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Old 07-08-2014, 17:31   #1
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Vesper AIS SP-160 "relay/splitter" test results, lab/real world

Hello to all,

A couple years ago, I upgraded from an AIS receiver-only (a stand-alone SiTex "Ais Radar", that I'd been using since 2006), to a Class B AIS transponder and Vesper Watchmate 650 AIS Display. I installed an aft-rail-mounted, bimini-height, VHF whip for my new AIS transponder, as I had been using a separate masthead-mounted VHF/UHF ham radio whip for my old AIS receiver.

This all worked well, and I wrote an article (w/ photos) describing my decisions, installation, and results.
http://www.c470.jerodisys.com/470pix/47148.htm


But, I also considered using a Vesper SP-160 "splitter / relay", that would allow both my primary VHF (M-602) and my new AIS transponder to share the masthead VHF-Marine antenna, as my "range" to/from other Class B AIS targets was limited with the lower antenna.
Since the SP-160's "fail-safe" mode (and powered-down mode) allows full use of the primary VHF radio, and I'd have a PL-258 barrel connector nearby to bypass it completely if ever needed, and since its specs showed a VHF thru loss of < 1.5db (transmit and receive), and its 12 db gain pre-amp for the AIS unit was spec'd to improve AIS reception / received S/N by approx. 6db, this seemed like an excellent piece of gear....

So last year, I went ahead and added the SP-160, and found (no surprise) excellent results....much improved AIS range (as expected), and NO noticeable degradation in primary VHF radio performance, both transmit and receive worked as well as ever. And, I now have the aft-rail-mounted antenna (about 10' off the water), fed with 35' if LMR-400uf, as my spare/back-up VHF antenna...

I attributed the good results to the Vesper SP-160's excellent specs, which say < 1.5db thru loss on primary VHF (transmit and receive) and a 12db gain amplifier on the AIS output (which is supposed to increase received AIS target S/N by approx. 6db)...

I made various transmit / receive tests, over multiple days, using SeaTow's "automated radio check"
system (which I can almost always use two of their systems, right from my dock, one close-by and one 25+ miles away...and many times also use a third one, ~ 30 miles away on a lower antenna), as well as using NOAA Weather Radio stations (of which I can always get at least 3 - 4, and many days I get 2 more NOAA stations that are weak, but readable....
Bypassed vs. Thru the SP-160 showed NO difference at all in any of the "automated radio checks", NOR in any of the regular NOAA stations, except for the very weakest (which at times was unreadable)....but even though there was some slight difference noticed by me, it was not enough to change the readability / intelligibility of the signal, and unless you were a trained/experienced radio op, it is doubtful that anyone would ever be able to notice this ever so slight difference...

(This is not surprising to me, as decades of radio experience has taught me that while I try to squeeze every last 1/10 of a db out of something in the lab / on the bench, etc....in the real world, using real signals, a "one db difference" is about the absolute minimum that can be noticed, the one exception was when I'm bouncing my VHF radio signal off the Moon, where there is a path loss of ~ 245db, and some of the stations S/N was zero or close to it (on CW of course), so if I can get an extra few tenths of a db out, and/or improve my antenna, feedline, rec noise floor, etc. a couple tenths of a db, I will find a slight noticeable improvement....But, VHF-FM Marine radio is NOT that!!
And of course when dealing with VHF-FM signals, the radio's rec bandwidth, noise floor, and the terrestrial noise, etc. mean that until signal levels are right at the C/N "threshold", there will be little advantage/notice with even larger changes...)


I also verified the VHF thru loss as < 1db, using my M-602 as transmitter and showing 24.5 watts on my Bird 43 wattmeter INTO the SP-160, and 20.4 watts coming OUT of the SP-160....giving a loss of 0.8db....pretty good!
(and even figuring some slight mis-cal of the Brid slug, I was happy to say that "it was < 1db"...)

Some purists will say that "every db counts!", and I actually agree!!!

But, with 25 watts of transmit power, on VHF-FM, and typical antenna heights of 65' HAAT, there is a LOT of margin in the Marine VHF-FM system.....and with the original Marine VHF-FM antenna systems design spec of 3db of feedline loss, I figured I was still good.....as I was very close to that design spec at 3.3db...
I use lower loss cable than most (70' of LMR-240uf @ 2.1db loss and 25' of LMR-400uf @ .4db loss = 2.5db + the SP-160's loss of 0.8db = 3.3db of total thru loss, from antenna to the M-602, transmit and receive...)

Note that someone using 95' of RG-213 / RG-214 (2.8db loss per 100') and using the SP-160 would place them only 0.2db lower (more loss), and that is hardly even going to be measurable with 1000's of dollars of test gear.....but I didn't have the room in my mast conduit for the thicker cable, hence the reason I went with the LMR cable...

{Also take note that even using the SP-160 "splitter / relay" and its added loss, and these lower loss cables mentioned here, still places us far ahead of those using "RG-8x" / "mini-8" coax, which has 4.5db of loss per 100', and NO "splitter / relay" at all!!!}


---- Now fast forward to this spring, when a friend asked my advice about installing a "splitter" for his new AIS transponder....
I made sure he understood that it was not just a "splitter", and said the only one I would recommend would be the Vesper SP-160...
And, when he asked "how well did it work?", I answered with the info above....but I always thought that if I was to post this info, someone would argue (rightly) that my single "one-user" anecdotal data is useless, and questioning the accuracy of my Bird 43 (whose VHF slugs have never been re-cal'd)....
So...
So, I went ahead and made some quality measurements using some of my lab equipment, which I have re-cal'd every year, and do a quick cal and normalize before each test....(although I did use my existing cables on-board, as i didn't want to introduce any possible variables for argument...)

And, what do 'ya know....everything checked out just as my earlier tests showed...
Here are the spectral scans of the Vesper SP-160 swept from 156mhz thru 162mhz, for everyone to see for themselves...
Note that my tracking gen was set at -15dbm, and cables swept/normalized...


This first image is the reference, SP-160 bypasses, cables connected together...(note the scale is 1 db / div)




This second image shows 0.6db to 0.9db loss from 156 thru 162mhz, on the main VHF line (transmit and receive on the main VHF radio) (note the scale is 1 db / div.





These next two images, show the 12db pre-amp gain thru the AIS (note the scale is 2 db / div, in order show this 12db change on the screen...)
But, please note that this does NOT improve your reception by 12db, nor your rec S/N by 12db....but rather approx. 6db....(I did not store any further test data, but if you could take my word for it, when looking at a narrow bandwidth approximating the marine VHF-fm rec bandwidth, I actually did see a rise in S/N....It was starting to storm and I wanted to disconnect things before my test equip got struck by lightning !)









---- Since I was there, I thought some may also want to see a sweep of my Shakespeare masthead 3' SS VHF antenna...and this is my usual first test (verify the antenna is working!), and I thought you may be curious what the VSWR is across the whole band, from 156mhz - 162mhz...







---- And, for those of you that wish to know a bit about RF loss thru connectors, it is effectively Nil / Zero!!!
I know some will disagree, but unless you're in a lab with 10's of thousands of dollars worth of equipment (and a few trained techs/engineers to set up the tests), you will NOT be able to measure the infinitesimal differences!!!
If you want to SEE what I mean, have a look at this photo.....the transmitter is outputting exactly 100 watts (measured with that same meter/slug), and after 23 connectors/adapter, etc. N's, UHF's, BNC's, including "T's" and "elbows", a short RG-58 jumper, and even including some "F" connectors and "phono" plugs/adapters (neither of which were ever designed to handle RF), the results are only marginally measurable....showing 95 watts out (a 5% power loss), which is a loss of 0.2db...

So, next time someone wants to tell 'ya that using an "N" connector will have less loss than a PL-259 {"UHF" connector), you can see for yourself that this will have no effect at all (at least until the freq gets past 400mhz)....take note that in my professional comm work, connector losses ARE figured into system design, link budgets, etc. but these losses are very slight, typically 0.01 to 0.04db, depending on connector and freq...
Enjoy...






I hope some find this useful....

Fair winds...

John
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Old 07-08-2014, 17:43   #2
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Re: Vesper AIS SP-160 "relay/splitter" test results, lab/real world

Great Post John!! Interesting results - I generally hate splitters - seen too much trouble with them, but as you say the vesper one you tested looks good! Digital yacht have a similar one. My advice (and I'm no radio geek like you!) is to avoid the basic types that are un-powered, and offer no gain. I'd be interested to see a test on one of those!
PS yes, I do sell the Vesper ones, and this is why!
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Old 07-08-2014, 18:58   #3
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Re: Vesper AIS SP-160 "relay/splitter" test results, lab/real world

All I can say is, I installed the Vesper splitter and XB8000 this spring and I'm happy. It works!
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Old 08-08-2014, 20:22   #4
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Re: Vesper AIS SP-160 "relay/splitter" test results, lab/real world

Nice testing. I bought one too an it was easy to install and works great! Very Happy!
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Old 09-08-2014, 09:46   #5
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Re: Vesper AIS SP-160 "relay/splitter" test results, lab/real world

Wow. This is for comms gear like "Maine Sail" level of detail and verification. And I don't throw such comparisons lightly. Thanks very much.
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Old 13-12-2015, 10:47   #6
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Re: Vesper AIS SP-160 "relay/splitter" test results, lab/real world

With all the recent discussion about "AIS Splitters" (which are really "splitter/relays"), I thought some might want to see this again....(maybe should be a "sticky"?)

Fair winds...

John
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Old 15-12-2015, 06:48   #7
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Re: Vesper AIS SP-160 "relay/splitter" test results, lab/real world

Oh noes! Yet more on the shopping list (actually a massive help John, as this has prevented a lot of head scratching and probably some unwise purchases).

So it actually reduces the size of the shopping list, when I think about it.
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Old 23-12-2015, 16:54   #8
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Re: Vesper AIS SP-160 &quot;relay/splitter&quot; test results, lab/real world

Thanks ka4wja for such a professional review.
Very timely for me as I am approving the Furuno TZTouch 2-15 upgrade and an AIS module is the last part of that decision

I am torn between ordering a XB-8000 with dedicated antenna
http://www.vespermarine.com/xb8000-a...nsponder.html/

Or their package deal with splitter
http://www.vespermarine.com/XB8000-n...-package.html/

Understanding that w/splitter it is an either/or use of vhf/AIS....in real world use....how disruptive to critical AIS tracking would be the use of VHF in say a close quarter situation?
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Old 23-12-2015, 17:59   #9
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Re: Vesper AIS SP-160 "relay/splitter" test results, lab/real world

I have never noticed my VHF use to disrupt the AIS. The AIS data is sent/received so fast that it would be hard to block it. You would need to hold the mic button indefinitely.

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Old 24-12-2015, 13:55   #10
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Re: Vesper AIS SP-160 &quot;relay/splitter&quot; test results, lab/real world

Pelagic,
You're welcome....but, I did all of this and posted it a year and a half ago...and just now bumped it back up, as there was quite a bit of controversy on-line, and thought some may not have seen this earlier...


Considerations when using a "VHF/VHF Splitter":

As for the Class B AIS transmissions disrupting VHF operation....
Not an issue....as they are very short (< 1/2 second) and happen only every 30 seconds...

As for your use of the VHF (you transmitting/talking on it), disrupting the AIS transmissions....
Yes, this can happen, and if you are actively communicating with other vessel(s) such as coordinating a crossing / passing, etc., it is possible that your updated/current AIS data might not be displayed until your AIS's next transmission....but, this is a rather rare situation...

So, in general, as travellerw wrote, it's usually not a noticeable problem....just something to be aware of..


I hope this continues to help...

fair winds...

John
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Old 24-12-2015, 16:39   #11
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Re: Vesper AIS SP-160 "relay/splitter" test results, lab/real world

If a situation has come down to the use of constant VHF traffic to coordinate a crossing situation, then the AIS data are pretty superfluous at that point.

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Old 24-12-2015, 17:17   #12
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Re: Vesper AIS SP-160 &quot;relay/splitter&quot; test results, lab/real world

Not necessarily Mark..probably more of my commercial training, but in a high density, narrow, multilateral crossing situation , like Singapore.....

you may have to identify your intentions to a number of targets while coordinating with Traffic Control their approval even if you are the stand on vessel....so that can mean a fair bit of VHF traffic

ARPA will obviously give you the changing CPAs, but with the slower refresh rate of Class B.....just curious if the splitter option was problematic
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Old 24-12-2015, 17:26   #13
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Re: Vesper AIS SP-160 "relay/splitter" test results, lab/real world

In the situation you describe, it seems like class B is problematic. I would think you would want a class A.

30 sec is a long time in that type of traffic and situation. It is most likely that other ships are not relying on your AIS transmission and instead are tracking you by other means or are relying on you to take care of yourself in their presence. So maybe your AIS is superfluous.

It is an interesting question - if the VHF is transmitting when the AIS wants to transmit, does the AIS wait another 30 sec or does it cue up to send as soon as free?

My guess is that it waits, but I'm too lazy to research it.

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Old 24-12-2015, 17:29   #14
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Vesper AIS SP-160 &quot;relay/splitter&quot; test results, lab/real world

BTW, receiving AIS data of class A ships is no problem, so the radar CPA isn't critical. Unless you are literally sitting on the Mic button.

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Old 24-12-2015, 17:51   #15
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Re: Vesper AIS SP-160 "relay/splitter" test results, lab/real world

Are small yachts choosing class A?
My example was more geared to commercial rather than a pleasure yacht who would normally transit during daytime and once crossed into their traffic lane, would stay at the outside perimeter.

Seems for us the splitter is not a problem
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