Aug 30, 2008

Getting some of those 'small projects' done

Ham radio operators keep upgrading their equipment, shack, antennas etc..
You visit a flea market and pick-up those things which 'you will surely use sometime in the near future'. You're at the beach dozing away in the sun, but your mind is fantasizing about new 'projects' to build at home. Your workbench is filled with all kinds of parts & stuff. You visit a ham friend and while having coffee, he shows you his 'latest project'. You're thrilled and his activities immediately hit you; there are zillion unfinished/non-started projects at home.

Make a list and prioritize ?
Well that's how I usually work; I make a long list of all what comes to my mind and then start thinking about how likely is it that such a project will end successfully, how long does it take, what does it cost, how does it affect the current situation or other future projects, does it really help me, how badly do I need it? etc..etc..
At my QRL we call this doing a feasibility study.

Since I'm not at work I thought it would be best to just start with something small and see where it all ends, right ? :))

Mains filtering

These are industrial parts which create a 500V/40A mains filter. I should probably need to add a kind of protection cover, but at this point it physically is already out of reach....

And while we're at it, take a look at my mains common mode filter. I have these installed at every power supply and any mains cable power block. This nickel-zinc-ferrite has a permeability of 1500 and has wide band coverage from low HF to UHF. It is available at: partno: U81-1500
It is 60mm long and allows for 10mm dia windings. 9 windings should bring already >1000 Ohms @3Mhz, which is very good.
I have never been able yet to measure any difference before and after, but its brute visual placebo effect certainly creates some dB's.

The already forgotten Elecraft noise generator kit appeared under a pile of paperwork and was completed in half an hour. It generates noise from DC into UHF and will serve me well when doing HF RX alignment in the future.

The outdoor antenna coax switch
I am using a 2 way remote coax switch up in my roof tower. But in order to activate it, I have to crawl under my operating bench, find that DC control wire and connect it to a 13.8V PSU.
A 'switch board' on my desk would be nice. Since I have plans to add more antennas, more remote switches for both antennas and rigs, this project was taken a bit more seriously.
Then there's the outdoor switch box for my HF Lowband RX antennas. Both the switch box and cable is already installed outdoors. It only needs some connection +control in the shack... Oh well let's take it one step at a time but keep in mind what else will come next soon.

The entry panel
This panel will cover:

  • DC wiring for remote switching
  • DC wiring for rotor
  • DC wiring for HF Lowband RX antenna switchbox
  • Central ground point connection
  • DCI 144-146 4 pole cavity filter
  • Various coaxial relay switching
  • Coax entry connection strip

The Dowkey Microwave coax relay is a 12GHz type, which provides 85dB isolation at 1 Ghz.

Next we need a control box. So look into the junk box for switches and dig out any plastic box from the supply cabinet.

The wiring was done with some junk CAT4 cable and RG174 for DC supply +more placebo's.
However, the Dowkey relay uses 28V. I tried using three 9V batteries in series but those lasted only a couple of hours. I located a non-used 12V/2A power supply which has 24VDC at the rectifying stage. It was quickly modified; just added a few zener diodes in series at the GND leg of the 7812 voltage regulator to bring it up to 21V (leave some room for operating DC offset for the regulator). The Dowkey relay already works from 13V up, so the 21V is within 'my' specification.

How does it all work so far ?
Very well.
I can switch between 3 VHF antennas and 2 multi mode rigs.
Both on sensitivity, selectivity and AGC behaviour I see interesting differences between the IC821H and TS790E (note: they are not in original state; both have there IF FM filters modified and are realigned. See my previous blogs).
The newly added versatility allows for more fun in the shack!

What next?
  • install the second relay and wire the DCI 4-pole 2m filter
  • .........

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