I’ve broken my Hexbeam – Again!

With the title to this entry, I can imagine a collective sigh from my readers, followed by “Oh no, not again”.

This time is different though, this time it was nothing to do with RF or with melted insulators.  A few weeks ago I decided to add some anti-bird measures to my aerial consisting of six bird repellant diverter discs.

I’ve changed the method of mounting these a few times and I think I’ve sort of got it right now.  I had problems with the discs getting caught on the elements but by moving the mounting position, I’ve resolved that.

Two weeks ago, after some high winds, I noticed that there were only two discs left out of the six.  I didn’t know what had broken, whether it was the clamps, the discs themselves or the cable ties holding them in place and it saddened me.

Last week, while out for a walk, I spotted one of my missing discs on the grass area at the end of my road, around 100m away.  When I checked it, it all looked intact so it appeared the cable ties must have broken.
The next day, two more of the discs appeared on our doormat.  Some kind neighbour found them and dropped them back to me.

How does this relate to my broken aerial?

Last weekend, I lowered the mast in order to replace the discs and also to modify the way the Hexbeam was mounted.  I lowered everything before Tony, G0MBA came along to help and I accidentally dropped the mast too far and too quickly and managed to split the end section of one of the spreaders.

Broken end spreader section on my Hexbeam

Broken end spreader section on my Hexbeam

These sections are under tension so Tony and I wound a number of thick cable ties around it to try and take some of the pressure off but as soon as it was back in the air, I realised I’d have to get it replaced.

The broken end section of my Hexbeam with the aerial in the sky

The broken end section of my Hexbeam with the aerial in the sky

I emailed Ant, the original supplier of my G3TXQ Hexbeam and he put a replacement end section in the post to me straight away.

This morning I lowered the mast, replaced the broken section and raised it again, all in about half an hour.

New end spreader piece on my G3TXQ Hexbeam

New end spreader piece on my G3TXQ Hexbeam

As you can see, I’ve gone from using cable ties for the bird repeller to nice bright paracord.  I use the same paracord (although in grey) to support my doublet.

As an extra point, when I put the mast back up last weekend with five of the six discs on, the kids from next door knocked on my front door with the remaining disc.  It had landed in their garden but they hadn’t realised where it came from until they saw the aerial go back up again with five discs on top.  I have nice neighbours.

I really can’t recommend the G3TXQ Hexbeam as made by Anthony, MW0JZE enough.  It’s a superb design, an incredibly well made aerial and he continues to support it, even though I’ve had this for nearly six years.  I know I’ve broken it many times (see the ‘broken aerial‘ category on this blog) but each time the design has been changed and the aerial has just got better and better.  It’s larger than my old MA-5B but I still think the visible impact is lower because it just looks more pleasing than the spiky beast that is the MA-5B.

If this aerial broke completely, I’d replace it with the same again without hesitation.

Posted in Amateur radio, Broken aerial, HF | Tagged , | Leave a comment

Are you transmitting illegally on 70cms?

An interesting subject came up on our 70cms voice repeater earlier today following an incident on a local DMR box yesterday and it got me thinking.

There are a lot of 70cms repeaters in the UK with input frequencies between 430 MHz and 431 MHz and many people don’t realise that our licence only allows reduced power in that part of the band.  I’ll put my hands up and say that although I’m well aware of the 100km Charing Cross rule, I wasn’t fully up to speed on what I’m about to talk about here.  Incidentally, I live within that 100km radius by less than a quarter of a mile!

Specifically, the maximum power for Full and Intermediate licensees is 40W ERP and that goes down to just 10W ERP for Foundation licence holders.
Power limits by ERP are unusual as apart from this small section of 70cms, only the two VLF bands have ERP power limits.

What this actually means is that our Effective Radiated Power is limited when working any of the nearly 150 repeaters on 70cms with an input frequency from 430-431 MHz.  These are almost exclusively digital repeaters, either DMR or D-STAR.  You can see the most recent list of 70cms repeaters by clicking here (hint: click on the [receive] column to sort by repeater receive frequency).

ERP is calculated by taking into account the output power of your wireless, the loss of your coaxial cable and the gain of your aerial.  Remember that aerial manufacturers generally quote the gain of their aerials in dBi which is a theoretical figure and is impossible to achieve.  All my calculations below are using dBd which is dBi minus 2.15.

Let’s look at a fairly typical mobile setup first and by coincidence, this will be exactly what I’ve got in the car.
An Icom ID-5100 has three power settings, it runs 50W, 15W or 5W on 70cms.

If I have the radio on the High power setting of 50W and am using a very common type of aerial, a 2 x 5/8 whip aerial with 10ft of RG-58 coax, my actual power going into the aerial will be about 40W.  The aerial gain is approximately 3dBd so my ERP will be 80W.  That’s illegal.  By reducing the power to Medium, I’ll have around 12W going into the aerial and so my ERP will be 24W which is legal.  With this setup, a Foundation licence holder can only run Low power of 5W to remain legal as that will give around 4W into the aerial and so be 8W ERP.

I think most people operating DMR use handheld radios – I’m not aware of anyone locally with an actual mobile radio transmitting DMR so if used in a car with an external aerial then the 5W output from a typical DMR handbag will still be legal.

It’s when you get indoors that things start getting a little more tricky because of the wide range of available aerials and radios.  I’ve tried to select common equipment.

At home, I have another Icom ID-5100, my aerial is a Diamond X510 and I have around 15m of EcoFlex 15 coax.  My coax loss is 0.9dB on 70cms and the aerial gain is 9.55dBd.  With the radio set to 5W output I’ll be getting around 4W going into the aerial and the 9.55dBd gain gives me an ERP of 36W.  Providing I only use the radio on the Low power setting of 5W, I’m legal.  Just.

Many people have smaller aerials such as the Diamond X50 or equivalent.  The gain on the X50 on 70cms is a fraction over 5dBd but let’s round it down to 5dBd for ease of calculations.

The MD-380 is a common UHF DMR wireless with 5W output. The Icom ID-51 runs the same amount of power on D-STAR so let’s go with 5W as our power for these calculations.

If you’ve got your dual band aerial up at a decent height, you may have 20m of coaxial cable.  I hope you’re using RG-213 as an absolute minimum on UHF.  If this is your setup then 5W output fed through 20m of RG-213 gives you 2.4W at the aerial.  Take into account the 5dBd gain from the X50 and you’ve got 7.5W ERP. You’re legal, no matter what your licence level is.

The same setup with a Diamond X200 gives you around 9W ERP but if you go to a Diamond X300 (or equivalent) then your ERP goes up to 12W.  You’re now transmitting an illegal power level on 70cms if you’re a Foundation licence holder with the 10W ERP limit.

The above examples are just that, examples.  You should know how much power you’re running out of your transmitter, you should know how much loss there is in the cable and you should know the gain of your aerial. With those figures, it’s fairly straightforward to calculate your ERP.  You could use this as a starting point for working out your coax loss (input cable type, cable length, frequency and power) and then this to calculate your ERP (using the calculated power from the previous link and aerial gain in dBd).

It’s worth being aware of this if you operate on 70cms digital repeaters as I suspect a lot of amateurs won’t have realised this power limit is in place.  I know that everyone is supposed to know how much power they can run on what frequency but this ERP limit is quite unusual, we’re more used to the limits of 10W, 50W and 400W that our Foundation/Intermediate and Full licences allow.

If you do transmit on 70cms between 431 and 432 MHz then you really do need to take a close look at your station to make sure you’re transmitting legally.  Remember that we are secondary users of the 70cms band and you don’t want to upset the primary users.

Posted in Amateur radio, D-STAR, DMR, FM, UHF | Tagged , , , , | 2 Comments

My amateur radio station in 1991

I was recently looking through some old photographs and I found some pictures of my old radio shack and aerials from when I still lived at home.  These photos would have been taken in the second half of 1991.

The first photo is the inside of my ‘shack’ which was really just one side of my bedroom.

My radio shack in 1991 showing my FT-736R

My radio shack in 1991 showing my FT-736R (click for a much larger version)

From the left is a dumb terminal which was connected to the PK-88 TNC for accessing the local packet radio mailbox.  Then there’s a PSU against the wall with a postcard of the Greek island of Paxos on top of it (this is how I’ve been able to date the picture).  Next to that is a Yaesu desk microphone, a Yaesu FT-736R multimode for 2m and 70cms and an external speaker for the wireless with a rotator control box on top.  Just next to this and barely visible is a Morse key, a limited edition key which was hand made by Mike, G4ZPE and I wish I still owned that.  Finally on the right side you can see a BNOS VHF 100W amplifier sitting on top of a BNOS dummy load.  On top of the 736 is an SWR meter and the aforementioned AEA PK-88 TNC.
On the wall are some coax switches which allowed me to change between a dual band vertical aerial or beams for both 2m and 70cms.

Moving outside.

My aerials in 1991

My aerials in 1991 (click for a much larger version)

Luckily my bedroom/shack was right at the back of the house on the top floor, ideally located for my aerials with the cables coming in through the window.

On the top of the pole on the left is a 48 element multibeam for 70cms.  Jaybeam aerials had a reputation for being very solidly built and this multibeam was a prime example of that.  Below it is a 9 element F9FT Tonna for 2m and below the rotator is a TV aerial.  On the pole on the right side is a Diamond X500 vertical for 2m and 70cms and below the second TV aerial is a small vertical dipole which was used to access the AX25 packet radio network.

Close up of the 48 ele multibeam and 9 element Tonna

Close up of the 48 ele multibeam and 9 element Tonna (click to make it bigger)

This setup worked remarkably well, especially considering that the location wasn’t particularly high above sea level.  I successfully entered a number of contests on VHF and UHF using this relatively modest station with good results and although I never won anything, I was generally well placed.  It was using this setup that I made the one and only auroral contact I’ve ever had!  I did enjoy chasing DX and working new squares on 2m and 70cms.

I don’t think I still own anything that appears in these pictures although my mum still lives in the same house and the brackets on the back now just sport a TV aerial – Mounted on a 20ft pole and naturally the highest in the area!

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Listening to the Camb-Hams from the Isle of Islay

The Camb-Hams are on their usual annual pilgrimage to Scotland and I’ve worked them on a few bands and modes.  I’ve also made a couple of recordings of them on 40m CW, showing how well the Kenwood TS-590SG can read Morse Code and on 40m and 80m SSB.

Posted in Amateur radio, CW, DXpedition, HF, SSB | Tagged | Leave a comment

Learning to code in Python – Hello Raspberry Pi!

After my posts about building an APRS RX iGate, I entered into email discussion with Alan, K2RHK who pointed me towards his website specifically to see his experiments in APRS.  While looking through his site, I noticed he’d recommended a book for those looking to learn how to program a Raspberry Pi.  I mentioned that this was something I’d just started doing and Alan contacted a friend of his, Marjan Bace at Manning Publications who very kindly posted me a copy of the book we were talking about called ‘Hello Raspberry Pi!‘.

I’ve only just started learning to program in Python but this looks like a fun and interesting book to get me going.  I’ve already sussed out some Python simply by examining existing code and tweaking it to do what I want but it’s good to get a proper guide to start me off with the basics.

Thanks Alan and Marjan!

Hello Raspberry Pi! by Ryan Heitz from Manning Publications

Hello Raspberry Pi! by Ryan Heitz from Manning Publications

Posted in Not amateur radio, Raspberry Pi | Tagged , | Leave a comment

What can be achieved in twelve hours of 20m JT65/JT9?

WSPR is great, I enjoy running WSPR and seeing how far I can transmit using very low power but there are a couple of drawbacks.  I appreciate this will sound as though I’m knocking WSPR but trust me, I’m really not.

Firstly, it’s not a QSO mode.  I accept that many years ago, some QSOs were made using WSPR but that was in the very early stages of development and I don’t believe that the software is there to actually facilitate that any more.  I find it frustrating to hear people say “Oh, I had contacts all over the world yesterday on WSPR”. No, you didn’t.  You transmitted and someone received you, that doesn’t necessarily make a QSO.

Secondly, although WSPR is incredibly good at penetrating around the world, just because someone in (say) VK land heard your 200mW WSPR signal with a strength of -28dB, that doesn’t mean the band is properly open and that you can complete a QSO using SSB or CW.  You almost certainly can’t.

This is where the low signal data modes come in, specifically JT65 and the newer JT9.  I’ve written about JT65 a lot, I couldn’t have completed my original QSO365 without using JT65 and I discussed JT9 here.

Rather than run WSPR for a day, I thought I’d spend twelve hours yesterday just receiving JT65 and JT9 signals on 20m.  In theory, I should be able to work any station I can hear using these modes.  I fired up the latest version of WSJT-X which includes JT4, JT9, JT65, QRA64, ISCAT, MSK144, and WSPR at just after 09:00z, configured it for JT65 and JT9 reception, switched it to 20m and let it sit there receiving and uploading everything to pskreporter to produce the map below.

The results after twelve hours were quite astonishing.  I know these modes are popular but I don’t think I realised quite how popular they’ve become.  You can click the following two images for much larger versions.

Map of stations heard on 20m JT65 and JT9 over a twelve hour period

Map of stations heard on 20m JT65 and JT9 over a twelve hour period

Over a period of twelve hours I received 2,124 individual transmissions from 554 unique transmitters spread over 74 countries.  That’s quite incredible.

List of countries heard on 20m JT65 and JT9 over a twelve hour period

List of countries heard on 20m JT65 and JT9 over a twelve hour period

To test my theory that all of these should be workable, I made four QSOs in the evening.  I worked Venezuela, Japan, Puerto Rico and Brazil, all with JT65 and all using just five watts.  I still like to run bucketloads of power when it’s appropriate but for these low signal modes, you really don’t need to run a lot of power to make contacts.

The low power/low power data modes aren’t for everyone but they’re not difficult to use and are a great way of getting the most out of a small to medium sized station.  They drag every dB of performance out of inefficient aerial systems and it’s no surprise that my first ever QSO with VK back in 2011 was using JT65 and a short ‘long’ wire aerial.

If you’ve never tried these modes, I encourage you to give them a try.  You’ll be happily surprised at what you can work.

Posted in Amateur radio, Data, HF, JT65, JT9, QSO365, WSPR | Tagged , , , | Leave a comment

More new test gear for the shack

Back in 2012 I wrote about some new test gear that I’d bought for the shack.  Well time doesn’t stand still and it’s always nice to have new toys in the shack, especially if they’re useful.

My miniVNA Pro always did me well but recently I’ve started doing things on higher frequencies, such as building aerials for ADS-B reception and it’s frustrated me that I’ve not been able to fully test them.  With that in mind, earlier this year I bought myself an AAI RF Vector Impedance Analyser N1201SA from Banggood.

AAI RF Vector Impedance Analyser N1201SA

AAI RF Vector Impedance Analyser N1201SA

This is a cracking little piece of kit which covers from 137 MHz up to 2.7 GHz in 1 kHz steps.  It can measure SWR, resistance, reactance and S11. It’s not stupidly expensive either at around £130.  Being battery operated and fairly simple to use, it’s a very good piece of equipment.

The only downside to it is that there’s no way to save the measurements it displays apart from taking a photograph of the screen.  There’s no denying that it looks good though, here’s a plot of my Diamond X510 from earlier today.  It’s also not a full blown VNA so it can’t be used for such things as measuring the performance of filters.

AAI N1201SA scan of my Diamond X510N on 2m

AAI N1201SA scan of my Diamond X510N on 2m

Despite these downsides, if there was an HF version of this analyser, I’d be all over it.

The next logical step for me was an upgrade to my old miniVNA Pro.  It’s a fantastic piece of kit that’s served me very well over the years but I wanted something to cover higher frequencies.  I looked into a number of items and decided that the best thing for me was to change to the newer miniVNA Tiny.  Despite the name sounding as though it’s a downgrade (Pro to Tiny), it’s actually a decent upgrade as it covers from 1 MHz up to 3 GHz which is far higher than I can ever think I’ll need.  It looks quite similar to my old VNA, it’s just a little smaller and has a different connector.

miniVNA Tiny from mini RADIO SOLUTIONS

miniVNA Tiny from mini Radio Solutions

One of the first things I did with this was to test my new Diamond X510N vertical which I put up a couple of weeks ago and here are the results on 2m and 70cms.  It’s encouraging to see that the 2m measurement matches up with the N1201SA image above.

Both these images are clickable for much larger versions.

Diamond X510N 2m SWR measured with miniVNA Tiny

Diamond X510N 2m SWR measured with miniVNA Tiny

Diamond X510N 70cms SWR measured with miniVNA Tiny

Diamond X510N 70cms SWR measured with miniVNA Tiny

Finally I’ve been able to get my hands on something I’ve wanted for quite a long time and it serves multiple purposes.  I’ve wanted an accurate power meter for measuring the output of my WSPR/QRSS transmitters. It’s all very well having a super-duper QRO meter but when trying to measure down to a couple of hundred milliwatts, that’s not exactly suitable.

I bought myself a Yaege FC1-Plus Portable Frequency Counter which covers a massive 10 Hz to 2.6 GHz from 409shop.  Not only is this a frequency counter (which is useful by itself) but it’s also a power meter which is good up to two or three watts.  I wouldn’t want to put any more power into it.

Yaege FC1-Plus Portable Frequency Counter

Yaege FC1-Plus Portable Frequency Counter

If you’re looking to buy one of these, be aware that there are two models.  The FC1 and the FC1-Plus.  If you want the power meter version then you must buy the FC1-Plus.  It’s a little more expensive at around £50 but if you want it as a power meter then it’s worth it.

Here’s the display in frequency counter mode, monitoring my WSPR transmitter.

Yaege FC1-Plus in frequency counter mode

Yaege FC1-Plus in frequency counter mode

This ties up within a few Hz of the frequency I’ve got my GPS based transmitter so I’m happy with the accuracy.

What I was really interested though was power.  I fired up my WSPR transmitter into the meter in power mode.

Yaege FC1-Plus in power mode

Yaege FC1-Plus in power mode

This reads fractionally higher than I was expecting although I am running a higher voltage to the output stage of the U3S transmitter.  I have no reason to disbelieve the accuracy as I’ve been assured from a couple of sources that these meters are pretty much spot on.  Even if it’s only within 10%, I’m still happy but it does mean that I’m probably running a little more power on the lower bands than I thought.

I think that good test equipment in the shack really is essential now – Long gone are the days when we only used an SWR meter to check and align aerials and although a lot of amateurs only use commercial products, it’s still useful to be able to test performance to make sure everything is working properly.  I play around with low power experimental transmitters so this sort of kit is essential really.

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