Center loaded mobile antennas ?

[The DB]

Yes I think it was TheDB that mentioned about the copper vs ali vs steel. unfortunately the image for the antenna in question was missing, maybe it was some microwave antenna, as I gather everything starts getting very critical at microwave wavelengths.

Unfortunately, I lost all my old stuff that I used to host myself. Now days I upload the image directly to WWDX. I've done the copper vs aluminum vs stainless steel multiple times. The resistance numbers for the three are:

Copper, .0000000168 ohms
Aluminum, .0000000282 ohms
Stainless, .000000690 ohms

This makes stainless steel significantly more restive than copper (you will notice one less leading 0). However when it comes to radio, most of the RF does not actually travel through the metal. Some rides the surface, this is where the "skin effect" you may have heard about comes from, but most of said signal is actually in the space around the metal itself. This is why coax needs shielding, and why both wires in ladder line needs to have a signal that is 180 degrees out of phase to prevent the signal from radiating.

I threw this together again for you. The metals had such a small effect on tuning that once I got the models dialed in I didn't even have to change the antenna length to maintain a descent tune. All of these antennas are tuned to have an X of +- 0.3.

[photo=medium]6366[/photo]

Click the image to make it a little bigger.

I've worked with all three metals extensively and have never once noticed a difference between the three.


The DB

 

[TheBlaster]

Thanks for the models. I am not sure to what that percentage efficiency was relating to then, sorry lost the thread as well, on this forum though.

 

[TheBlaster]

I tried to find your post The DB but had no luck, then I stumbled on this...this person (maths heavy theory) seems to think copper gives him 5dB (nearly an S point) gain over steel...

https://www.dk0tu.de/users/DL5BBN/Steel_is_a_Bad_Antenna_Material/

Albeit at 7MHz

 

[Low_Boy]

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.

This is a question. I was told a long time ago top load is the best. It is pretty impossible to find a top load that is not fiberglass.

 

[Marconi]

TheBlaster, I agree that 7 MHz might have a lot to do with a difference reported for this topic.

As we go lower in frequency with antennas being taller and more difficult to get up high, vs a CB setup, mitigating losses is King.

 

[TheBlaster]

I would not have thought lower frequency would affect efficiency as much, but when you mention the size of antennas, which start getting big and more awkward to set up it makes complete sense.

 

[Marconi]

No apology necessary.

 

[The DB]

What he is doing with the math is taking the diameter of the wire, adjusting that for the area once skin depth is factored in, which is fine. But then he makes his mistake. He assumes all the RF energy flows through this part of the wire, and none of it is in the space around this wire, which has very different properties. If all of the RF flowed within the wire as he assumes, his math would be accurate.

On the modeling side he used xnec2c, which is a graphical version of nec2c, which is a c version of nec2, so essentially the same software I ran just rewritten for a different compiler...

He used a vertical antenna at 40 meters? Nine meters long, so that will be about 1/4 wavelength. Is it ground mounted? How many radials? If ground mounted how long are they? Did he change the conductor on the radials as well? Was it a vertical attached to a ground rod?

One s-unit difference... S-unit... And he assumed that the s-unit will have a 6 dB difference, which doesn't actually happen very often, more than likely it is closer to 2 to 3 dB of difference, even on high end ham gear...

So hes in Erfurt? The beacon he mentioned is in Czechia, not line of sight, but it is a neighboring country so not likely to far away, but still, some form of propagation is in play which could have much more of an effect than simply one s-unit, even if that s-unit is the full 6 dB that s-meters rarely show.

I have many questions, and would love to try and duplicate some part of this, especially the modeling, but I simply don't have enough information at hand. I have no reason to disbelieve his measurements, but I also don't think they mean what he claims they mean. I will give him this though, he definitely put in the effort with his homework.


The DB

 

[M0GVZ]

I wish I could find a SO-239 to 3/8 convertor to try the 4000 Hi Power on this mount but they seem impossible to find.

Depending if you want to spend any money Sirio do a 3/8th thread version of the Performer 5000. Comes with a fetching camo coil cover, the Performer 5000 Fighter 3/8. They also do "trucker" versions of the 5000 too that have a short shaft under the coil with a 3/8 connection.

 

[TheBlaster]

I take your word for all that The DB, I know you know your stuff also in lieu of not really understanding the maths and me just taking that page at face value initially. Thanks for the time bothering to sift through it.

M0GVZ thanks for the info. I realize the reason why a 3/8 male to PL-259 male converter does not exist is because the top of the 3/8 on my mount is just the + part of the antenna so there is no + and - as there is with a PL-259, so a straight adapter for it would be an impossibility.

Yes I am just trying to get a cheap way to test the 4000 Hi Power against the Super Modulator II on the same mount I guess, but this I may fail. I have a long barrel double SO-239 here but I cannot work out a way to clamp it to the mount (space is a bit tight) and feed it with coax from one end and screw the SO0239 mount 4000 on.

It is by no means the end of the world and I don't want to spend any more money on it for now.

In desperation for a cheap solution the thought of using some left over insulator less single copper core cable 2.5mm and using wire cutters and pliers to try and tie/lash/twist tension it to the mount. (Hardly a robust and ideal way of making 2 bits of metal contact each other !)

I would imagine there would be an analogue needle's difference between the SIRIO Hi Power 4000 PL and the SuperModulator II - given the latter is centre load, the former base load, and that the latter is 1.7M and the former is 2M. I imagine they perform rather similarly. You know how it is though, it would be nice to test with a couple of locals for fun and interests sake. I'll work something out somehow. These things give my brain something to process in the back ground.

You never know maybe I will just treat myself at some point, live once and all that. I will see how that tank whip works out as well.

 

[Slowmover]

Or specify an unobtainable legend.

Pretend it’s the CB version of, a 1953 Vincent Black Shadow.

Ignore all naysayers.

(Keep the experiments going. The real fun).

.

 

[TheBlaster]

I tell you what I did spot a Sirio P2000 Trucker, not quite centre load but very long at 2,080mm, must perform at least as well as the 4000, 5000 with the coil on a 8 inch stub so neither base loaded or centre loaded.

You need to click the link to see it.

https://images-na.ssl-images-amazon.com/images/I/71jgEEfMaVL._AC_SL1283_.jpg

That is a good looking antenna and it must perform like a 4000/5000 given the length.

At the moment buying another similar antenna makes no sense. I want to test a 1/4 wave out next.

 

[TheBlaster]

Made my tank whip, literally a 3/8 mounted 2.7 M solid copper wire, must have cost about $0.70 / £ 0.50 Tuned it (SWR 1.3:1 at desired frequency) and tested RX and TX with a local. In his words "An S point stronger maybe a shade more." than the SuperModulator II. Rx was just a tiny bit better on the self made tank whip to this station than the SuperModulator II.

I was expecting a slight change but not an S point with TX. I also tested RX with 2 locals who were chatting.They were peaking as close as the eye on the meter could see slightly less than 1 S point more with the self made antenna. Their audio peaks were consistently peaking a little higher.

Difficult to be sure but that suggest a 2-3 dB increase approximately. That is not bad going for a straight piece of wire.

Of course most cannot go around with a 2.7M whip hanging off the back of the vehicle but fact is for static mobile work (for a practical vehicle attached antenna) it is pretty much impossible to beat the tank whip. A piece of wire with no coil/s. It is what has been said but nice to see it for yourself.

It is this that dispells the magic a bit, but it is made up by better performance, at best that is similar gain as a doubling of power, at worst say 2dB that is a nice bonus for TX and RX, 2dB could be the difference between a copy and no copy on line of sight SSB fringes. Coils are for sure lossy and a Super Modulator II is a well regarded antenna over here. Though to be fair it uses very thin gauge wire for the coil which cannot be helping the losses.

For the technical people does a coil making up for the shorter length on a mobile antenna losing 2-3dB in coil loss seem about right ? It seems a lot to me, but real world that is my best estimations 2-3dB difference.

To top it off I made one DX 680 mile E layer contact into Spain with 40W SSB on the wire.

An afternoon well spent.

 

[TheBlaster]

I was not sure where to post quite but I put the Gain Master back into static mobile service on 11m @ just 5m, 10 stations worked across Europe today and heard the E. Coast USA coming in, could not quite make it back, it will come in time though. Not that I have not spoke stateside before (have many times) Just been a long while now maybe 4 years after a break.Gain Master is in my favour again !

 

[Highway Man]

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.

How long is that?
Is That like the Hustler HQ27?