HF Radio and Antennas in Mooney Aircraft

[BCrystal]

Do you have HF in your Mooney?

• Have you thought about installing HF in your Mooney?
• What type of HF antenna do you have on your Mooney?
• What HF radio and ATU are you using in your Mooney?
• Was HF already in the plane when you got it, or did you have it installed?

Aeronautical High Frequency (HF) radio has been the mainstay of long distance Air Traffic Control for over 80 years, especially in areas of the world where coverage with line-of-sight VHF radio is not reliable or possible. Although aircraft satellite ATC communications are now commonplace, HF is still very active for Major World Air Route Areas (MWARA) as well as Regional and Domestic Air Route Areas (RDARA). HF is widely utilized for bush flights and NGOs to communicate with ground mobiles, remote outposts, camps, or portable units. Some pilots who are ham radio operators may also enjoy talking on HF radio with amateur radio enthusiasts. So, there are many reasons for Mooney pilots to want HF capability in their plane.

Edited March 15, 2017 by BCrystal

[BCrystal]

To kick things off... Below, you will find some information about an HF antenna installed on the Mooney M20K that Brian Lloyd is using for a Round The World flight. An attached file includes a Mooney M20K aircraft computer radio frequency model that anyone can use for analyzing their own antenna systems on Mooneys (the file is adaptable to other aircraft). The Mooney antenna file format is 4NEC2 (free software).

With the 4NEC2 software, one can simulate any frequency of antenna system. This includes HF, VHF, UHF and microwaves. The models provided here in the attachment below are suitable for modelling HF antennas on Mooneys.

A Micom 3 HF SSB ALE radio has been installed in the Mooney with a new under-fuselage "belly" HF antenna with ATU. Brian Lloyd designed the system and antenna for use with ATC as well as ham radio. The Micom 3 radio is a commercial 125 Watt HF transceiver which covers all the aeronautical HF and amateur radio HF frequencies from 1.6 MHz to 30 MHz (and also receives 100 kHz to 30 MHz). It has a main radio unit mounted in the aft avionics bay, and a control head mounted in the main cockpit control panel, which has been custom-made to fit.

The HF antenna is a tensioned wire that is under the belly of the aircraft, slightly offset to the left side of the fuselage.

The antenna installation utilized Dayton-Granger parts: 

• 10 inch aluminum antenna strut with insulated hole
• 10 inch non-insulated aluminum antenna strut 
• Antenna insulator angled feed thru
• Antenna insulated tensioner
• Insulated antenna wire

Computer modeling shows that the wire is resonant at about 17.9 MHz.

The aircraft skin of a Mooney M20K itself is resonant at a radio frequency of about 12 MHz.

An Antenna Tuning Unit (ATU) is required to match the belly antenna's capacitive reactance load with an impedance of less than 10 ohms on most HF frequencies. Here are some images showing the HF antenna system during installation, and some results of antenna computer modeling.

HF Belly Antenna radiation pattern for 11 to 28 MHz:

HF Belly Antenna radiation pattern for 3 to 9 MHz:

Diagram of the HF radio and antenna system:

Photos during installation of the HF Belly Antenna showing Dayton Granger struts, insulators, wire, and insulated tensioner:

Photo of Antenna Tuning Unit (ATU) installation and Feed Thru Insulator for the HF Belly Antenna:

Geometric view of the antenna analysis computer model of the Mooney M20K:

Geometric view of the antenna analysis computer model showing the HF Belly Antenna on the Mooney M20K:

Impedance curve of the antenna analysis computer model for the HF Belly Antenna on the Mooney M20K:

ANTENNA ANALYSIS COMPUTER MODEL of Mooney M20k file download: 

HF_ANTENNA_AIRPLANE_BELLY_MOONEY_M20K_231_4NEC2_MODEL_7A2.NEC

Polar format impedance Smith Chart of the antenna analysis computer model for the HF Belly Antenna on the Mooney M20K:

 

Edited March 16, 2017 by BCrystal

[BCrystal]

José Monroy (aka Piloto in this forum) published a pdf paper "706 in Mooney4.pdf", about the Icom IC-706 HF radio with HF top wire antenna installation in his Mooney.

Download on Mooneyspace.com: "HF ICOM 706 MKIIG Installed in a Mooney by Jose J. Monroy KP4DAC, May 8, 2008".

As thanks to José, a computer model was generated from the information in his antenna system paper, and it is attached below:

Geometric view of the antenna computer model of the HF Top Wire Antenna on Mooney:

 

Antenna computer model of the 13 MHz radiation pattern of the HF Top Wire Antenna on Mooney:

 

Antenna computer model of the impedance curve for the HF Top Wire Antenna on Mooney:

 

Antenna computer model n 4NEC2 file format for the HF Top Wire Antenna on Mooney, download:

HF_ANTENNA_AIRPLANE_TOP_WIRE_MOONEY_4NEC2_MODEL_1A.NEC

Edited March 15, 2017 by BCrystal

[Raptor05121]

While I am a ham and love playing on HF, the answer is no. I am far too busy to be playing with a VFO.
 

[thinwing]

I installed an icom ic-7000 in a glider I owned.Since it was experimental category ,fed approval was not an issue,,,,not sure how the above installations pass FAA approval.I note on first installation a lack of any doubler on the aft feedthru....wouldn't it had been a better install to come out aft 12 in next to the fuselage former?I found the additional uhf/vhf freq very useful to contact my ground crew using repeaters..regards k6zk

Edited March 15, 2017 by thinwing

[carusoam]

BC,

Would you like to take a moment to introduce yourself?

Share a website or some background of who you are.  

If I wanted to buy this service for my plane, where would I go?

That kind of thing.  

There is always going to be the next earth rounder.  They will likely choose a Mooney to do it in. They can learn more about what it takes from the work you have embarked on.

Thank you for sharing the technical details so far.

Best regards,

-a-

[Piloto]

HF reception in flight can become noisy due to the static build up by the antenna. To overcome this most airborne HF wire antennas are grounded at the end. I tried grounding the end but the SGC 237 tuner performance was degraded as indicated by the field strength meter. Aviation type tuners are designed to work with grounded or open wire antennas.

KP4DAC

[Piloto]

I found my cell phone to be a little bit more practical than my HF radio. To overcome the signal losses experienced in-flight I attached my cell phone to the pilot sun visor using Velcro strips. This provides a better signal coverage even at altitude. Besides getting weather I can text and talk on the phone.

José

[BCrystal]

26 minutes ago, Piloto said:

HF reception in flight can become noisy due to the static build up by the antenna. To overcome this most airborne HF wire antennas are grounded at the end. I tried grounding the end but the SGC 237 tuner performance was degraded as indicated by the field strength meter. Aviation type tuners are designed to work with grounded or open wire antennas.

KP4DAC

That's a very good point, Jose.

A possible solution to discharging static at the HF antenna is the use of a high inductance shunt coil or high value resistor (3k to 20k), at the antenna feed thru (hot to ground). A shunt 10k ohm 12 Watt wirewound resistor may be the easiest solution.

Also, there is the possibility that a 1:4 UnUn (12.5 ohms to 50 ohms) to transform the low impedance of the antenna to a higher impedance might solve the problem of matching and static discharge at the same time. In addition to impedance transformation, an UnUn provides DC grounding of the antenna.

We are exploring both of these methods for improvement of the HF belly antenna installation.

Edited March 16, 2017 by BCrystal

[Raptor05121]

When you get airborne, I would love to make contact with you. 40m and 20m seems to be quite open during the day

[wishboneash]

Thanks for the info. I have an Icom 706 MK II gathering dust :-)