开云体育

?Thanks for confirming that idea of how they work.? ?I have one sitting at home that I flat could NOT understand how it works, but the circuit is identical to what we're seeing here --- two coupled coils (it has two different sets with different number of turns each, making 4 total cols, two transformers) and they are marked for differnt frdquency ranges, and a built in dummy load and a tuningcapacitor (or more, can't remember).? ?I picked it up at a hamfest unsure of what it was but intrigued.? ?

Obviously I didn't realize what it could do, and will try it with a HIGH impedance antenna some time soon and see what happens.......??

Will be a very cool demo to give at club meeting if it does work......

gordon

try just this:
http://gapantenna.com/

开云体育

On Wed, Aug 1, 2018 at 11:47 AM, Gordon Gibby wrote:

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!!

I wanted to keep that separate.

There are several reasons one is tuned means any parasitic elements like lead lengths, circuit capacitance
are absorbed in the tuning and inductor.? ? ?The only reason for tuning other than that is it neatly sidesteps the?
loss issues with a high Q coil and a typical air variable is also a very high Q device so circuit losses are small.

FYI the old Johnson matchbox and similar were notable for being able to feed any parallel line and flexible
enough to match most anything from a short vertical without loading to a really high impedance like a half wave.
Those that know and understand them pay top prices for a clean one.? That and they are often radio art!

Allison

Just tried again and still get 'can't reach this page'
Must be something local

Dave G8PGO

Gordon,

The coupled coils approach is so old school I'd suspect is had origins in the late
20s or 30s if not before with spark. It persists because it is easy to understand,
build and?does indeed work.? It also offers selectivity as its a band pass filter.? That in?
a high BC radio environment might be very helpful.

They are of course local to the antenna as any form of transmission line tends to?
make a simple life, complicated.? The upside is even at power they can be fairly compact.

It can be done at the bottom of a half wave vertical.? As far as tuning remotely,?it could work
to the limits of the variable cap?at a harmonic of the base antenna.? But do keep in mind a?
full wave or longer 1.5 wave pattern is not the usual broadside sine-cosine pattern.? For a 1.5
wave vertical at 28 mhz the peak power is at something like 75 degrees, not very useful.
For a half wave it will be quite low more like 21 degrees, very useful.

The whole thing of compromise antennas is that for one this its that and for another its a solution.
Which is which is the exercise of experience.

Allison

It's warranted as new, so it is new.

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

73 Dave G8PGO

开云体育

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.

开云体育

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?