Johnson Matchbox 250-23 and Doublet questions.

[KX5JT]

Looks like I will be obtaining a Johnson Matchbox 250-23.  I presently use a G5RV with a gutted out MFJ-962D but I want to try out a Doublet.  I will be able use maybe 180 feet (90 feet each leg) inverted with the center up around 45 feet and the ends down to about 12 feet.  My question is should I use the longest doublet I can erect (180 feet) or would I be better off cutting it at a different length for any reason.  If I can get 160 meters great.  My DX-60 and SB-200 won't play on 160m but I am still working on the Johnson Viking I which will.  My plastic radio will too but that would be barefoot. 

My other question is.... I understand this model of Johnson Matchbox is rated for 275 watts carrier.  Is this conservative?  Will it handle a little more okay?  Not that I have that capability... yet.

73 and MERRY CHRISTMAS

John KX5JT

[ke7trp]

No 160 in that Matchbox.  I suggest you cut the wires for your area of the 75 meter band.  No point to go longer. The unit is bandswitched and you might not get it to tune. 

I have run a valiant at 150 watts AM through it without trouble.  1000 watts SSB.  Thats probably about it.  The key here is to tune on low power and get it flat before putting the power to it. If you fire off the heat into the little matchbox untuned, Its going to arc over. 

They are neat little tuners.  I own three of them.  Look for a KW matchbox if you want to run more power.

C

[KX5JT]

Hey Clark I appreciate the words.  BTW, I had heard you calling cq last week and tried to answer but just wasn't quite getting through... you asked for my call a few times but it wasn't quite happening.... maybe soon.

John KX5JT

[ke7trp]

Cool..  That was you!   I had the same thing happen tonight..  Band is real rough for me.  All the homes around me running modern heat pumps really makes the bands rough!

Hope to hear you soon!

Clark

[WA1GFZ]

John,
You might be able to get the match box to work on 160. make sure the primary tap is connected to the whole winding. Then you will need additional C across the output. The best thing to do is get 50 feet of 1/4 inch copper tubing and wind it on some 3 or 4 inch PVC pipe and build a good HD tuner for 160. Run the open wire directly to the tuner.
KB3AHE antenna configuration may be better because the ends will be higher. 160 meter inverted vee with the ends at 12 feet doesn't work all that well but it will get you on. Under 200 feet total length can be tricky to tune.

[K5UJ]

Hi John,

the 275 w. MB should handle 200 w. carrier out no problem; I think some guys run as much as 250 w. (1 kw pep).  Get rid of the G5RV by extending the balanced part all the way to the tuner.   I agree, shorten the dipole to 1/2 w. on 75 (around 130 feet) and make the feedline around 90 feet long and it should work FB.  The reason for making the dipole shorter (one reason) is that it will tune on 40 m. and give you a decent pattern on that band.   Also, the ends will be higher up.  In my opinion there is no point in trying to get it to work on 160 because it is too low.   Here's the thing with antennas:  as you know, they are not a digital binary type thing--they don't clearly either work or completely shut off.   They usually work well or work ..sort of.   That "sort of" situation traps many many hams (Gap Voyager, 43 foot "all band" verticals, Isotrons...).  If you have nothing good to compare a "sort of" antenna to, you may think it's working FB, and years may pass before you experience a truly good antenna and have that wow moment when scales fall away from your eyes etc.     With the current G5RV your height on average is around 30 feet.  You have to think of height in terms of wavelength on the band of interest.   30 feet high on 160 is like having a dipole 7 feet high on 40 m.   You would never have a dipole on 40 m. only 7 feet high would you?    Huge ground loss.  So, basically on 160 you are going to have to have a separate antenna, and if you cannot achieve height (at least 100 feet for a dipole) you are going to have to work against ground.  That means something like an inverted L with a lot of radials.  You can use the L for transmitting and by pass the Matchbox and use the dipole as a receive antenna on 160.   On 160 transmit antennas are usually not the best rx antennas, another thing about 160 that's different from the higher bands. 

73

Rob
K5UJ

[K1JJ]

Very good summary, Rob. I see your new antennas worked out FB and you learned the lessons they taught well....


On the 160M dipole - here in the Northeast, (and upper east coast) there is a concentration of AM stations not found anywhere else in the USA.  In this area we can get away with "low" dipoles for 160M having TO angles of 70-85 degrees cuz the paths are usually under 200 miles or so to work many stations.  It's a great local-work antenna. But as you inferred, out where John is in TX or any western US area, the stations are very far apart and a low dipole won't cut it. It IS better to work out a vertical system with radials out there if the dipole will be close to the ground.. However, there will still be certain cornditions that greatly favor high angles during the wintertime.

Another thing to be aware of is for 160M DX work, a vertically polarized antenna usually has about a 10db advantage over a horizontal due to Earth geo-magnetic attenuation. (I forgot the proper term)   I experienced this here when I had a dipole at 190' stretched between two towers (flat) and compared it to a vertical system with 360 radials. The vertical was ALWAYS much louder into Europe. On 75M and above, it was the opposite with the high horizontals aways 10db or more louder than a vertical - at least at my QTH.

But a good vertical needs lots of clear room to work (no nearby houses, etc) and a great radial system. I think for the average ham, the best antenna system for 160M would be a full-size dipole as high as possible WITH the option to feed it as a "T" against ground. (radial system)  Just tie the feedline inner and shield together and feed it against ground. Have a quick A-B switch to be able to see which is best on the fly. Being able to switch quickly low angle/ high angle during QSOs is what gives the advantage.


T

[KX5JT]

Great comments guys.  Actually, my goal is to optimiz 80/75 while achieving the higher bands through 10 as well.  160 is more of an afterthought here but the matchbox as previously noted doesn't tune 160 anyway without some modification. 

So with 3885 Khz as the main goal, should I cut the length for that frequency or will going a bit longer be more wise.... I do operated below 3.800 quite a bit as well.

Maybe I'll just throw up 135 feet and be done with it?  Then I can worry about 160 meter for a future project, maybe the inverted L at some point.

John, KX5JT

[ke7trp]

I used 130Ft with 450 ohm line with mine. Tuned every band flat.   You will like the little matchbox. Its a neat little tuner. Download and read the manual for it on BAMA.  Search yahoo for BAMA manuals and you will find it. 

C

[KX5JT]

Oh well... I got sniped on eBay in the last 10 seconds... I was the only bidder for that matchbox... until 10 seconds and they sniped it away...

Any one have one for sale?

[ke7trp]

Shucks..  I am not selling mine but I will ask around.. Post in the wanted section here on AMfone.


C

[KF1Z]

John,

I may have missed it somewhere.....

But, why not just build a tuner?

A couple variable caps, and some wire and/or tubing, and you have it made.

(and of course a box or plywood to mount it on)

You can build a very strap-escent tuner FAR cheaper than buying one, unless you are really lucky to find a reasonably priced unit.

[KX5JT]

John,

I may have missed it somewhere.....

But, why not just build a tuner?

A couple variable caps, and some wire and/or tubing, and you have it made.

(and of course a box or plywood to mount it on)

You can build a very strap-escent tuner FAR cheaper than buying one, unless you are really lucky to find a reasonably priced unit.

I'm beginning to think this way too.  Other than hamfests, where does one find the proper variable caps for a balanced tuner?  Well hamfest season is about to start here in the south.  I will be making the Orange, TX fest last weekend of Jan and then our local club has one two weeks after that in March at Rayne, LA.  I was just wanting to put up the doublet before new years.... ah well.

[ke7trp]

Thats the real problem.. People suggest you build your own tuner all the time. Great.. Send me the caps for a balanced tuner that will handle high power and I will sit down and build one. I dont have the caps and at ham fests dont ever come across large split stator caps.

C

[KF1Z]

I find them all the time on ebay...

Probably even have some here still, though I sold a couple off earlier this fall.

There are those here that say you don't NEED a split stator cap, and can use a regular single section cap, or a vacuum variable ..... which does seem to work fine.


But, if you just have to have a split-stator... let me know what value & voltage rating you want....I'll see what I have.

I have also taken single section caps, and cut the stator supports, and made them into dandy split-stator units....  a little lexan, a drill, and a hacksaw is about all you need!


And if you want an input cap, "broadcast" type, multi-gang caps are really easy to come by.

[KF1Z]

http://cgi.ebay.com/VARIABLE-TUNING-CAPACITOR-CARDWELL_W0QQitemZ170421579354QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item27adeaee5a


http://cgi.ebay.com/Variable-Capacitor-High-Voltage_W0QQitemZ290382891654QQcmdZViewItemQQptZVintage_Electronics_R2?hash=item439c2b4a86

[K1JJ]

HB tuner info:

http://amfone.net/Amforum/index.php?topic=18054.0


John,

There's nothing like building and using your own tuner. Real easy to make and will handle 10KW - no baluns.

Simple - just a single section cap, main coil, input coil and clips for the feedline. Add a BC input cap if desired.  Check eBay for vacuum variables - they will do the job best.  Billions and billions of AMers have built their own version of this antenna tuner. Do a search on AMfone for "K1JJ tuner" for more pics and info.

73,

T


LOOK how simple this 160-10M version is:  (Cleanly built by KA2J)

[w3jn]

Listen to Master Vu - he speaketh the truth.  Nothing at all wrong with the Junkston Flashbox, but the K1JJ tooner is extra simple and super low loss.  One coil, an input winding, and a variable cap and yer done.

I built one using an old BC xmitter tank coil and a vac variable, and it handles full scrote from the GPT-750 with ease.  Tuning the 75M dipole on 160 maketh a LOT of circulating current (enough to get a touch of talkback from the vac variable) but the coil barely gets warm.

[KX5JT]

Yes Tom I was looking at that a bit earlier and at you Super Tuner schematics.  So no split stator caps needed with that setup and it's balanced.  Very nice!  I think I'll work on the coil first.  Once I get a good coil built out of tubing I'll worry about the caps.  Thanks OM!

John

[K5UJ]

John,

You can get the copper tubing at most big box hardware type stores.  Before you wind and form the coil practice with wire.  You can also purchase a fixed value edge wound silver plated inductor and add a link around it with a few turns of copper tubing.   So there are lots of ways of doing this.   Vacuum variable caps have pros and cons.   They have a wide range and high voltage breakdown but moving through the whole range can take time and mounting them can take some doing.  And of course if you drop one it's all over   
Sorry you got sniped on eBay.  That stinks.  I confess I did that once in an auction and felt like pond scum afterwards.  Never again.  Assuming you elect to buy a tuner (I am in no way endorsing buying over homebrewing) the KW Matchbox is the best commercially made balanced feedline tuner out there.  If you are going to buy one you may as well look for one of those.  The 275 w. model is okay but if you have the KW model you'll never worry about arcing anything at typical ham power.   You are better off getting a tuner like that at a hamfest.  Don't know about your area but around here they turn up so you just have to be patient and have some cash with you.  Unfortunately we're out of the hamfest season now.  The 275 w. mb usually goes for $100 to $150; the KW model $300 to $350.   Given the components inside one that's not too bad a deal.   If you took what they listed for in 1959 and inflated that to 2009 a new one would be around $1000.  

Okay, about eBay--you have to employ a little strategy for anything on there.  Let's first assume you found a widget that looks okay and the seller has good approval and all that i.e. it looks like a square deal.   You don't do anything.  You want the widget to just sit there and sleep and hope no idiots show up and bid it up.  If that happens forget it.   About an hour before the end of the auction check it again.  Hopefully there will be only one or two bids or none.  About a minute before the auction ends put your bid on there, the maximum you want to pay.   That isn't sniping it out from under others but it isn't going to bid up the widget like an early bid would.  If you get it you can feel like you got it fair and square.   The amazing thing about eBay is that I have seem two identical items for auction at the same time, and one will get bid way up there and the other will go for a great deal.   Go figure.   So you can snag some good stuff on there but I guess it is all about timing.

73

Rob

[N3DRB The Derb]

ebay can be a great source for tubes and parts, just look for things that the audiophiles dont wanna mess with that will still serve your purposes.

[K5UJ]

Very good summary, Rob. I see your new antennas worked out FB and you learned the lessons they taught well....

Hey Tom tnx; say, 2 or 3 weeks ago I worked a guy in the pac. northwest on the dipole on 75 m. & sig. rpt. was S9 so I quickly switched to the 65 foot vertical and went up 10 to 20 dB depending on QSB.  So the sweat and money last summer suddenly seemed worth it hi hi.  73
r.

[ke7trp]

I need to put my Vert up.  I got a Vertical off a Battleship.  Its 65 to 70 ft tall in round sections with a 200 lb Ceramic insulator and mounting bracket.  Maybe next year. 

C

[KX5JT]

Well... I am pretty stoked now to build a K1JJ suppah tuna.  

For you ARRL members, this is a great link for ideas on rolling your own inductors...

http://www.arrl.org/tis/info/pdf/9708033.pdf

As I said, going to work on getting an inductor rolled then move on to the rest.   Any information on tubing size, number of turns and spacing for a 160-10 m range would rock!  Oh heck nevermind, I see the values in Tom's schematics.  Breadslicer caps too... I think I'll forego the vacuum variable caps at least for the initial version.

John KX5JT

[K1JJ]

Well... I am pretty stoked now to build a K1JJ suppah tuna.  

As I said, going to work on getting an inductor rolled then move on to the rest.   Any information on tubing size, number of turns and spacing for a 160-10 m range would rock!  Oh heck nevermind, I see the values in Tom's schematics.  Breadslicer caps too... I think I'll forego the vacuum variable caps at least for the initial version.

John KX5JT

Good decision, John.

It pays to shed the chains of any commercial gear you can and build your own.  For some stuff, like ssb riceboxes, it's close to impossible to duplicate yourself. But an antenna tuner you build will be far superior to any of the commercial stuff out there. You will also learn a lot about antenna matching and multiband openwire use very quickly.   I've seen many guys go through the same process you are about to and they couldn't understand how they put up with all that MFJ tuner stuff in the past.

Just make the main coil large enuff to cover 160M and then some. Not critical at all. You tap it where you want, so even if it's twice the size it needs to be, it won't matter. But you don't want it too small or you can't reach the lower freqs.

I would start looking on e-Bay for a turns counter and vac variable cap. Once set up, you can tune it quickly with exact pre-set accuracy. Also, be sure to mark the taps for each band so you can change bands with a 1:1 swr without even thinking about it.  Ease of use is what makes this tuner worthwhile.

Take some pics when you're building and finished...


Rob: Hope to hear ya on 75 soon. I'm about finished with some major rig mods here and starting to get on again.... both AM and DX ssb.

T