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Author Topic: Cushcraft R7 Problem with Matching Network....  (Read 4659 times)
K3NRX
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« on: September 23, 2004, 05:31:23 PM »

I was out checking my R7 (not yet erected or connected) vertical not too long ago and I noticed something rattling around in the matching network box.  It sounded like something(s) broke off inside ......I cracked open the matching network box to discover that portions of the ferrite core had broken to bits with the majority of it intact...I am not sure how this happened, if water got in there somehow or if the damn thing fell without my knowing it, but I have the bits of the ferrite core in sitting in my shack....My questions are these...how serious is this problem??....Is the antenna functional??....Will it still operate properly???...do I need to replace this matching network???....What can I do to save this antenna???...I'd hate like hell to junk it, cauz it's a very good vertical...

Vince P
KA3NRX


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KB9CRY
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« Reply #1 on: September 24, 2004, 08:18:47 AM »

You can repair it! You can make it better!

http://www.qsl.net/ei7ba/r7_vertical.htm


Phil  KB9CRY
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K3NRX
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« Reply #2 on: September 24, 2004, 08:37:51 AM »

Dude, I saw this site already...It does not answer my questions....Again, I ask, In English, is this antenna functional the way it is now, with portions of the ferrite core intact, or is this ferrite core that crucial to the antenna that it needs replaced?...What ever happened to giving a straight answer?

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WB2WIK
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« Reply #3 on: September 24, 2004, 08:49:07 AM »

I'd replace that particular device.  Cushcraft sells replacement parts, and they simply solder onto the board in the R7 tuning unit.

In my old R7 (haven't had it in many years, so this is a memory tug) I believe there were two separate ferrite core devices: One was a transformer, the other a choke.  

If the ferrite isn't cracked all the way through anywhere so the "doughnut" is still intact and just little pieces of it have cracked off the edges, it probably still works; but the material is brittle and once it starts cracking, it usually continues.

The transformer is critical to the operation of the R7, which is a high-impedance (1/2-wave, end-fed) antenna without the tuning unit.

WB2WIK/6

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K3NRX
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« Reply #4 on: September 24, 2004, 12:52:11 PM »

The broken portion is the choke...if you look at our friend's site:

http://www.qsl.net/ei7ba/r7_vertical.htm


and scroll down to the photo of the matching network, the broken doughnut is the gray one, with the brown cables wrapped around it....like I said b-4, portions of this doughnut are still very much intact, but if Cushcraft has this same puppy in stock, I will order one and pop it in....

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N0IU
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« Reply #5 on: September 28, 2004, 05:37:18 AM »

I am still scratching my head wondering why this question is being asked in the Antenna Restrictions forum, but anyway...

I have had an R7 since 1992 and I swear by it more than at it! While I have never had to replace or repair the matching network (knock wood), I did have to replace the bottom section because the fiberglass insulator ring became worn to the point where there was enough wobbling it broke the bracket that holds the top part of the matching network to the antenna.

The good news: Even though the antenna had long since become obsolete, Cushcraft was able to fabricate a new one for me. The cost was $90.00 which was a whole lot better than buying a new R8!

The bad news: Since it was obsolete, it took over SIX MONTHS for them to make it! They were in no particular hurry to make the part, but you bet they debited my credit card right away.

The bottom line is that the R7 is a great antenna and I say do what you can to put it back on the air.

73,
de Scott NØIU
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N0IU
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« Reply #6 on: September 29, 2004, 06:12:52 AM »

Well you can forget about going to Cushcraft for a replacement. I asked if the MN7 matching network was still available and here is their response:

"No long gone and when last sold maybe 7-8 years ago was $165 that's far more then a used R5 or R7 is worth today

Your best bet is a web site dedicated to R5 R7 restoration and has all the "roll your own "info and Schematics---see EI7BA web site you  will be pleased

Ed Hammond WN1I"

73,
de Scott NØIU
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KE6VG
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« Reply #7 on: October 13, 2004, 05:08:45 PM »

The antenna is no longer any good. So just package it up and send it to me. I will fix it and enjoy long evenings of CW. Seriously though, if you don't wan't to roll your own balun, I will buy the thing off of you. ke6vg@todays-online(dot)com

KE6VG, thanks.
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W9GB
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« Reply #8 on: December 05, 2004, 02:58:58 PM »

Vince -

If you really have to junk it, I will pay shipping to get it.  TAKE SOME TIME and review the PA0FRI web site (Dutch) for the Cushcraft R5, note the discussion of the matching nework:
http://home.planet.nl/~fhvgeerligs/Ant/R5/onhr5eng.htm

Repalcement of the 2 - 86 pf capacitors with a large 47 pF doorknob (5 kV to 10 kV rating).

greg
w9gb

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N8TVU
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« Reply #9 on: July 26, 2006, 11:41:37 AM »

http://www.iol.ie/~bravo/r7_vertical.htm

This guy has full documentation on what you need.
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W9GB
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« Reply #10 on: August 04, 2006, 03:46:19 PM »

The Dutch web site for Cushcraft R5/R7 has moved to:

http://www.xs4all.nl/~pa0fri/Ant/R5/onhr5.htm

w9gb
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W9GB
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« Reply #11 on: August 04, 2006, 03:47:43 PM »

That was the Dutch language version, here is the English:

http://www.xs4all.nl/~pa0fri/Ant/R5/onhr5eng.htm

w9gb
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W9GB
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« Reply #12 on: November 15, 2009, 10:00:22 AM »

I have actual photos of rebuilding on the MN5/MN7 boxes.  I just rebuilt 2 of these matching boxes with cracked FT-240-61 toroid cores.
New cores, rewind using original wire, or coax, etc.

w9gb
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