[Moon] 10 GHZ Options

[Serge Szpilfogel]

Hi Folks,

I recently received this valuable information, as I am struggling to get on
10 GHZ rx/tx.  After getting Bob's permission, I am sharing in the hope that
others will find this as useful as I certainly have.  Thanks so much, Bob!!

Serge VE1KG

 

 

The LNBF is the easy way to do RX I think. You can get a transverter, but it
will have sma connectors. You have to get a signal from and LNA at the feed
to the transverter, and any coax will be lossy. Waveguide is better, but the
"plumbing" is harder. Waveguide is rigid and will not bend. You can get
flexible waveguide, but it's harder to find and probably more lossy.

 

You can buy a preamp that has waveguide input and coax output (around
$200+), but you still have to build/buy a feed (see for example
<https://www.rfhamdesign.com/products/dish-feeds/offset-dish-horn-dish-feed/
index.php>
https://www.rfhamdesign.com/products/dish-feeds/offset-dish-horn-dish-feed/i
ndex.php), and the coax from the preamp to the transverter has to be short.
UT141 coax (normally used with SMA connectors) has a loss of 45dB/100ft, so
you wouldn't want to run much more than a few feet of it between the preamp
and transverter (depending on the preamp gain).  Using larger cable may not
be practical due to multimode propagation at the very short wavelength. This
means you probably need to mount the transverter out at the dish rather than
in the shack.

 

You can get coax in and coax out preamps (
<https://www.downeastmicrowave.com/product-p/l3-2ulna.htm>
https://www.downeastmicrowave.com/product-p/l3-2ulna.htm), but then you have
to run coax from a coax output feed the preamp. Evert ft of UT-141 will
increase your NF by 0.5dB, plus each connector may add another 0.1dB. 

 

The advantage of the LNBF is that it's small and light, there's no external
10Ghz connections to make and cable loss at the 618MHz IF frequency is much
lower - plus the LNBF has so much gain that cable loss of 10dB or more won't
affect the system noise figure. The disadvantage is you have to use an SDR
and figure out tracking and coupling to WSJT-X. That's a bit easier with a
regular rig, but most rigs won't tune to 618MHz. And of course you can't
transmit, though to make any contacts with a small dish you'd probably need
to generate 20-50W of power, and even then you'd only work the larger
stations.

 

Rather than an SDR you can use a 618MHz -> 2m converter. There's one here -
<https://www.ebay.com/itm/618-145-MHz-10368-10-GHz-RECEIVING-CONVERTER-3cm-1
0-368-shf-uhf-vhf-/223963858149>
https://www.ebay.com/itm/618-145-MHz-10368-10-GHz-RECEIVING-CONVERTER-3cm-10
-368-shf-uhf-vhf-/223963858149 - I have no idea how well it works, how
stable it is etc., but 618 to 145MHz isn't difficult to so, so I suspect it
probably works OK. My main concern would be the stability of the 473 MHz
oscillator module that they use for the LO. I suspect it's a simple OX
module. 1ppm drift of the IF would give you close to a 500Hz drift of the
converted signal and these things can drift from 10 to 50ppm over a large
temperature range. I suspect it would be good enough to get you within 1kHz
of 10368 and the drift rate (indoors at a constant temperature may be good
enough to allow decoding of signals. It would be better with a VCTCXO
frequency source, or a synthesized signal based on an OCXO. I don't know any
commercial converters like that though. They'd probably be too expensive and
you wouldn't expect a very large market for them. This one looks like a
cheap and simple way to get 618 to 145MHz conversions and would be an
alternative to an SDR of you already have a 145Mhz radio. 10368 would
probably then be found in the 144.95 to 145.05 Mhz region. It probably
wouldn't be exactly at 145.

 

So then you'd go   10368 -> LNBF -> 618 -> 618/145 converter -> 145 radio ->
PC/wsjt-x

 

Hope this gives you some ideas Serge.

 

Your trip to PEI sound like fun. He in Maine the covid-19 situation is
pretty good. Certainly much better than many other parts of the US. We are
both lucky to be in relatively safe areas.

 

73

Bob, KA1GT