing when I started checking the SWR.
I set it up to be lowest at 27.355 because I use mostly the upper freqs, and quite often up to 27.575 and even 27.705. Well, I didn't check to see how far I could go and stay below 1.5, but at 26.965 I am 1.4:1, 27.355 thru 27.395 flat, and all the way up to 27.705 is still at 1.3:1. I should have made a video of this, and I still may later on. I can't believe the difference from a generic RG-8x to the LMR-240. This is incredible. Plus, I'm using an ancient Johnson low pass filter with the match adjustments in the ends, so I COULD use it as a tuner if necessary.

 

[Justme]

Good work needs a reward, enjoy

 

[groundwire]

If im not mistaken, the adjustments on the Johnson low pass filter is to adjust for harmonics not vswr. The barrel one is like that for what its worth. It does change the vswr though

 

[Handy Andy]

Here's your sign...

​

 

[Greg T]

If im not mistaken, the adjustments on the Johnson low pass filter is to adjust for harmonics not vswr. The barrel one is like that for what its worth. It does change the vswr though

Not sure. I found a manual online but it said nothing about them.

 

[Handy Andy]

To understand the Lo-pass filter - the method of tuning to remove a "spur" of a CMC or even a 2nd harmonic, remember too, that the antenna may see 27MHz as 50 ohm (READ: Low SWR) but if you have a 2nd harmonic present - going out the radio - the antenna doesn't look like it's 50 ohms at that 2nd harmonic,

So to tune out the 2nd harmonic - and above - by retuning the "trap" or notch filter - at the filter - gives you the "breathing room" you need - you see lower SWR because the Filter is trapping that 2nd harmonic.

How do you know? Unless you have a spectrum analyzer on the output - the lowered SWR and your neighbors are now able to get sleep at night - are two good clues...

Else if you still own a 29 with that tunable 52MHz trap filter to remove the spur, you can see your SWR change by tuning that slug to reduce the harmonic.

At least, that is what it was there for - originally.​

 

[Greg T]

Um, dude... I'm talking about this:

 

[Shadetree Mechanic]

Um, dude... I'm talking about this:

View attachment 41390

I have one exactly like that. Works great.

 

[Greg T]

I have one exactly like that. Works great.

I'm not sure I need it but I leave it in there. Nobody had ever complained before I installed so its probably not needed.

 

[Shadetree Mechanic]

An actual CB radio should be pretty good but most exports will have a spur at 54 mhz so a low pass filter is needed. It also lowered my swr a little with my KL203.

 

[Keto]

An actual CB radio should be pretty good but most exports will have a spur at 54 mhz so a low pass filter is needed. It also lowered my swr a little with my KL203.

Spur at 54 mhz? What's this in layman terms, noise or ...

 

[Handy Andy]

Um, dude... I'm talking about this:

View attachment 41390

Maybe they needed some help to locate a thread post (or two) about that filter...

https://www.worldwidedx.com/threads/changing-the-look-of-an-antenna.258263/page-2#post-735265

I remember helping on this :"Tank" - the input and output trimmers work together - much like a Tune and Load - one handles RF on the Radio side, and another for the Antenna side.

That design makes it tunable - so if you have issues with harmonics - remember that harmonics are ever present if they aren't tamed back at the radio.

I Was only showing others that if they have such a "slug" in their radio - that is the purpose of it, a tunable notch filter to help keep you out of your neighbors stuff!

Sorry for the confusion...

​

 

[Shadetree Mechanic]

Spur at 54 mhz? What's this in layman terms, noise or ...

Yes, I will see if I can find a video that explains it better than I could.

 

[Greg T]

Maybe it would help to list my rig. I have a Yaesu FT-990 going into a TS DX-500V, going into a meter going into the filter going into the antenna. Now, my 990 has a built in SWR meter and tuner, but since installing the amp I don't need the auto-tuner. I have a flat input match on that amp, regardless of the freq. I am measuring the SWR between the amp and the antenna with amp OFF. Just passin thru...

My main point for this topic was the difference the coax made. My match was pretty touchy with the old generic feed line, whereas with the new LMR-240 this antenna has picked up about 50 usable channels without tuning. I will leave everything as is today and scan the freqs to verify the top and bottom freq from 1.5:1 to 1.5:1. Should prove interesting.

 

[338_MtRushmore]

I don't see mention of the antenna. Your low swr bandwidth could be good, and it could be bad. Without knowing what antenna you have I don't know what bandwidth to expect.