Center loaded mobile antennas ?

[TheBlaster]

I have installed a centre loaded 1.7 M whip (mirror mount with earth bonded panel, metal to metal wet and dry sandpapered for best metal contact, ugly balun/choke 5 turns 4.25 inch Super8 coax just below feed point) in the UK, it is somewhat of a classic. A Super Modulator II, originally designed in 1984. So far I am enjoying the antenna with my summer European max 1,400 mile hops. Typically averaging 1,000 mile hops and of course shorter as well, conditions driven.

So I have heard a few stories about centre loaded antennas and would like to understand your thoughts on them. I know there are some highly knowledgeable antenna folk on here : )

I have heard a few things.. like "coil needs to be near ground plane to work" and "centre loaded whips have a reputation that they don't do so well on the DX " and "centre loads are just to look nice".

So despite the antenna seeming to work quite well for me so far on at least short Hop E layer, 2 people I have spoke to think otherwise, which is fine I am here to enjoy thoughts surrounding radio and learn. This antenna's normal guise (the original design) is known as a bullwhip or just a modulator which is a long and narrow base loaded coil design and is copied by many other antenna makers this side of the pond including Thunderpole/Moonraker and a few others.

What is your view on centre loads. I did a little investigation and have read that they can lower radiation angle, increase the antenna current centre height and be more efficient and be the best compromise whip antenna, all of which is contrary to a couple of experienced operators over here.

Here is a pic of the centre loaded version the Super Modulator II, the one I own:

And the original version with base load..

Thanks for you time and thoughts.

 

[2NC995]

I don’t have any technical advice to offer on the subject, but I have worked DX with base load, center load and top load antennas (but probably more center loads than anything).

The most popular antennas in the US are of all three varieties. I certainly would not agree with the reputation that a center load doesn’t work well on DX.

It’s pretty well impossible to test antennas for DX...but when I’ve tested antennas local, from mobile to base, the length seems to be a much bigger factor than load location, (assuming all antennas are of quality construction). I would tend to think that if there were a large change in angle of radiation that be easily seen.

So, unless I learn any better, the most important factors to me are quality construction and overall length.

I used to run a loaded antenna and change to a quarter wave for DX, but now I run the 102” whip full time...it truly outperforms anything I’ve ever had my hands on.

 

[TheBlaster]

Thanks, yes I have been thinking of getting one, inexpensive and just about the best option for a vehicle, I was enticed by the classic status of this twig and I can literally just drive off with this one, less so the case with a 102 inch tank whip.

 

[2NC995]

Thanks, yes I have been thinking of getting one, inexpensive and just about the best option for a vehicle, I was enticed by the classic status of this twig and I can literally just drive off with this one, less so the case with a 102 inch tank whip.

I can definitely understand that.

Length is a factor that most people have to deal with...and I do also. I tie my whip down to about 6’ for driving around, but have a clip so I can easily right it for DXing. It’s not a perfect solution, but still easier than climbing into the bed and swapping antennas. I’ve found, however, that having the antenna pulled back has very minimal effect, and I often just leave it like that.

Anyway, coming back full circle: it’s my opinion that you are not short-changing yourself by running a quality center loaded antenna...but I would strive to run the longest antenna you can get away with.

 

[Captain Kilowatt]

For DX it won't matter that much or make any noticeable difference whether the antenna is base or centre loaded. Centre loading actually tends to be slightly more efficient and raises the high current point making it slightly better for local communications. It is for this reason you do NOT want the loading coil close to a groundplane actually. Given a choice of base or centre loading I would take centre every time.

 

[TheBlaster]

Thanks for the response, it seems to do quite well for me so far. 2NC995 Dan, yes I suspect a little loss of efficiency over the 1/4 wave "gold standard" but I am not sure I would notice it generally. I normally set up a 1/2 vertical on a few poles G clamped to whatever I can find, street sign, gate, tree, fence post out in the sticks.

I had a few dodgy DX days where I felt I was not getting out with the 1/2 wave vertical end fed (with coax choke near feed point) on a hill top say 500 feet ASL - with the E skip I could hear them great, but they could not hear me after 10/15 shouts @ 50W SSB radio power and wondered if it was performing a little too well (too low angle on a hill top - or had a few nulls in the lobes at critical angles for that days E layer DX)

I tried to work out what angles I should be hitting approximately for short hop Sporadic E DX and made a very rough estimate of 15-24 degrees. Given a max hop possibility of 1,400 miles and the layer in question being at 62 miles up above, I made some very crude roughly to scale drawings.

Since then I came to the conclusion that one way traffic E layer might be a thing ? And that I can hear better than I can get back (or maybe their end had QRM or just stations from other places in Europe were cracking through a bit better for unknown atmospheric reasons)

I do my best to control what I can at the station end (mobile static) but realize nature and atmospherics are a law unto themselves. It does not hurt to change from the 1/2 wave to a whip just to see if it works better when static mobile (change the angles/pattern/lobes up a bit).. I consider that part of the fun.

 

[2NC995]

There’s actually some prop between 2 and 26 Div now. Mostly to the Northern US states, but I can hear some low voices.

I’m not sure on one way propagation, but I have felt the same at times. For the most part I can work anyone I hear, and my ability to RX in the mobile is the more limiting factor for me - but that’s with mobile antennas, and not a 1/2 wave.

Im guessing that while you had good propagation others had better propagation, or you’re right that they were dealing with QRM.

 

[TheBlaster]

Cool, yes working today so cannot get out at the mo, I guess double/triple hop sporadic this time of year or maybe a freak F2 opening. I did hear a few burst of audio on 27.025AM a few weeks ago but I have just come back after 3 years off so was getting my head around the 11m band character again (Still as unfathomable as it ever was !). Yes the 1/2 wave ears are very good on a hill, although a generalization I can a normally get to those I hear, but this day was not happening at all.I have a very low RF noise floor S0 and very quiet in my hilltop spots so think I can hear a bit better than I get out. (I can do 200W SSB if I need but hover around 50 - 100W normally, that is usually fine, 200W kills my batteries fast)

I think it is really about the angles and if one way traffic is a phenomena, I would have thought not but, you know some days and all ???

In fact my 11m internal calendar could do with a refresh, as we are at sunspot minima (ish) I guess 2/26Div openings are not as good as they can be at the max sunspot peak ? Does the atlantic open up a bit more towards fall ? Sorry a bit rusty.

 

[2NC995]

There are several stations working 2TB131 on 27.540 at the moment. Reporting him S9.

 

[2NC995]

Does the atlantic open up a bit more towards fall ? Sorry a bit rusty.

Actually, it’s been off and on from
mid May through now. I believe this is multihop sporadic E, so unrelated to the solar cycle and actually a good time of year.

I don’t know that for fact, though...I’m really just learning.

 

[TheBlaster]

Well I will surely keep my ears open for it when I am out and about, thanks for the heads up.

 

[2NC995]

Well I will surely keep my ears open for it when I am out and about, thanks for the heads up.

You can always check 27.385 LSB for propagation. Probably a better indicator than 27.025AM.

If you hear chatter on 385, then try 375, 395....and so on.

 

[Marconi]

Baster, here is a link to a review.

https://simonthewizard.com/2014/06/05/les-wallen-original-modulator/comment-page-1/

I also see a current Ebay item that says the antenna is no longer available from Wallenant.

https://www.ebay.co.uk/itm/SUPER-MODULATOR-II-ORIGINAL-CB-ANTENNA-FROM-WALLEN-ANTENNAE-/152740698420

 

[midnight special]

been cbing for almost 45 years,, and always have heard that a centerloaded or top loaded antenna was the most efficient antenna,,,

 

[TheBlaster]

That is the kind of thing I am rusty on.. 27.385 LSB will keep a check thanks. Yes I always heard centre load were "better" as well. Maybe some extrapolated "not so good for DX" from the better for local.

It must look like a pretty weird thin centre loaded antenna for you guys in the USA with the giant coils.