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I recently wrote some comments about the G5RV antenna and pointed out that there can be problems in feeding it via coax cable because of the moderate VSWR that often occurs.
Quite by chance I stumbled across what I consider to be a very well written and informative web entry that shows very clearly the problems that arise, their cause, and how best to resolve them.

The web address is www.vk1od.net/antenna/G5RV/
In reality there is only one way to get the best out of a G5RV and that is to place an ATU at the foot of the balanced line. It was also interesting to see the writer’s comments about wet balanced line. I have used slotted 450 Ohm feeder and always felt it to be better than the traditional 300 Ohm ribbon. I have also used proper open wire feeder on a few occasions but never thought to carry out any comparisons. Certainly open wire feeder really looks the part!

It is also interesting to see that in effect the G5RV can cover the WARC bands when correctly terminated with an ATU. But that is not surprising because in that configuration it becomes no more than a doublet of a length that just happens to give a small amount of gain on the 20m band. If you are using or considering erecting this antenna, then I would recommend checking out this VK1OD site. Peter G3OJV www.wsplc.com
 

 

 

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Ham Radio Gambling   May 30th, 2013

There has been some movement on Yaesu prices here in the UK which were announced about a week ago. This is good news for wood be buyers but not so good for those who bought at the higher prices. they paid more than they would need to now, and of course it reduces the second hand price. Its always a painful process but it is a direct result of the importer’s price to the retailers who never have any forward notice of price movements. Of course sometimes it moves in the opposite direction and wood be purchasers then have to pay more than those who bought earlier. We have all been there and probably the computer market is the best example of price changes. And so the question is, when is the best time to buy?

There are probably two “best times to buy. The first is as soon as a model is launched as it is very unlikely that there will be any price movement for some while and so you have the satisfaction of having the latest model as soon as it is available. You get a fair return on your cash and it is very rare for there to be any movement in the first year at least. The gamblers will select the second best time and wait for the price reduction but the problem here is that the price may never come down. In fact there is an evens chance that it may go up. That really is a loss situation because you end up buying a radio that you may have waited a year or two for and then up paying more. Some may then just wait for the next model to be released and then wait another two years. They may never buy and just have persistent regrets year after year.

There is not a perfect answer or even a sensible one. Personally i think that if you want it and can afford it, why agonise over what “might be.” Best to go with “what is!” Peter G3OJV www.wsplc.com

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Has My Radio Gone Deaf?   May 29th, 2013

Is it my radio or are the bands pretty awful?

I just got back from the USA and wanted to check out a new receiver. Impatient as usual I connected it up to my home antenna only to find that there was a distinct lack of signals, and those that were there appeared weak. Now this is not a good start to an assessment of a new piece of gear! Was it the bands or the gear? Then I thought it could be my antenna system. But looking out into the garden it was still up in the air. I switched over to my transceiver and had the same results. So with a sigh of relief, that more or less ruled out the gear. It had to be the antenna or band conditions. But, I couldn’t be totally sure: was the feeder broken?

Well as it turned out it was the band conditions, but it took me quite a while to be absolutely sure. I was operating from home and my assessment of the receiver was being carried out subjectively. What was intended to be a five minute quick trial turned into a somewhat prolonged game of detection. Now if I had had one of my favourite buts of test gear to hand, I would have eliminated the receiver as the culprit in seconds.

I have mentioned before the little Elecraft XG3 signal source which generates accurate levels of signals down to 1uV on all bands from 160m to 2m. It’s a pocket self contained item that is never far away from me on the service bench. It would have given me the reassurance I needed that the receiver was not the problem. That however would not have proved that the antenna could be the cause. But to eliminate the antenna as a possible cause I would need to have turned to my MFJ antenna analyser. Unfortunately that was at work on the service bench as well!
Peter G3OJV. www.wsplc.com

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The G5RV is an antenna that frequently comes up in discussion with many of our customers. It is probably the best known wire antenna and possibly the most “tried” antenna in the hobby. It’s design goes way back to the 1950s, long before WARC bands. Today you can either build your own or purchase ready made versions. But it’s popularity is matched by the many misunderstandings of how it works, and for some, it seems it does not work at all.

Basically it is 102ft of dipole with 32ft of open wire matching line or ribbon feeder which in turn is connected to any length of 50 ohm coax feeder. The so called matching section is nothing more than a length of ribbon line that attempts to offer the best compromise of reactance and impedance for the non WARC bands. In reality, this can be any length, provided you can terminate it with a suitable ATU. BUT, you will never successfully match the antenna to coax feed on all bands and will have to live with VSWRs well above many would want. Just check your VSWR meter! it will be reasonable on some bands and poor on others. Using coax cable will always be a problem because VSWR can frequently be more than your internal ATU can handle. The exceptions are Elecraft and TenTec internal ATUs which have a far greater matchimg range than normal. Back in the 1970s and 1980s, transceivers had valve PAs with Pi-networks that could easily handle higher VSWRs and so the G5RV was never a problem when feeding with coax in the older days. And that may explain why the antenna became so popular. Today with solid state rigs it is a lot different.

There are two answers if you want minimum loss and good VSWR presented to the transceiver. The first is to use a balanced line ATU and use ribbon feed all the way back to the ATU.” The second is to use an external ATU in conjunction with a 4:1 balun and take the ribbon to this. Then take coax feed back tothe transceiver. Both ways avoid high VSWR being presented to the transceiver. If you can use one of these methods to present the transceiver with a low VSWR then the G5RV will still do a good job, just as it has for the last sixty years. Peter G3OJV www.wsplc.com.

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The MFJ-225 has caused quite a lot of interest here in the UK, even though it is not scheduled to arrive for another month or so. I have been a long time user of MFJ analysers as HF antenna design has always been one of my interests. For those who have not yet got the full details here are highlights of the MFJ-225.

It covers the range 1-180MHz and so has wide appeal to most ham operators. The most obvious feature is the backlighted LCD 3” graphic display as shown in the image above. But there is one other major feature that is not so obvious. That is the USB VNA port. This can be seen on the right hand side of the picture. Connect this to your PC and run the freeware VNA program to have a fully featured PC based antenna analyser as well as the one built into the MFJ-225. How clever is that? So what data can you measure and display?

The data directly available is: VSWR, impedance, return loss, phase angle, capacitance, inductance, coax cable length, cable loss, plus other factors that can be computed from this information. And here’s another lovely feature. The MFJ-225 will run from three optional internal AAA cella, an external 12v power supply or the USB port of your PC. Calibration and accuracy is guaranteed by the built in firmware program. The physical size is 3.2 x 6.2 x 1.5 (inches).

This is an exciting new product. Availability will be notified on our web: www.wsplc.com.

Peter G3OJV

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Some times in the Service Department, you can be chasing a fault that does not exist or that you have made assumptions about. It can waste time and shows that even experienced engineers can jump to the wrong conclusion.

A few weeks ago we received an Elecraft K3 that had “suffered damage from lightning.” The words in quotes were from the customer’s note. The receiver was working, but down about 40dB. This had occurred after a local storm. The owner switched the radio on and the signals were way down. Over the phone we agreed that the fault did indeed sounded like damage to the front end and we collected the faulty radio from the customer.

Switching it on confirmed the claim that the receiver was way down in sensitivity. Even 50uV could only just be heard. A sure sign that there was a problem in the front end. So off came the covers and we hunted for any signs of damage, but it all looked OK. So we started injecting a signal into the receiver path. This showed that there did not appear to be any damage to RF or mixer. So it had to be something between antenna socket and the main board. It wasn’t anything in the front filters that was causing the loss as the problem was on every band.

Well we spent over an hour with the K3 that had suffered storm damage and still we were no nearer solving the problem. The naked K3 sat there on the bench refusing to part up with its secret as to where the damage had occurred. And then all of a sudden I thought: perhaps there was another reason. I quickly ran through the menu items but these did not show up anything that had been changed and that would cause this problem. Then I looked at the front panel display and spotted the reason. The separate receive antenna had been selected so that on receive the input was from the BNC socket and not the main SO-239. It was that simple. A button pushed solved the problem! It’s a lesson that you have to relearn every so often. Don’t jump to too any assumptions, even when the owner assures you that he knows what the problem is and it’s cause. Check the obvious first. Peter G3OJV. www.wsplc.com

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The Yaesu FT-817 has been a remarkable radio. I have used one extensively myself for portable work and testing. It’s a real go anywhere radio. However the fact that it can be used anywhere, also means that used away from home in a base station situation, it sadly lacks power. You can squeeze 5W out from an external PSU, but there has long been a need for a suitable amplifier. I mentioned the KXPA100 amplifier from Elecraft, a few days ago, and early evaluations, show that the Elcraft amplifier will be a perfect match for theFT-817.

Early tests show that if the FT-817 is run at 5W, then the KXPA100 will produce 100W output on 160-6m. The PTT keying has to be via the accessory socket on the rear of the FT-817. RF sensing is not an option with any USA built amplifier equipment as it is banned by the FCC. When running the FT-817 into the KXPA100 you also have the advantage of fitting the optional auto ATU, something that has never been available for FT-817 owners. We also plan to have ready made interface leads for the FT-817. Delivery og the KSPA100 is scheduled for July once beta tests are completed. Peter G3OJV. www.wsplc.com

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Vanity Call-Sign Number Plates   May 24th, 2013

For many years, the US has permitted vehicle owners to choose vanity number plates for quite a modest fee. This enables hams to use their call sign as their number plate. And from walking around the car park at Dayton, it seems to be a very popular and widely used option.

In the Uk we are only able to select a plate that is, or has been issued in the government’s format applicable at the time. This doesn’t rule out all call series, but of course, in many cases the number wanted, may already have been issued. On the face of it, there does not seem to be any obvious reason why our government has to follow a rigid template. The fact that there are numerous examples of plates having adjusted spacing, and black headed screws placed in strategic positions, is testimony to the potential demand. This of course is not only a ham radio issue, there are many other vehicle owners that would like to be able to choose a plate related to their interest. One day – one day! Peter g3 OJV

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1000ft Mast for $25 Day Rate!   May 24th, 2013

We all dream of tall antenna masts and towers. in fact the smaller our garden the more we dream! Today I visited the Empire State Building in Manhattan New York. Nothing particularly special in that; thousands of visitors do it each day.

The security check is as tight as most airports, but I saw no bags searched. The 1000ft lift journey is fast, but not as quick as the one I took in Taiwan three years ago. However, unlike “101” in Taiwan, the USA building permits visitors to step out onto an open air 360 degree viewing area. What a magnificent site! I looked up at the mass of antennas on the very top, – something that was not present in the 1930s when the building was completed.

But then I spotted a guy with a handheld radio. Could it be? Yes it was. A ham radio operator with his FM handy at 1000ft. Now I don’t know what the US law is regarding this activity, so I will refrain from mentioning his call or name. Suffice to say that it was a W5 having a minor pile up on 2m. To operate 5W FM from 1000ft must offer amazing coverage. He was certainly having fun. Peter G3OJV

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The Oldest Data Mode   May 22nd, 2013

Walking around New York today I spotted a shop displaying an old Morse key. it reminded me of just how old CW is. It’s actually the first data mode in radio, used long before speech. And as it is the oldest, isn’t it amazing that it is still being used by hams all over the world today.

It is difficult to fault the mode. It is good under weak signal conditions, takes up a minimum of band space and requires the most basic of transmitters without any PC assistance. All the coding and decoding is done by the operator. Modern data modes can add speed and analysis that enables very weak signal communications, but none can offer the simplicity of Morse code.

I am encouraged by the number of newcomers that have come into the hobby in recent years and taken up C and developed excellent skills. On a future occasion I will talk about how I advise some of our customers to go about learning the cod. Peter G3OJV.

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