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I'm upgrading my 150L for IFR training. Anyone out there know of a Narco Nav 825 for sale? I'm looking for a unit with a glideslope receiver.

Thanks

Wally

What radios do you have now, Wally?

A reconditioned Narco 825 will probably cost you about $1,400 (click on this link for prices) [avionix.com] , and you still need the ILS head, plus installation.

You can buy used ARC (Cessna) G/S receivers with tray and harness, and ILS indicators, that all work through your current nav receiver, and have it certified and installed cheaper than just buying the Narco.

I just bought an ARC R-443B G/S receiver for $39.70, including shipping, that works through my MX-300 nav/com. Yes ....UNDER FORTY DOLLARS (I missed the one that sold for less WITH tray and harness). Then I found a tray for it for $.99 (ninety-nine cents) plus $7.90 shipping. I bought 3 ARC R-402A marker beacon receivers in a bundle for $9.99, plus $18.50 shipping. Indicators are expensive! I haven't seen one that sold for less than $50.

Why are these so cheap? These are advertised (yes, Ebay) as working units removed for upgrades, but have not been tested and yellow tagged! At these prices, I can afford to buy several until I find one to certify, and there's a good chance they all work. I'll have them all tested and yellow tagged if possible, pick out the best for 84G, then resell the rest (with yellow tags) to cover costs!

I might be cheap, but I'll be well equipped, and I might be able to pay for the instrument ticket with all the money I've saved!

Hi Karl,
I've got one King NavCom with a single VOR indicator. I saw a digital Narco 825 with GS that sold for $650 on eBay a few days ago. I just missed it!

How does one Nav radio supply both the existing VOR and a GS? (This question probably reveals my ignorance in spades)

Wally

The nav receiver, G/S receiver, and G/S indicator are connected each to the other in a triangular, or three way wiring network.

The glide slope frequencies are already received by your nav radio, but it can't decode them to drive the VOR/GS indicator properly. The G/S receiver frequency is married to the nav radio frequency by an existing output from the nav radio. If a VOR signal is received, the nav radio drives the vertical needle of the indicator in normal VOR fashion, while the horizonatal needle displays "off". The G/S receiver ignores VOR signals. If a G/S signal is detected, the G/S receiver decodes the signal, and sends the more sensitive course correction signal back to the nav radio, which only amplifies the signal and in turn drives the vertical needle normally. The horizontal needle is always driven directly by the G/S receiver.

Most nav/com radios already have the circuitry and pinout for adding a separate G/S receiver, but the radio mounting tray will need to have the wiring harness added to the existing connector. The cannon plug for the indicator will also need to be changed, using existing wiring from the nav/com (vertical signal), plus new wiring from the G/S receiver (horizontal signal).

The Narco 825 puts it all together in one package, but it won't be "plug-n-play", either! You'll need the correct mounting tray, preferably pre-wired with the correct cannon plug to drive the replacement VOR/GS indicator, and a duplexer for the existing nav antenna, which will double as a G/S antenna. On some installations, all of the ships audio passes through the comm radio's audio amplifier, so that's also a consideration.

If you plan to keep the King as nav/com 2, additional audio connections between the two radios and to the comm panel will be needed, and may not be completely compatible between brands. You'll need a second comm antenna and coax, a speaker isolation relay (to prevent feedback), and a triplexer for the existing nav antenna (two navs and one G/S on the same antenna).

The only disadvantage I see to a single Narco 825, is if the internal G/S receiver has problems, you loose everything while the radio is out for repairs. But, it is lighter than my system, and requires less installation of components and harnesses. If you can afford it, have the panel space, and the radios are compatable, I'd move the King to #2 position, and install the 825 in #1. Labor cost may rival radio and components cost, but it does pay to shop around!

Carl,
Thanks for the awesome lesson. I know it must have taken you awhile to type all that out. Great stuff. One other question. Is there more vulnerability if you run both the VOR indicator and the GS off the same Nav radio? In other words, with a second Nav radio, you have some redundancy, right? If one radio goes bad, you might lose the VOR or the GS, but not both at once?

Wally

I sense a little confusion, or it might just be the way I read it.

A VOR indicator, also know as an OBI (Omni Bearing Indicator) has only the one vertical needle, obviously driven by the Nav side of your nav/com radio.

The Glide Slope indicator looks very similar for a reason. It is still a VOR indicator, having the same vertical needle still driven by the Nav radio. You could use the G/S indicator as a VOR indicator whether you have a G/S receiver or not!

Adding the G/S receiver enables the glide path (horizontal) needle, which is driven by the G/S receiver ..... not the Nav radio. It also provides the course needle information (transmitted by the ILS system) to the Nav radio which drives the indicator the same as it would if receiving a VOR signal.

In essence, The G/S indicator is really two seperate indicators (built into one housing), driven by two seperate receivers.

You can't run separate VOR and G/S indicators off the same Nav radio (there's no good reason to even try), nor can you have two separate Nav receivers driving the same VOR or G/S indicator. For true redundancy, each indicator needs it's own separate receiver. I assume you don't yet have a G/S indicator, so you still need that anyway to use the Narco's G/S capability. If you buy the Narco (and G/S indicator), that leaves your King system intact to do with as you please. The whole idea of having dual nav/com capability (with or without G/S) is redundancy, especially for IFR/IMC flight. Only a complete electrical failure followed by a dead battery should incapacitate both systems.

The 152 I'm working on has 2 MX-300 nav/coms. The first drives the course needle of the G/S indicator in the top hole in the panel. The second MX-300 drives the VOR indicator in the second hole. A seperate G/S receiver mounted behind the baggage area provides the glide path signal directly to the G/S indicator. All 3 radios receive through the original Nav antenna mounted high on the vertical stabilizer, by using a triplexer (3-way antenna splitter).

I've tried to simplify the operation, but may have inadvertantly confused you in the process.

Thanks, Carl. I may have been confused, but I'm not now. I understand that you need the GS receiver in order to drive the horizontal indicator and that the vertical needle in the GS indicator is the same as the vertical needle in a VOR indicator. I also understand the three way splitter on the Nav antenna. Because you have two MX-300s, you have the redundancy I was talking about. If you lose one of those nav radios, you can still get a live signal to the other vertical needle, either in the GS indicator or the VOR indicator.

Thanks for taking so much time with this.

Wally