How high should my dipole be?

In this video, I show you why you shouldn’t worry about height for your wire dipoles and loops.

Unless you can achieve leaps of a quarter-wave in size, just go with the flow (or put up a DX Commander All-Band-Vertical! :)

Quarter Wave -vs- 5/8ths Wave Vertical

q-wave-vs-5-8th-wave

Compare Red 5/8th -vs- Blue W/wave

Anyone who has mucked about with verticals will no doubt have worked out that a full-sized quarter-wave for the 40m band, more or less tunes up for 15m band.

It wasn’t until my entry in IOTA Contest this year that I convinced myself that they are not a cloudburner (as many people suggest) but compare favorably with a quarter-wave, even producing more gain by 2 dB at 10 degrees above the horizon.

OK, so 2 dB isn’t a huge gain, but hey – it’s free. Take it when you can!

Don’t forget, you can do the same for 10m band too by making an element 6.83m long and folding it back a further 1.11m (for 28.5 MHz). So you’ll need nearly 8m of wire. Don’t forget, that’s insulated wire!

4-Element Home-Brew Folded Dipole Yagi Dimensions

I’ve recently “made” a 4-element Yagi in software for my YouTube channel which should give a great match to 50 ohms.

If you’re into MMANA software modeling, here’s the file:

NOTE: This is a ZIP file because my Content Management System doesn’t like files ending in MMA. By all means have your Virus Scanner check this Zip file. There is only one file inside this ZIP. Just the MMANA file.

Quick SWR Calculator for Vertical and Dipole Ham Radio Antennas

Here’s a really simple way of double checking how to much to trim your antenna elements.

You only need to type in the numbers in the Cyan boxes.

Just type in where it is resonant right now – then type in where you would like it to be resonant and the spreadsheet will auto-calculate the trimming.

Film: How to use the SWR Adjustment calculator.

TOKYO HY-POWER HL-700B 600 Watt Amplifier purchase

So I have just taken delivery of a very gently used Tokyo Hy-Power HF linear amplifier.

The previous owner (retired communications and instrumentation technician for a large, multi-national organisation) replaced both fans with ultra low noise “Arctic” fluid bearing units. These are installed in 2 speed via voltage regulation manner: Low speed during stand-by (RX) and High speed during TX. Continue reading

Adding 80m to DX Commander All Band Vertical (9-bands 80m through 6m)

Regulars will know about the DX Commanders very cool results which are now filtering through in real world successful contest scenarios.

My own issue is that I needed just one antenna that would deliver an all-band solution, certainly for the contest bands of 40m, 20m, 15m and 10m – but I also needed 80m in the mix too.

My holiday home has a very compact small garden so the option of putting up a dipole for 80m is out the question, but modelling suggested than exchanging the 30m element for an inverted L for 80m should work.

The 80m element therefore starts vertical, like all DX Commander elements and turns a sharp corner at 6.9m above ground and droops down for around 13m or so, hanging over a bush at around 3m off the ground. Probably not perfect but perfectly adequate to score 44 QSOs inside an hour on the Saturday eve of the IOTA contest. That score includes 16 different IOTA multipliers, certainly a wide spread around Europe.

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DX Commander Contest Antenna achieves top placed UK IOTA Station

IOTA-graphicI’m absolutely delighted to report that I was placed 4th overall in the world for IOTA-Fixed station, Unassisted, Low Power, 12-hour section. This was from a holiday home and I installed the antenna inside 1-hour.

Results here  – but what makes this more remarkable is that I only used the one antenna from 80m through 10m; DX Commander All-Band-Vertical.

For 80m, I confirgured the DX Commander as an Inverted-L, replacing the 30m element. Of interest, 30m was still achievable (albeit with a 4:1 SWR). Although 17m is not a contest band, I did notice some slight interaction with the new 80m element, however SWR was still acceptable without an ATU.

I logged 300 QSOs however I notice after adjudication, that fell to 289. Pretty good, only dropping 11 QSOs. And I was amazed at how effective the 40m element produced such startling results on 15m, effectively as a 5/8th. Even 10m as a 2.5m long, ground mounted quarter-wave was getting in the action with short skip too.

All in all, I’m extremely delighted that I test-proved this antenna from a holiday location in competition with my peers, who were using genuine fixed-station antennas.

Software Modelling your Vertical antenna ground radials with MMANA

I’ve been scratching my head for years how to model an appropriate ground with my ground mounted Vertical Antenna radials.

I’d like to thank Sigi, DG9BFC for clearing this up for me.

HOW TO:

NOTE: I like to draw a small feedpoint in all my HF antenna models, like a 5cm length of wire where my “source” (coax) is connected to. Particularly useful for fan dipoles and for making other adjustments. I’ve left that part out for simplicity on this How To since I’m trying to make this super easy.

Continue reading

DX Commander now shipping to USA / Canada / Aus

After much research, I’ve managed to get the price to under £30 for USA, an additional £10 for Canada with Russia and Australia incurring extra costs. I’m doing this shipping at cost folks via a tracked parcel. You can buy shipping cheaper – but with horror stories I’m afraid.

  • Still a hugely economical antenna for what you get.

PS Postage for USA is only £30 using MyHermes for delivery to OCS in UK and on to United Parcels Service for local delivery in USA.

Experience is suggesting that due to the low price, no customs or duty should be paid when it lands your end for most countries (although I can’t guarantee that – although my shipping people tell me it’s under the threshold).

Start here:

https://www.m0mcx.co.uk/store/products/dx-commander-premium-build-hf-multi-band-vertical-system/

Vertical Antenna – How many Ground Mounted Radials Do I Need

I’m often asked this question and after 5 years of development, I think I finally have the answer thanks to both real-worl experience and the work that Ruby Severns, N6LF did in a controlled scientifically based experiment.

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Read the PDF document on this link:

Raised Radials are a completely different kettle of fish. These are tuned to the frequency i question and can give varied results.

PS – Another superb read for the very clever folks is here:

Good luck!

M0MCX Banana Antenna – an end-fed choke sleeve resonant feedline T2LT antenna design

A new document fully documenting the design of the Banana Antenna has now been released entitled, “Banana, a Half Wave End-Fed Choked Coax Antenna”.

banana-antenna

Banana Antenna

Antenna can be known as – and is similar to:

Sleeve Dipole / Flowerpot Antenna

The Sleeve dipole has traditionally been used by VHF antenna designers by sliding an external metal sleeve over the coax and connecting the sleeve to the braid of the coax so that the antenna appears to be centre-fed with an outboard “sleeve”. Some commercial CB antennas are also made this way. Continue reading

20m band End-Fed Choked Coax Dipoles (T2LT)

WARNING: This post has been replaced with the following analysis and design:

Banana Antenna Design May 2017

– – –

The Resonant Feedline Antenna is also known as:

• Sleeve Dipole (& Flowerpot Antenna)
• Resonant Feedline Dipole (J Taylor, W2OZH)
• Tuned Transmission Line Trap, T2LT (CB folks)

For more about common mode chokes, see this article:

Pictures of this experiment follow including the 10-25 MHz >8K choke follow.

75 ohm to 50 ohm transmission line matching coax stub

Coax Transmission line coax stubs are frequency dependent. Making a stub for one frequency means it WILL NOT work for another frequency. My example is for a 20m Resonant Feedline Dipole, sometimes called a Sleeve Dipole or Resonant Coax Dipole or Tuned Choked Coax Dipole.

So you have an approx 75 ohm impedance antenna and you want to get the best match you can. Take the wavelength of the frequency, multiply it by the velocity factor of your 75 ohm matching coax and multiply again by 0.0815.

For example.

14.225 MHz = 21.089 metres
21.089 * 0.66 (what ever your velocity factor is) = 13.19
Multiply 13.91 * 0.0815 = 1.134m

Therefore, your transmission line coaxial transformer will be 1.134m long which is apparently about 29 degrees around the 360 degree circle.

Data found here: PA0FRI page.

Finally, I discovered MANY pages on eHam and QRZ forums of people asking the same question but most answers are with people answering questions which were not asked – or giving advice how to fix the antenna, or live with it. Why Americans need to argue the toss when others just need answers beggers belief :)

JT65 UK Band Plan and how to stay within

The 5 MHz band is pretty cool and I’ve written about it before however out the box, JT65 allows you to very easily transmit out of band on 60m band. The segment we’re interested in the UK is the freq block between 5.354 and 5.358. This has taken me a little while to get to grips with this because although the band-police are complaining – and the RSGB has also warned users, nobody is giving a clear instruction on how to achieve staying completely within the band allocated to us.

In the UK therefore, there’s a couple of simple steps to take to make sure you won’t transmit out of band.

If you don’t have JT65 already, get it here: http://jt65-hf.com/downloads/.

Run the installer and interface your rig as you would any other piece of software that connects to your computer. If you are after help with that part of the problem, there are other places to hunt solutions down, not this blog.

Go to file > Settings and click the Frequency tab at the top and edit the frequency for the 5 MHz band so it reads 5.356.

File > Settings > Frequencies

File > Settings > Frequencies

Continue reading