SSB Power Consumption

demonboy

demonboy

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I'm eyeing up the Icom M801 as my possible SSB solution. It's an area I've yet to investigate so I'm window shopping at the moment and one of my concerns is power consumption.

The M802 says it uses 3amps to receive and 30 amps to send. Is this a lot or is this acceptable? I really haven't a clue! /forums/images/graemlins/blush.gif
 
(This is Richard, not Becky.)

30 Amps total consumption at 12V is 360 Watts. 150 of this is going up the aerial. The rest of the power is going through the intermediate stages, the oscillator, modulator, filters, and lighting of the screen and push buttons etc. etc.

It doesn't seem outrageous to me.

It will only be consuming this power when you are transmitting. /forums/images/graemlins/grin.gif
 
Hi Richard,

I should have edited that thread. Apparently those readings are for the 24v version, so I assume the 12v version doubles those figures.
 
I would be very surprised if it did. The transmitter is rated at 150 watts so the unit might get to 300 watts inc fans etc but surely not to 600. Incidentally, on SSB (which is what you will be useing) the average tranmitted power whilst speaking is somewhere round the 50 watt mark. Only on FM will you output the 150 all the time you transmit. So the 300 (if that is what it is) is unlikely to be reached in practical use.

To get back to your original question, the max power is typical and in most cases is governed by regulation. So it will be the same on other makes / models. And it is a maximum - you can use less if you want.

The thing I would wonder is why you would buy this model rather than go the second hand ham radio route and simply have it snipped to use the marine frequencies. As a ham operator, I would not consider relying on SSB as an "I need help" device when the satellite phones are available. So to me SSB on a boat is much more for chatting and weather fax etc. In which case you dont need the DSC bit or really the "marine" bit either.

Just a personal view but these sets are expensive so best talk to lots of people before deciding
 
I have the similar 802 and it uses 2-3 watts receiving and up to about 30 to send (12v). However the consumption is in short bursts. The other day after 15 minutes of emailing I'd actually only lost a few amp hours out of the bank. So unless you plan to spend hours transmitting I would not worry too much. The only issue is that these radios do like a peppy battery and if you transmit when the bank is tired you will a) get a poorer transmission and b) slug anything else on the system.

Birdseye's provocation that you are better off with a satphone prompts another debate which has been well rehearsed elsewhere in these posts. I know some satphone users who are happy with them and some who are not. A good satphone installation needs a decent aerial and that drives up the cost somewhat.
 
It's an interesting point about second hand versus new. I'm naturally assuming that the newer models will be less power hungry and not generate so much heat, two of my main concerns. I also assumed they would have all filters built in and would literally be plug-and-play, as opposed to earlier models that require a steep learning curve in setting the kit up.

I'll mainly be using it for weatherfax and email but would like the option to transmit as we will be living aboard and I like the idea of communicating with other live-aboards and having a new 'toy' to learn and play with. Also I already have a DSC VHF so I don't need that functionality.

With these points in mind do you think I would be better off saving myself a good grand or so by buying second hand set instead of the new M802? If so could you make any informed recommendations on earlier models?
 
I would have no doubt about going second hand if you didnt want the DSC. And I would go ham since there is a lot of very good ham kit about at sensible prices. For example I use a ham transceiver in my boat which cost me £400 virtually brand new and still in the box. Using it in Spain I had no trouble in talking to other hams in Siberia and S America (as well as the UK etc). The ham kit seems just as good as the marine (you can buy ICOM if you wish but there are alternatives) but the markey is much bigger and maybe the kit is a bit less robust. That said, I have had no probs at all in 5 years albeit in a dry modern boat.

Many of the natter nets and weather nets are on ham frequencies - which brings me to licenses. The ham ticket is now pretty easy to get and many of the most useful nets are controlled by hams who will not respond to a pirate. (You can simply make up a ham call sign but it will show through at least at first.)
 
The rest of the power is largely being dissipated as heat in the heatsink.
The oscillator and driver stages will use small current in comparison.
A class C power output stage is at very best only probably about 60% efficient. Efficiency losses also rise with frequency.
You can not directly corrolate RF output power to power consumption, as there are losses throughout the system, particularly in systems using random bits of wire with ATU's.

Steve.
 
If its SSB it can't be a Class C output stage as its a nonlinear amplifier. Class C is only good for continuous carrier type transmissions such as FM. For SSB Class AB1 is more likely in which case it might be safer to assume 50% efficiency. (the theoretical is slightly more, but is never achieved in practice) Plus the driver stage will need power (at 50% efficiency as well), and you can see how the current drain adds up. 30 Amps peak current drain is not unreasonable for the output powers quoted.

There is no reason why very recent kit will be any more efficient that kit a few years old. After all, you can't deny the laws of physics.

Current drain on FM or AM (usually one sideband plus inserted carrier on some of these sets) is less peak, but higher average. The PA cooling in 'Amateur equipment' often isn't up for continuous rating at full power, which is why the sets are rated at lower powers for these 'continuous duty transmissions'.

Hope it all makes sense.

I had to design these things once.
 
So if I can get the M710 for about £500 rather than the M802 for £2000 then I should be ok with my requirements? (That's if the M710 is CE marked.) Anyone any ideas of comparisons between the two?
 
The current drain is as you say (for 12 volt) for the 802 (and other similar powered radios) - as others say on transmit the current depends on the power setting, the nature of ones voice and the gaps between words.

What most are not aware of is that if the radio is connected directly to the batteries there is a constant low level drain (can't remember what it is but is not insignificant if left for long periods) to the radio's oscillator heater which is always on in marine sets. I avoid that by connecting the radio's DC supply at the main service battery isolator switch so that one has the large (hopefully) conductors between the battery and the isolator and the lesser but still adequately sized ones to the radio from there (and should be fused, as normally sullied with the radio). If the batteries are isolated when one leaves the boat the radio's heater is isolated from a power source.

John
 
Unfortunately the power drain is one of the downsides of SSB. A lot of people are choosing to use sat communication instead for internet and calls.
 
Sat com is still very expensive though, and it's not as much fun /forums/images/graemlins/wink.gif

I guess I need to think about my requirements. The top two were weatherfax and email, and the secondary reason was for two way communication (especially in cases of emergency). I can do all this with both SSB and satcom and satcom is far less a drain on the battery. But that's another thread altogether.
 
Yes sorry, I was forgetting that it's not possible to drive sideband that deep without considerable distortion.
So the 50% or less is probably about right.
John makes a valid point about the reference oscillator oven, which will take a few amps undoubtedly.
If anything for more recent kit, the broadband power modules, common in todays gear, are less efficient than their discrete counterparts.
The only real way to get a true efficiency of the whole system is to approximate ERP (from antenna near field measurement).
I think many people would be suprised just how little is actually radiated...what could we say on an average installation with a short antenna tuned by ATU...say 30 watts erp at 2182khz..after all the feeder/grounding losses are taken into account.
Just a guesstimate but probably not that far off..only 10% of input power, although the power amplifier is working less hard at these lower frequencies the efficiency losses in the antenna circuit will be severe.
The power will of course rise as the frequency rises, and peak around the resonant frequency of the antenna and the centre design freq of the PA, so maybe 60 watts erp at 20MHz...
It would be interesting to draw the efficiency curve vs frequency for the average yacht installation...has anyone done this??
Bring back valves and National service I say!! I still use the FT101 at home, and it still stands up against any modern transceiver both in power and quality.


Steve
 
You should allow for 30A current draw on TX for all of the Icom radio's you are looking at.

The big advantage of the new kit over the M710 are built in DSC and remote head mounting.
The M710 is one big box.

The M710 and M802 are not CE marked.
The new M801 will be

Ham SSB unit are not designed for the marine market, this could lead to prblems in time

Hope that elps a bit.

Regards
 
Icom 710

The 710 will do you fine. Be sure you get the DSC compatible version so you can add a DSC controller later if required. My experience has been that you can yell Mayday all day on 2182 KHz and get no response so you really need 2187.5 DSC for distress alerting.

My 710 draws 3A receiving and 18A transmitting - at 12v.

BTW the efficiency of the set is more dependent on the quality of earthing than any other factor.
 
Re: Icom 710

Just to add to the pot,
The GM110 DSC unit for the M710 has a retail price of £1999.
So maybe the m802/801 would be the better option all round.

Regards
 
So you are looking at 2k for the pukka marine set or 500 for the ham. Jon Brooks tells you that the ham set is not designed for marine use and he should know. But its ham sets that the majority of sailors seem to use and few appear to get problems in todays dry boats.

Really depends on what you want to use it for. If you want it for calling for help, there's no choice. Go for the pukka kit. But think first about the alternatives such as EPIRBS, or satelite phones. Few of us can afford every possible bit of electronics, most of us have to chose between.

If you just want it for chat, then my personal view is that you would be daft to spend the full money for a new marine set when the ham is a quarter of the figure. Might only last (say) 5 years instead of 10, but I doubt it from my experience.
 
In reality, there will be very little difference in the electronics between a Ham set ,a land mobile SSB and a Marine SSB.
All will be built around the same circuit boards/designs. The differences are rather what is not there on a Marine/Land mobile set as opposed to all the bells and whistles on a ham rig.
Marine sets may be ruggedised, and probably have a xtal oven to compensate for frequency drift from temperature/humidity.
Basically the whole thing is a con...not just from Icom but from all the manufacturers...the ham market is much bigger so one pays less for that version of the set...but you pay three times as much for a marine set that has much less in it than a ham rig because the market is smaller, and because the leisure marine market is fairly captive...in reality only having two choices for SSB radios...and because there is no serious competition for the European Market because of the crazy rules and type approvals, they can more or less charge what they like.

Steve.
 
Very few amateur sets meet the spurious emission requirements for marine. Also, I am at least reasonably familiar with radio /forums/images/graemlins/smile.gif but its been more than a few times that I have operated an amateur set and wondered what the hell finger trouble it was that stopped it transmitting - for amateur work is just embarrassing but for a marine emergency with panic also thrown in could be serious. A marine set is almost foolproof in that respect, especially the DSC mf/hf ones where one just has the red switch to push.

Getting back to the original question, I have just measured the recieve current on an 802 and it was 2 amps. The oscillator heater seemed to settle at drawing 100mA (regardless of whether the set was turned on or not) - the temperature in the boat was 28C and it may be that the heater is temperature clever and draws less in warmer environment, maybe Jon knows if that is so).

Regarding some of the comments some have made about calling on 2182 - unless one is within 50 miles or so of a shorestation bit more or less depending on the set up on the particular boat, but somewhat further during the night, one is generally wasting ones time calling on 2182 to a station that maintains a watch on that frequency. Propagation will not support you.

2182, which harks from days of past, has been mostly displaced by VHF which has similar coverage unless one has a very competent mf station on board (generally meaning big antenna and good grounding to the extent not possible on a small boat), if one needs to call on ssb then choose a frequency which will be supported by propagation at the particular time of the day - the best frequency will almost never be in the 2MHz band unless you are very close to the station called.

There is plenty of material on the internet on how mf/hf propagation works.

John
 
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