The linear transponders can also work FM. On the Vo-52 we had reserved days when the linear transponder was used for FM. The FM satellites are actually more efficient with their power budget. The reason is that the transmitter doesn't have to be switched on unless you detect the 67 Hz CTCSS on the uplink. Now, the satellite receiver can be made to run with less than 20 mAs, the OBC takes another 5 mA (on sleep). A total of 25 ma Standing current. At 5v, that is 100 mW of power. The solar panels of a cubesat will generate 2 watts from each side when full lit, so, we are well within the budget. As most of the time the satellite over the poles or the Pacific /Atlantic oceans, as most of the activity is over North America/Europe and Asia, the FM transmitter will remain switched off. When it is switched on, it operates class C. At 0.5 watts of output, the transmitter will draw about 1.5 watts of power (including the power chain). If it does this for about 20% of the time, the average transmit draw is 300 mW. The total satellite power budget is 400 mw, well within the power generated by the tiny solar panels. Now, let's look at the linear transponder. The receiver will draw the same 100mw of power, however, the transmitter will be always switched on and it will continuously draw 1.5 watts (probably more as the PA is linear and it has higher standing current). We are looking at a continuous current draw of 2 watts. This is beyond what the 1U solar panels can generate unless we can add attitude control and increase the size from 1U to 2U or 3U format which will triple the cost of the mission. These are interesting exercises. You have to throw in the eclipse periods as well (usually in eclipse for 33% of the orbit). the eclipse changes with the time of the year (figure this out for yourself). You can usually do the power budget calculations with a paper and pencil. It is great education. - f
On Tue, Feb 2, 2021 at 12:22 PM Mike Lucas documike@comcast.net wrote:
I’ll throw in my $.02 into the discussion. I listened to the Sputnik in 1957 on my Hallicrafters S20R receiver my Dad got me. I got my ham ticket a year later at the age of 12. . I started using the satellites in the early 80’s, using SSB, CW, Packet, etc. I built my Trackbox for automated tracking, antenna pointing, etc. The TAPR Group put out some great kits for those who wanted to invest the time & effort. I got great pleasure working DX on SSB & CW through the satellites, or downloading camera data, or rag chewing with the MIR space station crew regularly.
It was never “easy”, but that is what made it so worthwhile. It was a challenge, a learning experience, but so rewarding once you had success. I’ve always viewed the hobby as a way to expand knowledge, not just push a button & talk, anybody can do that. Trying to navigate the QRM on FM satellites is of very little interest for me. If I want to rag chew, jump on a repeater or HF & do your thing. Most everybody I’ve met over the years who’s truly interested in satellite communications welcomes the challenges.
My thoughts are the digital modes are also fine for satellites, the narrow bandwidth lends itself well without taking up a bunch of passband. I don’t see the negative at all in modes other than FM being the focus. If there’s some skills & learning required, it weeds those out who don’t want to put in the effort & commitment. Let’s face it, there’s not enough satellites & bandwidth for hoards of users to all be fighting for nothing more than a callsign & grid locator.
To net it out, IMO putting up geosynchronous or LEO FM satellites does not serve the best interest of the hobby nor promote a place for people who have a thirst for broadening their horizons. It’s about evolution, invention, & discovering new things. I can talk to anywhere in the world on EchoLink using my cell phone but what fun is that?
Mike N7ASZ
*From:* Doug Person doug@k0dxv.com *Sent:* Monday, February 1, 2021 3:58 PM *To:* amsat-bb@amsat.org *Subject:* [AMSAT-BB] Re: Cubesats
Jim... So I take it you're not much of a fan of FT-8. I'm totally with you. FO-20, FO-29, The Russian RS sats - these were great.
For me FM is almost impossible. By the time I hear them they are jammed. I'm not going to fight my way through for a call sign and a grid square. In the 80's and 90's you could at least get a minute or two in and know who you were talking to and what he was running.
Doug -- K0DXV
On 2/1/2021 3:47 PM, Jim Walls wrote:
On 02/01/2021 11:22, Brad Smith via AMSAT-BB wrote:
Has AMSAT ever taken a survey to find out what the membership wants for future satellites, or are we so insignificant that our wants do not matter, just as long as the dollars keep flowing toward AMSAT? How many of us would rather see a couple of FM birds put into orbit, rather than the difficult to work satellites? How many of us members have their fun on the FM birds? I know that I do, roving, etc. The simplicity of the FM birds made satellite radio fun. A handheld antenna and one or two HT's out in a corn field or a park, giving different grids to those who need them. Just an opinion.
Brad Smith KC9UQR
Brad, that is your opinion - which you are totally entitled to.
Unfortunately, there are several major categories of amateur satellite operations. Each has their advantages and disadvantages. There are amateurs who favor one vs the others. In other words, you can't please everyone with any one satellite, and there is not the budget to do it all.
Just for the record, although I have over 1,000 contacts on FM satellites, I really don't give a crap about conversations that consist of nothing more than a callsign and report (if you're lucky). I actually want to be able to TALK to people. That applies to non-satellite operations too. Fortunately, being very close to the US west coast, there were a few of us that could regularly get on the FM birds when they were way out to sea and actually hold conversations with others. The vast majority of my satellite operating time has been SSB on linear birds - preferably at something higher than LEO. I got to operate on AO-10, AO-40, and was on AO-7 on it's first day in it's second life. FO-20 and FO-29 were almost daily operation for me.
So for me, I would prefer one FO-29 class satellite over a dozen FM or digital LEO cubesats. GTP or HEO would be even better. But that's my opinion.
--
73
Jim Walls - K6CCC
jim@k6ccc.org
Ofc: 818-548-4804
http://members.dslextreme.com/users/k6ccc/
AMSAT Member 32537 - WSWSS Member 395
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