[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: Popularity of 2m I.F.



At 04:21 30-05-2001, you wrote:

>Was on the phone with a good friend the other day,  extolling the
>virtues of ao-40 (of course).  He has always been interested in
>satellite communications,  and is real receptive to the idea of getting
>a mode S downlink setup running.  But he posed a question that I had
>no clear answer for - "Why does everybody want to use 2m as an I.F.,
>given the proliferation of good used hf radios?  Why not use 10m?
>
>So,  what should I tell him?

Well, as i see it:

Politicians are much like Downconverters:

1. A few of them are fine, but in many cases their willingness to do any 
actual work (Gain) is rather low, and the competence (NF) of any work they 
are finally persuaded to do can leave room (about the size of Pentagon) for 
improvement.

2. They often can have serious image-problems (using a high IF).

3. They like to stay as far from unnessecery trouble as possible, since not 
doing so would increase the problems in (1) and (2)....

In downconverters, as well as in receivers (superheterodyne), there are 
benefits from a high IF, such as avoiding (2). If you have anything on the 
image-frq in your area, this can be really important.

An IF on 10M (29Mhz) would give only little image-rejection because the 
separation between the desired signal and the image is so low. the solution 
could be to make the converter with dual conversion, but then complexity 
rises, and i doubt having two or more wind-cooled XO's would aid stability.

It's a much better idea to accept the 2M IF and then add an extra converter 
(2M > 10M), and if you make this a TRANSVERTER instead you can then also 
have 2M all-mode capability from this box, as opposed to if it were in the 
downconverter housing.
Just make sure it can't transmit into the downconverter!!!!

So, if your friend gets an extra transverter he will be able to use the 
downconverter on his HF-RX, and get on 2M SSB as well.

Good Luck, Rich!
73 de OZ1LRG

----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home