[TowerTalk] 12V through coax to switch antennas remotely

[Grant Saviers]

I have the same interest for a 160/80m relay switchable receive antenna 
feed design on RG6 and came to the following conclusions (probably 
better ideas out there).

The inductor should have its self resonant frequency at or above the 
maximum frequency to be passed on the coax.  I selected a Bourns 
652-RLB0608 180uH with 235ma current rating and corresponding low R and 
spec 4MHz SRF on a ferrite bobbin.  I've seen what appear to be 100uH 
Miller solenoid wound chokes in commercial designs but have never 
measured their SRF.

The capacitors should have a SRF well above the max frequency.   I chose 
0.1uF Kemet 1210 SMD size 500v rated chip caps for the LC block and the 
C pass .  The 500v rating is for a big lightning/static/crosstalk safety 
factor.   (I can show you some leaded 0.1uf HV ceramics with a measured 
SRF below 2MHz, I gotta wonder how one can make them so bad).  SMD 
multi-layer chip caps are really superior to any leaded ceramic.

Elsie showed the DC block yields a 2k or so impedance across RG6 on 160m 
and twice that on 80m, so a few percent loss of signal which for a 
receive antenna is negligible.

Everything in stock at Mouser, not yet delivered.

Grant KZ1W

On 4/3/2018 6:32 AM, N2TK, Tony wrote:
> Have a question about the values of the choke to keep RF from the relay and
> the caps for coupling of the signal. In different products I see quite a bit
> of different values of both components.
>
> For the coupling caps I see values from .01-.2uf. It would seem increasing
> the value of the cap reduces the Xc. And for the choke I see values of
> 100uh-2.5mh. And it seems increasing the value of the choke also increases
> Xl.
>
>   
>
> My application is for 160M and 80M only with receive antennas.
>
>   
>
> My question - does it really make a difference over the values listed above?
> Do all the values offer enough Xc or Xl to not cause any problems?  Is there
> really a recommended "good" value for the caps and coils? Even 100uh offers
> 1K ohms at 1.8MHZ and .1uf is .8 ohms.
>
>   
>
> Still learning.
>
> Tnx
>
> N2TK, Tony
>
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