Broadband HF Dipole

[MarkAT6]

I'm trying to source a reasonably priced commercial-off-the-shelf Transmit / Receive HF broadband dipole for a work application. Ideally its transmit PEP rating would be greater than 150W. An example of the type of antenna I'm after is the Diamond Wd-330 but with a higher power rating.

Any suggestions would be appreciated.

Cheers

Mark

[Radio Wrangler]

Frequency range?

David

[G6Tanuki]

The Yaesu YA-30 does 150W.

http://www.yaesu.co.uk/files/YA_30.pdf

For higher powers you're looking at commercial stuff - Barker&Williamson in the US is a supplier I've used in the past.

http://www.bwantennas.com/pro/bwds.pro.htm

Not cheap, but their stuff works!

The Yaesu seems to me to be a T2FD http://en.wikipedia.org/wiki/T2FD_antenna with a bigger termination resistor, like all untuned broadband antennas it is just a leaky dummy load. Best to go for an autotune system (SGC make very good ones such as the http://www.sgcworld.com/230ProductPage.html ) and some wire in the air.

[Radio Wrangler]

I agree that it looks like a T2FD with a big enough resistor to use it off of its resonances, and I'll second the SGC suggestion.

There are also autotune dipole units from Rohde & Schwarz where the autotuner has to be right up in the middle of the wires, but I hate to imagine the cost.

David

[Sparky67]

If you can get away with an antenna for spot freqs in a number of bands across HF rather than needing genuine wideband coverage you may be OK to spec a fan dipole, which is likely to be more efficient than a wideband dipole. For example, a...

http://www.freewebs.com/hypower/webdoc10.html

Martin

[G6Tanuki]

The "fan dipole" is indeed a good design if you're working on a number of fixed, non-harmonically-related frequencies. You could also look at rhe W3DZZ-type trapped-dipole approach (traps are available for all the amateur bands - it's relatively easy to produce traps using coaxial cable for other frequencies).

Another alternative could be a "terminated end-fed inverted-vee" - I've used these in the past too.

A 9:1 impedance transformer at one end, the long wire (the longer the better!) in inverted-vee formation, and at the remote end a non-inductive resistor of about 300-500 Ohms between the end of the antenna and ground. A bit like a classic 'Beverage' antenna.

See http://www.google.com/patents/US4511898

or

http://www.korpi.biz/hr.pdf

Yes, the resistor does dissipate some of the RF; but once your wire's more than about a wavelength long that 'dissipated' RF would be contributing to destructive interference patterns with the 'forward' wave anyway.

[G8HQP Dave]

My hunch is that the interference patterns are still there. Any folded dipole (whatever its termination) can be analysed as a combination of an antenna and a transmission line. It is the transmission line mode currents which get terminated by any resistor, yet it is the antenna mode currents which do most of the radiation. I suspect it is the presence of the interference patterns which push the antenna into often being used tilted.

It would be interesting to compare a T2FD with a normal folded dipole fed via a -3dB attenuator pad (or thereabouts).

[G8BBZ]

You might be interested in the range of broadband HF antennas made by Bushcomm in Australia (www.bushcommantennas.com.au)
The Robinson Barnes design on which these antennas are based claims higher efficiency than the usual broadband designs which rely on loading resistors to flatten the VSWR characteristic.
The Bushcomm antennas are also relatively lightweight in construction, meaning that you don't need big towers to support the weight and windage (unlike the Telefunken broadband antennas which I have used professionally which need serious supports!)
I have never used the Bushcomm antennas personally and so cannot comment on their effectiveness, but they do seem to have a good market down Under.
cheers
Peter G8BBZ

[G6Tanuki]

Looking at the Bushcomm site, it mentions "load boxes" and the diagram seems to show 'something' connected across the centre-leg of the 3-wire span just above the balun.

I'm inclined to think this is just a T2FD-variant but with part of it made using 3 wires in parallel.

Some of them are also apparently made using stainless-steel wire: I know from experience that such wire can be seriously RF-lossy (unless copper-plated). A distributed resistance in the aerial wire-elements will give you a low SWR but does nothing for efficiency.

[Martin G7MRV]

Originally Posted by MarkAT6

I'm trying to source a reasonably priced commercial-off-the-shelf Transmit / Receive HF broadband dipole for a work application. Ideally its transmit PEP rating would be greater than 150W. An example of the type of antenna I'm after is the Diamond Wd-330 but with a higher power rating

Mark,

Just specifying broadband and a certain power doesn't give much to go on. Can you tell us the frequencies of the application (you don't have to say exact frequencies, but something like '7.5MHz/2.3MHz' etc would be enough)

The suggestions above are mostly for broadband in the 'whole spectrum' sense, but perhaps your meaning broadbanded in just the 'wider than normal' sense, perhaps for a specific frequency but a very wide bandwidth signal?

[MarkAT6]

All,

Thanks for your suggestions so far - apologies for the lack of detail. The proposed antenna is going to be used at a company HF facility I'm resetting up for R&D purposes . The particular requirement I'm trying to fill is for a 2 to 30 MHz broadband antenna to support a swept chirp transmit signal. A few years ago we successfully used a Diamond WD-330 antenna for a similar application but managed to burn out the load resistor when we subsequently transmitted other test signals with a high peak to mean ratio!! Thus what we're looking for is something similar to the WD 330 but with a higher PEP rating, easily deployable (we have a fixed 15m mast) and at a 'reasonable' price.

Cheers

Mark

[Radio Wrangler]

Well the chirp rules out anything with a variable tuner. It needs to be simultaneously broadband.

Anything that covers that range is going to be either a lossy resistor in essence, or else a very long wire (Beveridge) sort of thing.

David

[Skywave]

Originally Posted by MarkAT6

A few years ago we successfully used a Diamond WD-330 antenna for a similar application but managed to burn out the load resistor when we subsequently transmitted other test signals with a high peak to mean ratio!!

Would it be totally impractical and out of the question to obtain a WD-330 and then simply replace its terminating resistor with one of higher wattage? Note that four resistors, each of resistance R ohms, when connected in series / parallel, give a net resistance of R ohms.

Al.

[Peter.N.]

A friend of mine makes a highly acclaimed multiband HF antennas, his name is Fred Western, I don't know the cost but I think they are reasonable, they were tested in Radcom a year or two back. He used to sell them on ebay but I don' think he does now but if you type 'western antennas' or something similar into Google you should find some info

Peter.

[G3PIJpeter]

Have you looked at the 'Australian Travelling Wave Dipole'?
- see http://www.paws.dircon.co.uk/draka.htm
I seem to remember Pat Hawker giving details in a 1970s 'Technical Topics' article.
There is also the Robinson Barnes broadband aerial
- see https://en.wikipedia.org/wiki/Robins...adband_Antenna
Interesting properties but no design details given and the link to the commercial BBA-100 is dead.

P.S.
Note that the text on the dircon site states:

"... Elsewhere, (the ARRL Antenna Handbook), the resistors are specified as 2-5 watts rating for up to 500 watts pep."

So the resistors are not going to dissipate much of the power fed to the centre of the aerial i.e. it is not in the same category as the T2FD.

- Peter

[G6Tanuki]

Originally Posted by MarkAT6

Thanks for your suggestions so far - apologies for the lack of detail. The proposed antenna is going to be used at a company HF facility I'm resetting up for R&D purposes . The particular requirement I'm trying to fill is for a 2 to 30 MHz broadband antenna to support a swept chirp transmit signal. A few years ago we successfully used a Diamond WD-330 antenna for a similar application but managed to burn out the load resistor when we subsequently transmitted other test signals with a high peak to mean ratio!! Thus what we're looking for is something similar to the WD 330 but with a higher PEP rating, easily deployable (we have a fixed 15m mast) and at a 'reasonable' price

You're using some kind of ALE system? I've experience of this [UK-to-Falklands, UK-to-Antarctica, UK-to-ships-at-sea-and-submarines-submerged]. Frequency-agile transmitters are usually capable of delivering RF into loads with a SWR of up to 3:1 - [the kit I design will deliver full-rated-power into *any* load irrespective of impedance] - from a pragmatic perspective an antenna-shunted-by-a-dummy-load has a lot to commend it.

[I bring to mind the Clansman "pineapple" broadband antenna - [http://www.armyradio.com/arsc/custom...roductid=1420] - you squirted lots-of-Watts into it but not-many-watts got radiated]

"Lossy" antennas have their place - TBH I'd suggest you erect the longest-possible length of wire, and terminate the far-point to ground through a resistor of something between 250 and 500 Ohms.