Author Topic: From my Junkyard to your Ears  (Read 7610 times)

Offline InterpreDemon

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From my Junkyard to your Ears
« on: June 07, 2012, 02:07:56 PM »
Thought I'd drop in a note about two new feeds I set up to try to capture NY Liberty East departure and the KHPN ATIS, both emanating from the CMK VOR ten miles over the hills and through the trees to the north of my location in Stamford, CT. When Dave first proposed it my knee-jerk reaction was "impossible", mainly because after years of flying based at KHPN I knew that VOR was tough enough to get from the air from the south, let alone from the ground. But as I could actually detect some modulation in the noise on ground transmissions with a scanner and quick-brew omni near ground level, and a more precise path analysis revealed the eastern edge of the intervening high ground I was concerned about was actually a quarter mile west of where I thought it was, I thought it might be worth a shot with better equipment and another 8 to 10 dB of signal.

So I brewed up a combination 3 element vertical / 2 element horizontal yagi array, put it up in the antenna farm and pointed it at CMK, which did the trick with the el-cheapo scanner. Just enough signal to pull in the ground station at 126.8 on the vertical array and solid copy of the ATIS broadcast from the CMK VOR on 116.6 on the "flat side". It's the array pointing left in the attached photo, the wide-band custom ground plane on the other side of the mast is for a future feed.

Now all I needed was better radio equipment, and I had it in the form of a pair of Narco MK-24 nav/comm's I had buried in my ample junk pile from years ago when I upgraded the stack in the PA-30. It was a simple matter of digging up a nice regulated supply, the service manual for the nav/comm and brewing up a pair of filter and pad networks to tailor the audio and optimize it for a sound card input. I also replaced the solid radio covers with perforated ones to promote better cooling since we are talking about 40 year old transistors, most of them germanium and many other components "unobtainium", which is why I saved both radios in the first place... if I had only one I would have pitched it years ago. Anyway, in another, much younger life I did a fair amount of commercial land/mobile radio work and when working on equipment of that era it seems that without exception the component that fails is the part that they build the rest of the radio around, and with avionics it's even worse. Anyway, I mounted all the stuff to a shelf and stuck it atop my HF gear rack (also to be in a future feed) in place of a retired reel to reel tape deck.

So far I am pretty happy with the results, especially since I started out thinking it was impossible, and right now the signal conditions are at their worst regarding foliage. The vertical array is directive enough to pull the ground station in reliably even if weaker than I would prefer, yet despite the 20db F/B ratio I can still pick up all of the guys climbing out from JFK on the back side. Any more gain in the array and I would have to fire up the other nav/comm on the omni to get the planes and brew up a voting system to choose the better signal, and Dave hasn't paid to upgrade to that service plan yet :-)

So, you got some pics to look at... the arrays, the VHF gear and some juicy boat anchors. I want to add a feed that is a combination of just oddball VHF... air to air and long distance/oceanic as well as HF when I have the big radios on, because I like to listen to the oddball stuff... toilets backed up over Iceland, passenger in seat 24A in a diabetic coma, hurricane hunters, search and rescue, ferry pilots talking about their girlfriends, etc., and it would be neat for others to be able to listen in as well. Dave just has to figure out how to get it in the system since the system is organized around aviation facilities... not mental facilities housing ad-hoc crackpots like me.

Here's the links:

NY APP Liberty east:

Feed Purveyor:
(KJFK) NY DEP Liberty East
HF CAR-A  3455/5550/6577/8846/11396
HF ARINC LDOC  6640/8933

Complaints should be addressed to: City Hall