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jason porter

DIY sharkfins (Ramsey LPY41)

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22 hours ago, Philip Perkins said:

..With the L brackets attached to the bar with a single bolt the antennas can pivot inward, so the thing folds flat--easier to transport--can even go in a case w/o being disassembled.   You can for sure think of a more elegant way to mount the fins, and I must say that they've held up really well over 15 yrs of use.  btw, what's inside the black fabric covering of an RF "Venue" antenna is basically the same "circuit board" type LPA.

I would not recommend trying to move the connector to the back--you might ruin the antenna by removing the connector from where they put it...

 

Sounds like it's worth a pic, next time you have it set up, Philip. Sounds easier to deal with. Yes, the connector should stay there. I didn't like the adhesive cable stays/zip ties method. So when I was ordering my cables, I found these SMA female jack right angle panel mount PCB solder square RF connector adapters, and decided to solder the disconnect there. The Kent LPDA only comes with putter holes at the small end of the LPDA.

Regarding the RG316: truly tough stuff. It has the feel of a something like a bike brake cable (not the housing, the cable). So strain relief doesn't seem to be a need. They coil very nicely, were custom made, and very inexpensively, too. I like the informal way the RG316 falls when  it's all built. I just need to find a suitable storage system for it all. Working on that now.

 

imgres.jpg

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What I made isn't that different from yours, yours will fold flat too I assume.  Mine might be lighter, kind of nice when mounted on a tall stand.  I also made the lines from the connectors shorties that are permanently attached to the fin, and terminate in strain reliefed BNCs so I could use standard cables with those surface mount connectors protected from pulling on the cable.

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My contribution to the Shark fin DIY...  I used a bunch of epoxy and some desk "through hole" covers to strengthen the BNC area... Have had them for over a year and they work great!!

Shark_fin.jpg

shark fin connector.jpg

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On 6/23/2015 at 2:05 PM, cmassey said:

Thanks for asking Robert...thought it was me!  The fellow that builds the PC board antennas is a friend of mine.  Want him to see how his stuff gets used...and build a couple myself.....

 Hey Cleve. Since you know this gentleman, request a version that has the connectors at the large end. That's how all of us use it. Just a thought. Please and thank you 

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Much skillful implementation in this thread.

Mark, I approve your use of plastic (Delrin?) to make the attachment mount for the antenna. I understand that antennas tend to "couple" to any adjacent metal so that the stand or bracket actually becomes part of the antenna design.

As it was explained to me, this phenomenon is present even when the components don't actually touch although the practical effect quickly becomes trivial with even small distance. Theoretically, if you were to stand outside the Empire State building, the frame of that structure would, in some probably immeasurable way, become part of your antenna. But to avoid the phenomenon altogether, you might have to work 100,000 miles to the lee of Pluto - not helpful. Anyway, a non-conductive mount made good sense to me.

When I was editing the 695 Quarterly (now Production Sound and Video), we made some tests of high gain antennas and included the Ramsey along with PSC, Sennheiser, PWS and Lectro products. The Ramsey's performance was a pretty good match to much more expensive units although it did have a more scruffy appearance and some sharp edges. But the clean-up work by "AFEW" and others addresses this nicely.

You may find the Quarterly issue with the test here:

http://www.local695.com/Quarterly/695QuarterlyPDFs/695-Quarterly-2010-Fall.pdf

David

 

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4 hours ago, stacysound said:

 Hey Cleve. Since you know this gentleman, request a version that has the connectors at the large end. That's how all of us use it. Just a thought. Please and thank you 

Hi Stacy,

From my understanding the feed line / phasing harness needs to be at the front of the antenna. I hope this diagram will help. I am learning a lot, but no expert! If the feed line could be placed in the back of the array, miles and miles of wire could have been saved over the years, (see color photo).

Mark

 

Screen_Shot_2017-03-04_at_10_19.18_PM.png

Screen Shot 2017-03-04 at 10.27.02 PM.png

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Hi David,

Your article for the 695 Quarterly is great! I reread it last night, thank you.

I looked at Delrin for the attachment to the antenna, but found a piece of super high-density polyethylene plastic scrap that was the correct dimensions, so I used that. I plan to replace as much metal as possible like the aluminum crossbar and light stand. I am at the “tinkering stage” in the building process.

My interest in antennas started with doing the SMA connector modification of the Sennheiser G3. Last week I connected a G3 receiver to one LPDA and did a line of sight test in my neighborhood. I was shocked that I got the same distance (600 + feet) as my earlier, Lectrosonics LR receiver / LT transmitter gear (using whip antennas). The G3 test did not have any “control” to compare with, just a quick test. It also relied on the output feed cable on the G3 as the “diversity antenna” as part of the original Sennheiser design.

Thanks again,

Mark

 

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The feed point of the lpda is at the small end of the antenna. It has to be balanced, hence the balun in Mark's schematic. However, regular coax is unbalanced and having coax hanging at the front small end of the antenna will distort the pattern. A clever way of accomplishing a balun is to run coax down the exact center of the lpda coupled to one leg of the dipole array (soldered along its length) with the connector at the big end. The connected coax should move perpendicular to the final dipole arms, not in the direction of the arms or next to them.

Lectrosonics uses a four layer board with internal microstrip acting as the balun. Others use external coax soldered to one layer of the dipole arms. Either works.

It is very difficult to measure or characterize the performance of an antenna without a very sophisticated setup. About all a hobbyist can do is follow the directions carefully.

A coat hanger soldered to a coax cable will work 90 per cent of the time. It doesn't mean it is a good antenna.

Just follow directions. There are a lot of solid reasons that things are positioned just so on antennas.

Happy Experimenting,

Larry Fisher

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In a moment of desperation I actually made an antenna out of coat hangers formed into two squares, soldered and mounted to a piece of wood.  It worked ok.  Desperation does strange things to you.  The home made Ramsey based LPAs are far from perfect, but they serve quite well even in their mangled DIY form, I can assure you.

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I received almost the same performance from my home made versions than from the real things...  It was so close I could not tell on my end any significant difference...  I say almost because I am sure there is some deficiency, but I couldn't find it.

 

Wind drag because it is a solid fin is one deficiency and on windy days, that matters...  especially when they are up 10ft.

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3 hours ago, LarryF said:

The feed point of the lpda is at the small end of the antenna. It has to be balanced, hence the balun in Mark's schematic. However, regular coax is unbalanced and having coax hanging at the front small end of the antenna will distort the pattern. A clever way of accomplishing a balun is to run coax down the exact center of the lpda coupled to one leg of the dipole array (soldered along its length) with the connector at the big end. The connected coax should move perpendicular to the final dipole arms, not in the direction of the arms or next to them.

Lectrosonics uses a four layer board with internal microstrip acting as the balun. Others use external coax soldered to one layer of the dipole arms. Either works.

It is very difficult to measure or characterize the performance of an antenna without a very sophisticated setup. About all a hobbyist can do is follow the directions carefully.

A coat hanger soldered to a coax cable will work 90 per cent of the time. It doesn't mean it is a good antenna.

Just follow directions. There are a lot of solid reasons that things are positioned just so on antennas.

Happy Experimenting,

Larry Fisher

 Nothing like a good RF discussion to get Larry to dust off the keyboard. Thank you kind sir for your expertise and knowledge. 

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17 hours ago, LarryF said:

The feed point of the lpda is at the small end of the antenna. It has to be balanced, hence the balun in Mark's schematic. However, regular coax is unbalanced and having coax hanging at the front small end of the antenna will distort the pattern. A clever way of accomplishing a balun is to run coax down the exact center of the lpda coupled to one leg of the dipole array (soldered along its length) with the connector at the big end. The connected coax should move perpendicular to the final dipole arms, not in the direction of the arms or next to them.

Wow..it acts as a balun. I have critical mods to make. 

13 hours ago, stacysound said:

 Nothing like a good RF discussion to get Larry to dust off the keyboard. Thank you kind sir for your expertise and knowledge. 

Yes, so true stacysound! Much thanks Larry. As always, we really value your input here. 

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Great to have Larry add information to this conversation!

 

I wrote Tamara White of Kent Electronics this morning, ( Kent Britain designed the log periodic dipole array 400 - 1000 MHz WA5VJB) that we are using as the antenna for our DYI Shark-Fins.

I asked if a balum was necessary for his antennas.

Here is the reply from Kent Britain, the design engineer: 
Most Log Periodics have a high impedance. 
The Balun or Transformer is converting 200-300 Ohms down to 50 Ohms.

The Kent Electronics PCB Log Periodics are designed to have a much lower impedance and sort of wander between 50 and 60 Ohms over the frequency range.They are designed for a direct 50 Ohm match, no balun or ferrites are necessary.

Sincerely,
Tamara Wlhite, Kent Electronics

 

 

 

 

 

Tamara's article:

https://turbofuture.com/misc/How-You-to-Use-a-400-1000-MHz-Log-Periodic-Printed-Circuit-Board-Antenna

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On 3/4/2017 at 8:05 PM, stacysound said:

 Hey Cleve. Since you know this gentleman, request a version that has the connectors at the large end. That's how all of us use it. Just a thought. Please and thank you 

DONE....note sent his way this mornng!!!!!

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Aluminum Round Tube Source

If you want to use aluminum tubing for the cross-bar on your antenna mast I would like to recommend

Marty at Trinity Metal Sales Ebay store.

http://www.ebay.com/usr/highdesertmartin

He cuts to length 24" 36" 48"

Tube outside diameters 1/2"inch,  5/8"inch* and 3/4" inch in 1/8" inch wall thickness.

Note: Read David Waelder thoughts above on reducing metal in and around your antenna. A fiberglass, plastic or even a wooden dowel maybe a better choice over aluminum. 

Mark

* my fittings used 5/8" OD stock

 

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On 3/3/2017 at 0:23 PM, stacysound said:

Question for those that know more about this than I do - Could you put a connector at the larger end of the Antenna? Looks like the trace runs from one end to the other. Scrape away the Epoxy (or whatever it is) and solder to the other end?

The connector can be at the large end by running a shielded cable from the front connection. 

Note Jason's DYI photos prior to the one Rachel posted.

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Posting 2 photographs of my finished log periodic dipole array antennas. I would also like to thank Doug Tourtelot for building the RG-8X cables for me and David Waelder for his articles and antenna tests.

DM1_3369web.jpg

DM1_3353web.jpg

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Nice.  It will last you for years and years, and probably still be working great when you are ready to sell-off all your stuff, and then it will last the newb you sell it to for many years too...(if we are still allowed to use RF mics by then).

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