So if using LMR400UF and an 8" circular form and wrapping 18' to 21' around it be about right or at least sufficient not to be too small of too large of a bend for it as far as radius goes?
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Beads, Ferrities ?..
- Thread starter Oatmeal
- Start date
On a larger form you would need fewer turns, not more. I can't tell you the total length that you would need because I do not know... The length would likely change with the size of the form as the length is not a key component, only the combination of inductance from the coils and capacitance between the windings.
If you choose to use a random amount over a form that no one happens to know how much to use, you will get a random result. Garbage in garbage out type thing...
The DB
If you choose to use a random amount over a form that no one happens to know how much to use, you will get a random result. Garbage in garbage out type thing...
The DB
So all these so called 18-21 feet wrapped around such and such is bs? As well as 8 turns around 8" or 10 wraps 10", 6 wraps 6"?
5 wraps around a 4.25 inch form is CB band choke, 5 wraps around a 7 inch form is close to 16 or 17 MHz, 7 wraps around a 7 inch diameter form is even lower, around 13 or 14 MHz.
The larger the size of the air core the lower the frequency the choke will work on. The more wraps, the lower the frequency the choke will work on. In the end it is a balancing act. For an 8 inch form you need to use less than five wraps to get the choke to function well on CB frequencies. How many less? I'm not sure... As I mentioned above, I switched to using ferrites and have never looked back...
The DB
The larger the size of the air core the lower the frequency the choke will work on. The more wraps, the lower the frequency the choke will work on. In the end it is a balancing act. For an 8 inch form you need to use less than five wraps to get the choke to function well on CB frequencies. How many less? I'm not sure... As I mentioned above, I switched to using ferrites and have never looked back...
The DB
I string them on before putting on an end. I use shrink tubing to hold them in place, although in the past I have used electrical tape and zip ties for holding them in place as well.
The DB
All technical data aside, one could use a commercially produced choke and be done with it.
I experimented around with air wound chokes, beads and baluns, and this worked the best with my mobile antenna controlling common mode currents. Of course the advertising is somewhat hyped up so don't believe everything you read.
Kind of expensive compared to what you can make yourself, but it is neat in appearance and gives your antenna system a uniform look.
DX Engineering Maxi-Core® Feedline Current Chokes
DX Engineering Feedline Current Chokes, using Maxi-Core® technology, prevent unwanted RFI by eliminating feedline current and radiation in 50 ohm, coaxially fed antenna systems. They provide excellent feedline decoupling and low loss performance from 1 to 60 MHz and are power rated for 2 kW continuous, 5 kW intermittent.
DX Engineering Feedline Current Chokes have significantly higher common mode impedance and a larger effective core area than similar line isolators, including conventional enameled wire or bead baluns. This results in higher power handling with lower loss, improved antenna bandwidth, and reduced RFI, and compensates for a less-than-optimal grounding system.
While the most common advice is to improve the station's RF ground, the root of the problem is in the poor isolation of the feedline from antenna currents. In other cases, as the coax feedline travels through the near-field of the antenna, the current can be reintroduced to the feedline after the balun. If your SWR is already low and you wish to reduce feedline radiation (RFI) and improve reception, DX Engineering Maxi-Core® Feedline Current Chokes are recommended.
This approach became my choice after a few tries at DIY. A higher one-time expense — at three (3) positions on a big truck cophase harness — for a radio system in constant use made sense: at the transceiver, and at the antenna feedpoints.
Now part of the quietest radio system I’ve had, and after many attempts over the years in Class 8 tractors.
(1) ea
(2) ea
A 1/2” i.d. snap-on ferrite over 5-6 turns of the supplied radio power cord was the rest of RF mitigation.
I may use ferrites on all lines, but it’s the above four (4) which made the greatest overall passive noise reduction.
These filters & ferrite plus DSP-integrated speaker (audio clarity increase; active noise reduction) and some misc was where my big truck mobile radio system went from being quite good (truck brand & model) to being comparatively dead-quiet after a radio chosen for best AM performance (plus SSB) was installed. (Galaxy DX-959b into an RM ITALY KL-7405v).
For perspective, the radio & amp account for under one-half the total cost of installed components.They can also be swapped out for any other choices in a mobile system which will highlight transceiver qualities.
To close the circle with approximate costs, my $50 Wilson FME Mini-8 Coax Harness is now part of a $400 antenna system in the same way the $125 amp is part of a $300 12V power system, or that the $300 radio is part of a $525 transceiver + speaker system. Etc.
I figure the grand total to be $1,400 or so. (Probably more, ha!).
A Radio System consists of sub-systems (is the right approach). Each sub-system has details to work.
Here, it is a radio system used for business 300+ days/year; 10-12/hrs per day.
— Effective use of which re-pays the outlay 2-3X annually.
What goes into my other vehicles (private) might not be less expensive. Or might be a good deal less. It’s still in attention to subsystem performance.
— I expect use to be up to ten years. So I don’t look at this as being disposable.
Someone not an OTR truck driver with greater patience, leisure and understanding could DIY a feedpoint choke with maybe good $$ savings (after testing) to bring down this cost versus commercially-available.
Dollars or Time
It’s worth the effort!!
.
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As you all know, I run 2 EF's here, one is a 4010 and the other one is a 8010.....
The 4010, ended up using the CMC choke on this wire and also have 3 beads on the coax behind the radio, and no RFI in the shack or pc anymore.....
The 8010, getting ready to put it back up and see what happens with it....
In the past, I did try the wraps of coax, on LMR 400UF coax and RG 213 coax too, but this didn't work for me....so I went with beads on my coax and a cmc choke so far working fine..
The 4010, ended up using the CMC choke on this wire and also have 3 beads on the coax behind the radio, and no RFI in the shack or pc anymore.....
The 8010, getting ready to put it back up and see what happens with it....
In the past, I did try the wraps of coax, on LMR 400UF coax and RG 213 coax too, but this didn't work for me....so I went with beads on my coax and a cmc choke so far working fine..