Friday, September 23, 2011

New Item in the Marine Radio Collection

Could not stop myself from buying an "Emergency Radio Type 610". I believe it is made by Clifford & Snell, but I am not sure about that.
The radio services the frequencies 500kHz (RX/TX), 2182kHz (RX/TX) and 8364kHz (TX). As in this sort of package, cranks are provided as a power source.

The transmitter seem to be built around two electron tubes (have not checked the types yet), while the receiver seem to employ OC transistors, Germanium that is.
Whilst test TXing into the built-in dummy load, on 2182kHz (A3E), the antenna current meter nicely peaks when the matching variometer (coil with dive-in ferrite rod) is agitated. The two other frequencies would require the operator to have a third arm!?? My radio was supplied with the emergency instructions, which showed one operator only, even the text referred to a single operator doing the cranks and the communications all at once. Who ever wrote this may have never operated a radio himself. While in A3E, a carrier in generated anyway. One hand operating the crank, the other to tune the variometer, no problems here.
It is a different story with 500kHz and 8364kHz. Those are A2A frequencies. No, there is not typoe, A2A it is, AF modulated code. And yes, that makes sense. The signal is received in both, an AM receiver as well as a receiver employing a BFO. However, when tuning the emergency transmitter, one would need one arm/hand operating the crank for energy, a second arm/hand for operating the manual key and a third arm/hand for operating the tuning knob.
The makers of the radio seemed to have spent some thought on this issue, although, maybe not enough. The radio is equipped with a mechanical auto-keyer. Keying the transmitter for tuning can therefore be done, sort of, without three arms. However, the designers seemed to never had the code operator in mind. The built-in manual key is so close to the position of the cranks, that operating both at the same time seems to be a challenge per se. However, if that was your option to survive at sea, that what you would be going for.

Enough about the transmitter, lets have a word on the aerial system provided. A system which managed to impress me. As in all of those sets, the aerial is contained in the box itself. Motto: if your vessel is sinking, throw the emergency radio overboard, get in the life raft and hope for the best. Hence, the floating waterproof box of the emergency radio has to contain everything required to perform emergency communication, including the aerial.
The 610 comes with an antenna base, about 1m long, having a rubber foot (for not damaging the life raft's soft bottom). On this foot, a stainless steel telescopic whip is to be mounted, the whip having an impressive length of estimated 4m (maybe more).

To the downside, and the reason why this radio is not widely available.
In order to keep it smaller, I presume, the designers choose to have a low profile for the cranks. Fair enough... however, they put the cranks so low that they can't be used when the radio laying perfectly flat on the ground. A problem that the very similar TRP1 does not have. Is the TRP1 really as similar? Maybe not... think of it, the TRP1 uses TTL circuits, whilst the 610 employs electron valves and Germanium transistors...

Do I regret having bought on of the 610s? No! Would I buy another one? No!
What is the best thing about the type 610? The aerial provided. I believe, there is no other (convenient) way to get your hands on stuff alike... Think of it!


Friday, September 16, 2011

Cheap Android Tablet Going Strong

Some time ago, I reported about a very cheap Android Tablet (from kijkshop), which I used regularly for this and that.
The table came with some port accessory, which holds two regular USB ports and an Ethernet connection. Writing this, I am presently using the tablet via Ethernet (thus no WLAN) with a wireless keyboard attached via USB for convenient typing. The port accessory actually seem not to have functioned when I got the device first. However, in the course of time, I really could not believe that a design fault was the cause. Well, the was a design fault, not in the electronics though. The plastics chassis appeared to be too large and had to be sanded down in order to allow all pins to make contact. Seen that the tablet costed € 100.-, I should have bought a second one, since said shop stopped selling those devices.
Still, I have not mentioned any details about the product...
it is an iLC 7" tablet PC using an ARM 800MHz processor with 256MB RAM
the OS being Android 2.2 (Android Market installed) on 4GB flash storage, allowing for a microSD card
the device is further equipped with WiFi, stereo speakers, a headphone connector and a built-in microphone
finally, there is the port accessory, providing 10baseT and 2x USB
All in all, the gadget look comparably cheap, matching up with the proce somehow. At times the device's response is somewhat sluggish. Would I buy the gadget once again? YES!

Monday, September 12, 2011

4:1, 6:1 or 9:1?

Thinking back and forth a bit, again on aerials, I came to the conclusion that using 75Ohms feedline some 4:1 would be appropriate.
But why?!

The developers at Diamond thought that for the BB6W, or the BB7V for good measures, a 6:1 transformation would be the way to go. This aerial design assumes a 50Ohms feedline. The aerial's feedpoint is therefore considered having an impedance of 300Ohms. Remember, in this design, there is 600Ohms of termination resistor to ensure a maximum SWR of 2:1.

Assuming that the average auto-ATU will match a transmitter's 50Ohms antenna connector to a 75Ohms feedline easily, a 4:1 transformation will do in order to match a feedpoint impedance of 300Ohms when using 75Ohms feedline.
This actually brings together good news from two worlds:
  1. 75Ohms coax cable has got less losses than 50Ohms coax (it is cheaper too)
  2. a 4:1 transformer is easier to make than a 6:1 transformer (QRP: old TV-xformers)
So, now what about the 9:1 UnUn that so many use with endfed aerials? Personally, I used a 9:1 transformer with 50Ohms feedline. The 450Ohms feedpoint impedance works with endfed wires, about as good as 450Ohms window line (using a suitable ATU).

As a side remark, the feedpoint impedance at the voltage maximum is considered to be 5kOhms. Neither window line nor a 9:1 transformer gets us there. This can only be matched using ladder line (or open wire line) with a symmetric coupler.

Friday, September 9, 2011

Kizomba, the Name of the Game

Hi folks,
this is completely off topic.You may have wondered why I am sooooo slooooow writing technical articles, well, there are some reasons. One of them reasons being, I am much more into dancing once again... and kizomba is the name of that game. Some may already know that I am severely into mambo dancing, this remains. For those of you readers that are into dancing, check out kizomba, aka. African tango. The dance is from Angola, the music is a mix of French creole "zouk" and Angolan "semba".
Dear fellow ham radio operators, there is more to life than a microphone or a Morse key. Get out, get social enjoy life, also on the dance floor!
BTW, WCS (West Coast Swing) is cool too! Go for it, grab a girl and off you go!