One thing I can tell you is that Fu728 is no match for the 4cx1500B's  excellent IMD performance. Its 3rd order IMD figures  is about  15db worst than the 4cx1500B .
The 4cx1500B was designed for linear SSB service by Eimac and is one of the best tubes around for IMD performance. There is a Chinese manufactured 4cx1500B.
I dont have any knowledge of how good it is. I have a good supply of genuine Eimacs which are used in a Collins 30S1.

You can find  tons of FU728's on the Chinese Ebay site called TaoBao. Many of those tubes appear to be rejects and suffer from flash over syndrome so be be warned. I know
several hams  who have tried to use them in their Emtron DX3's  with not very good tube life or immediate flashover even after conditioning the tubes. Tao Bao is like Ebay fully of crooks.

Rudy from Emtron  is apparently dealing with one of better suppliers and tubes sourced through him are reliable so I am told by owners of his amps. There will be skeptics about this claim  since he charges more than the internet price for the tubes. Special hand selection of tubes is a well known price gouging marketing technique used by many of the Russian Tube sellers.

Another thing to watch out for is that the input capacitance of the FU728's are higher so if you using them in amps like the Harris 110A you might have trouble on the higher bands with the amp taking off. Worst case scenario
is that you wont get the same output power as a pair  of genuine 1500B'S You wont find this information on the Emtron page for the DX3SP, it has very poor efficiency on the higher bands because of the input capacitance issue.
Really using 2 of any tubes in any amp design is bad engineering practice. You better off just using a single tube to achieve your power output objectives.

I agree with you we both posted the same answer within seconds of each other!

The general rule is  "the higher the sun the higher the frequency"

I think the best bands  for mobile are 40 and 20 meters. The antenna efficiency on these bands are reasonable and the propagation is very reliable and consistent.

I think like others here that another band with with  great mobile potential is 17 meters. The problem is that 17 meters is generally starved of stations because the majority of the ham population
still only have pre warc band antennas. However this is slowly starting to change with  antennas like ultrabeams, steppir's and optibeams becoming popular choices. 17 meters operates more like a spotlight
band with  openings and closing into distinct areas  as the day goes by. The lack of QRM is a big bonus on 17 meters.

 20 meters can open everywhere at once causing both an abundance of stations and QRM. Its really a double edge sword band but its my favorite band for mobile. It seems to be the favorite mobile band in the USA just judging
the number of stations that i work. I seem to work a lot of stations in the USA on 14.185 it seems to be a mobile station hangout.

Why I like 20 meters,  is that even lousy antennas when mounted high up on the roof will work well. 20 meters seems to cover up all the sins of bad mobile   antenna installation. This is not the case on 40 meters where if you install the antenna poorly your results will very poor. A manstick stuck up on the roof  produces good results. Even thought these antennas are bottom of the heap in terms of performance. I have found that hamsticks work good enough on 20 meters. I work more stations with hustlers and hamsticks than stations with the big professional screwdriver antennas.

Another factor to consider is where exactly you do your mobile operations. The noise and has in the cities and suburbs can be horrendous on the lower bands. 20 meters does not suffer as much as 40 meters and lower.
If you just like ragchewing   to local stations any band will do that has propagation.

I have heard you and your other ham friends with their portable mobile setups work the world. Amazing how well you guys do.

For my location on 20 meters there is NO   high angle propagation into the Oceania/Pacific areas, its all low angle. I had a 3 high stack 5 over 5 over 5. Top antenna at 150 feet.
I have switched this combination to the point where I wore out a set of relays on the stackmatch. The end conclusion for me was that the 100 and 150 antennas were best bet 99% of the time.
The Antenna at 50 feet was not doing much for the stack performance. Thats what i run now and if I need low angle performance I switch to the 150 high antenna alone. This combination over
my terrain profile is as good as 200ft high stack.  You do have to analyze the elevation angle statistics before drawing any conclusions. On 20 meters higher is better.
Many people suggest that 1.5 wavelengths is the optimum height. This conclusion was drawn by W2PV for East Coast USA / Europe propagation. From my location this height is actually worst
performer than than an antenna up at 2 wavelengths. There is no one height that is perfect for ever location which is stating the obvious. Any practical  antenna chosen will always be a compromise when you
have a single antenna and tower.

I only raised the comments made by the VK3 station because he stated that  this phenomena occurred both on long and short paths. He stated  that the path was an  extremely difficult path because of the distance
involved  beaming through the auroral  zone.. In all my testing I have never found  a low antenna say at 50 feet beat a higher antenna except on short local skip paths. As you have found its the antennas that are high up that dominate the band.

In general the stations that keep the band open with the biggest signals are those with high stacked antennas or  are stations located on very favorable high mountain top locations.
If you cant afford a 200 ft tower find a high mountain top or do what you guys do and use verticals within 1 wavelength of the ocean.  Another good location for any antenna is on  plane up 10000ft in the air.
Its amazing how well aeronautical mobile stations get out with such low efficiency antennas up high.   

How much on screen dynamic range can you get?
What will be the minimum resolution bandwidth be?

SM5BSZ has already been using LINRAD with  these DVT_B tuners. Linrad has a nice mode called TX Test mode which is excellent for checking transmitters for splatter etc.
You might check SM5BSZ's web page he has lot of data there.

Receiver only the Lowe HF150  if you can still find one. There is nothing better.

 You cant beat a radio with a decent VFO KNOB. Handle scanners like the Icom R20 and the AOR units are a pain in the rear end when  casually tuning around
the ham bands. A ham must have a VFO knob.

I like using capacitive the touch paddles. I personally think that they have a huge advantage over mechanical keys in mobile operation. You can build and adapt them to suit yourself.

http://www.cwtouchkeyer.com/

Look for a old Atlas 210. I sailed around  the world twice on a 35ft  yacht with a Atlas 210. I then used the same radio in my mobile for 10 years.
Its a reliable  radio thats easy to fix, I have seen them for sale for 150 to 200 dollars in good condition. 

What I would do is also add some parallel vertical wires or elements  to the flagpole to give a better  radiation pattern on the higher bands. 40ft verticals have a rather high radiation angles above 20 meters.
I would at least a 1/4 wave wire for 17 and 15 meters since these are good reliable bands that require a favorable take-off angle.

The Optibeam 9-5 is a very good antenna. Its just very expensive and overpriced in my opinion.

Another antenna that I know  that  works as well as the Optibeam 9-5 is  the   Mosley TA 54XL.

I couple of hams that I know who are both DX'ers and both live in the same suburb,  about 2 blocks apart. One has the OB9-5 and one has the Mosley TA54XL. They are both at the same
height and seem to be about equal. One 20meters there is a slight edge to the Mosly antenna because of the longer boom. The Front To back ratio  on the Mosley is better than the Optibeam 9-5 on 1 or 2 bands.

These antennas would certainly be more reliable than the motorized contraptions that are so popular.

Either one of these antenna will serve you well.

Another problem is now that many hams are such emotional delinquents. When they buy a product they dont want to criticize or say anything bad   about the products that they own. They become very
hostile towards others who raise the  faults of products that they own. Its made even worst by moderators of groups who deliberately resort to censoring  and curtailing any discussion  by any  individual who raises these issues.

The Icom IC7700 PA failure issues that  has been an ongoing problem It seems that Icom and its groupies are all trying to silence discussion on this issue. You cant  discuss this issue without being censored on various Yahoo groups. This kind of heavy handed tactic to silence critics has no place in open democratic free internet. It seems that these owners are more interested in protecting their investment than saving some poor guy from blowing his hard
earned money on a radio that has design faults.

We get better products by making them better by fixing up  and discussing design faults and issues. We dont fix these issues by being silent  or by  attacking those who report or who want to discuss these issues in a open manner.
People who try and censor discussions are behaving like ignorant fools who deserves the position that they hold because they are not being scientists or engineers but rather company lapdogs.

Yeah I am stuck on the S-meter and IMD wagon.

For the price that you paying for these radios I would expect a calibrated S-meter and a  clean low IMD transmitter.

Well thats the whole point. If you had a calibrated S-meter and the radio was calibrated you could apply something like an antenna factor to correction  for all the variables. You then will have a 100% repeatable accurate reading.
If you were doing antenna or propagation tests you would  then have a reliable  and accurate data not rubbish data.

Hams would complain if the volt meter or a the frequency  meter in their radio was off by a  factor of 100%, so why do S-meters have to be so lousy when it is such a simple job to fix or build calibrated S-meters. There
would be a riot if some radio had a SWR meter that was off by a factor of 100%. S-meters are simple circuits  that can easily calibrated and the data stored.

Why the current  uncalibrated S-meter's are even a big joke on hams is this. You get on the air and then ask a ham if they  can you give me reading between my amp and 100 watts, or for that matter the front to back ratio
on your beam. Most hams will reply "OM I see  5 s units difference with amp off an on, and 6 S-units difference from the front to the back" Hams will state this with a air of confidence like they are using a Fluke meter
to make the measurements. You never hear these hams say but I must tell you that my S-meter  could be off by 100% and by the law of physics going from 100 watts to 1000 watts is 10Db, not the 36db inaccurate reading my meter shows.
On some occasions you will have some nasty joker tell other hams what he saw on the S-meter and that station X  must be running illegal power because his useless S-meter told him so. You cant have it both ways,  by saying that having a calibrated S-meters is a waste of time and then behaving like you do have a calibrated S-meter is very hypocritical behavior

. I would prefer to have a calibrated S-meter that is accurate just like my volt, swr, impedance and frequency meter. Why is this asking for too much? I can buy a $1500 dollar Rigol spectrum analyzer with a color TFT screen thats as big as the IC7800 and TS9990S and it  will have  a guaranteed accuracy of  1 Db. Why cant you get this accuracy from something costing 10 times as much? Its joke on us and a huge rip off the junk thats being marketed to the ham  community by the manufacturers  at such an expensive price.  There are radios like The Flexradios, Elecraft K3 and many of the direct sampling receiver which all have accurate S-meters. Calibrated S-meters should be standard on all transceivers.

Commercial VHF and UHF radios have had the ability to produce accurate signal strength readings for years. Yet you cant buy 1 VHF or UHF ham radio that has the same ability. Is it because hams are becoming like Cb'ers, all brain dead black box operators with no technical skills  that cant understand the value of  something as simple as measuring a signal level accurately?

SDR receiver and radios like the Flex have perfectly linear S-meters,  why is it too much to expect this from a 10,000 dollar radio? The reason why people do have the 5/9 mentality is because  they all know S-meters are useless
and inaccurate, if you can hear them well you might as well say they 5 and 9. If S-meters were calibrated you still be able to do  this because the S-meter will train the operator on what is a good or bad reference point. After 1 contest you could be giving  far more accurate reports since you know exactly what a real 5/5 or 3/3 signal sounds like.

There are modes such WSPR and  HF grabber that can be excellent tools for reporting how effective propagation and antennas  are. Having the ability to produce accurate results could help us develop  better antennas and have a better understanding of propagation.  A calibrated S-meter  when used with  these modes gives you tool that is far more reliable than most hams and their equipment. It would be great one day to use one of the internet remote receivers
with a calibrated S-meter to do antenna comparisons. If all stations had this capability we could measure relative performance and quantify it very easily.

Botton line is this if I bought an expensive radio like a Hilberling., TS990S, FTDX9000, FTDX5000, IC7700 and IC7800 I would expect for the asking price that It would have a calibrated S-meter. I dont expect
a  meter that is no better than a 100 dollar CB radio. Why is that too much to ask for in this  when technology can deliver this for 10 dollars?  If you read the Icom 7800 brochure Icom  raves about how
their smart engineers spent so much time making the on screen S-meter behave like a real analog meter. It would have better if they spent that time learning how to  build a calibrated S-meter
into their expensive radio rather than some useless eye candy needle dancing on the screen. They truly have their design priorities wrong.

Having a calibrated S-meter might not seem important. Once you own a radio with a calibrated S-meter or a receiver that uses something like the DbUV scale you will never go back to the old  uncalibrated
receivers and transceivers. Its a must have especially for an expensive radio. But hey I could be wrong maybe some people like buying expensive 10,000 dollar radios that dont have calibrated S-meter and  that splatter
like a 100 dollar CB radio. I must be a freak I am expecting way too much!

If you cant afford a  very good amplifier build it yourself. If you cant afford a decent amplifier you can build one that will outperform and outlast any ham commercial amplifier.

The Chinese tube industry is in the same position as the Russian tube makers. The market is small and there is not much demand. So who knows what the availability of these Chinese tubes will be  in the future.

At least if you use a tube thats widely used in industry like the 8877, you have a good chance of finding  and buying one. Who in the west uses FU728's? Answer nobody.
The moment these Chinese Amps hit the USA market the price of the tubes will skyrocket. The Chinese are also price gouging on what they charge for their amps. Is it coincidence that
Chinese amps are  priced virtually identical to the OMPOWER pricing. They making a absolute killing. Last time I looked the Emtron Amplifiers from Australia were selling for a cheaper price than these Chinese Amps.

The days of tubes amplifiers are fast coming to the end. 2kW solid state amps will be the norm in the next 2 years. Why would you tool up for something thats going to be obsolete?
Besides the bottom line with anything Chinese is that it is Cheap Junk, despite  what other say about the quality improving  sometime in the future.
If you look at the lathe market the same  thing has happened. Chinese lathes flooding the market. Despite years of manufacture the chinese lathes are nowhere as good as the lathes that were manufactured
in Europe and the USA. There is always some problems with the Chinese lathe quality and design, they poor quality with lots of bigs. Thats junk in my book.

I would rather send my money to Slovakia and support a company that made a sincere effort to design and build decent amplifiers for the ham market.
 Why would anyone want to support these Chinese knock off crooks is beyond belief. Its amusing to read that so many Americans are so pro anything thats cheap. I wonder how many of them
actually realize how   the Chinese are really destroying their economic might by destroying the manufacturing base in the USA. Very soon the USA will have no manufacturing industry and everyone in the USA
will be consumers of Chinese manufactured goods. I wonder who is going to be the Sheriff of the world  when you can afford to be one because your  manufacturing base is gone offshore? So much for patriotism.

Depends on how much sag you have in your wire. You need to look at the wire gauge and determine how much the wire  will sag between poles based on the span length.
 If you look in this months QST there is  full details on how you can calculate and allow for wire sag. The article is written by Joe Hallas.
There are some online wire sag calculators floating around.

You will also need to allow for movement and the weights used to allow for wire movement also needs to be worked out based on the span and the weight. If you dont use moving weights the wire will snap.
There is full details in the ARRL Antenna Handbook.

If you want a simple answer, you need to give the distances between supports and the  wire diameter, I am sure someone will give you answer.

I have AIM as well as VNWA. What I like most is the clean simple layout of the AIM software. If the VNWA software had such a  clean and simple software interface like AIM, I am sure it  would be more popular.
I think the complexity of the VNWA software  puts a lot of hams off.  The VNWA is a very powerful instrument that delivers everything that the VNA 2180 offers and some more at a bargain price.
At the end of the day a instrument that can have a dual role as a simple analyzer and  then as a powerful VNA is the best approach, this can easily be done in software. The VNA2180 is   a very expensive
instrument. The VNWA and MiniVnaPro offer much better value for money and they are both 2 port instruments.