[Milsurplus] TCS matching

[Roger Basford]

Hi Rob,

Thanks for the message and all well here. Yes, I came across your 
YouTube video on a Google of TCS radios and, as I said in the posting, I 
was very impressed with the bug key and no sidetone!  I can do that with 
a straight key but it must take some practice to read those dots with 
the bug? Also saw the video taken on the war ship too, some 
powerful-looking equipment on there.

Several responses have mentioned the tuning cap either in series or 
parallel so I will give that a try followed by the coax balun if the 
caps don't help. Like your video, I've plans to set the station up in 
the field for a vintage radio day in July, so may have to use what's 
available in the way of antennas.  At home I have a 66ft end fed "L" and 
it was that which I couldn't match to, but I will give it another try 
today.

Many thanks!

73

Roger/G3VKM



On 06/05/2011 01:39, Rob Flory wrote:
> Dear Roger, copied to the group,
>
> How are you?
>
> I think maybe you were the one who commented on my youtube video, and then I saw your post on milsurplus about antenna matching with the TCS.  As others have pointed out the TCS (like so many other military radios) is made to tune into an electrically short antenna, meaning a low resistive with capacitive reactance.  The step down(looking from transmitter side) balun with a series capacitance serves well.  I have done well with hundreds of picofarads series cap.
>
> One way to implement the impedance transformation is to use 2 quarter wave sections(electrical, meaning take velocity factor into account) of 50-ohm coax paralleled up from the 50ish ohm resistive antenna to the series capacitor, and then the capacitor to the TCS antenna input.
>
> Transmission line transformers a la Jerry Sevick W2FMI do a nice and elegant job on multiple bands, but if no cores in hand and an antenna that needs feeding on one band, the coax setup does nicely.  I did this with a full quarter wavelength on 80m and it fed well on 160 and 80 with a 400pF cap in series.
>
> 73, RF
> K2WI
>
>