SMALL RANGE HF ANTENNA

Hello msidate

The IC-718 has 0.03-29.999999 MHz* * general coverage receive capability.

The specifications of your HF Transceiver are listed at: http://www.icomamerica.com/en/products/amateur/hf/718/specifications.aspx

Are you planning on transmitting/receiving on all frequencies in the design range of the unit?

If you are, there are complex antenna-matching problems across such a wide frequency range.

If your intent is to be transmitting/receiving across the Entire range of the transceiver, you would need an automatic antenna tuner unit, to ensure correct matching between the antenna and the unit.

If you are planning on transmitting/receiving in a small portion of one band as designated by the Specifications, then please advise the range of intended frequencies.

Is your intended location in a recognized "Hurricane or Tornado area"? That will have a significant bearing on what type/s of antenna/s could be useful in a Civil Emergency.

As your intended usage is "Emergency Services", you really need to allow for the worst, short of a direct meteorite strike on the transmitter, on the "Hope for the Best, Plan for the Worst" basis.

Reply with

Kind Regards....

Hi, thanks for your replies. The rescuers have licence for 3MHz, 7MHz, 11MHz, 13MHz... they can get other frequencies if needed. i have made DX communications from Morocco to all over the world. But in this case the rescuers want to use HF for close range communications. They have VHF and UHF radios (Motorola GP380) and trunking (smarnet and smartzone) even Tetra, but the scrambling and proprietary protocols made all these radios non interoperable. the only standard system is HF radios such as IC-718, IC-78, Codan and Barret. i look for a frequency and antenna that can suit that need. All radios have automatic couplers and some radios have ALE.

I agree with the previous reply.

You need to specify the desired frequency in order to determine a suitable antenna.

The dipole antenna is calculated using this formula:

L = 468 / f

where L is the length in feet

f is the frequency in MHz.

For example, a 144 MHz (2 m) dipole antenna would need to be 3.25 feet.

For close range, 144 MHz or higher is typical. The mobiles can use a whip antenna for these (FM) frequencies mounted on the trunk of the vehicle.

HF (40m, 80m, 160m) are not good at close range. These are for DX (long range). If a tuner is used, the antenna does not have to be resonant for the frequency because the tuner can compensate. The built in tuner can only compensate when the antenna is close to resonant for the frequency in question (SWR<3 for Icom 746).

Vertical multiband antennas can be used for the base station.

Repeaters are used to get over hills. The repeater relays your signal to the other guy (i.e. from the base to the mobile).

You cannot use this radio without a license. Knowledge of the stuff that I am presenting here is prerequisite to the license.

Contact ARRL in the US or the appropriate organization in your country.

For a circular coverage you will need an omni-directional antenna, such as a 1/4 wave ground plain. If a single frequency is used, than cut it to the desired frequency and that's all. If various frequencies are to be used, you will need an antenna tuner. With a 20 miles radius I see no reason to use various frequencies and your best bet for reliable 24/7/day/night communications would be around 7 or 11mHz. not so noisy, and out of possible skip zone.

Wangito.

Hello, there are some vertical HF mobile antennas on the market like the OutBacker NA is a good multi-tap antenna for mobile work or can be set up for base work. Also there are base vertical antennas you can google for them.

Here is a good starting point for to understand Near Vertical Incidental Skywave NVIS antenna with links out for more info and designs. They don't take up a lot of space to use.

Also you could look into NVIS style antenna from VCARS.

There is a simple NVIS antenna for mobile or with a little mod could be setup for base work. It's based on 1/4 wave length.

Hope this helps

metalSmith's

Hello msidate:

I would think the most useful both for mobile and home (fixed) use is either 1/4 wave or 1/8 wave. If you buy one it will already be 'tuned' but, if you want to make one make certain it is tuned exactly. It is not so critical of a half or full wave Antenna(if you have the room). But 1/8th of a full wave must be tuned carefully, and, the more time taken when tuning and setting up the antenna the more success you will have.

I would say for the type of use you mention as 'local' (though you do not specify the wave-length you will most likely be using) a directional antenna is going to be much more useful than say a fixed or straight-wire antenna.

The particular antenna you decide on depends on the range to want to receive and whether you want a mobile type.

I have only ever received not transeived. The important bit is the tuning for sure though.

Tell us what you want to use it for and we can advise the appropriate antenna.

good luck................ And there has been some very good info given on this post! But tell us more!

stay safe

babybear

Hello again msidate

Your best choice for an omnidirectional HF antenna would be the "discone" type, with a picture at left.

This type of antenna is suitable for the frequency range/s you intend using, although to ensure correct matching of transceiver to antenna across all those variable frequencies you shall still need an automatic matching device.

Check re that ST4 antenna here: http://www.summitsource.com/antennacraft-st4-outdoor-scanner-ham-discone-antenna-omnidirectional-signal-rooftop-local-offair-digital-ham-base-radio-band-reception-aerial-part-st4-p-7092.html

Regarding the automatic matching unit, refer second picture, also here:http://www.eham.net/reviews/detail/2842

There is a different maker of autotuners:

Trust that assists you.

Kind Regards....

Hello Sparkstation:

this looks like a really sensible antenna. Not too big and catches all the frequencies.

Good choice!

stay safe

babybear

Babybear,

It would be wise to read the post more carefully, if you had done so, you would have realized that the poster wants an HF antenna, while your suggestion is for a VHF one.

Furthermore, He has a one base station for which your design is not the best choice, and it is totally un suit as a mobile.

Wangito.

Hello wangito:

it has been many years since I last used HF and UHF radios and antennas. If I got the actual picture detail wrong.................you will note the info' I gave in post #7. And that other help like antenna tuning, plus, all the info' and links on the Larkfield site would have been of more use.

The antenna holder has inputs for HF and VHF by the way. And I intended it should not be used as a portable antenna 'per se', but, rather as a system which can easily be erected 'in the field' so as to speak.

With regard to your rudeness in 'advising' me on my 'wisedom'......... I could do without it. Because you have been a Radio Ham for a year, does not make you an expert. If I made a mistake in my posting with pictures then I ask your humble forgiveness!

By the way, please point out your advice to the original poster, as I cannot see any?