Heath Strobe Radio Noise

gfeher · Post by **gfeher** » Wed Dec 31, 2014 10:30 pm

My 52 B that I bought a couple of months ago has a Heath/Heathkit (yes, that Heathkit) OL-1155 belly strobe that the previous owner disconnected and placarded "inop" because it caused radio noise. He said that you could hear the capacitor charging and firing, and that the wiring just needs to be shielded. Has anyone had a similar experience correcting this problem? The strobe was installed in the early 70's via a 337, and I'd like to get it working without the radio noise so I do not need to deal with replacing it.

Thanks.

Post by **GAHorn** » Tue Jan 06, 2015 1:30 pm

Yes, you might consider replacing it's wiring harness with shielded cable.

gfeher · Post by **gfeher** » Tue Jan 06, 2015 5:47 pm

Thanks George. The power supply is integral with the strobe. In other words, the power supply is in the base of the strobe on the same board as the rest of the components, including the lamp. (Fortunately, I have a manual for the unit.) So the leads to/from the unit are just a 14v positive and the ground. I guess that's what's throwing me off. You say try shielding the 14v positive lead and the ground? Sorry to be a little dense about this.

bigrenna · Post by **bigrenna** » Tue Jan 06, 2015 11:43 pm

delete

gfeher · Post by **gfeher** » Wed Jan 07, 2015 2:01 am

That's what I'll do. Thanks for the clarification. Much appreciated.

hilltop170 · Post by **hilltop170** » Wed Jan 07, 2015 3:15 am

George-
I know you say ground the shield on only one end to keep from creating a circuit. What keeps the shield from grounding itself every time it touches the airframe and doing the same thing as grounding both ends?

Post by **GAHorn** » Wed Jan 07, 2015 6:53 am

Gene, you may have to install a noise filter in the power lead to that strobe. The noise is probably backing up into the main buss. Install it as close to the strobe unit as possible.

Richard, most modern shielded cable has an outer sheath. Older shielded cable did not, but the grounded end offers so much less resistance that it appears electrically to be the only ground. In both cases the cable should be stood off from the airframe with clamps and insulators.

gfeher · Post by **gfeher** » Wed Jan 07, 2015 4:00 pm

Thanks again George.

Post by **GAHorn** » Wed Jan 07, 2015 7:05 pm

You're welcome.
One of the things about better aircraft strobes is that they have incorporated better anti-noise power supplies. If you cannot find a cheap noise filter (which is nothing more than a large capacitor) then you might consider spending a little more and buying a replacement strobe. Whelen makes a nice direct-replacement.

gfeher · Post by **gfeher** » Wed Jan 07, 2015 9:16 pm

I didn't think that direct replacement was an option without losing my "grandfather" status with the current strobe. In other words, I thought that if I replaced it with a different belly strobe (even though it is a modern equivalent), I would then need to comply with the current regs for strobes, which I understand would require me to add a top strobe as well. I'd rather not cut a hole in the fuselage top for a second strobe. If forced to in that circumstance, I think I'd rather go with wingtip strobes and deal with closing the hole in the belly for the existing strobe. But I'm not thrilled with either of those two options. Is my assumption about triggering compliance with the current regs wrong? I'd be fine with just directly replacing the current strobe if it's an option.

Post by **GAHorn** » Thu Jan 08, 2015 4:30 am

Here's the rule: 91.205 (c)(3) An approved aviation red or aviation white anticollision light system on all U.S.-registered civil aircraft. Anticollision light systems initially installed after August 11, 1971, on aircraft for which a type certificate was issued or applied for before August 11, 1971, must at least meet the anticollision light standards of part 23, 25, 27, or 29 of this chapter, as applicable, that were in effect on August 10, 1971, except that the color may be either aviation red or aviation white. In the event of failure of any light of the anticollision light system, operations with the aircraft may be continued to a stop where repairs or replacement can be made.

So, ...WHEN was that Heath installed? If it was after Aug 11, '71 it doesn't meet the rule anyway. It would have to be on top of the vert. stab. to meet the rule in effect on that date.

But, since this is a visibility issue that is addressed by the rule change.... why wouldn't you want to install wingtip strobes and be seen?

Plug that old Heath's hole and get rid of drag too!

gfeher · Post by **gfeher** » Thu Jan 08, 2015 4:16 pm

It was installed in 1975 via a 337. I just checked the history of 23.1401. The version in effect on 8/10/71 required coverage of at least 30 deg above and below the horizontal plane. It was not changed to at least 75 deg above and below the horizontal plane until 9/1/77. So I guess the install was legal. But I hear you on the visibility issue. You make a lot of sense. Getting rid of the drag is a plus too.

Thanks again.

delarrow · Post by **delarrow** » Thu Jan 08, 2015 8:38 pm

Here is another option
http://www.aircraftspruce.com/pages/el/ ... extant.php
All this requires is to replace the wingtip and tail light with the combination LED strobe and light units,
they just plug in the light socket, no wire changes, all Fed legal and remove the old unit or just shut it off.
Problem solved!

bagarre · Post by **bagarre** » Thu Jan 08, 2015 8:49 pm

delarrow wrote:Here is another option
http://www.aircraftspruce.com/pages/el/ ... extant.php
All this requires is to replace the wingtip and tail light with the combination LED strobe and light units,
they just plug in the light socket, no wire changes, all Fed legal and remove the old unit or just shut it off.
Problem solved!

From the site:

The bulbs in this kit are replacement bulbs for nav lights only with the added strobe safety feature to be used at the pilot's discretion during daylight operation. Night operation requires steady on. They are not approved as a replacement for an anti-collision or strobe system.

The International Cessna 170 Association