Ignorant Radio Question

[Sven]

We have a couple old radios in the 20D that work just fine. However, they do not go to the third decimal. To do that we rely on a handheld. Needless to say, the handheld is weak and I don't enjoy switching. The handheld did come in handy when I lost my electrical system but I would like to use the big boys for all that high powered talking.

Where do I look for a used radio we can either add to the panel (maybe the LORAN spot) or replace one of them? What should I be looking for and is there a more technical name besides "radio that goes to the third decimal?"

Thanks folks!

[OR75]

Sven

I believe you are looking for a slide in replacement com with 760 channels instead of 720 channels

What kind of radio do you have  ? is it a King KX-170 ?

In which case a TKM MX-170B could work.

[danb35]

Quote: Sven

We have a couple old radios in the 20D that work just fine. However, they do not go to the third decimal.

[carusoam]

As of January 1, 1997, VHF aircraft radios with 50 kHz channel spacing (usually called 360-channel radios) may no longer be used to transmit. New or replacement VHF aircraft radios must have been type accepted by the FCC as meeting the required frequency tolerance of .003 percent. Channel spacing and frequency tolerance specifications for a specific radio may be found by consulting the user's manual for the unit, by contacting the manufacturer (listed at the end of this topic sheet), or by consulting a local aircraft radio dealer or repair shop. For now, the best advice is: Placard the communications radio "do not use to transmit" or remove it from the aircraft.

http://www.aopa.org/members/files/topics/radio.html

You can listen to them, but you are not allowed to transmit on them.  With the very old technology, they bleed over on the neighboring channels when you transmit.

The manufacturers were pretty smart, back in the day, offering slide in replacements for whatever you have.  Sometimes the letter R appears in the model name of the radio indicating this type of "replacement".

10years ago I changed out a Narco COM radio this way.

-a-

[Barry]

IMHO, kx-155, best bang for the buck. Older, but very serviceable radio ... You can find them on e-bay or trade-a-plane, etc.

[Barry]

double post ...

[mjc]

Another thing you may want to consider (in addition to replacing what may be an illegal radio) is adding a switchbox to allow the handheld to use one of the airplane's comm antennas. I found that my handheld would transmit maybe two miles with the attached rubber antenna, and around 20 miles when connected via the switchbox.

Example:

http://www.aircraftspruce.com/catalog/avpages/icomswitchbox.php

 

[Sven]

Wow. I'm not sure I'm glad I asked that question. I guess that's what happens when all three partners are out of aviation since the 80's and then all decide to get back into it again. I wonder what other kind of surprises we'll find. Next you'll tell me I can't go to my own hangar without a background check, fingerprinting, and a badge (at my expense).

We have two King KX 170B radios.

Thanks for the info folks. I guess we'll be making yet another purchase real soon.

[danb35]

'48Q had a 170B in it as well when I bought the plane--it still tuned the in-between channels.  Are you sure yours won't tune them?  Whether it shows the third digit is irrelevant--if you can tune a frequency ending in 2 or 7, you're good.  If not, you can buy a used 720-channel 170B, or if you want to upgrade, you can look at something like this:

http://www.bennettavionics.com/mx170b.html

as a slide-in replacement.  Either of those replacements can be done by yourself in about 5 minutes.

[Sven]

Nope, I'm not sure because I've never tried it. I'm starting to feel "dumb and dumber." I guess I just assumed I couldn't. We'll have to give it a try. And just so that folks don't think I'm a complete idiot, I did open a jar of pickles all by myself, once.

[Hank]

Remember when testing, pull the tuning knob out one click to get the .x2 and .x7 positions. If you get it, you're good to go.

[DaV8or]

Another drop in replacement option is the MAC 1700. It's a digital conversion of the KX-170. Used ones are all over the place and pretty cheap I would imagine.

MAC 1700 Info

[Sven]

Hank,

Literally pull the knob toward me? Does it need to be in the .x2 or .x7 position to do that? Is it a mechanical thing?

[maniago]

Quote: Sven

Hank,

Literally pull the knob toward me? Does it need to be in the .x2 or .x7 position to do that? Is it a mechanical thing?

[Lood]

If poossible, go for a KX155. I went through the same exercise last yaer and have never looked back. I put in a KX155 with glideslope as well as a KY197 as com 2. These radio's takes a lot less space than the 170/5 series and you'll save quite a bit of weight as a bonus.

[OR75]

No question that the KX-155 is a great Nav-Com: proven , sturdy , simple to use, reliable (more than a Garmin from my experience) and still great looking. I have a KX-155 and have no intention of trading it for anything else.

However, if cost is an issue, you should look at TKM radio

http://www.bennettavionics.com/mx170b.html

You will save yourself quite a bit of $$$ with the rewiring you would have to do with the KX-155 as it is a slide in replacement and it costs a lot less than a KX-155.

I have no experience with it though and indeed it uses more space than a KX-155.

 

 

[Ron McBride]

Sven   Come to Mariposa Open house on the 25th. We can look it over and of course you can display your very unique plane.

Ron

[Stefanovm]

I have Collins Microline. The #2 will not transmit, but seems to receive. I would like to know what might replace these without a lot of wiring changes. The alternative is to see if it can be fixed or replaced as they are fairly inexpensive. I had a KNS80, KX125, and Ky197 in my C152. I miss the KNS80 (enroute and approach certified) even though I now have a KLN94 (VFR only due to far right position and no CDI connection). The King DME remote is off by 10 miles and impossible to see from pilot's seat. Panel photos are in my photos, http://www.mooneyspace.com/index.cfm?action=gallery&userGallery=1544.

[Sven]

So, I re-read danb35's post. If I'm understanding you correctly, and to use an example, if I'm tuning in 122.97 on my radio I'm actually tuning in 122.975? That's really letting my ignorance flap in the breeze but I have no manual for the KX 170B and can't find one online or on Ebay. Wow, if that's the case I'm a happy and more informed camper.

[carusoam]

"if I'm tuning in 122.97 on my radio I'm actually tuning in 122.975" - Sven

Yes,  122.97 = 122.975 (there is no 122.970 = .025 channel spacing)

Like wise 122.92 = 122.925 (there is no 122.920)

Picture of modern radio....

2 decimal points in the comm field.  Actually goes out three decimal places in frequency selection.

122.70 = 122.700

122.72 = 122.725

122.75 = 122.750

122.77 = 122.775

122.80 = 122.800

Tuning:

Big knob, changes left side of the decimal point

Small knob, changes first number on the right side of the decimal point.

Pull small knob out, to get the last digit properly.  The hidden digit is just assumed by the tuner.

 

See the next list for radios that were obsoleted by the 720 channel rule.  Note that the KX-170 and KX-170A are on the list, But the KX-170B is not on the list.

Bendix / King / Allied Radios that did not make the cut....

Allied Signal Commercial Avionics System (formerly Bendix/King). Models: KX 100, KX 100A, KX 110, KX 120, KX 130, KX 150, KX 150A, KX 150B, KX 160, KX 160-1, KY 90, KY 90A, KY 95, RT-221, RT-221A-14, RT-221A-28, RT-221AE-14, RT-221AE-28, RT-241A, 350A1, 350B1, 351A, 351AE, 351B, 351BE, TA18BB-1, TA18C-1, TA20-A-1A, TA20-B-1A, TA21-A-1, TA22A, TA22B. (Note: King KX 170, KX 170A, KX 175, KX 175A and KY 195 can be upgraded to meet the new frequency tolerance, but they will remain 360-channel radios. Cost of upgrade set at $322 for parts plus 3 - 4 hours labor).

I believe the KX 170B is the modern version

Comm frequencies go from  

 VORs operate within the 108.0 to 117.95 MHz

localizer transmitter operates on one of 40 ILS channels within the frequency range of 108.10 to 111.95 MHz.

ILS  / GS frequency pairs...

TBL 1-1-4
Frequency Pairs Allocated for ILS

Localizer MHz	Glide Slope
108.10	334.70
108.15	334.55
108.3	334.10
108.35	333.95
108.5	329.90
108.55	329.75
108.7	330.50
108.75	330.35
108.9	329.30
108.95	329.15
109.1	331.40
109.15	331.25
109.3	332.00
109.35	331.85
109.50	332.60
109.55	332.45
109.70	333.20
109.75	333.05
109.90	333.80
109.95	333.65
110.1	334.40
110.15	334.25
110.3	335.00
110.35	334.85
110.5	329.60
110.55	329.45
110.70	330.20
110.75	330.05
110.90	330.80
110.95	330.65
111.10	331.70
111.15	331.55
111.30	332.30
111.35	332.15
111.50	332.9
111.55	332.75
111.70	333.5
111.75	333.35
111.90	331.1
111.95	330.95

[danb35]

Quote: Sven

So, I re-read danb35's post. If I'm understanding you correctly, and to use an example, if I'm tuning in 122.97 on my radio I'm actually tuning in 122.975?

[carusoam]

If you want to extend the range from 720 to 760 channels

http://www.kingsavionics.com/news/radio_range.html

"For years, most nav/comm radios in general aviation aircraft had 720 channels, which were sufficient for most users at the time. But today most new sets come with 760 comm channels, which increases the comm frequency range from 135.975 mhz to 136.975 mhz."

-a-

[DaV8or]

Awsome! Mooneyspace to the rescue! Carusoam just saved Sven a lot of money and headache! Love this place.

[carusoam]

Share the passion - Mooney Ambassadors

Share the knowledge - MooneySpace.com

-a-

[Sven]

I can't than you folks enough. I was almost going to say that I went out and bought a new handheld for nothing. Then I remembered that a few months ago my alternator belt ceased finctioning and I lost the electrical system. Having that handheld let me back into my home Class D airport without having to use the light signals. One of the radios isn't very functional and ATC sometimes gets upset when we use it so this is all good info for when we need to change it out.

Thanks to all who helped out and didn't throw the "stupid" card at me. We have no manual for the radios and being a new PPL renewal I just assumed we needed that third digit. I guess it never came up in my retraining because we never used a three digit frequency and they didn't exist in 1981 when I first got my PPL ticket.

Thanks for treating this "slow learner" with mercy and kindness. Now I don't have to switch to my handheld again unless I really need it.