Date   
Re: End Fed antennas w/ uBITX #ubitx

ajparent1/KB1GMX
 

Warren,

Notice that these peaks are attenuated as you approach 30 MHz. That is indicative of the loss in the system at those frequencies. The lower the loss of the transformer the higher and more uniform would be these peaks.

While the transformer may contribute along with coax losses bare wire testing also shows that.  By that I mean the wire
itself shows a progressing reduction in the peaks.  This is due to radiation, even though the mismatch may be there some
amount of RF is always radiated and the returned energy is not there as a result.  An infinitely (or very long)  long wire at
some high frequency exhibits a very low return loss with increasing frequency.  However in the real world this can be
seen with a 20M wire at VHF. 

I can detail why that happens but resistance of the wire is not constant due to skin effect and very long wires at very
high frequencies are very low Q as a result.

Allison

Re: 12MHz xtals and QER Filter

ajparent1/KB1GMX
 

If the sweep rate is too fast the filter will exhibit tilt.

Also when I went t 82PF I used ATC 100B 5% parts I had so the result was less random.
I also found that the terminating impedance was better and the filter ripple was better with a
differently constructed transformer (ft43-2402 2 hole cores).  I would later design a 100 ohm
transformer that gave better results (2.7khz and flatter).

Keep in mind we have no data across more than a small sample of crystals and maybe only
one vendor.  So variation is expected.

Allison

Re: Arduino v1.28 for BitX40 released #bitx40

Allard PE1NWL
 

As far as I know the stock firmware for BitX40 is still Asshar's initial version v1.01
You can still download it from https://github.com/afarhan/bitx40

73 Allard PE1NWL

Re: End Fed antennas w/ uBITX #ubitx

Jerry Gaffke
 

Warren,

My dummy load is twenty 1k metal film resistors of 3 Watts.  So 50 ohms at 60 Watts.
With around 50 volts peak going in (100 volts peak-to-peak), that's on the order of  50*0.707 * (50*0.707) / 50 = 25 Watts of RF.
At times I cranked the RF up to 100 Watts.  The toroids are admittedly more massive than the resistors, but no discernible heating
in the toroids does give a little added confidence to the conclusion that we are not burning much power there.

> The cyclic VSWR pattern is very likely the result of the 100 feet of coax

As I've said earlier, when I measure my antenna system with just a few feet of coax between the matchbox and the vector impedance analyzer,
I get the same peaks and valleys in the VSWR as shown on the website but the peaks are more pronounced.   
The peaks and valleys are due to resonance in the wire, not something about the coax.  
Adding coax primarily affects frequencies at which the matchbox has a high VSWR, when losses in the coax become significant.
On a positive note, the coax does lower the VSWR at somewhat off resonant frequencies, allowing use there without a tuner.
Most non-WARC bands are usable across the entire band without a tuner even with a short coax, 80m and 10m are the primary exceptions

> It is a puzzle to me that the antenna shows resonant characteristics on non-harmonically related bands like 30 and 15 meters.

30m is near the third harmonic of 80m:  3.6*3 = 10.8mhz       Though far enough away that you still want to use a tuner with this antenna
21mhz is near the 6'th harmonic of 80m:   3.6*6 = 21.6mhz    That one's usable without a tuner.

> Additionally, you were using the "2K" model 

These are both rated at "1kW ICAS".   Danny (and his competition) does offer 2kW transformers, I have no idea what's inside them.
I have nothing here capable of more than 100W, reports are that at 1kW the toroids do heat up badly if you hold the key down too long.
Since the box is sealed and up on the roof somewhere, your primary indication is that the SWR starts rising.
On bands such as 30m where the wire is not quite resonant, you definitely don't want to go more than a few hundred Watts.


>  And this combo was terminated in a perfect resistive load. When terminated in the wire the load will be very different
>  and highly reactive on some bands. As such the transformer losses will rise dramatically but the apparent VSWR
>  will not due to the losses. I sure would like to see a VIA plot of the wire itself through the transformer.

At any integer multiple of the fundamental, the wire is resonant and purely resistive.
I'd guess that this is closer to 3000 ohms than 2500 ohms.
At resonance the measured SWR of the antenna system when using just a few feet of coax
is down at 1.2 or less, suggesting negligible losses.  (See the published charts).
Losses do rise when somewhat off resonance, as is the case with 30m.

Jerry, KE7ER


On Fri, Aug 3, 2018 at 04:46 AM, Warren Allgyer wrote:

Jerry and Gordon

Great data Jerry! I too am scratching my head over some the entries but it is a start and good to know.

I don't understand the impedance variation of the terminated pair and the terminated transformers individually. My test did not show that and it raises a bit of a red flag. I also looked more closely at the SWR table published by the manufacturer. Having stared at similar VIA outputs in my lab I noted two things. The cyclic VSWR pattern is very likely the result of the 100 feet of coax, very close to a half wave at 80 meters, alternating between a quarter wave transformer and a half wave at harmonics of 80 meters or whatever is the actual length of the coax. Notice that these peaks are attenuated as you approach 30 MHz. That is indicative of the loss in the system at those frequencies. The lower the loss of the transformer the higher and more uniform would be these peaks.

A final note on the heat: the numbers you show indicate losses on each individual transformer between 0.2 and 0.8 dB which is significantly better than I measured using the spectrum analyzer/tracking generator. As such I would not expect much heating from the 5-8 watts of input power you used. Additionally, you were using the "2K" model which uses a double stacked transformer for additional heat dissipation capability. And this combo was terminated in a perfect resistive load. When terminated in the wire the load will be very different and highly reactive on some bands. As such the transformer losses will rise dramatically but the apparent VSWR will not due to the losses. I sure would like to see a VIA plot of the wire itself through the transformer.

Your antenna appears to accept power much better than I suspected. The strategically positioned 6 turn air wound coil has a lot to do with that because it is what allows the wire length to change electrically and let harmonically related bands fall into the integer related even harmonic. It is a puzzle to me that the antenna shows resonant characteristics on non-harmonically related bands like 30 and 15 meters. That may be the witchcraft element of the coil combined with a strategic length of coax feedline.

Thank you for doing and reporting on all of that work! Great job.

WA8TOD

Re: End Fed antennas w/ uBITX #ubitx

Jack, W8TEE
 

Jerry:

We did the same thing:

Inline image

but then put it in a quart can filled with mineral oil. It will take 250W for 5 minutes without damage to the components. (However, you could probably cook French Fries in the oil.) We added a simple display to give an idea of the power going into it:

Inline image

Jack, W8TEE

On Friday, August 3, 2018, 10:24:01 AM EDT, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:


Warren,

My dummy load is twenty 1k metal film resistors of 3 Watts.  So 50 ohms at 60 Watts.
With around 50 volts peak going in (100 volts peak-to-peak), that's on the order of  50*0.707 * (50*0.707) / 50 = 25 Watts of RF.
At times I cranked the RF up to 100 Watts.  The toroids are admittedly more massive than the resistors, but no discernible heating
in the toroids does give a little added confidence to the conclusion that we are not burning much power there.

> The cyclic VSWR pattern is very likely the result of the 100 feet of coax

As I've said earlier, when I measure my antenna system with just a few feet of coax between the matchbox and the vector impedance analyzer,
I get the same peaks and valleys in the VSWR as shown on the website but the peaks are more pronounced.   
The peaks and valleys are due to resonance in the wire, not something about the coax.  
Adding coax primarily affects frequencies at which the matchbox has a high VSWR, when losses in the coax become significant.
On a positive note, the coax does lower the VSWR at somewhat off resonant frequencies, allowing use there without a tuner.
Most non-WARC bands are usable across the entire band without a tuner even with a short coax, 80m and 10m are the primary exceptions

> It is a puzzle to me that the antenna shows resonant characteristics on non-harmonically related bands like 30 and 15 meters.

30m is near the third harmonic of 80m:  3.6*3 = 10.8mhz       Though far enough away that you still want to use a tuner with this antenna
21mhz is near the 6'th harmonic of 80m:   3.6*6 = 21.6mhz    That one's usable without a tuner.

> Additionally, you were using the "2K" model 

These are both rated at "1kW ICAS".   Danny (and his competition) does offer 2kW transformers, I have no idea what's inside them.
I have nothing here capable of more than 100W, reports are that at 1kW the toroids do heat up badly if you hold the key down too long.
Since the box is sealed and up on the roof somewhere, your primary indication is that the SWR starts rising.
On bands such as 30m where the wire is not quite resonant, you definitely don't want to go more than a few hundred Watts.


>  And this combo was terminated in a perfect resistive load. When terminated in the wire the load will be very different
>  and highly reactive on some bands. As such the transformer losses will rise dramatically but the apparent VSWR
>  will not due to the losses. I sure would like to see a VIA plot of the wire itself through the transformer.

At any integer multiple of the fundamental, the wire is resonant and purely resistive.
I'd guess that this is closer to 3000 ohms than 2500 ohms.
At resonance the measured SWR of the antenna system when using just a few feet of coax
is down at 1.2 or less, suggesting negligible losses.  (See the published charts).
Losses do rise when somewhat off resonance, as is the case with 30m.

Jerry, KE7ER


On Fri, Aug 3, 2018 at 04:46 AM, Warren Allgyer wrote:

Jerry and Gordon

Great data Jerry! I too am scratching my head over some the entries but it is a start and good to know.

I don't understand the impedance variation of the terminated pair and the terminated transformers individually. My test did not show that and it raises a bit of a red flag. I also looked more closely at the SWR table published by the manufacturer. Having stared at similar VIA outputs in my lab I noted two things. The cyclic VSWR pattern is very likely the result of the 100 feet of coax, very close to a half wave at 80 meters, alternating between a quarter wave transformer and a half wave at harmonics of 80 meters or whatever is the actual length of the coax. Notice that these peaks are attenuated as you approach 30 MHz. That is indicative of the loss in the system at those frequencies. The lower the loss of the transformer the higher and more uniform would be these peaks.

A final note on the heat: the numbers you show indicate losses on each individual transformer between 0.2 and 0.8 dB which is significantly better than I measured using the spectrum analyzer/tracking generator. As such I would not expect much heating from the 5-8 watts of input power you used. Additionally, you were using the "2K" model which uses a double stacked transformer for additional heat dissipation capability. And this combo was terminated in a perfect resistive load. When terminated in the wire the load will be very different and highly reactive on some bands. As such the transformer losses will rise dramatically but the apparent VSWR will not due to the losses. I sure would like to see a VIA plot of the wire itself through the transformer.

Your antenna appears to accept power much better than I suspected. The strategically positioned 6 turn air wound coil has a lot to do with that because it is what allows the wire length to change electrically and let harmonically related bands fall into the integer related even harmonic. It is a puzzle to me that the antenna shows resonant characteristics on non-harmonically related bands like 30 and 15 meters. That may be the witchcraft element of the coil combined with a strategic length of coax feedline.

Thank you for doing and reporting on all of that work! Great job.

WA8TOD

Re: End Fed antennas w/ uBITX #ubitx

Gordon Gibby <ggibby@...>
 

Jerry --- likely that a simulator would tell you how much and how quickly reactive components add in as you move away from the exact resonant frequency.   It does seem that significant reactive components might increase losses, huh?  (I'm not an expert on that).


Any information on how far from resonant you can be before reactance increases signficnat in an end-fed, high impedance antenna, and then next, how that changes toroid losses????   that might be the $64 question.



On my homebrew off-center-fed balun diplose they "appear" more broadbanded......suggesting that the closer you get to the end, the less the importance of small variations from exact resonant frequency?


cheers,


gordon




From: BITX20@groups.io <BITX20@groups.io> on behalf of Jerry Gaffke via Groups.Io <jgaffke@...>
Sent: Friday, August 3, 2018 10:23 AM
To: BITX20@groups.io
Subject: Re: [BITX20] End Fed antennas w/ uBITX
 
Warren,

My dummy load is twenty 1k metal film resistors of 3 Watts.  So 50 ohms at 60 Watts.
With around 50 volts peak going in (100 volts peak-to-peak), that's on the order of  50*0.707 * (50*0.707) / 50 = 25 Watts of RF.
At times I cranked the RF up to 100 Watts.  The toroids are admittedly more massive than the resistors, but no discernible heating
in the toroids does give a little added confidence to the conclusion that we are not burning much power there.

> The cyclic VSWR pattern is very likely the result of the 100 feet of coax

As I've said earlier, when I measure my antenna system with just a few feet of coax between the matchbox and the vector impedance analyzer,
I get the same peaks and valleys in the VSWR as shown on the website but the peaks are more pronounced.   
The peaks and valleys are due to resonance in the wire, not something about the coax.  
Adding coax primarily affects frequencies at which the matchbox has a high VSWR, when losses in the coax become significant.
On a positive note, the coax does lower the VSWR at somewhat off resonant frequencies, allowing use there without a tuner.
Most non-WARC bands are usable across the entire band without a tuner even with a short coax, 80m and 10m are the primary exceptions

> It is a puzzle to me that the antenna shows resonant characteristics on non-harmonically related bands like 30 and 15 meters.

30m is near the third harmonic of 80m:  3.6*3 = 10.8mhz       Though far enough away that you still want to use a tuner with this antenna
21mhz is near the 6'th harmonic of 80m:   3.6*6 = 21.6mhz    That one's usable without a tuner.

> Additionally, you were using the "2K" model 

These are both rated at "1kW ICAS".   Danny (and his competition) does offer 2kW transformers, I have no idea what's inside them.
I have nothing here capable of more than 100W, reports are that at 1kW the toroids do heat up badly if you hold the key down too long.
Since the box is sealed and up on the roof somewhere, your primary indication is that the SWR starts rising.
On bands such as 30m where the wire is not quite resonant, you definitely don't want to go more than a few hundred Watts.


>  And this combo was terminated in a perfect resistive load. When terminated in the wire the load will be very different
>  and highly reactive on some bands. As such the transformer losses will rise dramatically but the apparent VSWR
>  will not due to the losses. I sure would like to see a VIA plot of the wire itself through the transformer.

At any integer multiple of the fundamental, the wire is resonant and purely resistive.
I'd guess that this is closer to 3000 ohms than 2500 ohms.
At resonance the measured SWR of the antenna system when using just a few feet of coax
is down at 1.2 or less, suggesting negligible losses.  (See the published charts).
Losses do rise when somewhat off resonance, as is the case with 30m.

Jerry, KE7ER


On Fri, Aug 3, 2018 at 04:46 AM, Warren Allgyer wrote:

Jerry and Gordon

Great data Jerry! I too am scratching my head over some the entries but it is a start and good to know.

I don't understand the impedance variation of the terminated pair and the terminated transformers individually. My test did not show that and it raises a bit of a red flag. I also looked more closely at the SWR table published by the manufacturer. Having stared at similar VIA outputs in my lab I noted two things. The cyclic VSWR pattern is very likely the result of the 100 feet of coax, very close to a half wave at 80 meters, alternating between a quarter wave transformer and a half wave at harmonics of 80 meters or whatever is the actual length of the coax. Notice that these peaks are attenuated as you approach 30 MHz. That is indicative of the loss in the system at those frequencies. The lower the loss of the transformer the higher and more uniform would be these peaks.

A final note on the heat: the numbers you show indicate losses on each individual transformer between 0.2 and 0.8 dB which is significantly better than I measured using the spectrum analyzer/tracking generator. As such I would not expect much heating from the 5-8 watts of input power you used. Additionally, you were using the "2K" model which uses a double stacked transformer for additional heat dissipation capability. And this combo was terminated in a perfect resistive load. When terminated in the wire the load will be very different and highly reactive on some bands. As such the transformer losses will rise dramatically but the apparent VSWR will not due to the losses. I sure would like to see a VIA plot of the wire itself through the transformer.

Your antenna appears to accept power much better than I suspected. The strategically positioned 6 turn air wound coil has a lot to do with that because it is what allows the wire length to change electrically and let harmonically related bands fall into the integer related even harmonic. It is a puzzle to me that the antenna shows resonant characteristics on non-harmonically related bands like 30 and 15 meters. That may be the witchcraft element of the coil combined with a strategic length of coax feedline.

Thank you for doing and reporting on all of that work! Great job.

WA8TOD

Re: Arduino v1.28 for BitX40 released #bitx40

Praba Karan
 

Stock firmware support cat control ?
Just I want to know.


On Fri, Aug 3, 2018, 7:32 PM Allard PE1NWL <pe1nwl@...> wrote:
As far as I know the stock firmware for BitX40 is still Asshar's initial version v1.01
You can still download it from https://github.com/afarhan/bitx40

73 Allard PE1NWL

Re: Arduino v1.28 for BitX40 released #bitx40

Jack, W8TEE
 

There's a file named ubitx_cat.ino, so I'm guessing yes. A good way to find out is to download the code and look at it.

Jack, W8TEE

On Friday, August 3, 2018, 10:52:49 AM EDT, Praba Karan <vu3dxr@...> wrote:


Stock firmware support cat control ?
Just I want to know.


On Fri, Aug 3, 2018, 7:32 PM Allard PE1NWL <pe1nwl@...> wrote:
As far as I know the stock firmware for BitX40 is still Asshar's initial version v1.01
You can still download it from https://github.com/afarhan/bitx40

73 Allard PE1NWL

Re: End Fed antennas w/ uBITX #ubitx

Jerry Gaffke
 

Jack,

It's not an accident that mine is similar.
Thanks for the pointer to the cheap metal film 3W resistors a few months ago!
Mine's much uglier, just twisted the ends together, though kept the
resistors spaced far enough to allow some airflow.
In your case, that's french-fry oil-flow.

I'm using 20 of this 1k 3W part from Mouser at $0.10 each
    283-1.0K-RC
Four of the 200 ohm 3W part in parallel would be plenty as a dummy load for the uBitx:
    283-200-RC

If somebody were to kit them up for the group along with a schottky diode RF probe,
the surface mount resistors might be easier to mail.

Jerry 

 
    


On Fri, Aug 3, 2018 at 07:30 AM, Jack Purdum wrote:
We did the same thing:
 

Re: End Fed antennas w/ uBITX #ubitx

Jerry Gaffke
 

Gordon,

I think just measuring the SWR into the antenna system using a short 5 to 10 foot of coax from matchbox to antenna analyzer 
gives a pretty good indication of where things will start getting lossy, for both loss in the toroid and in a long coax.
The published SWR charts on myantennas.com (and QST review) are a good indication of what you will get,
agree well for frequencies at which the SWR is under 2.0.  With a long piece of coax, the low SWR numbers
remain about the same, the high SWR numbers shoot up considerably. 
That's as I recall, it's been a couple years since I looked hard at that.

You do need some coax between antenna analyzer and the matchbox.
Take it down to a few inches with an electrically isolated analyzer and things get whacky
due to lack of counterpoise.

Jerry, KE7ER


On Fri, Aug 3, 2018 at 07:33 AM, Gordon Gibby wrote:

Jerry --- likely that a simulator would tell you how much and how quickly reactive components add in as you move away from the exact resonant frequency.   It does seem that significant reactive components might increase losses, huh?  (I'm not an expert on that).

 

Any information on how far from resonant you can be before reactance increases signficnat in an end-fed, high impedance antenna, and then next, how that changes toroid losses????   that might be the $64 question.

 

 

On my homebrew off-center-fed balun diplose they "appear" more broadbanded......suggesting that the closer you get to the end, the less the importance of small variations from exact resonant frequency?

 

cheers,

 

gordon

 

Re: experience with Sunil VU3SUA's enclosures #ubitx

Dave New
 

I found the headphone jack on the front panel PCB only had audio going to the left channel in my stereo headset.  I pulled everything apart, and discovered that there was no PCB trace going to the right channel pin on the headphone jack. I soldered a jumper from a cut-off wire across the left and right channel pins, and put everything back together.

The headphone works fine, now, both channels, and it still disconnects the internal speaker, as expected.

73,

-- Dave, N8SBE

-------- Original Message --------
Subject: Re: [BITX20] experience with Sunil VU3SUA's enclosures #ubitx
From: "Philip" <philip.g7jur@...>
Date: Thu, August 02, 2018 6:16 pm
To: BITX20@groups.io

Yes same problem here.

Philip.

Interesting antennas for QRP

Bo Barry <bobarr@...>
 

Probably old news for most, but i just stumbled upon it.

Http ://qrpguys.com
Noticed the EFHW no tuner antenna uses a 64:1 instead of 49:1 unun transformers.
Bo W4GHV 

Re: Arduino v1.28 for BitX40 released #bitx40

Allard PE1NWL
 

Just to avoid any confusion: Please note that this topic was for BitX40, not ubitx.
The file ubitx_cat.ino won't work on a BitX40.

Back to Praba's question:
The stock firmware v1.01 for BitX40 only provides basic LSB functionality.
So no cat control.
(v1.28 doesn't support cat control either, though)

73 Allard PE1NWL

Re: Interesting antennas for QRP

 

That's a great antenna, I have one right in front of me. The price is right also. I don't what the difference between 1:49 vs 1:64, but both seem to work the same, you just have to cut the wire to match the SWR.

Joel
N6ALT

Re: Interesting antennas for QRP

 

Let me rephrase that, I know what the difference is between the two, I just don't know if one performs better than another as I use both and can't tell any difference in performance.

Joel
N6ALT

Re: End Fed antennas w/ uBITX #ubitx

Warren Allgyer <allgyer@...>
 

Got it Jerry. I read your voltage as peak to peak rather than peak. My bad.

The resonant frequency of a wire that is multiple half wave lengths long does not occur at integer multiples of the base frequency. For example, an antenna cut to resonate at 3.6 MHz will not also resonate at 7.2 but at a higher frequency. How much higher depends on the characteristics of the wire but it will certainly not fall naturally within the 40 meter band. There will be a cyclic pattern visible from these resonances on the wide range VIA.

The fact that the antenna you have has resonances that fall at integer multiples says there is something else going on there. I suspect this is the function of the 6 turn inductor which would have the effect of electrically lengthening the wire, and lowering the resonant frequency, with greater effect at successively higher harmonics of the fundamental.

A length of 50 ohm coax attached to this adds yet another cyclic pattern of impedances that will cycle between the actual impedance at the transformer at any point where the coax length is an integer multiple of a half wave, to the transformed impedance value of the cable combined with the transformer at any odd multiple where the cable is a quarter wave.

So between the varying impedance of the transformer itself, that of the loaded wire, and the length of the cable between the rig and transformer, there is likely a brew which will give multiple resonances that fall within the ham bands. There are, however, combinations and frequencies that will present highly reactive, high VSWR loads for the transformer which will multiply its losses by a factor of 10 or more. The insidious thing about these frequency combinations is the VSWR  will remain artificially low due to those very losses. So, in operation, you actually have no way of knowing, other than transformer heating whether you are operating at a real, low loss VSWR null or one produced by high losses resulting from a mismatch.

If I could the VIA plots of the transformer/antenna with a very short cable, and again with the operating length cable, I could know which low VSWR points are real and which are simply created by loss. Short of that, if it makes contacts and the toroids don't explode (some have!), you are good to go.

WA8TOD

Re: End Fed antennas w/ uBITX #ubitx

Arv Evans
 

Seems that most EFHW impedance matching transformers are wound on ferrite
or powdered iron cores.  For experimental purposes it should be possible to use
air-core (PVC or Acrylic, or wooden cores) transformers.  The number of turns for
a given inductance is not that much different between metallic core and air core
transformers.  This is especially true if the air-cored units are wound on toroidal
forms.  Those with a lathe could easily turn toroidal formers from wood or plastic.

Possible advantage of winding one's own matching transformers is that modification
and adjustment of impedance transformation is more easily done if the transformer
is not potted inside a plastic box.  Winding one's own transformer might also allow
connection of a variable capacitor in parallel with the antenna side to make it into
a end-fed wire tuner (L-match) to achieve a more perfect match

Arv  K7HKL
_._
.


On Fri, Aug 3, 2018 at 8:24 AM Jerry Gaffke via Groups.Io <jgaffke=yahoo.com@groups.io> wrote:
Warren,

My dummy load is twenty 1k metal film resistors of 3 Watts.  So 50 ohms at 60 Watts.
With around 50 volts peak going in (100 volts peak-to-peak), that's on the order of  50*0.707 * (50*0.707) / 50 = 25 Watts of RF.
At times I cranked the RF up to 100 Watts.  The toroids are admittedly more massive than the resistors, but no discernible heating
in the toroids does give a little added confidence to the conclusion that we are not burning much power there.

> The cyclic VSWR pattern is very likely the result of the 100 feet of coax

As I've said earlier, when I measure my antenna system with just a few feet of coax between the matchbox and the vector impedance analyzer,
I get the same peaks and valleys in the VSWR as shown on the website but the peaks are more pronounced.   
The peaks and valleys are due to resonance in the wire, not something about the coax.  
Adding coax primarily affects frequencies at which the matchbox has a high VSWR, when losses in the coax become significant.
On a positive note, the coax does lower the VSWR at somewhat off resonant frequencies, allowing use there without a tuner.
Most non-WARC bands are usable across the entire band without a tuner even with a short coax, 80m and 10m are the primary exceptions

> It is a puzzle to me that the antenna shows resonant characteristics on non-harmonically related bands like 30 and 15 meters.

30m is near the third harmonic of 80m:  3.6*3 = 10.8mhz       Though far enough away that you still want to use a tuner with this antenna
21mhz is near the 6'th harmonic of 80m:   3.6*6 = 21.6mhz    That one's usable without a tuner.

> Additionally, you were using the "2K" model 

These are both rated at "1kW ICAS".   Danny (and his competition) does offer 2kW transformers, I have no idea what's inside them.
I have nothing here capable of more than 100W, reports are that at 1kW the toroids do heat up badly if you hold the key down too long.
Since the box is sealed and up on the roof somewhere, your primary indication is that the SWR starts rising.
On bands such as 30m where the wire is not quite resonant, you definitely don't want to go more than a few hundred Watts.


>  And this combo was terminated in a perfect resistive load. When terminated in the wire the load will be very different
>  and highly reactive on some bands. As such the transformer losses will rise dramatically but the apparent VSWR
>  will not due to the losses. I sure would like to see a VIA plot of the wire itself through the transformer.

At any integer multiple of the fundamental, the wire is resonant and purely resistive.
I'd guess that this is closer to 3000 ohms than 2500 ohms.
At resonance the measured SWR of the antenna system when using just a few feet of coax
is down at 1.2 or less, suggesting negligible losses.  (See the published charts).
Losses do rise when somewhat off resonance, as is the case with 30m.

Jerry, KE7ER


On Fri, Aug 3, 2018 at 04:46 AM, Warren Allgyer wrote:

Jerry and Gordon

Great data Jerry! I too am scratching my head over some the entries but it is a start and good to know.

I don't understand the impedance variation of the terminated pair and the terminated transformers individually. My test did not show that and it raises a bit of a red flag. I also looked more closely at the SWR table published by the manufacturer. Having stared at similar VIA outputs in my lab I noted two things. The cyclic VSWR pattern is very likely the result of the 100 feet of coax, very close to a half wave at 80 meters, alternating between a quarter wave transformer and a half wave at harmonics of 80 meters or whatever is the actual length of the coax. Notice that these peaks are attenuated as you approach 30 MHz. That is indicative of the loss in the system at those frequencies. The lower the loss of the transformer the higher and more uniform would be these peaks.

A final note on the heat: the numbers you show indicate losses on each individual transformer between 0.2 and 0.8 dB which is significantly better than I measured using the spectrum analyzer/tracking generator. As such I would not expect much heating from the 5-8 watts of input power you used. Additionally, you were using the "2K" model which uses a double stacked transformer for additional heat dissipation capability. And this combo was terminated in a perfect resistive load. When terminated in the wire the load will be very different and highly reactive on some bands. As such the transformer losses will rise dramatically but the apparent VSWR will not due to the losses. I sure would like to see a VIA plot of the wire itself through the transformer.

Your antenna appears to accept power much better than I suspected. The strategically positioned 6 turn air wound coil has a lot to do with that because it is what allows the wire length to change electrically and let harmonically related bands fall into the integer related even harmonic. It is a puzzle to me that the antenna shows resonant characteristics on non-harmonically related bands like 30 and 15 meters. That may be the witchcraft element of the coil combined with a strategic length of coax feedline.

Thank you for doing and reporting on all of that work! Great job.

WA8TOD

Re: experience with Sunil VU3SUA's enclosures #ubitx

Kevin Rea
 

Hi Sunil,
Do you have any plans to make a case that will House a 3 1/2" or 5" Nextion display ?
Kevin Rea
K6REA

Re: Interesting antennas for QRP

ajparent1/KB1GMX
 

There are some general reasons for that.  One being the 1:64 transformer is more difficult
and most installed wires are at a lower height so the feed point resistance is lower.

Also 50*49 is 2450,  50*64=3200  most wires are in that general range such that
there is overlap.    If the wire is thinner and higher the 64 transformer may be better
but for most installations the 49 will do fine.

Also 1:36  (50*36=1800) is a doable transformer (2t:12t wire) as even for a nominal
2500 ohm wire the mismatch is 1.4:1.  And low wires as would be typical for
field installs at lower frequencies like 80 and 40M are lower in feed point resistance.

Allison

my mic

hirosmb <hirosmb@...>
 

This took for a hour. :)

// hiro, JJ1FXF