[NLRS] 23cm ATV Question -- 75 Ohm SMA connection?

[Dr. Gerald N. Johnson]

On Thu, 2006-10-05 at 12:28 -0500, Brad Phelps wrote:
> 
> Recently I bought a 1.2GHz transmitter/receiver ATV bundle as seen here: 
> http://www.hamtvstore.com/html/special_offers_.html.
> 
> Upon looking at the descriptions a bit closer, I noticed that the antenna 
> hookup is a 75 Ohm SMA connection on the transmitter and receiver: 
> http://www.hamtvstore.com/html/23cm_atv_transmitter.html.
> 
> Originally I wondered if maybe this was a normal thing for  ATV, but it 
> looks like ATV transmitters/down converters made by PC Electronics and MFJ 
> use 50 Ohm connections.  ... When I ordered this, I saw that the supplier is 
> out of the UK, so I am wondering if 75 Ohm connections are "normal" for ATV 
> overseas?

75 ohm is common in CATV because the cable uses a bit less copper in the
center conductor while it has a bit lower transmission loss. I've not
yet found mixing 50 and 75 ohm transmission lines to upset my equipment
from DC through 1296. One thing to be sure of is whether the SMA is made
for 50 or 75 ohms, a 75 ohm male center pin may not make contact with a
50 ohm female socket pin and once a 50 ohm male pin is shoved into that
75 ohm female pin it may be broken or subsequent trial of a 75 ohm pin
may not make contact. Thing is, at least at Mouser, they don't list a 75
ohm SMA, though they have a 75 ohm SMB.

> 
> Does anybody know where I can get 1.2GHz rubber ducks that will work with 
> these boards in the US?  I can order them from this same supplier, but it 
> took forever for the ATV boards to get here.  I don't want to repeat the 
> experience on the antennas if I can avoid it (stupid me for not ordering 
> them in the first place.)
> 
> More importantly, if I want to use the transmitter with an amp (like the 30W 
> one offered by DEMI), what sort of problems am I going to run into?  It 
> would also be nice to hook up the receiver to a beam at some point too.

Its not sure that the SWR of preamp, antenna, or PA will be as low as
1.5:1. I expect no problems at all.

> 
> ... Probably newbie type questions, but what can I say...  I'm new to this. 
> ;-)
> 
> Thanks in advance for your help.
> 
>  - Brad
>     AI0BP 

-- 
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer