Topics

Portable antenna(s) #antennas #v6

KB9WOO
 

New to the uBITX, kits, HF, and the group.

Looking for something small, easy, and quick just to get on the air so I'm looking at grabbing a MFJ-1820T single band antenna for 20m, which was designed for the FT-817.  This antenna needs a counterpoise and the 817 apparently has a ground screw on the chassis that the counterpoise is connected to.  I thought I'd just use a clip to attach it to the BNC elbow, or I might even use a small tripod instead.

Mostly just wondering if anyone has used one of these MFJ-18xx antennas with the BITX.  There is also the multi-band 1899t.

--
Mark, kb9woo
Milwaukee, WI uBITX v6

Curt
 

Mark

let me suggest a plan B -- if you would like to operate on more than one band consider an 'End Fed Half Wave.'  many homebrew references on the web.  also check out QRPGuys here in the US - they have some nice inexpensive EFHW kits. 

'counterpoise' is merely a poor approximation for having many radials.  advantage of the EFHW is that the 'counterpoise' shrinks to being very small, because of the unique physics. 

if you expect to have some space, I strongly recommend the EFHW.  if you are on a ridge etc with no trees - QRPGuys has a cool matching network to use with a 'Squid pole' vertical. 

ham radio is about learning - keep at it !  enjoy your radiations with that new rig ! 

73 Curt wb8yyy

PS - there is a trick to use an EFHW over 80 to 10 meters, by placing a little coil near the feedpoint.  this is described various places on the web. 

Jack, W8TEE
 

Mark:

I agree with Curt. I live on about 3 acres but "someone" (not to be named) says a tower-and-beam are a no-no, so I purchased an EFHW-4010 end-fed from Myantennas. It's not the cheapest EFHW, but it works like a champ. This is a picture of a 7-25MHz scan (horrible picture, but conveys some info) of the antenna:

Inline image

The antenna in the scan was from several years ago and a tornado put it down somewhere in PA (I think). I replaced it with the 80-10M version. I think it does a good job.

Jack, W8TEE

On Monday, February 17, 2020, 3:01:31 PM EST, Curt via Groups.Io <wb8yyy@...> wrote:


Mark

let me suggest a plan B -- if you would like to operate on more than one band consider an 'End Fed Half Wave.'  many homebrew references on the web.  also check out QRPGuys here in the US - they have some nice inexpensive EFHW kits. 

'counterpoise' is merely a poor approximation for having many radials.  advantage of the EFHW is that the 'counterpoise' shrinks to being very small, because of the unique physics. 

if you expect to have some space, I strongly recommend the EFHW.  if you are on a ridge etc with no trees - QRPGuys has a cool matching network to use with a 'Squid pole' vertical. 

ham radio is about learning - keep at it !  enjoy your radiations with that new rig ! 

73 Curt wb8yyy

PS - there is a trick to use an EFHW over 80 to 10 meters, by placing a little coil near the feedpoint.  this is described various places on the web. 

--
Jack, W8TEE

KB9WOO
 

I've considered the EFHW and wire dipoles.  Definitely a better option, but requires trees or something to get the end off the ground.  I've also looked at magnetic loops, like the Alex Loop, but I'm priced out of that one at the moment.  I know this MFJ is going to be even more of a compromise compared to other options even in the price range, but the simplicity of setup is what I was going for.

QRPGuys has a $20 kit no tune EFHW... that's definitely in my price range.  Maybe I'll get both.


--
Mark, kb9woo
Milwaukee, WI uBITX v6

Curt
 

Mark
Also check the 3 band vertical matching unit at qrpguys. I got a squid pole from Asia in a few weeks, or try cabellas.

Jack

I confess to owning 80m qro efhw from myantennas. But for qrp easy to make one, web has the info, main part is a ft120-43 or an order to qrpguys. The trick for all band is that loading coil near the feed.

We know an efficient antenna avoids discouragement with a few watts.

73 curt

Gordon Gibby
 


Our group built well over a dozen Endfed 49 to 1 baluns for resonant half wave antennas (against ground.  ) FT – 140 Dash 43 from kits&parts.com in Florida   Because it’s a high impedance system, even a 1 foot stake in the ground works pretty well. 

After we did the project, I got to working with the  spectrum analyzer and discovered we could reduce the losses even more by going to 4 turns/28 turns total. (improved design) That gets the losses considerably lower.   For higher power operation, consider one or two FT– 240 Dash 43 toroids ,3 turns/21 turns.   These will not have the capacitive adjustment that the commercial units have, but they will work quite well.  I’ve gotten a look inside some commercial units and they are designed very similarly. 



Gordon Kx4z 



On Feb 17, 2020, at 17:33, Curt via Groups.Io <wb8yyy@...> wrote:

Mark
Also check the 3 band vertical matching unit at qrpguys. I got a squid pole from Asia in a few weeks, or try cabellas.

Jack

I confess to owning 80m qro efhw from myantennas. But for qrp easy to make one, web has the info, main part is a ft120-43 or an order to qrpguys. The trick for all band is that loading coil near the feed.

We know an efficient antenna avoids discouragement with a few watts.

73 curt

KB9WOO
 

Gordon,

Can you explain what it means when you say "4 turns/28 turns"? 
 
I'm not following that part.

--
Mark, kb9woo
Milwaukee, WI uBITX v6

Gordon Gibby
 

Hi -- take a look at the PDF for better description.   Basically, the way we did ours is an AUTOtransformer; so this refers to having 28 total turns, and taking a 50 ohm tap at only 4 turns up from ground (common)   The 28 turn end will reflect 2450 ohms (theoretially).   

A 7:1 turns ratio causes the voltage to go up by 7, and the current to go DOWN by 7 (conservation of power) and the result is the impedance goes up by 49.    (49*50 = 2450 ohms).  

I hope that better explains it.   If you don't have enough inductance in the 50 ohm part, you have losses....if you have too many turns you have other losses (?capacitance? i'm not sure) and there are losses in the ferrite.   Unfortunately I'm not enough of an expert to do much more than build two devices, put them back-to-back across a spectrum analyzer and measure the total loss, divide by 2.   Getting the right number of turns experimentally is the best that I can do.   There may be a better core than type 43, but that is the best I have done so far.   Forget iron cores for this particular application....for the lower bands.

Gordon



On Mon, Feb 17, 2020 at 8:57 PM KB9WOO <kb9woo@...> wrote:
Gordon,

Can you explain what it means when you say "4 turns/28 turns"? 
 
I'm not following that part.

--
Mark, kb9woo
Milwaukee, WI uBITX v6

Ken Hansen
 

+1 for EFHW if thTs an option.

I'm not a fan of that particular MFJ portable antenna - it's a series of compromises intended for a specific application, mounted on the back of a QRP Radio.

I'd suggest the 17 ft MFJ telescoping antenna, as well as The full-sized MFJ hamsticks, either one as vertical with a collection of ground radials cut to be resonant on the given band, or as a pair in a 'hamstick dipole' configuration.

Each of the above have 3/8" x 24 stud mounts.

If end-fed is an option, consider building the Hawaii EFHW described here:


They offer a kit, but construction is simple.

Ken, N2VIP

On Feb 17, 2020, at 12:27, KB9WOO <kb9woo@...> wrote:

New to the uBITX, kits, HF, and the group.

Looking for something small, easy, and quick just to get on the air so I'm looking at grabbing a MFJ-1820T single band antenna for 20m, which was designed for the FT-817.  This antenna needs a counterpoise and the 817 apparently has a ground screw on the chassis that the counterpoise is connected to.  I thought I'd just use a clip to attach it to the BNC elbow, or I might even use a small tripod instead.

Mostly just wondering if anyone has used one of these MFJ-18xx antennas with the BITX.  There is also the multi-band 1899t.

--
Mark, kb9woo
Milwaukee, WI uBITX v6

Gordon Gibby
 

I'd like to see some LOSS DATA on that Hawaii endfed.   It is an autotransformer design, but the concern that I have is that the toroid chosen is iron (type #2) permeability = 10.   Using some online calculators, at 40 meters the primary would have about 1.2 microhenries and 50 ohms of inductive reactance.   I think you'd rather see the self-inductance many times that of the resistive impedance desired.....   Would want to see two built back to back, and losses measured.    That test has been humbling to me at times.....

my 2 cents worth.   If anyone has loss data, would be useful for me to hear....
gordon


On Mon, Feb 17, 2020 at 9:36 PM Ken Hansen <ken@...> wrote:
+1 for EFHW if thTs an option.

I'm not a fan of that particular MFJ portable antenna - it's a series of compromises intended for a specific application, mounted on the back of a QRP Radio.

I'd suggest the 17 ft MFJ telescoping antenna, as well as The full-sized MFJ hamsticks, either one as vertical with a collection of ground radials cut to be resonant on the given band, or as a pair in a 'hamstick dipole' configuration.

Each of the above have 3/8" x 24 stud mounts.

If end-fed is an option, consider building the Hawaii EFHW described here:


They offer a kit, but construction is simple.

Ken, N2VIP

On Feb 17, 2020, at 12:27, KB9WOO <kb9woo@...> wrote:

New to the uBITX, kits, HF, and the group.

Looking for something small, easy, and quick just to get on the air so I'm looking at grabbing a MFJ-1820T single band antenna for 20m, which was designed for the FT-817.  This antenna needs a counterpoise and the 817 apparently has a ground screw on the chassis that the counterpoise is connected to.  I thought I'd just use a clip to attach it to the BNC elbow, or I might even use a small tripod instead.

Mostly just wondering if anyone has used one of these MFJ-18xx antennas with the BITX.  There is also the multi-band 1899t.

--
Mark, kb9woo
Milwaukee, WI uBITX v6

zl1bnb
 

I have my doubts about the effectiveness of end-fed antennas when operated at even harmonics of the half-wave frequency.

Consider an end-fed 80 metre half-wave operated at 40 metres.  One end of the antenna will be radiating a field which is in anti-phase to the field generated by the other end, and surely this will cause cancellation of the emfs developed in in any incident antenna. 

Sure, the antenna can readily be matched, and it may be an efficient radiator, but the opposing fields will generate opposing potentials , causing cancellation.

Where am I wrong?

73 de miken,  zl1bnb

Gordon Gibby
 

Hi Miken.....

Well, you see, those ends are separated in SPACE....and therefore in TIME.    Therefore the superposition of the signals from each end, at any other point, will have to take into account the different DISTANCE (and therefore TIME) from each end, and therefore the PHASES will be affected.

The simple answer is that there will be points where they add, and points where they subtract.   Exactly the same thing like when looking at the effect of the reflected wave off the presumed ground causes antennas to have lobes of maxima and minima in the elevation plane.     I think on one of the exam questions, one has to deal with the impact of various antennas being fed in- or out- of phase and separated by different distances.   AM radio stations do this to create a beam pattern to emphasize their signal in desired directions.   

I've been very effective with a 40-meter half wave antenna operated on its 2nd harmonic from a bus-stop, by the way!   Made some well documented great connections!    So yes, you do radiate quite effective power.

73,

gordon gibby kx4z


On Mon, Feb 17, 2020 at 11:23 PM zl1bnb <mdnewman.nz@...> wrote:
I have my doubts about the effectiveness of end-fed antennas when operated at even harmonics of the half-wave frequency.

Consider an end-fed 80 metre half-wave operated at 40 metres.  One end of the antenna will be radiating a field which is in anti-phase to the field generated by the other end, and surely this will cause cancellation of the emfs developed in in any incident antenna. 

Sure, the antenna can readily be matched, and it may be an efficient radiator, but the opposing fields will generate opposing potentials , causing cancellation.

Where am I wrong?

73 de miken,  zl1bnb

Patrick Pelletier
 

Hi,

I believe that antenna is an end fed random length wire antenna.  If it were an end fed half wave, the transformer would be a 49:1...

73

Patrick
VE9PAX


On Mon, Feb 17, 2020 at 10:36 PM Ken Hansen <ken@...> wrote:
+1 for EFHW if thTs an option.

I'm not a fan of that particular MFJ portable antenna - it's a series of compromises intended for a specific application, mounted on the back of a QRP Radio.

I'd suggest the 17 ft MFJ telescoping antenna, as well as The full-sized MFJ hamsticks, either one as vertical with a collection of ground radials cut to be resonant on the given band, or as a pair in a 'hamstick dipole' configuration.

Each of the above have 3/8" x 24 stud mounts.

If end-fed is an option, consider building the Hawaii EFHW described here:


They offer a kit, but construction is simple.

Ken, N2VIP

On Feb 17, 2020, at 12:27, KB9WOO <kb9woo@...> wrote:

New to the uBITX, kits, HF, and the group.

Looking for something small, easy, and quick just to get on the air so I'm looking at grabbing a MFJ-1820T single band antenna for 20m, which was designed for the FT-817.  This antenna needs a counterpoise and the 817 apparently has a ground screw on the chassis that the counterpoise is connected to.  I thought I'd just use a clip to attach it to the BNC elbow, or I might even use a small tripod instead.

Mostly just wondering if anyone has used one of these MFJ-18xx antennas with the BITX.  There is also the multi-band 1899t.

--
Mark, kb9woo
Milwaukee, WI uBITX v6

Gordon Gibby
 

Aha!   As Allison i think has shown, RANDOM length end feds, with 9:1's perform terribly from a loss standpoint.
To each, their own.

Gordon



On Tue, Feb 18, 2020 at 6:14 AM Patrick Pelletier <ve9pax@...> wrote:
Hi,

I believe that antenna is an end fed random length wire antenna.  If it were an end fed half wave, the transformer would be a 49:1...

73

Patrick
VE9PAX

On Mon, Feb 17, 2020 at 10:36 PM Ken Hansen <ken@...> wrote:
+1 for EFHW if thTs an option.

I'm not a fan of that particular MFJ portable antenna - it's a series of compromises intended for a specific application, mounted on the back of a QRP Radio.

I'd suggest the 17 ft MFJ telescoping antenna, as well as The full-sized MFJ hamsticks, either one as vertical with a collection of ground radials cut to be resonant on the given band, or as a pair in a 'hamstick dipole' configuration.

Each of the above have 3/8" x 24 stud mounts.

If end-fed is an option, consider building the Hawaii EFHW described here:


They offer a kit, but construction is simple.

Ken, N2VIP

On Feb 17, 2020, at 12:27, KB9WOO <kb9woo@...> wrote:

New to the uBITX, kits, HF, and the group.

Looking for something small, easy, and quick just to get on the air so I'm looking at grabbing a MFJ-1820T single band antenna for 20m, which was designed for the FT-817.  This antenna needs a counterpoise and the 817 apparently has a ground screw on the chassis that the counterpoise is connected to.  I thought I'd just use a clip to attach it to the BNC elbow, or I might even use a small tripod instead.

Mostly just wondering if anyone has used one of these MFJ-18xx antennas with the BITX.  There is also the multi-band 1899t.

--
Mark, kb9woo
Milwaukee, WI uBITX v6

KE0GYC
 

With regards tonsoace considerations, if you are going with a 20m monoband the support system could be pretty simple.

My first portable antenna mast was a 20ft Shakespeare Wonderpole that can be had for not much over $20 and is very light.  You could support a sloper EFHW for 20m with that.  I often leave the top section collapsed (for greater rigidity) and set up a 40m EFHW in an inverted V with that very setup.

I also have a Jackite 33ft pole that could do a 20m EFHW as a straight vertical, but that is significantly more in cost, weight, and guying requirements.

Doug W
 

lots of good information over at https://groups.io/g/antennas/topics
--
www.bitxmap.com

Don Gamble
 

Some portable operators have used vertical or near vertical off center fed dipoles for 20m.  It does change the radiation angles but it brings the feed point closer to you shortening the coax needed.  

Good luck with your antenna system.

73 de Don KG5CMS.

On Tue, Feb 18, 2020, 11:06 AM Doug W <dougwilner@...> wrote:
lots of good information over at https://groups.io/g/antennas/topics
--
www.bitxmap.com

lowalacrity
 

Mark, If small, quick and easy is what you're looking for, look at my listings on eBay. I offer novel 9:1 ununs using dual ferrite beads that have proven to be very popular and also ferrite toroids for EFLWs. No wire or enclosures included but they might suit your needs .I'm also calling them variable ratios as I have found with the 9:1's that adding and subtraction hi side windings can help "dial in" a particular band, (with the appropriate long wire length). My prices make them a big draw. John (eddieson)

Tom, wb6b
 

Hi,

I run a non-resonate end fed antenna because it offers a reasonable tradeoff between efficiency and the space needed to string it up on my property. I only need about 55' to cover down to 80 meters. 

The antenna in not a random length. It is a specially calculated length to provide as close as possible to the correct impedance, into the 9:1 unun transformer for the bands you want to operate on. 

Not much different the efficiency tradeoff people make using shortened verticals with all sorts of rods, spikes, spiders, coils and whatnot gizmos to make them "resonate".

But if you have more room, the bigger the better seems to apply. 

Here is a presentation regarding end-fed non-resonate antennas.

https://palomar-engineers.com/wp-content/uploads/End-Fed-Antenna-Secrets-YUMA-2020-Hamfest.pdf

Tom, wb6b

Gordon Gibby
 

Thanks, Tom, that’s a very nice presentation, but I did not see loss or efficiency data (other than FoR common mode chokes) 




On Feb 18, 2020, at 23:23, Tom, wb6b <wb6b@...> wrote:

Hi,

I run a non-resonate end fed antenna because it offers a reasonable tradeoff between efficiency and the space needed to string it up on my property. I only need about 55' to cover down to 80 meters. 

The antenna in not a random length. It is a specially calculated length to provide as close as possible to the correct impedance, into the 9:1 unun transformer for the bands you want to operate on. 

Not much different the efficiency tradeoff people make using shortened verticals with all sorts of rods, spikes, spiders, coils and whatnot gizmos to make them "resonate".

But if you have more room, the bigger the better seems to apply. 

Here is a presentation regarding end-fed non-resonate antennas.

https://palomar-engineers.com/wp-content/uploads/End-Fed-Antenna-Secrets-YUMA-2020-Hamfest.pdf

Tom, wb6b