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

To:, Towertalk <>
Subject: Re: [TowerTalk] "bias Tee" from MFJ and others
From: Eric Rosenberg <>
Date: Thu, 7 Sep 2006 13:42:50 -0400 (EDT)
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At a job which involved setting up commercial LEO satellite stations and when I 
was active in the VHF and satellite world, I used Bias Tees from Angle Linear   Very nice stuff... not inexpensive, but well worth 
the $$ spent.  Angle Linear is owned/run by Chip Angle, N6CA. It's been some 
time since I've been in touch with Chip, but when I was, he was good at 
answering emails and phone calls.  I still have a 2m preamp and a couple of 
Bias Tees somewhere around the shack! 

Here's their blurb. on Bias Tees. While it's geared to the VHF/UHF crowd, 
they'll work in the HF domain. 

I have *no* financial or other interest in Angle Linear. 

73 + GL, 

Eric W3DQ
Washington, DC 


"BIAS TEEs for DC powering of remote preamplifiers"

Angle Linear produces high performance bias tees for applications requiring 
remote tower mounted preamplifiers. These devices were designed specifically 
for use with GaAs FET preamplifiers. A two stage transient suppression network 
with reverse voltage protection is placed in the DC input path before 
connecting to the 50 Ohm transmission line. It uses the same high speed 
transient absorbers that are used in our GaAs FET preamplifiers. To date, our 
DC protection circuits have a mean time between failure rate of better than 
several hundred million hours. In other words, we've never had a DC regulator 
failure in over twenty five years of production.

Construction is identical to our standard GaAs FET preamplifiers; the same 
rugged enclosure with twenty screws attaching the covers for maximum RF 
shielding and stainless steel hardware throughout . The feed-thru capacitor 
provides better then 80 dB of attenuation from .5 MHz to several GigaHertz. 
Standard connectors are small flange type "N" with gold center pins and ptfe 
dielectric. Other connectors are available: SMA, TNC.

The transient protection network can handle 40 KV pulses for 1 micro second and 
1.5 KW for 50 milliseconds.

Insertion loss is less than .4dB to 1500 MHz
Return Loss is better than 17 dB to 1500 MHz

The DC voltage is internally connected to the "output" port and the "input" 
port connects to the receiver or multicoupler.

P/N: BT2-(conn), N = type N, S = SMA, T = TNC, + T (T for top mounting)

BT2NT for type N connectors.

If you plan to supply the DC power to the preamplifier through it's output 
coaxial cable, our preamplifiers can be ordered with an internal connection to 
pick-off the DC voltage; add "-bias" suffix to preamplifier part number.


Jim Lux jimlux at 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)

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.

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.

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