Discussion in 'Mobile Radio Systems' started by K4VUQ, Mar 1, 2016.
Hmm. If I really believed that, I too would have a tuner. I don't!
Yeah exactly, I was literally making mention of the only, and FAR STRETCHED, use of a tuner while mobile. There truly is no place for one in a mobile application. Actually rephrase that .... there is no useful function /end story.
I'll go as far a saying in all honesty the only use for an antenna tuner is on a loop antenna with balanced line feeding it. That is about it. Really even coax fed antennas using tuners are just ... not fundamental - pun intended.
I use a bugcatcher. It "works" well. I am not sure exactly why, but I have never wanted a screwdriver. The bugcatcher is easier to take down when I park inside, and may offer less wind resistance than a screwdriver of comparable performance. And I don't mind getting out of the car to change bands. Whatever.
I do have an autotuner in line to extend the excursion of the antenna on 80, 60, and 40 meters. The SWR curves on those bands are VERY sharp, as they should be. The tuner is unneeded on 20 and above (on 30, I only listen!). I am happy with this arrangement.
As for the OP's question, I vote for an IC-7000.
In the end what matters is what you find that works best for you. And I too vote for Icom 7000 over Kenwood or IC-7100 model.
So what I see is you only run mobile on the easy bands - If you operated HF 40 and especially 80 and 160 you would understand the need for a tuner. On 160 meters just parking in a different location can have a significant impact on SWR. I operate nearly exclusively on those bands - On 80 meters there are several frequencies fairly close together that I like to talk on. However they are far enough apart that they significantly change my SWR. With the tuner I can easily talk on all of them. When I am on the antenna's resonant frequency I can bypass the tuner. I don't know what makes you guys think you are so much smarter than the rest of us - your quote above just proves who the close-minded one is...
So - just to prove to myself that I'm not close-minded and I am still willing to experiment I rebuilt and re-tuned my antenna this weekend - My field strength meter is kaput so we will have to judge on future performance whether it actually made any difference. I posted a pic on my QRZ page. If indeed the change is positive I intend to install a true cap hat - Always striving to make it better.
Here is another solution you might look at—1/4 wave, shorted stub matching. To do it correctly requires an antenna analyzer. But unlike inductive shunt matching, a shorted stub's reactance curve is opposite that of the antenna's. This fact extends the bandwidth. How much it does, depends on factors not in evidence. This said, in most cases, if you take your time to get the match correct, the bandwidth will increase by a factor of about 5 times. Even on 160, this allows a monobander to cover all of the 160 DX window, and on 75 meters, close to 65 kHz.
One of the reasons you're seeing great variations in the SWR is the loading coil itself (assuming you're using the large diameter coil I see on your QRZ page on 160 meters?). Large diameter coils, and ones with poor DL rations have an inordinate amounts of distributed capacitance. This narrows their bandwidth, and reduces their Q. After all, bigger isn't always better when it comes to loading coils. In other words, anything over ≈3.5 inches in diameter is too large for any band if Q and bandwidth is the goal.
An ideal size for 160 meters (≈650 uH, #12 tuned copper, one wire width spacing), is 3 inches in diameter, by 15 inches long. The Q will hover around 150 if you do everything correctly.
You didn't ask, but the easiest way around the issue is to use a screwdriver like a Scorpion. You'd still have SWR variations due to location, but retuning the antenna will address that issue handily.
A standard power cable (3 meters) for a 100 watts transceiver (200 watts input @ a nominal 13.8 vdc), has a voltage drop of .4 volts. This is just under the rule of thumb of .5 volts.
I once owned a 480Hx. At 200 watts out, dead carrier, 13,8 vdc input, the draw was 43 amps. This is exactly what their specs say it should be.
Thank you Alan - I've really never been interested in using a screwdriver type antenna - I have had a great deal of satisfaction from working on the bug catcher projects. I don't remember the man's call sign but about 15 years ago a guy built a tune-able bugcatcher antenna that worked something like a screwdriver and was selling them at the Belton Hamfest here in Texas. A couple of my friends bought them but never had real success with them. One of my friends still has his and offered to let me have it. I think my next effort may be seeing if I can make it work. It has a 12 volt controller similar to a screwdriver and a contactor that moves up and down the inside of the coil. Anyway sounds like a fun project to me. One reason I prefer the bugcatcher antennas is the ease of removal for various reasons. Everything I have is on quick disconnects so I can pop it off and store it. And I guess you have to take my word for it but I've put my homebrew antenna up against commercially built antennas and it has outperformed them every time. I consistently get signal and audio reports comparable to most base stations on 40 and 80 meters. Obviously I may not keep up with the DX guys and their beams but in the ragchew community my mobile station has a reputation that speaks for itself. As far as the different matching methods what happens to the match when I change bands or even antennas? With my current matching setup I simply change to the appropriate tap on the matching coil - simple simple. Oh, and yes the large coil on my page is my 160 coil - That one however was built by Henry Allen's people. It works very well but has extremely narrow bandwidth.
I think I mentioned this before, so excuse me if I have. Short tapping a large coil ends up lowering Q somewhat more than the way a screwdriver does. Nonetheless, if you go the route you're thinking about, keep the metal mass around and inside the coil as minimal as you can!
If I can find the ad, I'll post it, but Master Mobile made one like you describe. The metal inside was about as minimal as you can get. I used one many years ago, before going back to the monobanders.