[NLRS] Ku-band equipment at 10.45-10.50 GHz frequencies

[Dr. Gerald N. Johnson]

I have had several of those apart. There is almost no tuning for the RF 
stages, just short high impedance (about a quarter wave, at least 150 
ohms characteristic impedance) lines for bias and drain. There usually 
is a complex filter after the RF stages before the mixer. That will 
limit the performance at 10.4, yet there are several articles in MUD and 
CSVHF over the past decade or two on applying them at 10,368. The 
earliest ones cut out the filter and put in a new one or coupled to coax 
and used only the RF stages. I'm working on that to provide a preamp for 
my 10 G rover. While the filter will reduce the gain, there often are 
two or three RF stages and probably enough excess gain to keep the NF 
good a few hundred MHz out of the band pass filter. The bias feed chokes 
have a wide bandwidth, at least 20%.

I've been using a LNB feed horn from Direct TV without horn 
modifications, just bored the tapered diecast waveguide out to 3/4" 
diameter and stuck in a probe. I haven't tuned it, so far I figure the 
loss in tuning screws may exceed the improvement in match. It measured 
32 dBi at MUD 2009. Few have measured better though at the St Louis 
CSVHF one was recorded as 34, yet the actual measurement was 32 dBi. 
With the horn interior corrugated, it probably will make it work poorer 
to try to increase the aperture proportional to the frequency decrease.

Roving without a preamp, I have noticed Jon and Gary using rectangular 
horns hear better than I do but they also have preamps. Its known that 
round horns have a bit different beam widths in E and H planes, so the 
W1GHZ feed horn design is has a rectangular opening. Of course the 
original satellite application is for circular polarization and the 
round horn is appropriate.

I asked Paul at MUD last year if there was a loss feeding the offset 
dish with the round feed vs the rectangular feed and he thought less 
than a dB difference where the round feed may be slightly underfeeding 
the dish in one plane and overfeeding it in the other plane.

Some LNB depend on DRO for the LO and some commercial types use a PLL 
for better stability, likely at the cost of more phase noise. Stability 
of the DRO may be marginal for SSB bandwidth.

It has been suggested to supply a signal to put out an IF of 600 MHz and 
pick that from the IF and use it to heterodyne the desired signal to 
144, that way the final IF stability is as good as that local signal.

A recent article in DUBUS on using a DRO based proximity detector as a 
signal source that in a SSB receiver it sounded like noise. The article 
didn't mention the bandwidth.

There was such a LNB converted to a preamp at MUD 2008 that measured 
with a very respectable NF. The one I plan to use claims 0.8 dB NF and 
it has WR75 input. I'll probably test it with sun noise rather than my 
waveguide gas discharge 10 GHz noise source.

73, Jerry, K0CQ

On 5/9/2015 6:44 PM, John Toscano wrote:
>
>
> Does anyone want to hazard a guess (or better yet, measure performance) of
> a Ku-band "universal" LNBF (rated to operate at 10.7 GHz - 12.75 GHz) if
> one attempted to receive weak signals in the 10.45-10.50 GHz amateur
> satellite sub-band?
>
> I suppose the feedhorn could be milled out a bit to lower the operation
> frequency just as is done with DirectTV dishes that are modified for use at
> 10368 MHz, although less milling would be needed due to the higher target
> frequencies. But the application I have in mind would also use the LNB
> electronics since it would be intended for receive-only duty. I'm thinking
> it might be paired with an RTL-SDR dongle so the LO would not need to be
> changed, because the dongle should receive OK at 750 MHz - 800 MHz (the
> "universal" LNBF's use an LO of 9.750 GHz for the lower frequencies).
>
> Thanks in advance.
> John, W0JT/5
>