Mobile E rig

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Mobile E rig

Postby n1ps » Wed Oct 17, 2007 6:53 pm

Its been a while since anyone has posted anything about mobile operations (80M). As the season is upon us, I thought I would bring up the mobile discussion once again.

Has anyone placed a mobile E (or D?) rig on air? Perhaps someone is considering it?

It seems the big issue is the power supply. It is pretty easy to go get an auto 1KW inverter...and they are cheap. But it seems such a waste to rectify back to DC. On the other hand, I really do not like the idea of adding a bunch of batteries in a series/parallel arrangement.

Also, another concern is to make a compact unit with perhaps a tradeoff for output power. I'd like to see a 100-150 watt TX with PWM for maximum efficiency.

I'm on the road a lot and "upgrading" to a mobile E rig is appetizing because of the E class efficiency.

Anyone? Anyone? :D

Pete
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Re: Mobile E rig

Postby kf1z » Wed Oct 17, 2007 7:58 pm

n1ps wrote:Its been a while since anyone has posted anything about mobile operations (80M). As the season is upon us, I thought I would bring up the mobile discussion once again.

Has anyone placed a mobile E (or D?) rig on air? Perhaps someone is considering it?

It seems the big issue is the power supply. It is pretty easy to go get an auto 1KW inverter...and they are cheap. But it seems such a waste to rectify back to DC. On the other hand, I really do not like the idea of adding a bunch of batteries in a series/parallel arrangement.

Also, another concern is to make a compact unit with perhaps a tradeoff for output power. I'd like to see a 100-150 watt TX with PWM for maximum efficiency.

I'm on the road a lot and "upgrading" to a mobile E rig is appetizing because of the E class efficiency.

Anyone? Anyone? :D

Pete
n1ps


a 1kw inverter is one approach.... though you'd want an extra batt, and a large alternator.


there's some stuff out there...and in the works.... so i'm told.

I guess there is some problem with the changing antenna load, with mobile ops....

hope someone else pipes in.........



good to see you're still around peter.....

bruce
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Postby WA2WVL » Thu Oct 18, 2007 12:46 pm

Peter:
There are several FETs available that will make a lot of power on 12v. One I like is the IRFP2907 which is 75V, 209A, and .0045 ohms. It has low feedback capacity for better stability. I have been working with a similar part at 14 Mhz with excellent results.

One way around the SWR problem is to run two amps at 90 degrees and use a Quadrature combiner to the output. This is a 4 port circuit and all reflected power goes to a dummy load. The amps always see a good 50 ohm load. You will find info on the internet about Quadrature combining.
I belive at a fixed frequency (or band) it can be done with just C's and L's.

Also not too dificult to build a modulator delivering 30v peak from 12V.
Floyd
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Re: Mobile E rig

Postby Brent » Fri Oct 19, 2007 10:05 am

n1ps wrote:Its been a while since anyone has posted anything about mobile operations (80M). As the season is upon us, I thought I would bring up the mobile discussion once again.

Has anyone placed a mobile E (or D?) rig on air? Perhaps someone is considering it?

It seems the big issue is the power supply. It is pretty easy to go get an auto 1KW inverter...and they are cheap. But it seems such a waste to rectify back to DC. On the other hand, I really do not like the idea of adding a bunch of batteries in a series/parallel arrangement.

Also, another concern is to make a compact unit with perhaps a tradeoff for output power. I'd like to see a 100-150 watt TX with PWM for maximum efficiency.

I'm on the road a lot and "upgrading" to a mobile E rig is appetizing because of the E class efficiency.

Anyone? Anyone? :D

Pete
n1ps

The other consideration was antenna impedance...young Bill KE1GF abandon the project because of this problem...perhaps class-d might be a better amp design to deal with moving load impedances?

Mobile ants input impedanceat 80 meters tend to float around.

Brent W1IA
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Postby WA2WVL » Fri Oct 19, 2007 12:06 pm

Pete if you are interested in Quad combining give me your Email and I will send you a design for 75 meters.
Floyd
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Postby WA2WVL » Fri Oct 19, 2007 7:06 pm

Pete:
Take a look at the LTC3814 data sheet. It looks like you could step up 13.6v to 30 volts at nearly 96% efficiency. Also I think you could add an op amp in the regulator fedback loop and make it a modulator.

Also a pair of IRFP2907 fets in Push/Pull would do 100 Watt carrier with 500 Watts pep at 90% efficiency on 75 meters.
Current drain at 13.6v would be 8.5 Amps for the carrier and about 20 Amps when modulating (up to 40Amps peak from power supply).

I hope this info helps.

Floyd
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try step up configuration

Postby N9NEO » Sat Oct 20, 2007 5:43 pm

If you want gobs of mobile power then you should look at a full bridge modulator or forward converter. You can get from 13v battery power to any modulator voltage you want. Interleaved forward is a good topology. There was an article in nov/dec 2004 QEX I think.

regards,
NEO
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Postby n1ps » Mon Oct 22, 2007 6:33 am

TNX to all for the posts. I meant this mostly to see if anyone has actually built anything and put it on the road. I talked to Jamie this weekend, KF2VM, who said he has a mobile E rig in construction. I think he said he is looking at using some sort of hybrid combiner (I don't know if he monitors this site).

I'm definately not leading in this arena. :roll:

I was not aware of the VSWR problem, though I do see see it now. I wonder what would be the maximum VSWR swing that would be tolerated? It sounds like a quad combiner would work. I wonder if one could construct a (3 port) ferrite circulator for 75M? I have not thought this out however, so it may or may not work.

Bruce, yes, I have not been on the air too much. Its been a busy summer. However the season is upon us. Had a great time at Deerfield. The E rig is doing well. I still have a couple of things to clean up on it, but basically it is done. It is Steve's latest and greatest, using the PWM deck.

Pete
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BTW...I'm listed in QRZ.
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Re: try step up configuration

Postby kf1z » Mon Oct 22, 2007 12:27 pm

N9NEO wrote:If you want gobs of mobile power then you should look at a full bridge modulator or forward converter. You can get from 13v battery power to any modulator voltage you want. Interleaved forward is a good topology. There was an article in nov/dec 2004 QEX I think.

regards,
NEO


Was that Your article? Or a different one?

Nov 2004 QEX 47 A New Approach to Modulating the Class E AM Trasmitter LaFrance, Robert, N9NEO
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