And Another(s) NEWBE questions

[tsudtell]

I need to get my HiQ screwdriver working. In the location it is in now I can only tune on 80 and 40 with a 1"dia, abt 1" long hand made coil. On the higher bands the best I can get is 3 to 1 and it is very narrow. Oh, did I mention that this antenna stuff is hard even after 40 Years a Ham. .

I know it can be done with a loading coil at the base and I have heard I should have about 40 ohm on the low bands (adj with the coil).
Question is, is there any info on how to do this you can point me to.

A tarhill screwdriver has worked ok in the same location.

Thanks

Ted
N6RQR

[w0qe]

This task is a piece of cake to do with the 4170 and I have done it many times. Try the following:

1.) Remove the existing base coil.
2.) Disconnect the mobile antenna from the coax and calibrate the 4170 to the end of the coax so that you are measuring the only antenna impedance (including losses in the antenna and to ground).
3.) Reconnect the coax to the antenna and resonate the antenna on every band you want to operate on and measure the real part of the impedance.
4. ) Either download a free SmithChart program such as Jim Tonne's SuperSmith of use some algebra to figure out the best compromise shunt coil to use.

For example if the 3.8MHz impedance is 15+j0 at resonance and the 14.2MHz impedance is 35+j0 then you would use about a 1.2uH shunt inductor (which is easily measured with the 4170.

After installing the inductor retune the antenna (shorter) to be slightly capacitive and the net impedance will be a pretty good match.

For example after shortening the antenna a bit:
3.8MHz Z = ~15-j23 and with the 1.2uH shunt L Z = 47.9+j10 (SWR=1.25:1)
14.2MHz Z = ~35-j22 and with the 1.2uH shunt L Z = 47.4-j8 (SWR=1.19:1)

The shunt L and the series C of the antenna short form an "L" network does the impedance matching. The final lowest SWRs on every band will be slightly reactive and the goal is to raise the real part of the feed point impedance to near 50 ohms. However with only 1 variable to adjust the result is a compromise.

I do a lot of mobile contesting and run multiple resonators for as many as 7 bands on a single 6 1/2ft mast with every band having an SWR that is quite good. Take a look at www.bnk.com/w0qe/Toyota_4Runner_setup.html for pictures if interested. All setups and the losses are different so a single inductor value doesn't work for everyone.

73, Larry W0QE

[tsudtell]

Thanks very much for the reply.

I will get to work on it today - Why did I not think of calibrating at the end of the coax??

I can say this because I am the worst speller in the world. There is a typo on your very interesting web page. "A mobile trip from Colorado to Virgiunia at the"

Ted N6RQR

[w0qe]

Ted,

Spelling error fixed but I'm sure there are others. In my case spelling usually isn't as big of a problem as typing is.

Consider posting your interim measurements as I sure many will find them interesting.

73, Larry, W0QE

[w0qe]

Grrrr..... Make that "as I'm sure many will find them interesting"

73, Larry