Archive for the ‘Uncategorized’ Category
Spark transmitters and modern simple rigs
November 25th, 2014 | 
Author: In the early days of wireless, spark transmitters were all they had. Selectivity and bandwidths were not major concerns. These days it is all so different with sometimes very crowded bands and the bandwidth of both transmitter and receiver being of major importance.
See http://en.wikipedia.org/wiki/Spark-gap_transmitter for some interesting reading. I recommend you do not try a spark transmitter as you would be very unpopular because of the wide signal and interference caused. By all means read about them though.
A modern challenge is to see just how simple rigs can be made yet still function credibly on the amateur bands today. Rigs like the Pixie are fun, but such ultra-simple transceivers are let down by deaf or easily overloaded receivers. To my mind, the receivers have to be selective, sensitive, have netting, and not be easily overloaded. The challenge is to overcome these issues! Often TX power is not the deal breaker.
UPDATE 1740z: W5OLF has just shown me a photo of is tiny 1 inch ferrite rod antenna on which he has had some success with on 10m WSPR. I tried some WSPR experiments with ferrite antennas some years ago on 40m, 30m and 20m. As long as the ferrite does not saturate they do work. See www.g3xbm.co.uk .
630m Resources – Part 2
Using the transverter approach offers the advantage of providing a higher-stability signal generated by the main station's transceiver oscillator system. Most of the digital modes require a higher stability than would be needed for straight CW.
If your main interest is normal speed CW, then a digital VFO, such as the one devised by GW3UEP, would do the job.
If you are content operating on 475.0 kHz, then an inexpensive 7.6MHz crystal, in a divided-down oscillator will work well, and with good enough stability for some QRSS work as my earlier "GW3UEP Transmitter In QRSS Mode" report indicated.
The other option for frequency generation is a DDS.
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| N3ZI DDS |
For those wanting something a bit more robust, W1VD describes a very nice high-power transmitter. His website is packed with useful circuits and ideas for both 2200m and 630m.
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| W1VD Dual-Band Kilowatt : http://www.w1vd.com/ |
W7IUV also describes, in great detail, his method of generating high-power on 630m. There is much to be learned from his document describing the design and operation of his unique 'linear-mode' transmitter.
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| W7IUV 630m TX: http://www.w7iuv.com |
Another practical way of generating moderate power, certainly enough to meet the Canadian 5W EIRP limit, is to combine two or more 100W transmitters, such as the GW3UEP transmitter. It is reasonably simple and inexpensive to combine several modules with the use of a homebrew power combiner, as previously described.
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| Homebrew 630m two-Port Power Combiner / VE7SL |
RSGB
I have been a member of the Radio Society of Great Britain (RSGB) for 52 years now. When I first joined I was an SWL associate member – A3554 – as a young teenager. In those days you had to be proposed and seconded. Joining is much easier today. When I started there was just one licence. I took my RAE exam in 1966. It was on Friday 13th May as I recall. I attended RAE classes at Plymouth Tech every Monday night, catching the bus to Plymouth after school. Long gone days!
Over the years I have not always agreed with the RSGB’s decisions. In fact, quite recently, I did not like the decision worked up with OFCOM to allocate the 146-147MHz band to some UK amateurs by NoV. I think the RSGB could have got a much better deal for UK amateurs, but that is my personal view.
Despite this, the RSGB is our national society and deserves our support. Over the years they have supported UK amateurs very well and have a much better relationship with OFCOM than the ARRL has with the FCC in the USA where bands we have had access to for years are still not available! The monthly RadCom magazine is a good read with a mix of technical and non-technical articles.
So, if you are not an RSGB member and you live in the UK, may I encourage you to join?
See www.rsgb.org .
TX Factor at UK’s National Hamfest 2014
Episode 6 is now live at txfactor.co.uk. It features the best from the UK’s biggest rally, National Hamfest 2014. The team meets the exhibitors and visitors and brings a flavour of this amazing annual ham event to those who couldn’t make it this time.
There’s also a chance to win the compact, yet function-packed dual band VX-3 transceiver in our next free-to-enter competition.
We hope you enjoy the show and look forward to your comments and feedback at [email protected]
73 from the TX Factor team
Gifts for Ham Radio Operators
A post I read online today reminded me of something. Last week a friend’s XYL ask me for some good Christmas stocking stuffer ideas for her husband. I drew a blank! I didn’t have a good answer for her.
Mugs? Vehicle decals? T-shirts? That was about the best I could come up with on short notice.
So, what under-$30 ham-related items would you like to see in your Christmas stocking this year? Leave your answers in the comments and we’ll have a list of good ideas!
Here’s what I’ve come up with so far…
Laser Engraved Ham Radio Callsign Plaque
 | This is a pretty unique idea. They take your ham license details and put it into a template. Then they laser off the metal lacquer leaving shiny metallic writing underneath and mount it on a oak plaque.– $22.99 from HamCrazy.com |
 | Another unique gift idea, this is a beautifully crafted 3-D version of your call sign. Available in several different varieties of wood.— $4 per letter on k7bon.com |
Engraved Brass Plate for the Elecraft K3
 | Granted, we’re all not lucky enough to own an Elecraft K3. But if you do, here’s a beautiful way to let everyone know who assembled it!— $5.50 from Arkay Engravers Associates |
Please don’t forget the awesome t-shirt designs offered by our sponsors, HamShirts.com and Hip Ham Shirts! They always make great gifts — who couldn’t use another t-shirt?!
146-147MHz in the UK – why?
I find it extremely odd that OFCOM has granted access to an additional 1MHz of VHF when the existing 144-146MHz band is grossly under-occupied most of the time. Take a listen 144-146MHz in YOUR area in the UK or elsewhere in Europe. Mostly you will hear white noise!
This is only ad interim, only by NoV to full licence holders, and only in some areas. It is clearly a sop for messing with the microwave allocations. It is very unlikely much new (to radio science) will be gained by this 1MHz allocation. MUCH more would have been learned by a 100kHz allocation around 40 or 60MHz or by allowing UK amateurs free access below 8.3kHz or back onto the withdrawn 73kHz band.
I know it is heresy to say “no, I am not interested” but OFCOM could have done so much better and it has lost credibility in my eyes as a result. I cannot believe allocating this spectrum to radio amateurs serves any useful purpose at all. The RSGB talks about digital TV etc. Sorry, this is rubbish: it is hard enough getting anyone on digital TV on 432MHz and 1296MHz where most ATV activity takes place! I can see perhaps a small handful of people forcing themselves to use this band. On 40MHz, the Es possibilities would have been wonderful.
No, in my humble opinion OFCOM should not have given radio amateurs this band at all. It would really have advanced radio science if they had allocated new, smaller, bands at more interesting places in the spectrum. Let us at least hope OFCOM supports moves internationally to a contiguous new amateur band at 5MHz (60m) at WRC2015 next year. This will be useful in the quieter years to come.
Moonraker
Ever since the spring when Moonraker supplied me with rubbish patch leads that just fell apart because the crimping was so poor, and a dual band VHF/UHF yagi antenna that had to be glued to fix one of the loose elements, Moonraker has not been my favourite supplier. They clearly did zero quality checks on the goods sold. I hope they have improved.
However they have some nice 10m radios at sensible prices including a 20W FM/AM unit for under £100 and a multi-mode 10m rig for under £150.
See http://www.moonraker.eu/ .
UPDATE 2200z: Moonraker also supply PMR446 and LPD433 dual band transceivers. The latter band is within the 70cm amateur band, which is perfectly legal at 10mW with no amateur licence, here in the UK. On UHF, 10mW goes a long way from a local high spot. See http://www.moonraker.eu/professional-radio-and-446/pmr-446 . There are several to choose from.
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| http://www.moonraker.eu/media/catalog/product/cache/1/image/602f0fa2c1f0d1ba5e241f914e856ff9/S/L/SL-02_big.jpg |
