Nov 16, 2008

Give me a reason NOT to buy;

dynamite, a gun, barbed wire etc....
Possession is all strictly prohibited in our country.
All for many good reasons. But after our latest 'experience', reason is a bit lost here.
Oh well.... get over it !

Above picture shows the result of our burglar visit.

What happened?
02:30 AM; I wake up because of a crackling loud sound. I switch on a bedroom light and go downstairs to the living room. There I find nothing abnormal; all doors are correctly locked, all windows seem OK. So back to bed again. I sleep quickly, so QSY zzzzz...
02:45 AM; again this loud noise. Instead of going downstairs, I put aside the window curtain, look downside left at my parking see a guy in total black tight clothing, hand gloves and baseball cap. Upon detection he winks his fellow man and both run away quickly. There's an attempted burglary going on.
I jump into my hobby overalls, put on a pair of sneekers, open my front door and run into the direction they went off. I spent some 7 minutes looking at several cars, checking alleys and several roads.
It is not my intention to force a confrontation being alone without any arms whatsoever, but at least I want them to know that I do not just sit back and p*** my pants. And besides, I was being just a bit upset...

Burglar result
Using a 200m glass sucker, they tried to break the lock of the sash windows, which are on the side of my house where the parking lot is. They needed several attempts before the plastic window-chassis broke.
Only one lock of the outer windows is broken before they were detected while performing their profession.
No other damages have been found.

Police assistance
I call the alarm number at 02:55 AM and report the attempted burglary. At 03:30 they arrive, look at the window and enter my house to write a report. Upon their leave I ask if there have been any other attempts recently in my area; "no, not that we would know".
Later that day,I'm visited by two officers of the forensic research who take prints of the glass sucker and a hand glove on the second inner window.

Property owner action
Since I never open these windows, I decide to fixate the window permanently using glue. Next, I have cut some 25x25mm bars to block the windows:

More protection is needed; a Halogen floodlight with motion detector is mounted on the bottom of my antenna tower. It switches in after dark automatically.

The back fence can use an upgrade too; so I add a new layer of treated plywood. The most vulnerable part is done first. Next week I will do the rest.

Next to installing extra safety-locks, there are some more tricks&tips I will
be implementing this week.

Neighbourhood monitoring
A quick check at the closest neigbours revealed that there was a succesfully burglary 6 doors away, just the other week. Talking to these people and others across the street I learned that 2 more houses in our area have been victims last month. Would have been nice if there had been a short informing letter to everyone. Let's start doing that ourselves.

With regard to possible psychological effects

I experience no anger, extreme frustration or other negative effects. In fact I went to bed again 30minutes after the police left the house that morning. But I do understand very well that such might show up sometime. For now let's just say that at this point I regard the whole story a 'negative business encounter'; they want something from me, I want to avoid that deal as much as possible. I need to put more effort in my work there.
The story is different for my girlfriend though. Thank god she slept through the whole story. But she's seeing burglars everywhere and she hasn't slept well ever since. I'm doing my best to bring back that comfort to her.
Let's end this with the simple fact that there are other more serious issues in life and we will grow over this too.

If you have any tips or remarks, please feel free to add any comment

Nov 2, 2008

New omnidirectional verticals for 145 and 430 Mhz

The Half Wave Sleeve Antenna
This model acts similar to the typical J-pole designs; a 0.5 wave radiator plus a 0.25 matching section. However, the coaxial pipe or sleeve section in this antenna has a much better choking action. This should keep the coax free from radiating and result in a better radiation pattern. In theory that is.
The popular J-pole is easier to construct, but the brutal feeding of the (unbalanced)coax to the (balanced)matching section is questionable. But there are new, better variations of the J-pole.
And let's not forget; both offer plenty of fun as they are very efficient antenna's.

Bad alternative; the commercial 'collinear' dual-band vertical
OK, I admit; I have used these typical white fiberglass collinear constructions for years. Everyone has (had) one right? It is by far the most succesful commercial antenna for VHF/UHF. Offers plenty of QSO's too, nothing to bash about that. I still have a 'short' Comet GP3 VHF/UHF for portable use.
But as soon as SWR acts funny you start investigating what this antenna is all about.
What I do not like:
- collinear sections, having no true stacking distance, do not offer the "theoretically calculated" gain. Funkamateur magazine did a comparison between a single rod 5/8 home made antenna and various commercial collinear antenna's back in 2005. Even the super 3x 5/8 (5mtr high) offered no more than some 2 dB gain.....
- bad connection joints "offer" a variation in SWR in due time
- capacitor failure in the bottom section
- 3 metal spokes function as 'groundplane'
When opening up such antenna you find pieces of welding copper, matching coils and small ceramic caps.

The Sperrtopf (german) or Fietspomp (dutch) antenna
Actually this sleeve antenna was designed by A.B. Baily and described in u.s. patent #2184729 in 1937.
The german word 'Sperrtopf' refers to its coax sleeve section.
The dutch word 'Fietspomp' refers to what it looks like; a cycle-pump. I always found them very ugly to look at, but this is not about cosmetics but performance & durability.
You can find some more info on how to build your own at:

The 438-470Mhz Sirtel CX400D
I bought 2 of these a few years ago on a flea market. There's already one on my roof, see my blog of feb 24th.

To get them to resonate correctly in our 70cm UHF band section, I need to lengthen the radiator by about 6cm, or was it 8cm? Darn! Why do I forget to write down such evident info? My antenna analyzer stops at 30MHz. Well, l know someone who has an HP network analyzer AND makes great coffee. I will do a separate blog on his Barrista qualities soon :)

See above a really pathetic attempt to measure and adjust the radiator length. Surely the HT batterypack was near empty. And so was the reserve pack.
Let's finish this blog quickly and go to that coffee....

The Wimo 145MHz version offers a finished version at an extremely cheap price.
I pop-riveted the short alum mounting section to a clamp. A few layers of spray paint should ensure weather durability. The horizontal tube section is meant for creating a distance from my antenna tower, in order to get the best omni pattern. Mind you; I cannot mount this antenna on the top of the tower. Local restrictions do not allow this. Long story, let's not go there.
It is all about maximizing efficiency and setting priorities.

Where was I ?
Ah, time to get me that coffee :)