Towertalk
[Top] [All Lists]

Re: [TowerTalk] "bias Tee" from MFJ and others (followup)

To: towertalk@contesting.com
Subject: Re: [TowerTalk] "bias Tee" from MFJ and others (followup)
From: Jim Lux <jimlux@earthlink.net>
Date: Thu, 07 Sep 2006 07:36:52 -0700
List-post: <mailto:towertalk@contesting.com>
At 07:26 AM 9/7/2006, Jim Lux wrote:
>Does anyone have practical experience with HF bias tees used to send
>DC power up the coax?  For instance, MFJ has one that is about
>$50/pair. (MFJ-4116) 
>http://www.mfjenterprises.com/products.php?prodid=MFJ-4116

>I'm sure they are just a series capacitor in the RF path and a RF
>choke in the DC path, but what sort of values do they have? and, more
>interestingly, what are the component ratings?  The MFJ site says 1
>Amp and 50VDC, which is the DC path (what's the series resistance of
>that choke, though?), but I'm curious about the RF path.

The picture in the QST review
http://www2.arrl.org/members-only/prodrev/pdf/pr0605.pdf

shows the disc capacitors and says rated at 200W (although I couldn't 
find that in the manual online at MFJ).  It also says that the loss 
was <0.03dB, which is quite low, but, if you pushed a kW through it, 
that half a percent loss is 5W, which could make that cap pretty  toasty warm.



>We have some MFJ remote switches at W6VIO which use the same
>technique to send the relay current up the coax, and as I recall,
>there's just a couple of disk caps for the DC block.  At 1.5 kW,
>those caps have to handle 6 Amps or so of RF without significant heating.
>
>Other sources than MFJ? (e.g. Tessco?)
>
>What about designs to handle more DC power?
>
>What about interaction with transient suppression devices?   What
>order do you put the bias tee and transient suppressor?
>
>Feedline to antenna: transient suppressor: bias tee: rig?
>
>What about at the antenna end?
>
>How could you do this and still have a DC grounded antenna? (the load
>at the antenna end is presumably low Z for DC, and you could bypass
>around it for RF that gets through the choke
>
>
>I'm looking at schemes to run equipment that's a bit more than just a
>bunch of relays at a remote antenna location and sending the the
>power and signalling up the same 1000 ft run of coax.
>
>
>_______________________________________________
>
>
>
>_______________________________________________
>TowerTalk mailing list
>TowerTalk@contesting.com
>http://lists.contesting.com/mailman/listinfo/towertalk


_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk

<Prev in Thread] Current Thread [Next in Thread>