Month: June 2017

70 MHz Cumulative Contest #4

The RSGB CC run a series of cumulative contests through the year, you can partake in either a fixed station or out portable. I prefer to operate out portable, as this gives me a significant advantage to attempting this from home.

Using our contest site at Kelvedon Hatch SNB and with the assistance of John M0UKD we set up the following station.

12m Racal 714 push up mast

Homebrew 4e 70 MHz beam a DK7ZB design

Icom 7100

Honda EU20 generator

Expert SPA 1.3k FA Solid state amplifier

The weather was forecast to be dry and breezy and so we opted to set up in the fields overlooking the bunker and the mast. The contest ran from 3 till 5 pm, and with around 1hr setup time to organise the portable station, you can maybe see why some people operate from home. It’s quite a lot of effort for a 2hr contest, but on the positive side, you would expect the activity to be condensed into this short timeframe.

Setting up the beam.

The makeshift shack was constructed to keep out the wind, and the odd  spot of rain.

The beam worked really well, having very good directivity and F/B ratio despite its small size.

Over the course of the next 2 hrs, we worked 45 stations, in 4 countries. England, Wales, Guernsey and Northern Ireland. Our best DX was  GI4SNA at 527 KM.

You can view the claimed scores online.

The Good the Bad and the Ugly Part 3

The good, the bad and the ugly Part 3

If you haven’t already seen this started with Part 1 and Part 2

This evening I tested 2 common micromagnetic aerials often used as quick fixes for using the handy in the car. The last antenna is a stubby found on the Motorola MT200 series handhelds, often used by amateurs for 433 MHz.

Our first micromagnetic antenna is around  300mm (12 inches) long and has the very lossy thin coax.The antenna surprising has a match point on both 145 and 433 MHz

 

 

 

You can see from the VNA plot it makes a good effort on both frequencies.

Our second micromagnetic antenna doesn’t fair as well, providing a poor match on 145 MHz, and a poor match on 433. It’s slightly shorter than the first version around 25cm (10 inches)

The VNA plot shows the match at both 145 and 433 MHz

Our last candidate is the stubby found on Motorola MT2000 handsets, these are often used on the 433 MHz amateur bands. The handheld and antenna look like this.

The antenna doesn’t do too bad on 433 MHz but it’s clearly been optimised for further up the PMR band.

 

It’s worth noting on 433 MHz using the very thin RG174 coax you should expect to lose 50% or more of you power before it even reaches the aerial. Yes, they will often work better than the stubby in the car, and they may very well do exactly what you want for local repeater access but it’s worth knowing the limitations.

 

50 MHz Trophy Cup

I once again took part with the in the 50MHz trophy cup with the SNBCG, the contest runs for 24 Hrs from 3 PM on Saturday. This year the contest had been booked for one of the hottest days of the year, with temperatures reaching 30C (around 220F in old money)

We set up Saturday morning,  using the 5e 50MHz beam and a 10m pump up mast.  A solid state amplifier provided 400w and a light weight tent to keep off the sun.

The most important issue throughout the weekend was trying to keep cool, with copious cold drinks from the fridge. Fred G3SVK was kind enough to lend us a fan and this became an essential item for the shack.

Fred spent some time operating on CW, working mostly EU with the odd notable exception.

In total, we worked 250 stations, with our best DX being 5B4AAB at 3161KM. You can view the claimed scores here and map here.

144 MHz Backpackers and Hill toppers contest

Sunday 11th June was the #2 backpackers, hill toppers and QRP contest. The RSGB contest ran from 10 till 2 PM and had two categories 25w or 5w. I decided to enter the 25w category, the radio had to be battery powered and the power limit was 25w.

The antenna was a 9e tonna mounted on a Racal push-up mast at 6m. You can read the complete rules online.

The exchange is a signal report, serial number and then your locator, so a typical exchange may be 59, 001 in JO01DP.

I worked a couple of stations who was aware it was an activity day, but not aware of their locator. I found the best way is to look it up online or download one of the many phone apps that will do this for you. I started a little late at 10.30 as on this occasion I was operating alone.

Using the Icom 7100 and a 68Ah leisure battery I was able to operate for the complete contest. I used a small netbook to log, it’s important to find something that can be battery powered for the duration of the contest. I did have one unexpected problem, if the laptop was within 1m of the radio it did cause some QRM, interesting, as I had never noticed that before.

Conditions seemed flat, but the bands were very busy, I think this contest coincided with the practical wireless QRP contest.


Over the next few hours I was able to work 75 stations in 4 countries (England, Wales, Isle of Man and Gurnsey) The best DX was 430KM into the Isle of Man.

Thanks to everyone who took part, a really enjoyable afternoon in the sun.

Interesting Condition on 28 MHz

Last night 5th June I noticed some interesting conditions on 28 Mhz. I could hear some relatively short sporadic E into Ireland and Scotland.

It’s not often you hear stations that close on that band, so it’s nice to say make the contact. The signal from Steve in Lanarkshire was 59+ at times.

Steve MM0VPY from Scotland

Peter MI5JYK from Northern Ireland

This type of propagation can be very dificult at times, with deep fades and often signals go from 59 to unreadable in seconds. Keeping the OSO short is therefore essential to maintain communication.

It’s unpredictable, you never quite know who will call next.

Lisa LA8FNA from Norway.

Just a small selection of the stations worked, others included Austria, Finland, Poland, Slovak, Estonia, Sweden, Russia, Latvia and Croatia.

28 MHz is great fun when it’s open, happy hunting.

The good the bad and the ugly (Part 2)

If you arrived here without reading Part 1, it may be worth checking that out.

eBay is full of fake Diamond SRH805S antenna, so in this article, we take a closer look at 3 or these versions. Only one of these is real, as it will become obvious

Click on the images to enlarge.


eBay 99p version. A look outside and inside.


145 Mhz – 203 Ohms

433 Mhz – 57 Ohms

1.2Ghz – 4.6 Ohms

VNA plot credits @DTL

 


eBay £5 version.


145 MHz – 510 Ohms

433 Mhz – 36 Ohms

1.2Ghz – 62 Ohms

VNA plots credit @DTL

 


Genuine version £25


Picture and measurement credit to John M0UKD

The antenna provides a good match on 145, 433 and 1.2Ghz and unlike the fake versions, this would actually seem to work on the specified bands.

 

 


 

 

 

 

 


So how do you spot a fake SRH805S?

I guess you need to ask yourself 2 questions.

If you purchasing it from eBay then it’s most likely fake. The other clue is price, the genuine version would cost around £25.

If you would like to purchase the genuine article, then I would suggest you use a recognised ham radio outlet.

The fake and genuine antenna both look identical, but as you can see that’s the only thing they share.

You can continue reading Part 3

 

© 2015 Dave, M0TAZ