Can't get to Gap Antennas web site. Is it just me or something else that I have missed

73 Dave G8PGO

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Hi -- I read the suggested pages, including:

?

Those are indeed quite simple and apparently effective?tuners --- but they do require tuning, and at the base of the antenna (since you wouldn't want to run this through coax!!!)....one might be able to run it through some open wire feed potentially....with some wild impedances of course along the smith chart!!!!

The article doesn't go through a smith chart explanation of WHY one needs the TUNED circuit, but I would guess it takes out whatever reactance is there....? ?I have an ANCIENT tuner at home that works EXACTLLY this way & I've never before understood how to use it ---- but now I might be able to get it working with an endfed and amaze and amuse my ARES group!!

The simplicity of the non-tuned transformers is seductive to many peopple I'm sure as then they can put the stuff out near the antenna and just run coax back to their shack.? ?(A more advanced build would have a remotely controlled capacitor, but in that case, just use some form of auto-tuner....)? ??

There are compromises in every design.? ?I've never tried a tuned coupled set of coills like this one, so I learned even more!? ?Thanks!!

Gordon

The combined effect of the rely mod and? the audio switch mod do help greatly.

If the DC switching scheme also used a pair of contacts to pull the floating TX+/RX+
to ground it would help as well.? It can be done with the N3GO two transistor mod.


Allison

ABSOLUTELY! This is a no-no and needs to be corrected on all v3 PWBs. I noticed in the new design (v4) he does not use this T/R relay audio switching scheme.I suspect it was done in part to deal with the speaker thumping everyone has complained about. There are other ways to handle that issue and many are discussed at length in other posts. You need to cut the two traces that run that audio connection near the relay. One trace can be "cut" by simply removing R70. The other trace is the one just over that trace when the PWB is positioned with R70 down at the bottom. Then, remove C51 and tombstone it on the upper pad where it formerly was. Add a jumper wire between the top exposed end of C51 and the left pad where R70 was located. Now, that will completely eliminate the RFI in your audio on your PWB. The speaker thumping may in fact become worse after you make this mod. Farhan has made an easy improvement to switch off the audio on the newest version of the PWB. I hope this helps!
N2AJX?

Gordon,

There is no need to do the testing at high power. I simply terminated the transformer in a 2470 ohm load made up of a 2K and a 470, 1/8th watt resistors in series. My testing is done at a maximum of 1 mW so low power is fine.

The lowest loss 49:1 transformer that I have been able to construct uses BN-43-7051 cores and I have been able to get to 0.2 dB with them. For 160-20 meters I use a 14:2 ratio and for 20 - 10 a 7:1. With a true resonant half wave wire these cores get barely warm after a full minute of key down at 100 watts.

However(!!!), that 0.2 dB loss rises dramatically if the cores feed a reactive load and are not substantially better in that case than are the big toroids.

The best case for the EFRW (random end fed wire) remains a simple tuner.

WA8TOD

If you buy it, it's "new" to you.

Vince - K8ZW.

--
Michigan VHF Corp.

One has been sold and shipped, still have the other one.

W0EB

Wow. Perfectly satisfied with mine.
I did remove paint a couple places to insure the case was grounded. No biggie.
A LOT of effort and material for a tiny price in my opinion.
73, Bo W4GHV since '54

for the parallel resonant see:



Also:


As to what toroid for tuned usually iron powder type -2 or -6

However I use a L-network for monoband EFHWS.? I grind the number in a spreadsheet
make a coil using iron-powder or conventional solenoid coil and a capacitor with enough?
voltage rating (at least 2000V) and I'm off to the races.? One trick is if I don't have the
exact capacitor value needed I go with the next lower and parallel it with a section of
teflon coax (about 29.4pf/foot good to 2500V).? Also if vibration is not an issue the
Arco trimmers work.

For wide band trasnformers I tend to do a lot of build and test to see what works.
Depenign on how its would and the type (transmission line, hybrid or....) wire used
and many other parameters it may use different materials.? But its been measured
and tried a few ways for best result.? For the 1:49 I've had better result with
mu=125 (61ish material) or sometimes 43.??

One I have copied many times with good results is a multi ratio design by K3MT.
ITs part of his grasswire antenna but generally useful for many things.? The article
attached.? It would be a good 1:9 transformer for those wanting to try the
non-resonant 53ft or longer approach with a counterpoise.? Try the Grasswire
while your at it, its easy to install!

Allison

omitting the word "new" is more accurate. I have purchased several refurbished Dell box PC's with great success. $300 is a great price to pay for this PC.

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Chuck, Alyson, and others: ?could I get a schematic of your parallel resonant tuning system? And could I get Alyson and or Warren to come yet on what permeability toroid is optimal?

I don't accept their .2db.? Also their process is only workable if they do the math to back out the?
mismatch loss.

Do I think their procedure is a good way to do it.? No.? Did that do the math to correct their data
for mismatch loss? No I see no mention or statement correcting for that.

If your argument is their test is wrongly done or has a incorrect conclusion then we do agree.

The process and procedures normally used to make that kind of measurement are likely
to disagree with their result and conclusions but will produce an accurate answer when
performed correctly.


Allison

Tim,

I did see that.? I appreciate that but I do have stock here thank you.

Allison

Chuck, I haven't yet built two 49:1 (one is not enough for the back to back test hi hi ), but I would use ferrites with permeability close to 800, not the powdered iron toroids like the red and the yellow you have selected (permeability is less than 10). I imagine that the inductance needed at 2500ohm needs to be very high. I might be wrong as I have not made yet one with such a high transformation radio, but I feel I am quite right, IMHO.

Mine took about 6 weeks to get to Arizona, but it was worth the wait.? Good looking cabinet.? I agree with others that paint in the openings was heavy, but a little sanding with a Dremel tool took care of that.? Isn't that why you have those fun tools.? You need something to use them on!!? Also, I had to replace the on/off switch, but a trip to my local electronics supply store and $3.00 fixed that.? Besides, I found $40 worth of other stuff that I just couldn't pass up.

Moral of the story, be patient. His case is very well made and the extra parts are useful. I don't have to go looking in the junk box for a knob.?

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BTW:

in the original BITX20 these diodes were in eacht RX and TX path leading to the individual amplifiers.

Henning Weddig

DK5LV

So for BITX40 a diode in series with R111 blocks C11 from supplying Q16 as well. Now supply that diode direct from +12, no on/off of U1 and less current through K1 pin 3. R111 can then be either reduced (to 10) or eliminated/shorted.

On Wed, Aug 1, 2018 at 09:04 AM, Gordon Gibby wrote:

At any rate, it will be a huge improvement over what most of them had beforehand (NOTHING HF).? ?

I've gone this route also, Gordon.? I bought 4 uBitX units, with the intent that I will have several HF rigs for operating activities such as Field Day, and as HF rigs to loan to new hams.? For both of those use cases, a simple and efficient antenna is needed, and I've chosen to go with EFHWs using parallel-resonant matching units built around T82 toroidal inductors - T82-2 for the 40/30/20 meter units, and T82-6 for the 20/17/15/12/10 meter units.? I used magnet wire and mica compression 'trimmer' caps which I had NOS in my parts collection, so the total cost of each matching unit for me was? ~$10.? The enclosures turn out to be the most expensive part (~$2.75 each).

one year ago these hams?didn't know a resistor from a transistor.....

and that is a real WIN.