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Wednesday 29 August 2012

Antenna woes

Now, today I spent a lot of the day, in between writing a letter to my fiancée and other things, getting the CB antenna up into the loft space above my flat, however I have hit a small issue, it seems difficult to get the antenna into a proper V shape, and so I have preliminary installed it without tying off the ends, this led to a recorded VSWR of approximately 10:1 or just over, which is unacceptable.

In order to ensure the RG213 cable was not the culprit, I put the dummy load onto the end of the cable on the in the loft space, this returned the expected 1:1 VSWR reading and the radio’s full 4 watts is being sent up the cable, which is making me suspect strongly that the antenna system is at fault

I am going to try to reconfigure the antenna into an L shape in the next few days if I cannot get it into the V shape that I desire, that is running the 1/4 wave radiator vertical, and the lower part of the dipole laid across the floor, maybe running parallel with water pipes (though this may not be good either).

I know the antenna system is working on receive, as I monitored UK35 for a little while and the morons that I heard on there a few weeks ago that discussed doing certain acts that would have Ofcom revoking Amateur and broadcasting licenses for if discussed on those bands.

I verifed the VSWR issues with 2 SWR meters, both are consistent in their readings, so if I can find time tomorrow or Friday, I will go back up into the loft and try and retune the antenna, although if my fiancée was here she’d have been able to help or she may have even thought of a good idea.

I shall update this in due course


73 de 26CT730

Tuesday 28 August 2012

One step closer to a working antenna.

Today I went out to a nearby branch of the UK DIY and hardware store B&Q to buy the final parts needed to build the choke balun and a hot-melt glue gun.  If you’re American it’s the British version of The Home Depot, except not related to that company in any way shape or form, but that’s a debate for a different blog and a different time.

I spent the last few hour after arriving home putting the balun together, I now have it completed and almost ready for operation, I enclose a picture of my work below.


I have not stripped the end of the coaxial cable on the top of the balun yet, that will be done before it goes into the loft.  With a bit of luck this should be in service with the antenna tomorrow and the gateway will be tested on it.

If you’re on the Free Radio Network keep an ear out, you know my callsign by now, if you’re coming in to the Free Radio Network via PC, the CB gateway is RMDCBG, though I may change this to be prefixed with 26, owing to it being in England, which is 26 division on the AT division list.

I’ve taken the dummy load and SWR meter off the CB gateway radio, and have these plugged into the Moonraker FA5000 instead, this radio is parked on EU1 in preperation for the tuning tomorrow.

I will report back tomorrow once the antenna is tuned or whether I’ve not been able to get the antenna tuned.


73 de 26CT730

Saturday 18 August 2012

The war against PLT–seeing the destruction caused by BT supplied Comtrend PG902 UPA PLT adaptors

I have had another look on the Ban PLT website, a new video has been added, the video is by a licensed amateur showing what a pair of Comtrend PG902 PLT adaptors, the ones supplied by BT, can do to shortwave.  The results were that effectively the band is wiped out by noise.  Shortwave is part of the HF range 3-30 MHz, which includes some amateur radio bands, the CB allocations, as well as shortwave broadcasting.

Shortwave is still used by many people every day although most domestic radios sold these days lack the shortwave band, although the receivers are still obtainable and still used.

For some people from overseas, shortwave may be the only way they can hear news from their home country, these people may not have access to the internet and may prefer to listen to the radio.

Shortwave listening is a part of the Amateur radio community as well, even for those that are not licensed and thinking about taking the exam to get their foundation license, just because someone has an interest in radio does not mean they wish to transmit, shortwave listening is just as fun as transmitting.

So, do you have a pair of Comtrend PG902 PLT adaptors?
Do you use your Comtrend PG902 PLT adaptors?
Do you know that you are destroying a precious natural resource that people everyday need to use?
IF you answered “yes” to any or all these questions, unplug the adaptors, contact BT straight away, tell them you want an alternative (they HAVE to give you one) to the PLT adaptors, the BT Home Hub is a WiFi router, and most laptops built since 2004 have WiFi built in, but if the WiFi doesn’t work due to congestion, just run some ethernet cables, these can be discreetly run along the skirting boards and under carpets, or if you own the property you can have your home wired to contain ethernet cabling and sockets on the wall where you just plug your computer into, it’s a one-off hassle and causes NO interference to radio services.

You may not think of it as this, but the radio spectrum is a precious natural resource which is why many radio services require a license to use them, why radio equipment must meet certain Interface Requirements, and why all equipment, radio transmitters or not, must be tested to make sure that any RF emissions will not cause harmful interference to legitamate services, tests which all PLT adaptors, not just the Comtrend PG902, are not cabaple of passing, and although many seem to differ on this, they are a type of radio transmitter but they are spectrally unclean, causing unwanted interference.  I compare them to spark-gap transmitters from the early days of radio, which used large amount of spectrum and thus they are now illegal to operate, so it should be the same for PLT.

So, I urge you again, please stop using PLT adaptors if you have not already done so, and bin them, they pollute the radio spectrum, and we all need the radio spectrum every day, don’t take it for granted.

73 de 26CT730

Thursday 16 August 2012

Old antenna, new tricks, or I hope so…

I have dug out my wire dipole (made from coaxial cable), this was cut from the coaxial cable, which is currently set aside, in order to attach it to a choke balun, the last small piece of insulation has been removed from the centre of the dipole and both ends attached to a terminal block each,  This will be put into service once the choke balun has been built, and if found to work it will be used as the main antenna, thus saving me money.

I found some scrap twin-and-earth cable in the attic, sadly though a lot of it is still running to the sealed-up conduits so it therefore is not usable, and because it’s in close proximity to cables that are in service there is a risk that I could cut the wrong cable, something I wish to avoid, a cheaper option is to use steel-cored washing line

I have never been able to see how good a performer the wire dipole actually is, though when I had it draped down the side of the building at my previous QTH, it worked relatively well, although it lacked the choke and I was getting feeder radiation, revealed by slight changes in the SWR reading when moving the cable during transmit, the dipole at the time was against a stone wall in a vertical arrangement, in it’s new duties it will be in an inverted v arrangement, the terminal blocks being the connection between the choke and the antenna elements.

Once it’s up and I have managed to get the SWR to an acceptable level across all 80 channels, the gateway will be connected to it and the testing phase can begin. 

I hope to be on the air very soon


73 de 26CT730

Monday 13 August 2012

Another CB gateway update

Late last week the dummy load on the CB gateway radio failed, which caused the SWR to go very high, and for most of the weekend I had to wait and hope the radio wasn’t damaged as a result.  I had ordered a new dummy load and a combined power and SWR meter to reveal any issues, as a visual inspection of the transistors proved inconclusive and I had no other way of testing the radio.  Upon reconnecting the radio back to the power and connecting the new dummy load and meter to it this morning, the output was measured at 4 watts, meaning that no damage had been done to the radio.  I used the radio’s supplied microphone to transmit rather than the gateway computer as I felt it more convenient to do so despite the computer still being connected to the microphone socket.

This means I need not replace the radio and can safely progress to the next stage, the antenna building, although the built antenna will be tuned to work from 26.965 – 27.99125MHz rather than specifically for 27.94125MHz, that antenna will come later on.

More updates to follow.


73 de 26CT730

Thursday 2 August 2012

Another gateway update

The CB gateway radio arrived yesterday morning, and using the spare few hours I had before I went out I removed the shelf from the cabinet where the main CB is fitted, and installed the bracket for this radio.

The radio is connected to the existing power supply, with a 12 volt fan glued to the underside directly over the speaker grille, the speaker having been removed from the radio.  This was because the original fan, despite it’s small, and slimline, profile, did not fit inside the radio due to the location of a transformer directly under the speaker.  The fan draws it’s power from the same power supply, rated at 12 volts, 7 amps, more than enough for a CB transmitting at 4 watts and a computer fan that is rated well under 1 amp current draw.

The radio has it’s auto squelch enabled while it is on the dummy load, and the keys are locked (except for the 9/19 key which, owing to the use of those two specific channels in most CB bandplans. makes some kind of sense.  The volume and squelch controls are two switched potentiometers so are not electronically locked and can be changed.

Transmitted audio appears to be good, though I’ve so far only had my trusty Intek H-520 Plus to hear it on though I did connect my extension speaker to the handheld knowing that it would provide better quality audio than the speaker that is in the handheld, received audio I cannot get a good answer on just yet, though the parrot output in the test room on 446 Muppets showed promise.

The last stage is to install an antenna, this will allow me to take the gateway off the dummy load and put it on air, though, to begin with, I may set it up as a shared system, alternate weeks, one with my gateway on the antenna and one with my home CB on the antenna, until a second antenna, tuned to be resonant only at, or close to, the gateway’s frequency, will be installed.  Once an antenna is installed, on air tests can be carried out (the gateway will have the testing announcements added during the on air testing phase).  The antenna will be tuned on my main CB as this is what it will spend most of it’s time being used on once the gateway has it’s own antenna.

The estimated completion date will be sometime after the Olympics.

More updates will follow


73 de 26CT730