[amsat-bb] Cables loss

Fri Jul 20 19:18:30 UTC 2018

In the commercial satcom industry an ODU use is common enough that one might ne able to purchase old ODU (outdoor units) with tight seals and a world of RF components and mixer stages for dirt cheap to several hundred  watts and very small sensitivity parts in the receive chains. Of course they are in the wrong band but internal microwave shielded enclosures and bulletproof clean power supplies along with a LNA or LNB might interest some. My wish is to setup a station in DC using this method for ham sats. Has anyone alreday done this ? Hint .. old Anacom units. Plus it can and was designed to be integrated into high wind antenna structures. HPA sections can be uncoupled and replaced (I fixed them in remote sites) and replaced with ham sat stuff. Comments welcome.

Samudra N3RDX

Sent from a device with a small screen.

On Thu, Jul 19, 2018 at 4:13 PM -0400, "k6vug at sbcglobal.net" <k6vug at sbcglobal.net<mailto:k6vug at sbcglobal.net>> wrote:

 Hi Dave,
You said everything I have learned and observed up until now, but please allow me to add one complication to it -

FM discriminators (aka de-modulators) cannot handle very low signals well, for example, the downlinks of older lower power birds.  I observe this when I switch between a vertical and a Yagi, the extra signal strength from even a short 3 element Yagi keeps the FM discriminator very happy.

I find this issue less noticeable in SSB modes and adding a preamp is almost as good as turning up the volume control at the radio.

73!
Umesh
k6vug

    On Thursday, July 19, 2018, 12:07:26 PM PDT, Dave .  wrote:

 While I'm still new to the sats I have been doing VHF/UHF weak signal work
since the 80's and I've always preferred to spend the money on feedline
rather than pre-amps. Given that pre-amps amplify the rx noise and signal
you really don't improve signal to noise unless the noise figure of the
pre-amp is better than your receiver. Usually your just amplifying the
signal to make up for the loss that's going to happen as the signal makes
it's way down the coax.

You also add complexity when you want to TX on the antenna since you will
need to add a t/r relay at the antenna. In addition, you are still losing
tx power with the higher loss cable so depending on your ERP goal you may
need an amplifier, generally not an issue with the LEO's.
LMR-600 or hardline is my feedline of choice for 2m and up. I'm not
suggesting that pre-amps can't or shouldn't be used but usually aren't
needed if good low loss feedline is used to begin with.

Dave
N2OA

On Thu, Jul 19, 2018 at 9:17 AM Roger Titmuss  wrote:

> Hi as a newcomer to this part of the hobby I have a couple of questions.
>
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> 1. When using the M2 egg beaters how important is it to install a masthead
> preamplifier?
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>
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> 2. Again with egg beater will 30 watts be enough to get back to the bird?
>
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> I am using about 80 feet of RG213 to connect the antenna.
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> Many thanks
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> Roger G0AWY
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> 73
>
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_______________________________________________
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Not an AMSAT-NA member? Join now to support the amateur satellite program!
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_______________________________________________
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to all interested persons worldwide without requiring membership. Opinions expressed
are solely those of the author, and do not reflect the official views of AMSAT-NA.
Not an AMSAT-NA member? Join now to support the amateur satellite program!
Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb

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