April 2018 - AMSAT-BB - mailman.amsat.org

Re: [amsat-bb] Lindenblad or DCA??? (neither?)
by Robert Bruninga 02 Apr '18

02 Apr '18

Neither are going to hear much on the horizon for typical weak amateur satellites where they spend most of their time. These antennas have gain that is at best 3 dBi It is very important to understand that all Low Earth Orbit sateliltes spend more than 70% of their in-view time below about 22 degrees. And satellites that low are 6 to 10dB farther away than when they are high up above 45 degreees. See the scale drawing of an orbit on the right side of this page: http://aprs.org/LEO-tracking.html The DCA and Lindenblad and Eggbeaters and all other such omni antennas are designed to give good performance over all elevation angles for sateliltes. But to do this, they are equally poor in all directions. This is wasteful since you need less gain at high elevations and much more gain at lower elevations for LEOS (98% of all amateur sateliltes?). So you have two choices. Use an omni and only get high passes (less than 30% of all time-in-view), and hear only strong satelites down on the horizon... Or, use a terrestrial style antenna with gain on the horizon... but by definition, these will have a null higher up, and for a typical mobile whip, that null might be at 15 or 20 degrees which is right where satellites spend their most time. Best option is to switch back and forth... but then if you are going to be sitting there, y ou may as well control a beam... (I still have not found such an ideal antenna (though lots of claims are made)... On the other hand, if I am going to simply want OMNI coverage for satellites above about 30 degree, then I prefer the simple 19.25" quarterwave whip over a big ground plane. Because this gives 5 dBi on 2 meters and about 7 dBi on UHF and is nothing more than a 19.25" piece of wire sticking up from a large ground plane. Much easier than all those other omnis that provide less gain everywhere. Though I have never done rigorous studies to prove its performance. But what could be simpler to test. If I had any of those complex omni's., I'd love to do such a comparison some day... after I retire... Bob -----Original Message----- From: AMSAT-BB <amsat-bb-bounces(a)amsat.org> On Behalf Of Hans (BX2ABT) Sent: Monday, April 02, 2018 10:16 AM To: amsat-bb(a)amsat.org Subject: [amsat-bb] Lindenblad or DCA??? Hello Joe, Thanks for the reply, appreciate it. Yes, the phasing harness is different, but my guess was that this shouldn't make a lot of difference as long as you get the 90 degree phase and the impedance right. If you look at the radiation patterns for both then they are nearly identical, hence my question if they are not one and the same thing. It came up here because I have two DCAs right now, one for 2m, one for 70cm, both RHCP, no pre-amps. I do hear some birds, but signals are very weak. The 2m one works fine when receiving the NOAA wx sats, so I was wondering if the 30 degree angle of the Lindenblad would be better for amateur sats. I lack the knowledge to understand the difference between, what you say, the geosynchronous orbit of NOAA sats and the LEO orbits of our sats. NOAA wx sats are also LEO sats, not? I'll see if Google turns up something there. It's easy for me to change the tilt of my DCAs to 30 degrees, so I'll try that this week. Should be a nice experiment. 73 de Hans BX2ABT > Hans, > > Here are links with antenna patterns for the DCA: > > https://drive.google.com/file/d/0B0Dkk87YYl-xX2gzLXk5MHZKVU0/view > > and the EZ-Lindenblad: > > http://www.amsat.org/wordpress/wp-content/uploads/2015/08/An-EZ-Linden > blad-Antenna-for-2-Meters2.pdf > > The difference is in the lengths of the "RG-59 (75ohm) phasing harness" > and dipoles to achieve a 50 ohm impedance at the required frequency. > > The angle of the crossbooms affects the directivity of the antenna, in > the examples given, 60 degrees for a NOAA satellite in a > geosynchronous orbit and 30 degrees for a LEO orbit. > > The only differences I see are the 50 ohm load feedpoint and the > Lindenblad dipoles are not exactly in the same plane as the DCA. > > -73, Joe Spier, K6WAO > President, AMSAT _______________________________________________ Sent via AMSAT-BB(a)amsat.org. AMSAT-NA makes this open forum available 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

1 0

Lindenblad or DCA???
by Hans (BX2ABT) 02 Apr '18

02 Apr '18

Hello Joe, Thanks for the reply, appreciate it. Yes, the phasing harness is different, but my guess was that this shouldn't make a lot of difference as long as you get the 90 degree phase and the impedance right. If you look at the radiation patterns for both then they are nearly identical, hence my question if they are not one and the same thing. It came up here because I have two DCAs right now, one for 2m, one for 70cm, both RHCP, no pre-amps. I do hear some birds, but signals are very weak. The 2m one works fine when receiving the NOAA wx sats, so I was wondering if the 30 degree angle of the Lindenblad would be better for amateur sats. I lack the knowledge to understand the difference between, what you say, the geosynchronous orbit of NOAA sats and the LEO orbits of our sats. NOAA wx sats are also LEO sats, not? I'll see if Google turns up something there. It's easy for me to change the tilt of my DCAs to 30 degrees, so I'll try that this week. Should be a nice experiment. 73 de Hans BX2ABT > Hans, > > Here are links with antenna patterns for the DCA: > > https://drive.google.com/file/d/0B0Dkk87YYl-xX2gzLXk5MHZKVU0/view > > and the EZ-Lindenblad: > > http://www.amsat.org/wordpress/wp-content/uploads/2015/08/An-EZ-Lindenblad-… > > The difference is in the lengths of the "RG-59 (75ohm) phasing harness" > and dipoles to achieve a 50 ohm impedance at the required frequency. > > The angle of the crossbooms affects the directivity of the antenna, in > the examples given, 60 degrees for a NOAA satellite in a geosynchronous > orbit and 30 degrees for a LEO orbit. > > The only differences I see are the 50 ohm load feedpoint and the > Lindenblad dipoles are not exactly in the same plane as the DCA. > > -73, Joe Spier, K6WAO > President, AMSAT

1 0

Re: [amsat-bb] "CHORDS" and "Tiangong-1 " Predictions.
by gw1fky＠aol.com 02 Apr '18

02 Apr '18

Hi all, I have been following on the "Amsat-bbs" the various messages and information regarding the predictions on the Re- entry of "Tiangong -1" Of course the re-entry transpired in the ball part as predicted at approx. 00.15 hrs GMT. Many will be aware of the work carried out by " CHORDS " but perhaps many have never even heard of the organisation and its work. They are greatly involved with the work and tracking of "Space Debri" and the concerns. Tiangong -1 with co-ordination from a number of parties was fitted with an "REBR Probe" - It logged an sent various data from the spacecraft to enhance its locations for predictions. I understand that further work and developments of the probe have also been made recently so many may find this topic of interest. Ken Eaton GW1FKY

1 0

1296 ISS bounce
by Bob- W7LRD 02 Apr '18

02 Apr '18

Here's something to think about. L band is a lot of fun. We do get 24 hours once a week (not complaining). With several ISS passes every day. It is a good reflector. Plus we can use CW, SSB, many digi modes. Just google it. 73 Bob W7LRD

1 0

DM07 Yosemite QSOs
by Bob Keating 02 Apr '18

02 Apr '18

BTW, All of my QSOs from DM07 in Yosemite were uploaded to LoTW under my N6REK/P call sign. Hope this didn't cause any extra hassle, I am a bit new to this... my apologies!!! 73, Bob N6REK

1 0

Tiangong1 reentry - "live tracking"
by John Mitchell 02 Apr '18

02 Apr '18

You may find this twitter post about the 'live' on-line tracking sites interesting: https://twitter.com/Marco_Langbroek/status/980549243701268482 john mitchell KK4VUR

3 2

Grid DM07 Yosemite QSOs
by Bob Keating 02 Apr '18

02 Apr '18

Thanks to everyone that contacted me while we were enjoying our "mini dxpedtion" to Yosemite. I had a total of 43 QSOs on all four FM satellites over a span of 4 days. I have uploaded my QSOs to LoTW and QRZ.com and will upload to eQSL this evening. There were a couple of call signs that I apparently did no get correct. I had them listed in my log as KA7FBP QSOed on 3/29 and KK6DDT and K7ULF both QSOs on 3/28. If this looks like your call, please let me know so that I can correct my log. Thank you! 73, Bob, N6REK

2 2

FW: entry time
by Andy 01 Apr '18

01 Apr '18

FYI From: Gil Carman Sent: Sunday, April 01, 2018 8:56 PM To: Andy <w5acm(a)swbell.net> Subject: Re: entry time StratCom has confirmed that it entered at 7:16 pm CDT, a southbound pass into the south Pacific.

1 0

Fwd: Polluted time server causing issues with digital modes
by Brad WF7T 01 Apr '18

01 Apr '18

I am forwarding this for anyone interested. I think my discovery is correct and invite additional review/scrutiny. 73 Brad WF7T On Sunday, April 1, 2018 at 12:21:36 AM UTC-5, Brad WF7T wrote: > > *I have discovered a polluted time server that is wreaking havoc with > time-synced digital modes, and worse. For everyone using round-robin style > time synchronization like Dimension 4, please remove the following time > server: rackety.udel.edu <http://rackety.udel.edu>.* It is consistently > sending time sync corrections that are between 10 and 41 seconds different > than every other SNTP server in the world. This will cause your PC clocks > to skip this amount and stay that way until another time sync occurs, e.g. > 5 to 15 minutes later, causing another massive time correction by another > accurate time NTP server. Please pass this information along to all > digital-active hams. > > While this amount of time is not of any consequence for RTTY, PSK and the > like, this behavior is detrimental to WSJT and QRSS modes. Terrestrial WSJT > modes like FT8, WSPR, Meteor scatter MSK144, and EME modes fail to decode > and will cause out of sequence transmissions. > > I also noticed a number of out-of-sequence FT8 tranmissions on 40M this > afternoon (BTW, open early to EU), which clued me into the situation. This > messed up time server could have been a contributor. > > *Remove or disable the following server: rackety.udel.edu > <http://rackety.udel.edu>.* Apparently it has been getting increasingly > worse since 3/8/2018 or so. I only discovered this tonight while I was > decoding WSPR on 474.2KHz (630M) and saw a huge time jump and lack of > decodes of some fairly strong signals. > > And yes, this is also an InfoSec problem. Time bases are important for > MANY Information Security purposes, but beyond the scope of this discussion. > > Excerpts of my Dimension4 time-base logs below. Please contact me with > questions/comments. > > 73 Brad WF7T > Nashville, TN > > --- > > ... First noted occurrence in my time-base logs > > 2018-03-07 10:36:44.461 -7.962988e+000 rackety.udel.edu SNTP <-- 7 second > correction > 2018-03-07 10:39:52.480 7.980464e+000 clock-1.cs.cmu.edu SNTP <-- fixed > on next round-robin sync > > ... Persists for a second day, appearing to get worse > > 2018-03-08 09:17:25.217 -1.015543e+001 rackety.udel.edu SNTP <-- 10 > second correction > 2018-03-08 09:20:35.240 9.963055e+000 clock-1.cs.cmu.edu SNTP <-- Fixed > on next round-robin sync > > ... Jump ahead a week; yup, getting worse > > 2018-03-15 05:34:10.880 -1.761963e+001 rackety.udel.edu SNTP <-- 17 > second correction > 2018-03-15 05:37:29.176 1.812267e+001 ntp.cais.rnp.br SNTP <-- > Fixed on next round-robin sync > > ... Skipping ahead to tonight; SNAFU > > 2018-03-31 23:29:34.849 -4.165045e+001 rackety.udel.edu SNTP <-- 41.6 > second correction! > 2018-03-31 23:33:35.421 4.192192e+001 ntp2.kansas.net SNTP <-- fixed on > next round-robin sync > >

4 3

Article about cubesat space junk
by John Brier 01 Apr '18

01 Apr '18

Not your typical space junk article. It leads with the release of 100+ sats by the same Indian rocket that launched AO-92. https://www.wsj.com/articles/we-need-satellitesa-speeding-mass-of-space-jun…

1 0