[MAMS] 47 GHz

Mon Nov 13 13:38:51 EST 2017

Essentially all antennas with gain have side lobes. We had problems 
copying K0KFC in the 10 G September rove though others in his yard had 
great signals he was often weak. Gary suggested that he had peaked a 
side lobe. I switched to calling him on CW and worked his weak signal 
successfully.

In years past I have suggested an adjustment in the feed to underfeed 
the dish for initial alignment could be a solution for difficult aiming 
and for side lobes.
http://geraldj.networkiowa.com/papers/2012/dishgainreduction.pdf

Basically a larger feed horn aperture underfeeds the dish.

Side lobes could come from defects in the dish surface too. 47 GHz could 
be nearly as picky as optical.

I think it was N5AC a few years ago suggested the large dish on 10 G 
while roving be moved by a slow speed servo instead of by hand so as to 
be easier to find the peak.

On year I sat next to MHC or KFC on Buck hill running my 18" dish next 
to his 1meter plus dish with preamp and 10 watts while I have no preamp 
and only 3 watts and I made more contacts than the big dish operator. I 
think it was because the big dish beamwidth was so narrow they passed 
the peak between the dits from the rover beacon.

73, Jerry, K0CQ

On 11/13/2017 10:51 AM, Zack Widup wrote:
> Yeah, it was more difficult to align than my 10 GHz dish (we used 10
> GHz for initial alignment). I noticed that the dish I have, an Andrew
> VHLP1-370 which is meant for use at 39 GHz, works fine on 47 GHz but
> has several sidelobes on either side of the main lobe. Making sure I
> had the main lobe was the hardest part.
>
> 73, Zack W9SZ
>
>
> On Mon, Nov 13, 2017 at 10:14 AM, Dr. Gerald N. Johnson
> <geraldj at netins.net>  wrote:
>> Very good. Looks like the 1 foot dish at 47 Ghz has abaout 41 dB gain so a
>> quarter mw works out to about 2.5 watts ERP. Unfortunately 1.5 degrees
>> beamwidth for difficult aiming. Not everyone is consitently successful with
>> the 5 degree beamwidth of the Ku band TV dish on 10 GHz. The 3 KW ERP sure
>> helps distance on 10 GHz.
>>
>> 73, Jerry, K0CQ
>>
>>
>> On 11/13/2017 12:58 AM, Zack Widup wrote:
>>>
>>> Pete K9PW came down to my area on Saturday Nov. 11 to see how far we
>>> could work on 47 GHz. Pete is using the new DB6NT system that has a
>>> receive preamp and a power amp with about 100 mW output (I think). He
>>> has a 1 foot diameter dish and a horn antenna. His station is
>>> configured to use a baseball switch so that when one antenna is on
>>> transmit, the other is on receive and vice versa. That way he can
>>> rotate the setup 90 degrees to use the other antenna. I have a basic
>>> DB6NT harmonic mixer with no preamp or power amp. I estimate the power
>>> out is 150 - 250 uW. I also have a 1 foot diameter dish.
>>>
>>> We started out with me on a hill on a country road that stretched for
>>> some miles. We worked at 5, 10 and 15 km distances on SSB with Pete
>>> increasing distances from me along the road. At 5 km we were pinning
>>> each others' s-meters. Pete was still pinning my s-meter at 10 km and
>>> I think he was hearing me at 40 over 9 then. At 15 km he was 40 over 9
>>> at my end and and I think I was 20 over 9 at his end. These were all
>>> line-of-sight paths.
>>>
>>> Pete then drove to another hill which is line-of-sight from where I
>>> was. I was in EN60af and he was in EN50ue. It was about a 25 km path.
>>> I was copying him at least 20 over 9 from there and he was copying me
>>> 10 dB over 9. We made another QSO on SSB on that path.
>>>
>>> Things were going a lot better than we expected, so I moved to the
>>> hill I like to use for contesting in EN50rl. The EN50ue to EN50rl path
>>> is 40 km. This is the longest line-of-sight path that I know of
>>> anywhere in this area. I got set up there and, once we got the dishes
>>> aligned, I was copying him S9 and he was copying me S4 to S5. We
>>> worked on CW this time.
>>>
>>> This was far better than I expected and it made my day! I'd been
>>> wondering for a long time if a couple hundred microwatts could make
>>> that path.
>>>
>>> 73, Zack W9SZ
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