Antenna tuning

[briankk]

Installed my old President Grant in my old Jeep, put my garage-sale K40 on the roof, got out the SWR meter and started fiddling. Concluded that the K40 was too short, lengthened it a bit and tried again. after a while I'd grown the K40 by and inch, and the SWR readings hadn't changed a bit.

Any ideas as to what this is all about?

TIA

 

[WA0CBW]

Bad coax? Bad connector? Someone replaced the K40 whip with the wrong length?
BB

 

[oldcb]

Installed my old President Grant in my old Jeep, put my garage-sale K40 on the roof, got out the SWR meter and started fiddling. Concluded that the K40 was too short, lengthened it a bit and tried again. after a while I'd grown the K40 by and inch, and the SWR readings hadn't changed a bit.

Any ideas as to what this is all about?

TIA

what are your readings now?.........i had the same issues in my truck, i tried several different antennas including wilson 1000, 5000, and got my best results with a wilson little wil, about a 1.6, but i just recently tried using an unloaded 5" mag mount with a 4" spring and used a center load similar to a tram-browning penetrator ssp-63 antenna, i was shocked to get a near flat 1 reading all the way across, no change in mounting location,you might want to give one a try..............

 

[briankk]

K40 installed length, 54 3/4", overall whip length, removed from base, is 57 3/8".
SWR readings, ch. 1 = 1.5, ch. 19 = 1.0, ch. 40 = 0, the needle just lays there.. SWR meter is an GE EA68X90, FWIW..

Read someplace that K40 has a special capacitor that might bugger swr readings.

bk

 

[K7MEM]

K40 installed length, 54 3/4", overall whip length, removed from base, is 57 3/8".
SWR readings, ch. 1 = 1.5, ch. 19 = 1.0, ch. 40 = 0, the needle just lays there.. SWR meter is an GE EA68X90, FWIW..

Read someplace that K40 has a special capacitor that might bugger swr readings.

bk

Just curious. How do you get a reading of "0" on a SWR meter? There is no zero on the SWR scale. The lowest you can read is 1:1. Are you reading a different scale or do you mean zero reflected power?

 

[ka3nxn]

GROUND??????

 

[kd7mxi]

averaged

 

[briankk]

If you Google up a picture of the GE EA68X90 meter, you will note that when the thing is totally disconnected and just sitting on the desktop, the meter needle is at rest on the left end of the scale, indicating 0. 0 % of full sweep, 0 Watts, 0 SWR. Not moving at all just laying there. Nada.

This may be an anomalous reading, but that's not whats bugging me, the fact that I cant change any of the readings by changing the antenna length is what I'm on about. Beginning to think K40 may be K put.

bk

 

[jonwienke]

If you Google up a picture of the GE EA68X90 meter, you will note that when the thing is totally disconnected and just sitting on the desktop, the meter needle is at rest on the left end of the scale, indicating 0. 0 % of full sweep, 0 Watts, 0 SWR. Not moving at all just laying there. Nada.

Nope. Minimum scale on SWR is always 1, by definition. If you're looking at a scale that has a 0 minimum, you're looking at the wrong scale.

 

[briankk]

Nope. Minimum scale on SWR is always 1, by definition. If you're looking at a scale that has a 0 minimum, you're looking at the wrong scale.

Ah yes, but to get to "1", the meter must arise from 0, which it doesn't.

I suspect we may be talking past each other, look at the picture of the meter and you'll see what I mean. In Brian's world, 1 is more than 0.. To get to 1 on the scale, first the needle must leave the zero, marked by an "0"..

 

[jim202]

Go to the lowest channel and then go to the highest channel and see which one has the lowest reading. That should give you some indication which way the length antenna needs to go. If the length is way out, this may not help.

If the SWR is lower on the lower channel, then you may have to lengthen the antenna. If the SWR is lowest on the high channel, hen your antenna needs to be shorter.

If it's too short, you could try using a pair if vice grips to prove the antenna is too short. Just clamp it up near the top and you can slide it up or down to get an idea what you need for length.

 

[briankk]

It's not about what the readings are, it's about the fact that changing the whip length does not change or otherwise effect those readings. Suspect dead K40.

 

[K7MEM]

If you Google up a picture of the GE EA68X90 meter, you will note that when the thing is totally disconnected and just sitting on the desktop, the meter needle is at rest on the left end of the scale, indicating 0. 0 % of full sweep, 0 Watts, 0 SWR. Not moving at all just laying there. Nada.

This may be an anomalous reading, but that's not whats bugging me, the fact that I cant change any of the readings by changing the antenna length is what I'm on about. Beginning to think K40 may be K put.

I did Google a image of the GE EA68X90 before I posted. That is what prompted my question. There are three scales on that meter. One for power and the other two for determining SWR. When you are in the SWR position, the power scale is meaningless and should not be used.

To check the SWR:

1. Put the switches in the SWR and FWD positions.
2. Key the transmitter and adjust the SET & FS control for full scale. Full scale will be 10 on the bottom scale.
3. Unkey the transmitter.
4. Switch from the FWD to REV position, key the transmitter and then read the SWR scale.

You will need to reset the SET & FS control for each frequency you are testing the SWR. Otherwise your readings will be inaccurate.

There is nothing wrong with getting a 1:1 SWR. That is what we all strive for. Most of the time however, we get there with matching devices of some type. Normally a vertical antenna has a pretty low input impedance (20-30 Ohms), so I would guess that the K40 has a matching device in the base that makes it a little less sensitive to changes in the antenna length.

Martin - K7MEM

 

[N0ZQR]

If I remember right those K40 antennas were pretty "wide band"(80 channels or such), so you might have to move that rod quite a ways to see any difference

I told a lot of my customers to just "bottom" the rod, put your finger at the top of the feral, pull the rod out and then put the rod back in half way. Never had a problem with doing it that way..

Ron

 

[oldcb]

K40 installed length, 54 3/4", overall whip length, removed from base, is 57 3/8".
SWR readings, ch. 1 = 1.5, ch. 19 = 1.0, ch. 40 = 0, the needle just lays there.. SWR meter is an GE EA68X90, FWIW..

Read someplace that K40 has a special capacitor that might bugger swr readings.

bk

i looked at a pic of this GE meter, swr oddly does start from 0, my guess is that your antenna isn't that far off, may need raised a little, i'd also try using another meter that starts at one 1 just to compare reading results from both meters..............

 

[jonwienke]

Again: SWR scale always starts at 1, not 0. If you're using a scale that starts with 0 to read SWR, you're wrong. If the meter labels a scale starting with 0 as "SWR", the meter is wrong. There is no such thing as SWR <1. Ever. Period. No exceptions.

 

[K7MEM]

i looked at a pic of this GE meter, swr oddly does start from 0, my guess is that your antenna isn't that far off, may need raised a little, i'd also try using another meter that starts at one 1 just to compare reading results from both meters..............

You may be reading the wrong scale or you accidentally looked at a incorrect image. Google tends to give a lot of results that don't seem to have anything to do with what your searching for. I found it difficult to get a good image, with the meter nice and clear. But I did find one. Note that the SWR scale starts at "1". Is the image below correct for the GE meter in question?

But that isn't saying you can't use a linear scale, that starts at zero, to determine SWR. You just have to take your readings and run a little calculation. The SWR scale eliminates the need to do a calculation.

In the early 80's, while I was living in Germany, I obtained a reciprocal license (DA2EU) and bought some Heathkit gear to build and use. When I got everything together I realized that the only thing I was missing was a SWR indicator and a dummy load. So I built them. The meter on the SWR indicator was a linear 0-100 scale and I never did add a new scale. But I knew that when I set the Forward reading to 100 and then the Reverse reading was 33, my SWR was 2:1 using VSWR = (VF+VR)/(VF-VR). A index card with a table that translates meter readings to SWR is all you need. You can do the same thing with the GE meter if you only use the lower FS scale.

In the end, my antenna (fan dipole/inverted V, no balun) was kind of cheesy and gave me a 10:1 SWR. I never bothered to fix it because I was transmitting from a upper floor and only 10 feet from the feed point. Cable losses were minimum. The TX had tubes and an output network that allowed me to operate just fine, without damage to the output.

 

[oldcb]

i looked at a pic of this GE meter, swr oddly does start from 0, my guess is that your antenna isn't that far off, may need raised a little, i'd also try using another meter that starts at one 1 just to compare reading results from both meters..............

my bad....after a closer look (i was initially looking at the field strength section of the meter) , the SWR reading on the meter does start at 1, so i don't see a reason why when set for swr you you wouldn't be able to set your antenna length as needed...........

 

[rwier]

my bad....after a closer look (i was initially looking at the field strength section of the meter) , the SWR reading on the meter does start at 1, so i don't see a reason why when set for swr you you wouldn't be able to set your antenna length as needed...........

That's the way I understand that device in the picture. There are three(3) scales, Two(2) have zero(0) at the left, and the middle scale (bottom side of the top scale) has a one(1). I had to put two pair of reading glasses to see the "1", lol.

 

[briankk]

my bad....after a closer look (i was initially looking at the field strength section of the meter) , the SWR reading on the meter does start at 1, so i don't see a reason why when set for swr you you wouldn't be able to set your antenna length as needed...........

My bad too, and apologies to all for being so ironheaded. The meter pictured above is indeed the meter I'm using, and when the thing is not is use, the needle points to 0 on the power scale, and exactly covers the 1 on the SWR scale, so naturally, I assumed..
When I was reading the K40, the needle just sat there, covering the 1 and pointing at the 0..

I'll go away now until I can find something else to confuse myself with. Thanks to all for providing me with detailed instructions on how to use the meter, confirmed my though that I was doing it right in the 1st place Gotta get my glasses checked out..

KI6UZD