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Mobile anybody on here run a high power (5kw+) suburban? i need some advice

How are you mounting the antennas - on a crossmember or are you bracing between members to handle this?

Thinking - maybe not to focus on the SWR as the MOUNTING issue itself...

Are you able to use something similar to Catamarans and other pleasure sailboats use for stability.- or does it restrict/disqualify you from your ability to compete...

upload_2020-8-6_20-41-54.png

On the Left your vehicles Roof (similar?) - Right - Internal Brace- but used for Fiberglass older model Surburbans that had the removeable Fiberglass top.

Ok, here's what I'm looking at, I did something similar to a Toyota Scion xA not for competition, but to survive the outback woods area I used to live in...

I built a brace on it's roofline to the antenna wouldn't torque off while I drive - used Francis Amazer, 102" and 5' Hot rods - so the roof cargo carrier - like above - also had a brace using the Crossmembers of the framing inside and used washers as spacers to bolt that "bar" to the skin of the roof.

I'm showing you the Crossmembers so you'd have a means to utilizing that which Catamarans have a a means to stay upright - spreading out the loading if the Roof Rack can't - use a "bar" or other thick metal to "raise" the driven element - but use this "bar" not just to the Driven, but to the rear Reflector too - bolted to it.

This may not seem like much and more of a bother, but look, you know that by roof area is square feet alone, your feedpoint impedance is going to be roughly 36ohms or less, that is one "ding" against you...

You're lifting your feedpoint if only by inches - up - to change the feedpoint impedance to help with the SWR.

You already have the holes, just use them to attempt the method to add on height using the bar. But the Crossmember Bracing can help offset the twisting torque loading the Bar may not fully handle from side to side.

upload_2020-8-6_21-9-35.png

When using Beams - they always have a "Hot" element but it's isolated from the Boom - the Reflect and director elements are part of the boom but at a spacing making the Driven element more in-step with the other two.

With this in mind. is your mounting of the Driven, "raised" from the Roof - so the pitch angle that element uses for "image" to the truck - raises the question of the Bracing to work in your favor of elevated feedpoint of the driven element using the Bar to offset the Feedpoint problem with "too much metal".

So, if you got down to here to hear all that, thanks for reading the above...you said you've tried many different ways, with this recurring problem - did any of those include some type of Roof rack or raised roof system?
 
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Ok, it's the one thing you keep avoiding but you presume it's fine...

im out of ideas. when i run the bounceback setup its still to high as well. also the fact that two different antennas are tuning exactly the same at 1.6 is making me think something else is going on. not the location of the antenna on the roof. i posted elsewhere and of course the answers where all over the place.the main two answers where the antenna shaft length is too short. but if thats the case how do other guys get 1.1 swr with short shaft antennas (r55 etc). next was location on the roof, its all measured out. next main answer was coax is wrong length. people were saying resonant half wave (which i have now), resonant half wave WITH line section included, 11ft, 11 1/2ft, 12ft, 15ft, 18ft were the main lengths given.

The above shows, tells me, you "copy" what others do and think it will all sort itself out.

That's fine, but you come here and tell us - ignore us, when we offer tips to resolve the issue - the one thing I admire about you though, is you did attempt to install bracing using a Roof Rack system, there are other methods and/or systems and installs using the Roof Rack to elevate that feedpoint above the roof to allow the antenna some "free air" with a lowered counterpoise angle or slope - down and away from the main radiator-to change the Feedpoint impedance to RAISE it closer to 50 ohms.

Well, one thing Competition Doesn't do - is tell you EVERYTHING...

So when you say "I've tried everything" - and you still have this issue, means you haven't.

I see three Urban Myths in the above...

"Not the location of the antenna on the Roof..." <<<-You sure about that?

"1.1 SWR with Short Shaft antennas" <<< - How do you know this? By word or you verified? Not a lot of people running power even with a tight circle of friends are willing to show proof directly on how they do it...they don't like competition - "Walking the Dog and Kickin' the Cat." better than anyone else.

Sigh...now the obvious...Coax lengths...I'm not going to bother quoting - it's in the above...

Man! Unreal - I get called names trying to talk at a level others can relate to and yet we still have the "People we're saying...resonate this and this and that - multiple lengths..." - Why do you heed their advice? Only to come here and ask why and yet state "I've tried everything" ...

Are you going to allow us to help you or are you just venting...?

Ok, let's see here, the antennas shown in other photos are "perpendicular" as much as possible - you did a similar setup...but in other messages you skipped an important point...

i was using the 400 with my 8 pill, the 600 is on the way for the 16 pill. low power swr 1.6, high power swr 1.6, the only thing that rises with power increase is the reflected power.

And...

radio is stock, yaesu ft-891. the whole system runs perfectly on a dummy load. once the antenna is connected back up high swr, so its an antenna issue. either the shaft height, mounting location, roof rack cross bars causing it (which i just thought of last night. im gonna take them off.

Ok, I mentioned earlier in my post that the Roof Rack MAY BE NEEDED to raise or elevate the Feedpoint... you use "puck-mounting" so that means you've committed to the roof no matter what holes and all...

The ROOF may not be the problem - the harmonics in both radio and amp might...(AHEMN) just be the very nemesis that you're dealing with.

Radio? Would like to rule that out but you say...

radio is stock, yaesu ft-891. the whole system runs perfectly on a dummy load. once the antenna is connected back up high swr, so its an antenna issue. either the shaft height, mounting location, roof rack cross bars causing it (which i just thought of last night. im gonna take them off.

Yaesu - FT-891?
upload_2020-8-7_7-51-23.png
Nice radio!​

Has it been modded?

Mods - filter sections bypassed to allow for extra bands(?) It - may create that which you don't want...

Spurries. There's enough bandwidth product in any amplifier developing power in the kW ranges that WILL amplify the harmonics - so, don't tell me no - verify your radio is ok, else the 1.6 may be a 2nd or even 3rd harmonic out and your amp is simply following thru it's guaranteed Analysis of Spread Spectrum with all its Vitamins and Minerals fortified with it, to produce that 1.6 SWR burning up your amp due to reflected power.

It seems, at least to toy with the notion - you have not told us ALL the details; for if all else - everything being equal - the simplest Explanation is the most logical one to follow - or fix...

Dummy load is NON REACTIVE - you get good SWR...

Antennas are REACTIVE and require tuning - or RESONANCE as well as it's FEEDPOINT will work against it as an Impedance shown (Reflection) against the system...so you have a problem...

Don't you see it?
 
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Had a guy say my Interceptor 10K could not be tuned right, as his power increased so did his VSWR. After a few phone calls, I asked him to transmit into a Dummy Load and the results were the same, increased VSWR with increased power from a large transistorized amp.

This proved that the amp was not correctly made or designed and had a output that was NOT 50 Ohms, causing the constant VSWR. A 1000 watt dummy load can probably work that isn't to expensive. Please let us know what the fix is.

Jay in the Great Mojave Desert.... "Next Gas 150 Miles"
 
Simple question? Why n hell you need that much damn power driving around?

This reminds me of what my Dad said when I came home with a brand new Boss 429 He took his pipe out of his mouth he said rev that thing up again so took it up to about 4 grand and let settle down he looked at me and "WHAT THE HELL DO YOU NEED WITH THAT MUCH POWER". I said the same reason you don't need it.
 
Had a guy say my Interceptor 10K could not be tuned right, as his power increased so did his VSWR. After a few phone calls, I asked him to transmit into a Dummy Load and the results were the same, increased VSWR with increased power from a large transistorized amp.

This proved that the amp was not correctly made or designed and had a output that was NOT 50 Ohms, causing the constant VSWR. A 1000 watt dummy load can probably work that isn't to expensive. Please let us know what the fix is.

Jay in the Great Mojave Desert.... "Next Gas 150 Miles"
the mobile works perfectly into the dummy load.1w to 4kw is the same, perfect. its the antenna setup somehow.
 
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Do you have a base station and would that antenna handle the power? Run the coax out the window to it? The dummy load is a good idea for something to check too. To see if the antenna reactance makes a difference. I have learned that the input tune of the amp can affect the output swr. The output tune affects power. Have you talked to the amp builder? Maybe he has seen this before?
 
the mobile works perfectly into the dummy load.1w to 4kw is the same, perfect. its the antenna setup somehow.
Ok now we have a direction. The reactance is throwing the amp out of balance. The question is what to do next. The reactance of an antenna can change with power? I don't know, maybe. Maybe if it can't handle it. Ok there is one direction to go. If the antenna is ok then I start to think about the amplifiers feedback on the transistors and the input tune. This would be another direction. The next question is how do we apply the process of elimination with the resources you have available? If you could post some pictures of what you have, it might get the attention of someone who has been down this road. @Crusher might have a few ideas too.
 
Could be an amplifier oscillating. It's not uncommon for a problem child amplifier to work just fine on a dummy load and everything goes to hell when you put it on the antenna. My fatboy 16 pill did this because the assembler didn't tune the output.

If these are typical comp amps they are crude. Sometimes different jumper lengths will make them play.

If you have a properly installed puck on a suburban I really doubt this is an antenna problem. I assume you buffed the paint off the bottom so the coax shield has a good connection to the roof.
 

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