Mar 26, 2009

Receiving splitter II

Another one?
Yes; in my previous blog of January I mentioned needing another splitter.
It would need a better spec at 28Mhz. The IF output frequency of my 144Mhz & 50Mhz transverters.
I have plans for:
- analysing signals during reception
- comparing different IF rigs at readability
- combining different IF rigs to create sort-of-diversity reception

And not for?
This blog is not for writing a paper on already existing applications, home built equipment and such. There are lots of other, better web resources for that, like: W8JI, VK1OD, hard-core-dx to name a few.
I just want to record my findings and describe the equipment used while in the process. It will serve me when picking up a project again in the future.

What do we have so far?
A quick & dirty W8JI style Magic-T combiner, using #73 ferrite binocular.
The frequency sweep shows the port to port isolation from 1 to 30Mhz.

W8JI version Magic-T splitter_MKII
A more serious attempt this time, using:
- alum die cast box
- #43 ferrite binoculars
- 24 AWG red enamelled wire
- BNC chassis parts, pop riveted to the box
- 1W 100 Ohm metal film resistor

I have ordered carbon composite resistors. If that offers a significant better specification at 28MHz I will do some more testing and create additional versions of the splitter. When time allows.

How do they compare?

attenuation port to port isolation
1.8Mhz 28Mhz 1.8Mhz 28Mhz

MKI -3.52 -4.33 28.0 15.5
MKII -3.05 -3.30 38.0 19.2

Remarkable that using #43 ferrite brings better specs at 1.8Mhz, right?
There sure are other possible reasons for that: using a shielded box and different wire.

Other remarks:
Port 1 to Port 2 isolation and vice versa differ 1 to 1.5 dB.
The measuring coax cables have been calibrated in the test set-up by the HP network analyser.
The cables (RG58) might have a small negative influence on the isolation measurements due to the limitation of their shielding.

Yes; it has low attenuation, sufficient port-to-port isolation and it is easy to reproduce.
Let's get using it and do some of the tests I've on my mind.
I'll be back.....

Mar 22, 2009

Backyard 7 Mhz Vertical

For the sake of making contacts on the 'upper' Low Band I decided to do a quick & dirty GP set-up for 7Mhz.
The current 'Simple HF Multi band Vertical'(see previous blogs) had to go. There's no sunspots to expect in the next coming months, so no interest in the NCDXF beacon monitoring station currently. Even more because I have Hi-jacked the TRX (TS570SG) for the coming 6m season.

How to create a simple backyard GP

1. Make a full size radiator
Take a typical fibre glass fishing rod and any kind of conductive wire. Note: insulated wire intruduces a velocity factor of about 0.92 - 0.97, depending on the insulation type and thickness. Now start calculating the 0.25 wavelength, using the lowest frequency you want to be able to use; add another 5 % for adjustment.
Slightly spiral wind the wire around the rod and use electrical vinyl tape to fix it.

2. Install a ground rod
Just hammer(-drill) down any kind of 1-3m length copper pipe. It serves as a lightning rod and makes a good bonding point for the radials. Note:it is does not protect against a direct hit. When zapped by lightning it might avoid that all your shack-gear is toasted. There's lots of good websites on that subject so take proper care and be responsible.

3. Lay out some radials
Again; use whatever conducting wire you have available.
My backyard is 7 x 8 mtrs and the GP is mounted right at the corner. So no space available for 120 even spaced 'full size' (what is that crap?) radials. Just lay down whatever you can manage. I have 9 lengths between 4 and 8mtrs spread around the backyard. It covers 110 degrees around the GP. Why not 360 degrees? Simply because there is no space available.

4. Add a current balun.
Take a proper piece of ferrite (FT150A-K), put 8 windings no 16 AWG Thermaleze wire on it. Some 10-12 windings of thin teflon coax on a proper ferrite will be a good alternative too.
Use proper protection against moist.

4. Adjustment
Do the adjustment after you have layed out all radials. Adding more radials can alter the radiation resistance and shift the resonance frequency, certainly when you have only a few lying around like in my example. But my point was not to create a High-End antenna (what is that?), only to start being able to make contacts on another band.

How does it perform?
We have a full size vertical (3 out of 3 points), a ground rod + 9 short radials, covering only 110 degrees between north and south-west(1 out of 3 points) and a tiny backyard in a small village (2 out of 4 points). That makes 6 out of 10 points on the 5MW scale.
Within 24 hours I make numerous contacts to the USA and several to Asia. There are no radials in the direction of Asia, but I get through the pileups of BY and BV without severe drama involved. My operation is CW (only) and at a max. of 50W
Let's face it; ANY kind of antenna will allow you to make contacts. And depending how many effort you put into the process, you can master fine dx contacts at will.

Am I happy?
The antenna is up since February 6th and does perform as one might expect.
However, I kind to start disliking the band. Or today's hamradio operators behaviour to be more exact.
The art of rudeness and jamming from so many, makes me shutting of my TRX to often. If I would be able to put more effort into a directive high performing receiving antenna I might avoid them a bit. I also wish the dx-clusters would cease to exist. Tomorrow please..... ??

Anyway, time to return to my roots on the Low Bands: 160m !