MS119 SUPER SCANNER weird swr?

[nitroturbo4u]

<More audio>Got the new relays in and all is working fine with switching....
However....SWR on chnl 40 is like 1.1 Channel 1 is 1.4
Each element test great...When i go all directional swr is 3.0
Any ideas>????<can not stand it>

 

[RADIOOMAN]

I did a web search for the purpose of trying to assist you in resolving this issue and found some information that might shed some light on the problem you are having with the antenna.

The following is a link to that website and an excerpt from that website:

http://home.ptd.net/~n3cvj/superscanner.htm

There were other shortcomings too.
The older versions of the antenna used a coaxial stub to match the impedance when in the omni mode.
You could run a fairly good amount of power through it with no problem.
But the newer version used a different impedance transforming scheme (internal inductors and capacitors), which could only reportedly take about 50 watts or so before burning out.
Running in the directional mode, and you could run up to 1500 watts with no problem.
-----------------------------------------------------------------------------
If you have the newer version then what I take from this is that most likely a capacitor or inductor that is associated with that matching circuit has been over-dissapted.

If this is actually the problem then it might be a simple fix to correct it.

 

[nitroturbo4u]

ms119

Thank you for all your help.....I got my schematic out and the new ones used a 9 turn inductor and a 240 pf cap...
The older ones used a 9 foot long cable shorted at one end.
If i gonna run some juice in omni mode how would this go in the circuit???
the omni matching network as they say is the cap and inductor in parallel
on the shield leg...:bdh:

 

[RADIOOMAN]

I cannot say with absolute certainty, I would asssume that the unshorted end of the ~9 ft long coax (RG-58) would attach as follows: Shield to shield of the other coax shields and then the center conductor of the matching stuf would attach to the appropiate relay contact.

 

[W5LZ]

You should also keep in mind that '9 foot' section of coax is an electrical 1/4 wave, so has to be figured using the velocity factor. It'll come out a little 'shy' of 9 feet.
- 'Doc

 

[Shockwave]

This is a 1/4 wave shorted matching stub so it's a good idea to use quality cable. The RG-58 will have a good deal of loss when used as a matching stub even at lower power levels. I'd use at least RG-8. It may be a good idea to cut this a little long and trim the shorted end to get the best match in the omni mode. Since the coax stub runs down the mast it should be easy to cut an inch at a time off and twist the conductors back together to check the SWR.

 

[RADIOOMAN]

You should also keep in mind that '9 foot' section of coax is an electrical 1/4 wave, so has to be figured using the velocity factor. It'll come out a little 'shy' of 9 feet.
- 'Doc

It might be mechanically 1/4 wave but electrically it's not.

It is not a 1/4 wave, but it is a stub.

The owners manual says it is approximately 9 foot of RG-58 shorted on one end.

Now unless you are willing to dispute what the owners manual says then this should be the end of this dispute you are trying to instigate.

Geez. what is it with you?!
Are you getting low on your meds again or are you abusing your meds?

 

[9C1Driver]

That's cool that you were able to research the issue for the correct answer. Bravo.

 

[W5LZ]

"Now unless you are willing to dispute what the owners manual says then this should be the end of this dispute you are trying to instigate."

Instigate a dispute? Think that one through again. And what dispute with the owner's manual? It said 'approximate' didn't it? And if it isn't an electrical 1/4 wave, just what exactly do you think a 'stub' is in this sort of situation? Sorry, but I don't think I'm the one with a problem.
- 'Doc

 

[RADIOOMAN]

You should also keep in mind that '9 foot' section of coax is an electrical 1/4 wave, so has to be figured using the velocity factor. It'll come out a little 'shy' of 9 feet.
- 'Doc

"Now unless you are willing to dispute what the owners manual says then this should be the end of this dispute you are trying to instigate."

Instigate a dispute? Think that one through again. And what dispute with the owner's manual? It said 'approximate' didn't it? And if it isn't an electrical 1/4 wave, just what exactly do you thing a 'stub' is in this sort of situation? Sorry, but I don't think I'm the one with a problem.
- 'Doc

Evidentally you have been misinformed; A coaxial stub does not have to be an electrical quarter wave length.
And if you bothered to think this through you would realize the error of your thinking
A shorted 1/4 wave stub would theoretically present an infinite impedance at the other end and how that is gonna help correct an impedance match on this antenna when it is in the OMNI mode is beyond me.
I stated that it was a shorted stub that was made from RG-58 and it was approximately 9 feet long and you thought it was necessary to indicate that it was a 1/4 stub and you're wrong; It is a stub but it ain't a 1/4 wave.
If it was a 1/4 wave stub of RG-58 it would be nearer 6 feet at CB frequencies.

Do you really think that "approximately 9 feet" is close to 6 feet.
I am pretty sure that if it was supposed to be a 1/4 wave stub then they would have said "approximately 6 feet". (assuming RG-58)
Are you really having that much trouble understanding this?

 

[Shockwave]

The following website has some good info on this antenna: Antenna, VE3SQB Ham radio antenna design software programs and sstv,qha, amateur radio,sstv,antennas,j-pole,quad,dipole,discone,antenna program, super scanner, pdl, omni, rhcp, bazooka, coaxial dipole,skyhopper) The site has a calculator to build your own for use on different bands. When you open the calculator there are the following notes on the matching: For omni position the original scanner directions give a series capacitor of 250pf and a 9 turn inductor. I do not know the diameter or length of the coil but it must be under 1 mh. Older versions had a simpler way of just adding a quarter wave matching stub . This was shorted out at the end and left dangling down the mast.

 

[RADIOOMAN]

The following website has some good info on this antenna: Older versions had a simpler way of just adding a quarter wave matching stub .[/I]

I visited this web site associated with the link shown in the previous post and read the article and download the software and NO WHERE DOES IT SAY ANYTHING ABOUT A "1/4 WAVE MATCHING STUB" being associated with the Super/Scanner type of antenna.
It talks about the feed lines going to their respective dipoles as being a 1/4 wave length but the Antenna Specialists Instructions that come with the antenna indicated that the feedlines are 29 inches long.
They are that long so that when in one of the directional modes the other two dipoles are loaded with the right amount of inductance that is provided by an open stub of that length for the purpose of making the those two elements appear to be longer so as to act as a reflector; But this is not what we are talking about, we are talking about the matching stub for the OMNI Posistion, and that stub length is not a 1/4 wavelength according to the Instruction book provided by Antenna Specialists and according to common sense it cannot be a 1/4 wavelength shorted stub.

Like I said in a previous post in this thread; A shorted 1/4 wave is zero Z at the shorted end and extremely HI Z at the open end.

If you look at the schematic for this antenna the 3/8 wavelength stub is in shunt with the 3 dipoles when in the OMNI mode.

A 1/4 wave shorted stub would present an impedance so high that it would effectively do NOTHING.

Additionally you say a "SERIES" capacitor; It is not in series, it is in parallel with the inductor and then that is in shunt (parallel) with the 3 dipoles when it is in the OMNI mode.

 

[nitroturbo4u]

Power Capacity?


So if i use the 9 turn and cap 2nd gen as opposed to the coax version ...
Guess i'll be limited to around 50 watts all directional.With the coax stub
can i do around 1,500 continuous????<can not stand it>

 

[nitroturbo4u]

Matching stub

I copied this from the diagram....It is highlighted.

When not active, the element lengths are made to appear longer by the quarter wave coax sections. If
the coax does not add the correct amount of inductance, the elements will not act as reflectors and
the pattern will be an oval shape with equal gain front and back. Computer modelling shows the
following required amounts.
20 m 1mh and 5 pf
17 & 15 m .8 6.25
12 & 10 m .6 8.3
6 m .1 50
2m .1 5
440mhz .03 1
For omni postion the original scanner directions give a series capacitor of 250pf and a 9 turn inductor.
I do not know the diameter or length of the coil but it must be under 1 mh. Older versions had a simpler way of just adding a quarter wave matching stub . This was shorted out at the end and left dangling down the mast.

 

[nitroturbo4u]

1/4 wave ?

When not active, the element lengths are made to appear longer by the quarter wave coax sections. If
the coax does not add the correct amount of inductance, the elements will not act as reflectors and
the pattern will be an oval shape with equal gain front and back. Computer modelling shows the
following required amounts.
20 m 1mh and 5 pf
17 & 15 m .8 6.25
12 & 10 m .6 8.3
6 m .1 50
2m .1 5
440mhz .03 1
For omni postion the original scanner directions give a series capacitor of 250pf and a 9 turn inductor.
I do not know the diameter or length of the coil but it must be under 1 mh. Older versions had a simpler way of just adding a quarter wave matching stub . This was shorted out at the end and left dangling down the mast.