MFJ 915 INSTALLED AT THE ANTENNA'S FEED POINT

[loosecannon]

I'd like to let everyone who's helped me know why the antennas not in the air yet. I have a a very bad back. when i say bad think about the worst back injury someone could have then times that by ten. I need help with the install and if I could've done it myself it would've be in the air weeks ago.
Now. If this is fact I'm going to have to make a 110 " jumper. Correct? Well if this is the fact. This will be the catalyst for putting the brand new 2000 instead of the a99. I mentioned it in an earlier post that the only reason for sticking with the a99 was the fact i received not a singal rfi complaint and didn't want to push my luck. I'm done putting my station together as my cousin stopped by yesterday and the setup is ready to go. It's the neatest wiring job that a station i owned ever had. No cobwebin . So neat i cant beleve it mysrlf. Ill take a few pics tomorrow. Antennas going up on Wednesday rain day Thursday. Like I said if this is fact the 2000"s going up. All I needed was an excuse for either grabbing the box with the a99 or 2000 in it and thismaybe it..

you'll be happier with the imax2000 anyway.
be sure to use the ground plane kit with it, as this antenna actually benefits from having one.

i realize that you already bought the other stuff, but just as an FYI; palomar engineering makes a kit that includes a bunch of snap on ferrite beads for common mode filtering.
using this kit, you dont need any breaks in the coax, extra connectors, or anything like that. (this is what is inside your MFJ unit BTW)
it costs about 30 bucks.

with the IMAX, you can put the CMC right at the feedpoint.
LC

 

[Stellasstillarat]

you'll be happier with the imax2000 anyway.
be sure to use the ground plane kit with it, as this antenna actually benefits from having one.

i realize that you already bought the other stuff, but just as an FYI; palomar engineering makes a kit that includes a bunch of snap on ferrite beads for common mode filtering.
using this kit, you dont need any breaks in the coax, extra connectors, or anything like that. (this is what is inside your MFJ unit BTW)
it costs about 30 bucks.

with the IMAX, you can put the CMC right at the feedpoint.
LC

 

[Stellasstillarat]

I can't go with the gp kit. My backyards kinda small. I thought about getting the gp when I purchesed the 2000 but being I'm only 12' off the ground it'll look like a rocket ship taking off.

Honestly if I were going to go with a ground wave antenna I would've purchased a maco or high end 5/8 or a similar aluminum groundplane.

I have the dubble male 259 connector fot the 915. Which will put the 915 as close to the antennas so 239 as possible, and no breaks in the coax.

I recall asking questions about the initial install of my a99 and if the fact it would be only about 12' off the ground and answers were all over the place some said go for it and a some said it's just not gonna work.
Well it worked very well. That is until I decided to mess with it and fxxxed it all up.
I'm tempted to ask if the 2000 at only 12' off the ground is going to be problematic but I'm not going too, ask that is.

The Imax 2000 will be going up at 12' with the mfj 915 connected to it's so 239 via a double male 259. If it works it works. If not ill move on and possibly go with my coax made 11 meter dipole in a horizontal configuration (purchased off an eday seller who makes them for every band from 10-160 and they look well made). This was my first antenna and in an inverted v it worked good. At that time I was just using the sonar on AM only for local chew and had yet to use the madison for ssb at that time.
I just wanna get to skipping.
As for local rag chew my furthest locals about 20 miles away and I'm fairly positive he'll hear me. The AM local radio is a sonar fs 2340 with a palomar 300a. Im not sweting it im just gonna go for it anf cross my fingers. QUOTE="loosecannon, post: 528179, member: 1368"]you'll be happier with the imax2000 anyway.
be sure to use the ground plane kit with it, as this antenna actually benefits from having one.

i realize that you already bought the other stuff, but just as an FYI; palomar engineering makes a kit that includes a bunch of snap on ferrite beads for common mode filtering.
using this kit, you dont need any breaks in the coax, extra connectors, or anything like that. (this is what is inside your MFJ unit BTW)
it costs about 30 bucks.

with the IMAX, you can put the CMC right at the feedpoint.
LC[/QUOTE]

you'll be happier with the imax2000 anyway.
be sure to use the ground plane kit with it, as this antenna actually benefits from having one.

i realize that you already bought the other stuff, but just as an FYI; palomar engineering makes a kit that includes a bunch of snap on ferrite beads for common mode filtering.
using this kit, you dont need any breaks in the coax, extra connectors, or anything like that. (this is what is inside your MFJ unit BTW)
it costs about 30 bucks.

with the IMAX, you can put the CMC right at the feedpoint.
LC

 

[loosecannon]

yes, your antenna will work at 12 feet off the ground.
is it optimal? no.
but it will work for you, and you will be able to talk skip when conditions are in.

with the antenna only that far above the ground, you REALLY want to go with the imax.

with the A99, you are actually only about 4 feet off the ground to the bottom of the radiating element. (remember, it uses the first 8 or 9 feet of your coax)

with the antenna that low, the main concern is interference to yours and your neighbors electronics.
the CMC won't help with this, unless the interference is being caused specifically by common mode currents.

usually, with an antenna at this height; the issue is simple overload because the signal coming off the side of your antenna is right in line with a bunch of "unintentional receivers".

if you are looking for an antenna that is easy and cheap to build, doesnt require an antenna tuner, can be built on the ground, and actually has a little gain, then look into building a half square antenna.
it is only bi-directional, but unless you specifically want to talk to canada and mexico, an east and west orientation will work quite well for DX.

basically, you have an SO-239 connector with a 102" piece of wire soldered in the center pin.
you mount the connector up above 102", and let the wire hang straight down, so its end is just off the ground. (not touching the ground)

then you solder a 1/2 wavelength of wire to the ground side of the connector, and extend that out horizontally perpendicular to the directions you want to work.
at the far end of the horizontal wire, you solder another 102" length of wire going straight down.
this end should be just off the ground like the other one.

the antenna ends up looking like an H without the top bars.

SWR should be right at about 1.5:1.
if pruning is needed, you cut equal lengths off of the vertical wires.

ive built one before, and it worked pretty darn well for how far off the ground it was.

LC

 

[Stellasstillarat]

I'm gonna make it as simple as possible for myself to get back on the air asap and screwing those three lengths of imax 2000 doesn't get any simpler.
I'm concidering getting a low pass filter. I've installed a Dawia two way antenna switch. I have it setup to switch between the Madison/phantom and sonar / 300a. If I purchese a low the low pass filter (and I'm posit I will) does it get placed between the Dawia and meter or after that at the meter? I this i something i should know but I don't . If I had to guess I'd say at the meter but I won't know until I hear it from you. By the way lossecannon even though my Madison is no where as nice yours as s I obviously couldn't do it my self as you did but with an alignment , new caps, a frequency counter and vfo/slider type frequency/channel selector it really works great. The recive is very nice an the audio with the silver eagle gets unsaliseted ssb compliments all the time. Thank for every one's help. I'm almost there.

yes, your antenna will work at 12 feet off the ground.
is it optimal? no.
but it will work for you, and you will be able to talk skip when conditions are in.

with the antenna only that far above the ground, you REALLY want to go with the imax.

with the A99, you are actually only about 4 feet off the ground to the bottom of the radiating element. (remember, it uses the first 8 or h 9 feet of your coax)

with the antenna that low, the main concern is interference to yours and your neighbors electronics.
the CMC won't help with this, unless the interference is being caused specifically by common mode currents.

usually, with an antenna at this height; the issue is simple overload because the signal coming off the side of your antenna is right in line with a bunch of "unintentional receivers".

if you are looking for an antenna that is easy and cheap to build, doesnt require an antenna tuner, can be built on the ground, and actually has a little gain, then look into building a half square antenna.
it is only bi-directional, but unless you specifically want to talk to canada and mexico, an east and west orientation will work quite well for DX.

basically, you have an SO-239 connector with a 102" piece of wire soldered in the center pin.
you mount the connector up above 102", and let the wire hang straight down, so its end is just off the ground. (not touching the ground)

then you solder a 1/2 wavelength of wire to the ground side of the connector, and extend that out horizontally perpendicular to the directions you want to work.
at the far end of the horizontal wire, you solder another 102" length of wire going straight down.
this end should be just off the ground like the other one.

the antenna ends up looking like an H without the top bars.

SWR should be right at about 1.5:1.
if pruning is needed, you cut equal lengths off of the vertical wires.

ive built one before, and it worked pretty darn well for how far off the ground it was.

LC

 

[loosecannon]

happy to help.
ive actually been accused of running a ham rig on SSB with my madison.
i also use a silver eagle mic with it. (but it's been modified too )

as for the low pass filter, it should be the last thing in line before the antenna, but you can install it before the meter also and you shouldnt encounter any problems with it.

the biggest deal is to put it after the amplifier if you use one, because they are the biggest culprits of creating harmonics.

the cool thing about putting the low pass filter before the meter, is that you will get to see the actual 27mhz wattage out from your amp, whereas without a filter in place, the meter would just add the harmonics to the fundamental signal and add them together, giving you a false higher reading. (trying to convince some cb'ers of this can be tough)

so if you put a low pass filter after your amplifier, before your wattmeter, and you see the "normal" output of your amplifier drop, then you know the amp was emitting harmonics.

as for recommendations for a low pass filter; i would go with a used one from the 70's or 80's that was made by any reputable ham equipment manufacturer.
they will all be well made.
my favorite is the drake 1000 watt version, but thats just because its what ive always used.
i would stay away from anything made specifically for CB use, anything that includes any tuning adjustments, or anything from MFJ.
again, i dont have a specific reason for not liking the MFJ units, its just that ive had bad experiences with some of their other products, and tend to stay away from their stuff as a rule.

i do want to make one big point about your low pass filter.
you really should ground the case of the filter to your ground system.
the optimal setup would be a ground rod installed right outside the shack, all your equipment grounded to a metal panel on the wall, and a big solid copper wire going from that panel to your ground rod that is less than 8 feet long.
this ground rod should be tied to the AC service ground for your house for safety.

as for how well a low pass filter will work when its not grounded to anything except the shield of your coax; well, i think i used to know the answer to that, but have forgotten. LOL
it would be worth your while to do a bit of searchin' and askin' around the ham sites to find the answer to this.
who knows, you may find that a filter is a waste of money if its not grounded, or you may find that im full of crap and it makes no difference.
LC

BTW- love the pics of the madison. i have installed one of those kits in a 148, and it worked well.
i dont like how the encoder doesnt have any detents though.
i believe the intention was for it to act like a VFO, but i always ended up under or over shooting the channel i was going for and having to backtrack.
also i think he should have used bigger LEDs and centered the display in the window.

 

[222DBFL]

RF limited makes a decent low pass filter that can handle some power. I've one and use it and it does work well. Keeps the neighbors happy too. If you can, get 2, one for after the radio and one for after the amp. jmho.

 

[fourstringburn]

what they dont tell you that the "quarter wave" part of the antenna is the first 9 feet of your coax

Where did you learn this from???

And just how can only a portion of your feedline, 9 ft. as you say be part of the 1/4 wave AND NOT THE REST OF IT???

For this to be possible the radiating coax (if it did) would have to be broken up 9 ft. below the feed-point by a line isolator choke balun or else the whole coax will radiate down to the shack.

This is how my OCF Carolina Windom antenna works by using a 22ft. vertical radiator connected from a 4:1 voltage balun and then using a choke balun below. This keeps the vertical coax INTENTIONALLY radiating it's 22ft. length as part of the antenna system and the choke balun at the end of the vertical coax stops the radiating RF from continuing down the coax into the shack.

The Antron is basically a 1/2 wave end fed dipole with shunt loading matching coils as shown in the pic below. This antenna does not need 9ft. of coax for the 1/4 wave part, That would be like a stub match. That's what the matching coils are there for to bring the feed point back to 50 ohms.

Antron 99

 

[loosecannon]

fourstringburn, you are correct in your supposition that if the coax was not broken up by a line isolator, the coax would radiate down into the shack.
on the A99 antenna; it does.
remember this is a CB antenna, and the manufacturer isnt going to include a choke balun with their "magical" antenna.
im sure you can see why this would be an "unadvertised feature".

im not the only one who knows this. it gets forgotten if not talked about for a while, but its been common knowledge for a while.

when i say "uses the first 9 feet of coax", maybe i should rephrase it to say "needs the first 9 feet of coax".

the currents just get really low after that point in the coax, and yes, A99's have a history of causing TVI and other interference because of this "feature".
the first 9 feet or so of the coax is the counterpoise of the antenna.
just imagine how hard it would be to tune a half wave antenna that didnt have some sort of counterpoise.

if the A99 has the ground plane kit installed with it, then you can put the choke at the feedpoint.

if anyone doesn't believe me, try putting a choke balun at the feedpoint of an A99 antenna and see what your SWR is.

LC

 

[fourstringburn]

the first 9 feet or so of the coax is the counterpoise of the antenna.

What it seems your talking about is using the first 9 ft. of coax as a counterpoise. This could work theoretically, but you must break the coax with a choke balun for it to work like this as I said so already, you didn't say anything about using a choke you just said that it is common knowledge that the 1st 9 ft of coax makes up the 1/4 wave which is wrong. It is not a designed feature of the antenna to automatically use the first 9 ft. of coax as a counterpoise. This sounds like CB shop urban myths.

I wouldn't recommend this especially since the ground plane kit is cheap enough and has 3 radials which would be far more effective. Vertical antennas are only one half of a complete antenna sort of speak, therefore you should use a ground plane kit or ground radials which need to be 1/4 wavelength of the frequency band the antenna can resonate on. Multi-band antennas need at least two 1/4 wavelength radials for every band the operator can work on. The ground radials make up the other missing half of the antenna.

Most antennas including Amateur antennas don't come with a supplied 1:1 choke balun. Certain Amateur antennas usually come with transformer or other types of baluns specific to that antenna.

What we are talking about here is keeping common mode currents minimized, not antenna matching or counterpoises.

When controlling common mode currents, the choke balun should be at or near the source of the common mode current to start with, the antenna and at the feed point. That's a fact.

Common mode currents can manipulate SWR meters in the shack so it's always best to use an antenna analyzer if possible or an SWR meter at the antenna feed point with a short jumper to check the antenna. If there is a difference between checking the SWR with a balun on or off, then I would question the balun since I have had bad luck with the MFJ 915.

I have had good luck with the ones made by Better Balun Designs.

TVI can be reduced if common currents are minimized, but other things can cause TVI as well.

 

[loosecannon]

What it seems your talking about is using the first 9 ft. of coax as a counterpoise. This could work theoretically, but you must break the coax with a choke balun for it to work like this as I said so already, you didn't say anything about using a choke you just said that it is common knowledge that the 1st 9 ft of coax makes up the 1/4 wave which is wrong. It is not a designed feature of the antenna to automatically use the first 9 ft. of coax as a counterpoise. This sounds like CB shop urban myths.

not sure why you are trying to give me an antenna lesson, but you should probably do some additional reading before doing so.
that is not said to start a fight, its just faster to say that than to type a book to explain where you are incorrect.

most of what you posted is correct. however, the paragraph i quoted above is where you are incorrect in your thinking.

you do not have to "break the coax with a choke balun for it to work".

yes, you do need to insert a coax choke in the coax line in order to stop the common mode currents from traveling past whatever point you put it.

you do not need to put a choke in line in order for the antenna to "see" its counterpoise.

think of it like the radials coming off of the bottom of groundplane antennas.

what would happen if you made the radials longer than 1/4 wavelength?
they would still work, its just that you would notice less and less current along the length of the radial once you got past the 1/4 wavelength point.

this is the same idea as your coax shield coming down off the bottom of an antron 99 antenna.

ever study up on the design of an avanti astroplane?
they tell you right in the patent sheet that the antenna needs 102" of either coax or mast underneath the hoop in order to work right.
how do you explain being able to use more than 9 feet of coax to get from that point to your shack?

again, if you don't believe me, try it for yourself.
or, failing that, do a google search on this and see for yourself.

as for the matching network and advertisements; antron themselves claimed it to be a " half over a quarter wave, mutual transductance tuned antenna."
guess where the quarter wave part is...

BTW- i am a guitar player, so its in our nature to argue with eachother! LOL

LC

 

[M0GVZ]

yes, your antenna will work at 12 feet off the ground.
is it optimal? no.
but it will work for you, and you will be able to talk skip when conditions are in.

OK I'm going to put a stop to this nonsense....

For local it is less than optimal. For DX it is just fine.

with the A99, you are actually only about 4 feet off the ground to the bottom of the radiating element. (remember, it uses the first 8 or 9 feet of your coax)

Utter utter bollocks. It is a halfwave end fed antenna. It is voltage fed, not current fed. It does not use any of your coax as part of the antenna. Any RF on the outer of the coax is incidental and caused by local environmental issues and not a deliberate design feature of the antenna. Therefore the bottom of the radiating element is where the wire comes out of the top of the matching section in the base.

....half square.....

ive built one before, and it worked pretty darn well for how far off the ground it was.

LC

For fairly local DX I'm sure it is but the Half Square take off angle is around 20-30 degrees making it optimal only up to a couple of thousand miles.

 

[wavrider]

http://www.w8ji.com/end-fed_1_2_wave_matching_system_end feed.htm

Place an RF choke at the feed point, let the mast the A99 is mounted to as well as a tower if installed on a tower be the counter poise.

I have installed both the A99 and the I2K with rf chokes at the feed point, NO CMC noted and very broad banded due to the lossy matching circuit.

I believe IF a 1/4 wl of mast is not used then sure the feed line becomes part of the antenna system.

IF a 1/4 wl or longer of mast pipe is used and an RF choke or isolator at the feed point then CMC is minimum.

 

[fourstringburn]

not sure why you are trying to give me an antenna lesson, but you should probably do some additional reading before doing so.

So give us a antenna lesson.

You still don't get it.

Without a balun after 9 ft to do what you describe, the whole coax can radiate not just 9 ft. automatically. I pointed this out earlier on how it works in detail with a visual reference using my Carolina Windom antenna as a reference on how to make only a portion of the feed line radiate to become part of the antenna system.

You haven't explained in any detail and back it up with real references how just 9 ft. of coax will radiate and the rest of your feed line won't, unless you are just using 9 ft of coax to start with.

What you are saying is using the Antron antenna without a ground plane, the first 9 ft. of coax automatically becomes the antennas counterpoise, but not the rest of the coax.

The Antron antenna needs to be D.C. grounded with a metal pipe mast and needs either the ground plane kit or ground radials cut at the proper wavelength to be most effective.

ever study up on the design of an avanti astroplane? they tell you right in the patent sheet that the antenna needs 102" of either coax or mast underneath the hoop in order to work right.

It did not say that at all in their instruction manual and it makes references to more CB shop urban myths about using specific overall coax lengths and gives different length multiples between using solid or foam dielectrics.

BTW- i am a guitar player, so its in our nature to argue with eachother! LOL

Yes I'm a musician, but unlike most people whom call themselves musicians, they can't read it's written language. I call them fretboard pattern players.

I'm both a Bass player and a Classically trained Pianist and I am well read in both Clefs so if we were on a music forum, I would easily challenge you there.

Time to let others chime in and see if other will support your claim.

 

[binrat]

OK,
I still say as close as practical to the feed point. As an end feed 1/2 antenna it uses the mast as a counterpoise.
Some reading on the A-99.
http://xoomer.virgilio.it/ham-radio-manuals/a99.pdf