Center loaded mobile antennas ?

[TheBlaster]

I wonder if it got the name "bull whip" from bull rushes ? It sure looks like one when mounted. Then again it probably got the nickname from an actual bullwhip, it was the base load one that got that name and I guess it was like a bull whip hand grip.

 

[2NC995]

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.

27.025AM can be a good early indicator of a band opening. So I do watch for Europe SWL spots of that frequency. But...there’s so much power involved with .025 that it doesn’t always mean much for the rest of us.

27.385 LSB is the US’s most popular 11M SSB frequency, and because it typically involves much less power than 27.025, it’s a more realistic propagation indicator for across-the-Atlantic contacts. I see a few European contacts logged on 385, but often it’s far too busy for that kind of contact. Talk over each other, instead of QSY, is the way things are often happening here.

The upper end of our 40 channel plan is what’s typically used for SSB here...so 27.365-27.405 (and above our legal channels up to around 425) On the zeros, 360-420 can be good also. All LSB on those frequencies; not required for us but nearly ubiquitous.

It’s very likely you may hear some activity on that portion of the band before you hear anything on the traditional 11M “freeband” centered around 555USB, just because there are so many more operators in that freq range.

If you’re patient and don’t mind listening to some silence...drop by 27.155LSB every now and then. You’ll still find some guys operating on that freq which was popular when we had a 23 channel band plan...much, much less busy.

 

[TheBlaster]

Thanks, all noted.

 

[M0GVZ]

A centre or top loaded antenna will move the RF current maximum up the antenna which should mean you put out a more horizontal signal and get better range than a base loaded antenna.

Hate to say it but mirror arm brackets don't do anything for performance, even with ground straps. Might look good and you'll get low SWR but it won't be optimal.

If you do ever want a 1/4 wave whip Knights CB at Kirton Lindsey inbetween Scunthorpe and Lincoln sells single piece ones but it's collect only. Been using Knights for years.

 

[TheBlaster]

I guess you mean a signal that is closer angled to 0 degrees to the horizon MOGVZ. Of interest is that the Supermodulator II is giving about 3 to 4 S points down to local contacts line of sight, which is to be expected really compared to the 1/2 wave (1.7m antenna vs 5.5m on 4.5M of pole). I was calling someone 35 miles away who usually always hears me the other day and he said I was on his noise floor and he was struggling to hear me.

I did read something that confirmed what you say (comes down to amount of metal directly under the antenna), however the mirror arm is solid aluminium and high up on the vehicle (1cm down from roof line) and I got the mount within 1cm of the bodywork, I wet and dry'd all contacts, earth bonded panels and made sure good metal to metal contact is made, the best I could do.

The reason I did it this way is that I thought it would be better solution than a mag mount option which I have used before and was not blown away by performance. (I have a Sirio 4000 Hi Power 2m long base loaded whip PL-259 version but it was hard to find a SO-239 through hole that fitted this 3/8 inch mirror mount.)

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.

SWR is 1.15:1 with the SuperModulator II

Unfortunately through roof hole is a practical impossibility, I was hoping this was preferable to a mag which I have never been very impressed with. I cannot think of any other way to mount the antenna. Unless there is some super high quality mag mounts that I am not aware of. I had a Sirio PL-145 mag mount and broke it, now just have a cheap 6 inch CRT one. Triple mount won't fit the vehicle.

 

[TheBlaster]

Maybe I could crocodile clip/G clamp some radials on the bracket, I will have a think about that, it is not beyond the realms of possibility, not exactly convenient but also not that difficult.

Any suggestion of what a practical working length could be.. and they cannot be 102 inch.

Or maybe some other kind of metal sheet, biscuit tin lid etc. Maybe I need to think out of the box with it.

Maybe some aluminium mesh (used for car body repairs/holes) would do the job, light, sturdy, let's rain through. Might think about that. Or maybe it is just best to leave it as it is, it is not as if it is not working and maybe it is best not to expect too much from a short antenna given its compromised mount.

 

[TheBlaster]

I am going to make a tank whip, 1/4 wave out of solid copper mains electrical wire (as I gather even more efficient than stainless steel for antennas). I just need a 3/8 insert with a grommet, then I will run the wire up a short fishing rod whilst attached to the mirror mount, length tune it for lowest SWR. A very cheap tank whip option.

Then I can see how that performs. Most of the time I will use my base antenna static mobile as I generally find mobile antennas are a bit of a compromise, I just want an efficient whip so I can swap if I find my 1/2 wave is not cutting through, change the radiation angles up as an alternative option. I want to see how a 1/4 wave works out. There is nothing like finding out for yourself with a little experimentation.

Would I be correct in saying the current centre of this antenna 1/4 wave whip would be right at the base?

 

[Marconi]

I am going to make a tank whip, 1/4 wave out of solid copper mains electrical wire (as I gather even more efficient than stainless steel for antennas)

Blaster, this is just my opinion, but I think you will likely need a Lab Type Network Analyzer to see a difference between Copper vs Stainless using a CB 1/4 wave radiator. You might see a very slight difference in the matching details. but I don't know how you would measure efficiency.

A tree sitting 6' feet away from your antenna might cause more of a difference.

 

[TheBlaster]

Thanks Marconi. Yes I think I saw something in a thread where efficiency dropped from 50 to 25pct from copper to steel (which did sound like a huge drop) in some thread here, it was probably some worst case scenario antenna system to demonstrate a point.

I won't be losing much to find out how a 1/4 wave whip works out. If for whatever reason the DX is not working on that it is not likely to be the antenna, given it is the gold standard for a static mobile vehicle mounted whip.

I know £30.00 is not much to pay for a tank whip but I can make one for peanuts given it is just wire.

 

[Marconi]

I applaud you for the effort.

I use to try and check out claims that I heard folks make on the air and on the Internet. I mostly determined that CB claims were much about nothing.

 

[TheBlaster]

I think there is much saying and not so much doing in general. Doing can solidify knowledge usually. On the the DX side propagation makes mince meat of testing/knowledge, though that can come over many years of continuous daily operation.

I am only a lowly CB'er and don't have a ham licence but is not to say I am not deeply interested and wanting to run the best ship I can. It is nice just to know you did whatever you could do your end. Then there are no regrets or concerns about how you operate.
It is not about being better than others just doing the best that I can with my budget and for my own satisfaction.

Frankly speaking I could not imagine trying to make an efficient and well performing station for multiple bands, like hams do. Keeping one little set up running nicely for one band seems plenty for me.

Just for interest's sake, made a contact into Ireland, 2 into Scotland (350 - 400miles approx each contact) and Poland (900 miles) yesterday, quite weak Sporadic E conditions, very unstable up and down over the course of 2 hours that was on the Super Modulator II and just radio power around the .555. It is difficult to cut through with a mobile whip and radio power but it can be done. Heard Denmark, Germany, Sweden, Slovakia calling but despite attempts could not break through, some days you can some days you can't and that is just about the long and short of it.

 

[2NC995]

I’ve used a copper pipe and a stainless whip. Identical lengths, and they show zero difference in use, or on my analyzer.

But..I think your thoughts on copper was a side comment and not necessarily your motivation for building this way...

More importantly, you get to see how a full 1/4, no load antenna works for you.

 

[TheBlaster]

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.

 

[2NC995]

Well, when you get that 1/4 up and running let us know what you think and how it compares with the half wave you’re running. I’m very curious on that. As I mentioned, I’ve considered a number of antennas for static mobile...but I’m kind of leaning towards a delta loop. But some day I’ll get this 20’ fishing pole up in the air and see what I think about a half wave Omni...lol.

 

[TheBlaster]

I sure will. At a guess it will be a little down on the 1/2 wave vertical for local line of sight mainly due to a little less pole height and anyone's guess on the E layer DX.

When the F2 layer prop comes back (especially at start and end of cycle when it is weaker), that is when you need to start getting high performance antennas with a nice low angle lobe as high as is practically possible. I only deal with verticals, beams are way too cumbersome for a one man portable station.

Although I am not sure the Sirio Gain Master on top of 10M/30feet of pole static mobile will be coming back in a hurry ! Though that is the set up of best results IMO for the long haul F2 Layer blasting. That is quite some effort to be rigging up and taking down.

The good thing about being on a hill for the F2 layer DX is something called the Brewster angle. The steep drop off either side of your hill means your antenna has constructive phase interaction with any ground reflections at the lowest angles of radiation, rather than deconstructive. This means on a hill you can potentially have a lower radiation angle than on flat land. If you want to blast 10,000 miles or more with a vertical I am sure this helps. With just a vertical you need all the help you can at the start and end of the solar cycles. This is where good antennas and set ups show their true value.

Although I cannot underestimate the value of those at the other end with their beams. If everyone DXing run omni verticals and not beams that would be very interesting indeed. Though ultimately I suspect many less really long haul DX contacts would be made.

So beam users, a sincere thank you !