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
>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
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 mailing list