Tuning GAM SS-2 for Voice Channels and AIS

VHF Marine Band radios, protocol, radio communication theory, practical advice; AIS; DSC; MMSI; EPIRB.
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f8f1
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Location: Roseville CA

Tuning GAM SS-2 for Voice Channels and AIS

Postby f8f1 » Wed Jul 20, 2016 2:40 pm

I am in the process of upgrading my VHF and AIS antenna. I currently have an unknown model 8’ SHAKESPEARE antenna. I want to upgrade the performance of both my VHF and AIS. I have a GARMIN AIS 600. The GARMIN AIS 600 has an internal antenna splitter, there is an antenna “in” port and a VHF “out” port. I have always used a single antenna to operate both the VHF and AIS.

The port I mainly operate out of in the summer is an isolated area of the California North Coast. The majority of my communications are on Channel 68 156.425. The DSC channel 70 156.525 would also be important to me, although the Coast Guard is at best an hour away. If I need help my best chance of a rapid response would be my local fleet on 68.

My OUTRAGE 18 is a little small for two antennas. I noticed that DEFENDER.COM has the GAM SS-2 available in the “uncut” version. The VHF version is cut to 35” and is then center tuned 156.8 MHz. The AIS version is cut to 33.5” and is then center tuned to 162.0 MHz. If I cut the antenna to 34.25”, I would then have an antenna tuned to 159.5 MHz. An antenna tuned in the middle between Channel 16 156.8 MHz and AIS-2 162.025.

I spoke to Kevin at GAM Electronics, and asked if “tuning to 159.5 MHz would be a viable alternative to having two separate antennas?”. It was his opinion that if it was his boat, he would do exactly as I had proposed. The alternatives I discussed with him also included – Center tuning to 156.8 for both VHF and AIS – Center tuning to 162.0 for both VHF and AIS.

The only other concern I had was if the “splitter” technology that GARMIN uses in the AIS 600 would in any way be compromised by my “custom” antenna tuning. I have emailed to GARMIN tech support with no response in three days.

In the mean time I have ordered -

GAM Electronics SS-2 $49.99 + shipping DEFENDER.COM (+$10.50 special handling)
ADAP-II $ $24.99 + shipping DEFENDER.COM
SHAKESPEARE 498 - $29.99 + Tax, Free shipping to store WEST MARINE (still in stock as of July 2016)
Total $104.97 + Shipping @ $31.24 = $136.21

I can cut the antenna to any length I need when I am ready.

Jim, what do you think about center tuning to 159.5 for a combination VHF/AIS antenna?
John Handcock and Abalonee
18' 1986 Boston Whaler Outrage
150 ETEC
Clare Mary WDH3114
Class B AIS

jimh
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Re: tuning the GAM SS-2 for VHF/AIS

Postby jimh » Wed Jul 20, 2016 4:05 pm

Do you have a good directional wattmeter?

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f8f1
Posts: 22
Joined: Fri Oct 16, 2015 8:44 am
Location: Roseville CA

Re: Tuning GAM SS-2 for Voice Channels and AIS

Postby f8f1 » Thu Jul 21, 2016 12:37 am

No. I'm a General Contractor - carpenter. I have a pretty good Fluke DVM. That's about it for electrical test equipment.
John Handcock and Abalonee
18' 1986 Boston Whaler Outrage
150 ETEC
Clare Mary WDH3114
Class B AIS

jimh
Posts: 5712
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: Tuning GAM SS-2 for Voice Channels and AIS

Postby jimh » Fri Jul 22, 2016 11:53 am

Try cutting to length as GAM recommended.

The worst that can happen is the AIS transmitter complains about the VSWR.