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Kilrah

High speed data RF transceivers

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Hi all,

A friend of mine just gave me this link: http://www.aerocomm.com

They sell trancseiver modules in 868, 900 and 2400MHz, with speeds up to 880kbps and power up to 200mW in 2.4GHz (have not checked the other ones).

He had bought a development kit 1 year ago for $1000 for a full scale car telemetry application. He said that after experimenting he found out that the range was far better than with MaxStream modules (the aerocomm one was a 200mW 2.4GHz one, don't know for the MaxStream one).

I was wondering what the price for the module itself was so I checked it out. Turns out to be $100/pc, and the DK is now only $200, so the price of 2 modules, but it includes 2 PC interface cards, cables, power supplies, antennas... and 2 modules!

So I've ordered a 2.4GHz 200mW DK straight away.

BTW all their different models are exactly the same price.

Maybe at last a reasonable alternative to the audio channel?

Thought it could be useful to some of you, thus sharing the link...

Regards,

Kilrah

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Little update, during March Maxstream have a very interesting offer, that is if you have bought a competitor's development kit within 90 days they offer you one of theirs for free.

I'll get my aerocomm kit tomorrow, and order the maxstream one right away :D

$200 for 2 kits instead of $1400 when at normal price is quite cool and really gives a good occasion to try!

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I was at the San Francisco hosted Embedded Systems Conference today and spoke to Maxstream. They mentioned that the free offer is only valid until the end of the month (March 2005). So, all those interested in this deal should keep that in mind.

One thing I learned was that the 1 Watt module is only FCC registered if you use *their* Yagi antenna. It is over a foot long and made of hefty aluminum channel. All other antennas invalidate the registration (even a lowly whip). Of course this is not an issue if you aren't interested in FCC Part 15 compliance.

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Seems to work!

I received the Aerocomm DK yesterday, and the Maxstream is on it's way :)

The $100 shipping of course are not offered <_<

Maxstream have quite an aggressive marketing policy, as my friend told me from the emails he exchanged with them, and it's confirmed by mine:

I think you will find no problem in chosing which manufacturer to purchase from once you try the MaxStream wireless RF modems

I actually already know which one I'll choose for this application, as figures don't lie, and Maxstream radios only transmit at 19.2kbps vs 882kbps for the Aerocomm ones. Aerocomm claims 170kbps simultaneous bidirectional throughput, that's a lot!

Assuming I want to send R/C data trough the modules, it's way too much for the Maxstream ones to handle. It's already around 5kbps uplink if the goal is to have a decent number of channels with a good refresh rate...

Maxstream's advantage is the sensitivity of the receivers, with 4 times less power the range should theoretically still be longer. I like this, but unfortunately it's not enough.

(Of course I'm only talking about the 2.4GHz modules).

The aerocomm kit is really good, and the modules and antennas can then directly be removed to be used in the application.

Will have to do some range testing, and also check for interference with the video TX. At least there is no problem with adjacent WLAN from what I've tested yet.

post-8-1110361880_thumb.jpg

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Maxstream radios only transmit at 19.2kbps vs 882kbps for the Aerocomm ones. Aerocomm claims 170kbps simultaneous bidirectional throughput, that's a lot!

The Maxstream throughput data rates depend on the module. The Xstream is 19.2kbps. The Xcite is 38.4kps. The Xtend is 115.2kbps.

Aerocomm's 882kbps is the interface/raw RF data rate. That spec does not factor in the required overhead; the data rate appears to be limited to 115kbps when used in the common RS232 interfaced radio modem mode.

I was interested in the Aerocomm 900Mhz modules. From looking at the data sheet, the highest effective full duplex data rate that I found was shown as 24kbps. So it seems the throughput rate depends on the module.

Assuming I want to send R/C data trough the modules, it's way too much for the Maxstream ones to handle. It's already around 5kbps uplink if the goal is to have a decent number of channels with a good refresh rate...

With Aerocomm, the published synchro time is up to 1500mS (avg 750mS). That might be a problem for direct R/C control of a fast model. In contrast, the Maxstream synchro times are typically 50mS. And, they claim to be able to support 5mS synchro times too (per the Maxstream sales Engr I spoke too).

In any case, at this point I am not sure which brand is the best. There is good and bad with both. Aerocomm's prices are lower and Mouser sells them, so that is a plus.

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The Maxstream throughput data rates depend on the module. The Xstream is 19.2kbps. The Xcite is 38.4kps. The Xtend is 115.2kbps.

That's right, I only compared the XStream ones because they are the only ones they have in the 2.4GHz band. As I (unfortunately) can't use 900MHz here...

Aerocomm's 882kbps is the interface/raw RF data rate. That spec does not factor in the required overhead; the data rate appears to be limited to 115kbps when used in the common RS232 interfaced radio modem mode.

Yep, it's the RF data rate in all conditions, and the maximal interface rate.

There's no limit at 115200 bps, but it's the highest available value on a PC. The baud rate can be customised up to 882kbps (2 registers), as long as you're able to set one in your host that matches it at +/- 3%. The module's operation doesn't differ at all if you change the baud rate.

The overhead is taken into account in the 170kbps full duplex spec.

I was interested in the Aerocomm 900Mhz modules. From looking at the data sheet, the highest effective full duplex data rate that I found was shown as 24kbps. So it seems the throughput rate depends on the module.

The 900MHz ones are specified at 76.8kbps RF rate. So that makes sense.

The sync time effectively could be an issue, but I was planning to use antennas with enough gain not to lose connection. From what I've tested loss of sync happens quite late. When the signal gets very weak, the rate will fall down near to zero, but sync is still kept.

And the goal of sending R/C data by this way is to have the onboard unit doing all the control tasks, including changing to autopilot mode if the link drops for a certain time like 1 second. Link drops being less likely to happen close to the ground station (and thus to the ground itself), I think that there should be enough time to recover.

Of course, like always, there are advantages and disavantages with each one.

That's the good point of MaxStream's offer :)

From what I've seen the prices are the same for Aerocomm's AC5124 (Mouser) and MaxStream's 24XStream (Digi-Key), that is $100...

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Sync Time issue: With microwave RF, especially at 2.4Ghz, intermittent signal loss can occur often. Even at very short distances. Sources of this are due to RF multipathing, antenna orientation, cross polarization, etc. With the high sensitivity of these RF modems, some of these issues can be exaggerated when used in mobile apps.

A good example of this can be seen in downlinked airborne video as short video or sync loss, even when the signal is otherwise strong. If you do not experience these where you fly then you are probably going to be fine with the Radio Modems. But, keep the re-sync time in mind so that surprises are avoided.

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OK.

I was also hoping that FHSS modulation would be much less interference-prone than our good old analog FM transmitters... Am I wrong?

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Some of the basic RF issues do not change much (antenna alignment, multipathing, etc). Part of the advantage with FHSS based devices is the included error checking and retransmission features. That is what makes it robust. But that still requires a reliable mobile connection to work seemlessly. The FHSS does allow more tolerance in the presence of coherant RF sources, but that is not a problem that I have run into where I fly.

In my opinion, the biggest FHSS advantage is Gov compliance related. In the USA, the allowed ERP RF cannot exceed about one milliwatt. With FHSS, a "1-watt" RF signal will effectively have ZERO average power. That is allowed. So, decently powered devices can be certified for use by unlicensed consumers under the FCC Part 15 rules.

Overall, I have seen & heard mixed stories about wireless data installations. When it works, it is great. When it doesn't, it can be a significant frustration. I have experienced the latter with a relative's wireless link at their house. It works in some spots, but move two feet and it is no-go. Moving the base station around only moves the dead spots from "here" to "there."

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is up to 1500mS (avg 750mS).

Sync time isn't actually a ptoblem, 'cause resync doesn't occurs during normal operation. Two modules can remain synchronized even in sleep state (2 minute for 4490/4790, 2 seconds in 5124)

What is really meant, is data latency. Both Maxstream and Aerocomm have published these specs, and here is the result:

1) All Aercomm except 5124 (not described) - 9-23 ms (depending of operation mode), add some milliseconds here for interface timeout

2) Xtend (9600 bps) - 94 (!) msec, i.e. 1/10 of second

3) Xtend (115200 bps) - 9.4 ms, but this setup is very, very prone to screening, interference, and, yes, still really slow.

So you see, we cannot control out UAV operatively if it reponds our commands slower than 1/25, or, maybe, 1/33 sec (an industrial "real-time" criteria).

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They sell trancseiver modules in 868, 900 and 2400MHz, with speeds up to 880kbps and power up to 200mW in 2.4GHz (have not checked the other ones).

A little note here: 882 kbps module (5124-xxx) has been canceled at May, 2005.

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Okay thanks :)

But as we aren't doing mass production it's no problem, I've still found a number of dealers who still have stock!

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But as we aren't doing mass production it's no problem, I've still found a number of dealers who still have stock!

Oh, maybe... but i failed - at least, in Moscow.

:(:(:(

Edited by nightfall

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I know some people have obtained both Maxstream and Aerocomm transmitters and I was wondering what your thoughts are on them. Do you prefer either one or find they have similiar performance?

Edited by jheissjr

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I know this post is a little dated so I was thinking the people who have the Maxstream and Aerocomm transmitters might have played around with them by now. Do you have any thoughts on them ?

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