Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 17-03-2015, 13:27   #16
Jd1
Registered User

Join Date: Aug 2011
Location: Victoria, BC
Boat: Catalina 36 MKII
Posts: 1,095
Re: backstay HF antenna and split backstay

I had more or less decided on using a 23 ft Morad vertical for the main HF antenna and a shroud as the HF-DSC antenna but I have run into an intriguing alternative that I would like to run up the proverbial flag post and see what kind of response I get ......
How about a Delta (I hope that is correct) antenna. Fed at the bottom of the forestay and grounded at the foot of the mast. Apparently no insulators are required and it wants the mast to be grounded (which it is already). Supposedly this is a very forgiving design with broad tuning. It is of course fed with an antenna tuner.
It requires NO additional hardware and the antenna tuner can be squeezed in at the bow, very close to the feed point!
The only tricky bit is how to access the bow fitting from the inside to attach the GTO-15 to. There is a small access hatch that requires renting a midget with long arms

Thoughts ?????
__________________

__________________
Jd1 is offline   Reply With Quote
Old 17-03-2015, 14:20   #17
Registered User
 
ka4wja's Avatar

Join Date: May 2007
Location: Florida
Boat: Catalina 470
Posts: 2,033
Re: backstay HF antenna and split backstay

Jd1,
Again, I don't have the time to write a treatise on this...
But, here goes a brief reply...


1) Although a 23' whip isn't a bad antenna, I'd recommend a longer antenna (such as the backstay or "alt backstay antenna") for better low band performance....
But, the choice is of course yours...


2) As for the "Delta" antenna you wrote of...
I've steered clear of that discussion mainly because of a few big reasons...
a) "any" antenna works better than no antenna,
b) no mention of various radiation angles of different antennas on different frequencies, and most importantly how you use different angles on different freqs to communicate to different locations....(which means that there is no such thing as "the best antenna", but rather which one works best for most of our operating and is most reliable, etc...)
c) even that poster wrote that the insulated backstay is a good antenna and "you will probably find that the insulated backstay is more efficient at some frequencies"
d) when someone has already built and used something (and written about their good results) there is no way to politely suggest that there are other/better alternatives,
e) the discussion was touting "antenna bandwidth" as a plus....but the 2 disturbing facts are that antennas with narrower bandwidth generally have more gain / higher efficiencies....but, the real important part here is that our modern tuners can couple our transmitters to our antennas without too much loss, on a WIDE range of freqs, with a WIDE range of antenna lengths (despite the old, carried-over from limited-tuning-range systems, tradition....our modern auto-tuners CAN provide excellent matches even into 1/2-wave end-fed antennas...oh, and BTW, with the large diameter of our backstays taken into account, typically the highest imped of an end-fed 1/2-wave backstay is about 1500 - 2000 ohms max...certainly within range of the AT-140 or SGC-230...)


Sorry about the rambling....but, I just wanted to point out this one important fact:
ANY antenna is better than no antenna....but why would you compromise when the "overall most useful" (sometimes thought of as "best") antenna for HF marine comms on our sailboats is an end-fed backstay or alt backstay antenna!!
(with long 23' - 35' whips second place...)

Jd1, only if you cannot rig a backstay antenna, or alt. backstay antenna, or a 23' whip.....then would you want to start looking for alternatives....

Here are some brief specifics in red...
Quote:
Originally Posted by Jd1 View Post
I had more or less decided on using a 23 ft Morad vertical for the main HF antenna
Good...(but, I still think the backstay or alt backstay antenna is better..)

and a shroud as the HF-DSC antenna
Also good, and is what I use....but many will say that it is "overkill" (and I cannot argue that)....as many do successfully use a simple, stern-rail-mounted, 49" SS whip as their HF-DSC receive antenna...


but I have run into an intriguing alternative that I would like to run up the proverbial flag post and see what kind of response I get ......
There are an almost infinite number of "alternatives", but few if any, will actually work as well as the backstay from 2-26mhz, and be as reliable....
But, understand that you CAN always build/add other antennas to your boat (yes, even on a 36 footer!)....
And, if for instance, you decided you needed better "short-range" comms of say 100 - 300 miles on 8mhz daytime, then a horizontally polarized antenna (such as a bottom,center-fed full-wave loop antenna) would be a great antenna!! But, please note that this is for a specific application, NOT for an all-around / close and distant / full-freq design...


How about a Delta (I hope that is correct) antenna. Fed at the bottom of the forestay and grounded at the foot of the mast.
See my details about this above....

Apparently no insulators are required and it wants the mast to be grounded (which it is already). Supposedly this is a very forgiving design with broad tuning. It is of course fed with an antenna tuner.
It requires NO additional hardware and the antenna tuner can be squeezed in at the bow, very close to the feed point!
Jd1, FYI....you can take your antenna tuner and connect it to ANYTHING metallic and it will work as an antenna.....

And, you can connect your remote tuner to any stay, backstay, or otherwise, non-insulated, etc...and it will work!!!
BUT...

But, not as good as the ubiquitous insulated backstay or alt. backstay antenna...
(I've been studying, experimenting with, and teaching antenna design and radiowave propagation for 40+ years, and I can tell you that there are a LOT of antennas that will work a LOT better than the insulated backstay, etc....But, most are NOT small, NOT strong, and NOT going to fit on you boat, nor mine, or at the least are single-band/non-tunable designs....and some/many will cost you a LOT of $$$....)
Thoughts ?????


Jd1, again I don't have the time to write a treatise on this....but hope the above brief comments are helpful...

Fair winds...

John
__________________

__________________
John, KA4WJA
s/v Annie Laurie, WDB6927
MMSI# 366933110
ka4wja is offline   Reply With Quote
Old 17-03-2015, 14:47   #18
Jd1
Registered User

Join Date: Aug 2011
Location: Victoria, BC
Boat: Catalina 36 MKII
Posts: 1,095
Re: backstay HF antenna and split backstay

Thanks for the reply John!
My biggest issue with the backstay is that I have a split backstay. The feed line coming from the AT140 would be going about 15 ft parallel to one of the backstay legs before it would get to the monkeyface. The isolated backstay section would be from the monkeyface to about 3 ft below the mast top. Also, the backstay is used for the support of the helmsperson a lot so running the feed line with standoffs is likely to cause issues.
Using the front stay seemed to be very cost effective and a very clean install.
__________________
Jd1 is offline   Reply With Quote
Old 17-03-2015, 15:17   #19
Registered User
 
ka4wja's Avatar

Join Date: May 2007
Location: Florida
Boat: Catalina 470
Posts: 2,033
Re: backstay HF antenna and split backstay

Jd1,
Unless your C36 is different from other Catalinas, the backstay chainplates are not grounded....and running the GTO-15 directly along the lower part of the backstay (below the insulator) will NOT couple into anything except that small length of SS wire, and this will NOT be detrimental to your signal in any way!!

The only time that running the GTO-15 directly up against the stay is problematic is when:
a) the stay is grounded (and therefore some, a very small amount BTW, of your transmit/receive signal is shunted to ground....)
b) the stay is not insulated (no upper insulator) and your RF is coupled into the stays, rig, mast, other wiring, etc....(such as when using the GAM Split-lead antenna...)

Other than those specific situations, there is NO issue running the GTO-15 directly against the SS stay, and then attaching the wire to the insulated part of the backstay...
As I wrote earlier, Bill gave you this answer earlier....and the physics of it hasn't changed since..
And, as I wrote with another smile...no need to reinvent the wheel....(this has been done like this for many decades without issue!!)
I'm not clear on what the problem might be???
You have the stay already insulated, so no additional cost there....why not just connect the GTO-15 wire to the insulated part of the stay, run the GTO-15 wire along the bottom part of the stay (which is technically insulated by the fiberglass hull), and then directly to the tuner output???
This IS the accepted and recommended way to do this....and has been done this way for decades....
Am I reading your description incorrectly??


Quote:
Originally Posted by Jd1 View Post
Thanks for the reply John!
My biggest issue with the backstay is that I have a split backstay. The feed line coming from the AT140 (which is GTO-15 wire) would be going about 15 ft parallel to one of the backstay legs before it would get to the monkeyface. (there is NO problem with this!!) The isolated backstay section would be from the monkeyface to about 3 ft below the mast top. Also, the backstay is used for the support of the helmsperson a lot so running the feed line with standoffs is likely to cause issues. (there is NO need for stand-offs!!!)
FYI, I use a Sunbrella-covered, padded covering, OVER my turnbuckle, Hydn Hi-Mod insulator, and GTO-15 wire, etc. and in 10+ years have never any issues with this...

Using the front stay seemed to be very cost effective and a very clean install.
I'm not going to bother to try to talk you out of this, if you've decided already....
And, to be clear....it will work....just like ANY antenna will work....but, I'm not changing my recommendation/advice....
Here is a photo of my current backstay lower insulator, etc. (with cover removed)....




BTW...
The biggest issue I see, and this would be an issue for anyone with this....that is that you have receive antennas supported by the backstay??
AIS (transmit & rec??) and GPS antennas???
I'm not clear on where/how these are attached to the backstay??? Nor, more importantly, where are the wires run for these antennas???
These are the REAL issues that you should be concerned about....getting RF from the HF rig into the AIS and GPS systems???

If you wish to discuss further, please advise...
But, at first glance, you may find the 23' whip to be a good choice here, considering these other antennas on the backstay...




I do hope this helps...

John
__________________
John, KA4WJA
s/v Annie Laurie, WDB6927
MMSI# 366933110
ka4wja is offline   Reply With Quote
Old 17-03-2015, 15:40   #20
Jd1
Registered User

Join Date: Aug 2011
Location: Victoria, BC
Boat: Catalina 36 MKII
Posts: 1,095
Re: backstay HF antenna and split backstay

Quote:
Originally Posted by ka4wja View Post
Jd1,
Unless your C36 is different from other Catalinas, the backstay chainplates are not grounded....and running the GTO-15 directly along the lower part of the backstay (below the insulator) will NOT couple into anything except that small length of SS wire, and this will NOT be detrimental to your signal in any way!!
John
Ahhhhhhh !!!!! Well here is something I did not realize .... You are correct that the backstay chainplate is not grounded but I was under the impression the standoff's were still needed. Most importantly, I was under the impression that the distance between the AT140 and the isolated backstay was fairly critical and as such, the 15 to 20 feet of GTO-15 cable used was a big negative.
This is obviously not the case and shines a completely different light on using the backstay!
__________________
Jd1 is offline   Reply With Quote
Old 17-03-2015, 15:48   #21
Registered User
 
ka4wja's Avatar

Join Date: May 2007
Location: Florida
Boat: Catalina 470
Posts: 2,033
Re: backstay HF antenna and split backstay

Jd1,

For clarification....
Quote:
Originally Posted by Jd1 View Post
Most importantly, I was under the impression that the distance between the AT140 and the isolated backstay was fairly critical
It isn't the length of the GTO-15 per se, that is spoken about as "critical", but rather the length that is routed thru the boat, along rails, in a odd/unusual way, which can be detrimental to antenna system performance (and cause RFI issues)....
Placing the AT-140 close to the base of the antenna, as long as this does NOT place it too far from the RF ground system / counterpoise, is important....
But, the length of GTO-15 wire running up straight abovedecks, in the clear, is NOT a problem....(and technically the 14ga tinned copper wire inside the GTO-15 is a better conductor that the SS stay anyway...so, NO worries there at all!!)


and as such, the 15 to 20 feet of GTO-15 cable used was a big negative.
This is obviously not the case and shines a completely different light on using the backstay!
Okay, now were gettin' somewhere!!

I hope this helps...

John
__________________
John, KA4WJA
s/v Annie Laurie, WDB6927
MMSI# 366933110
ka4wja is offline   Reply With Quote
Old 18-03-2015, 09:26   #22
Jd1
Registered User

Join Date: Aug 2011
Location: Victoria, BC
Boat: Catalina 36 MKII
Posts: 1,095
Re: backstay HF antenna and split backstay

John, pm sent ....
__________________

__________________
Jd1 is offline   Reply With Quote
Reply

Tags
antenna

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
For Sale: SPLIT BACKSTAY ADJUSTER Sailorman Ed Classifieds Archive 0 19-03-2014 20:47
SSB split backstay advice toddedger Marine Electronics 11 28-11-2013 09:42
Alternator / ACR Split / Split Diode Conundrum Sulaire Electrical: Batteries, Generators & Solar 8 12-03-2012 20:03
Split Backstay Tensioner on a Ketch Stillraining General Sailing Forum 27 26-07-2010 21:23
SSB and Split Backstay denverd0n Marine Electronics 6 15-10-2009 15:17



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 07:31.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.