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33cm LTR System RF Diagram (draft)

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Jonathan KC8RYW
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Joined: Fri Dec 28, 2001 4:00 pm

33cm LTR System RF Diagram (draft)

Postby Jonathan KC8RYW » Thu Jun 03, 2010 2:00 pm

http://www.kc8ryw.net/900ltr/900ltr.gif

Comments welcome.

I planned for horizontal separation due to roof-top site.
73 DE KC8RYW
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SlimBob
Posts: 911
Joined: Thu Dec 18, 2003 11:38 am
What radios do you own?: I sold my soul for a Saber.

Re: 33cm LTR System RF Diagram (draft)

Postby SlimBob » Tue Jun 08, 2010 10:03 pm

Only problem I see is that you need the cans before and after the preamp. You've got to keep it from going into compression and amplifying anything near it.

Why are the cans after the receive multicoupler?
An armed society is a *polite* society.

Jonathan KC8RYW
Posts: 1747
Joined: Fri Dec 28, 2001 4:00 pm

Re: 33cm LTR System RF Diagram (draft)

Postby Jonathan KC8RYW » Fri Aug 13, 2010 9:25 am

SlimBob wrote:Only problem I see is that you need the cans before and after the preamp. You've got to keep it from going into compression and amplifying anything near it.

Why are the cans after the receive multicoupler?

Thanks for the feedback!

I revised the diagram, and put your suggestions into it.

http://www.kc8ryw.net/900ltr/900ltr_2.png

I threw out the idea of transmitter combining. It just made one big failure point for all the transmitters.

A friend and I found that the DB4090S pass cavities are broad enough that we just tuned them at 902.7500/927.7500, since I'm using xxx.5000 and above repeater pairs.
73 DE KC8RYW
Random Motorola Part Number:
SYN1894B - V3m Sprint-branded Battery Cover

SlimBob
Posts: 911
Joined: Thu Dec 18, 2003 11:38 am
What radios do you own?: I sold my soul for a Saber.

Re: 33cm LTR System RF Diagram (draft)

Postby SlimBob » Wed Nov 17, 2010 3:32 pm

You may want a 10dB distribution amplifier before the splitter on the RX. Otherwise, it looks solid. Sure, it's expensive to use five TX antennas and heliax, but there's otherwise not much of a good way to go about doing what you need/want to. Combiners do have losses. I like the idea of combining at a low level and amplifying, but one of the issues you have there is that you need a 1KW amplifer to pull off combining those carriers to reach any real power. And on top of that, it has to be exceptionally linear with good IMD characteristics as well.

For six carriers, you're looking at -1.37dB from what would normally be "0", per carrier. So if you're expecting to get 2x 50W signals out of a 100W amp, you're going to see a maximum of -1.37dB below 50W. That's a gross oversimplification but what I'm trying to say is that it's -1.37dB below whatever fraction of power is available from the amplifier (assuming all other carriers are at the same level). For example: 50dBm = 100W. 50dBm - 1.37 = 48.63dBm = 72.95W. 72.95W

My chart includes this note: "Available Power Per Carrier vs 1 Carrier: -9.15dB". Which I believe is to mean to say that if you have a 1000W amplifier and you're trying to amplify six carriers, each one will be below the top by that amount. (1000W - 9.15dB = 118.85W). 118.85 * 6 = 713.1W, not the 1000W expected.

http://www.moonblinkwifi.com/dbm_to_watt_conversion.cfm
An armed society is a *polite* society.


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