Troubleshooting mylack of distance, receivng and transmitting.

Go back to cutting coax ,,,,

 

I'll read 'Saga of Conjugate Match.' I suspect I have already read it since I followed most of what he wrote over the years.

I simply ask where you was located thinking I might know you. But since you wish to remain Anonymous that's fine my me.

The one question I do have is about the use of an antenna tuner.

In this or one of the many other threads Mike has written he says this conjugate match, that you brought up, worked where a antenna tuner wouldn't.

My question is why not? Since I'm sure you would agree an antenna can be tuned to match any impedance with a antenna tuner. If a length of coax can be used to match a load then a antenna tuner would match that same load.

Any way as I said up front I have no desire to get into some long discussion on this subject in which most on this thread could care less.

BTW I an a retired trucker and also Electronic Design Engineer. Plus being a Ham operator for over 50 years.



Leon
(kc0iv)

 

A little experment ...

Antenna R7 .... Feed is 45 foot of RG-8X

SWR ...

50.125 2.2:1
29.600 1.6:1
28.450 1.4:1
24.895 1.1:1
21.075 1.3:1
18.133 1.2:10
14.150 1.1:1
10.110 4:1
7.160 1.5:1

NO COAX was cut making this measurement NOW it cutting coax works how come I cam go from 7-50 mhz with ONE coax ????

It's the Antenna ......

 

That's what I was trying to say in a round the cabbage patch way. It's all about the antenna. If the antenna is tuned properly the length of the coax won't matter. Reflection causes more problems than you know. Counterpoise (ground plane) or lack of, is another MAJOR issue with these plastic and fiberglass trucks. You can have a 100 watt radio with a lousy antenna and not talk across the street.

Example. I have a KENWOOD TS 440 SAT. I also have an inverted V antenna (1/2 wave) cut for resonance at 14.300. I worked 9Y4 station in Trinidad with 80 watts on that antenna. My G5RV is set up as an inverted V as well but it is not resonant on any specific freq. I have to use the tuner in the radio. I couldn't even hear the station in Trinidad on the G5RV.

Again, it's all about the antenna. I would bet 100 bucks that if he could get that antenna a foot away from the side of the truck, the SWR would drop considerably. Maybe not enough to fix the problem, but enough to show where the problem is.

 

Bruce,

The coax cutters are NEVER going to answer that! I have basically been saying the same thing. The "screwdriver" antenna (you can read about that on Google) goes from 3.5 MHZ to 29 MHZ fluidly and 'matches" on ANY band with ONE coax of no particular length. If what the CB gurus are saying is true, then one would have to have 10 pieces of coax cut for 10 different bands, each ranging from 60 feet (or so) to 18 feet. WHERE would one PUT all those pieces of coax to cover all those bands in a small pickup truck? . Yet, I (and a whole lot of other mobile operators---commercial, ham, military----) operate every single day with ONE antenna with ONE coax with an average SWR (not SWR'zzzzzzzzzzzzzzz) of 1.2 to 1 on ALL those bands.

Can you cut coax to get them swr'zzzzzzzzzzz down? Sure you can. You can also use a tuner, a capacitor at the feedpoint and several other options. Coax AIN'T the best way. You can also load up a 50 ohm resistor, and have low "SWR'ZZZZZZZZZZZZZZ". Be prepared not to get out very far! LOL! Yes, there are some specific antenna designs in which coax is an integral part of the design, and has to be a "certain" length.

And, if I were faced with a plastic truck like so many techs and drivers are, I would still NOT use coax as the fix-all. I would first provide a non-resonant ground for the ANTENNA. Then I would used a capacitance (I prefer a small coil of wire) at the FEEDPOINT to bring the MATCH to 50 ohms. At 27 MHZ, it doesn't take a lot, and in a normal installation, it is often unnecessary.

Again, if you WANT to trim coax, and it makes you happy, be my guest! It is NOT, however, the best way, nor is it a good practice except in specific instances. You are masking the REAL problem in the antenna with a "bandaid solution" that has become CB "gospel" since it first started.

Wanna know where it REALLY started? When CBers first started installing radios (equivilent to a backyard mechanic), they bought antennas that had '18 feet' in the box along with the antenna, mount and accessories. Back then, cars required about 18 feet to get from the bumper to the radio. They believed that this was the "right" length of coax. They didn't consider that there are OTHER radio services who correctly use what is required to get from A to B. It became a "gospel truth" that everybody had to use 18 feet of coax. It just ain't SO!

GF

 

Just for a point of interest.....I have hooked several radios up to my Cushman communications monitor (back when I had it) to tune the radio. I noticed that the impedance of the radios varied from 43 to 60 ohms. The typical impedance is 50 ohms, but now you see another reason you need to adjust the antenna. The coax is only the messenger to the antenna. If the antenna was perfectly tuned at 50 ohms, the coax is 50 ohms and the radio is 45 ohms, you have a mismatch. You can NOT tune out the mismatch by varying the length of the coax. You can ONLY tune out the mismatch by changing the resistance of the antenna.

 

I think you will find it started from firestick antenna company.

What most Hams don't seem to understand is some truckers, Like Mike, did find a length(s) of coax that worked for their installation. If I remember correctly Mike said he had to use different coax lengths depending on which truck he was driving. I also recall Mike said it was not the best solution only that it worked for him.

Leon
(kc0iv)

 

I'm not saying it can't happen because of things like capacitive reactance and other complex anomalies. I've never had any luck tuning by cutting coax.

Stranger things have been known to happen....

 

Me likey the .60 - .70 per mile average on each pay check!!! So I'd drive for them without a radio.

 

Let me know if I can help.