On Sep 7, 12:30*pm, dave wrote:
RHF wrote:
On Sep 6, 8:27 pm, wrote:
On Sep 6, 8:51 pm, John *wrote:

On 9/6/2010 4:58 PM, RHF wrote:

...
JS - it sounds like you are . . .
still stuck on "17" - pal ~ RHF
* *.

I can't believe they can take my tax dollars, good money, and have the
school system turn out witless idiots ...

Regards,
JS

Unfortunately- more often than we hope our hard earned (read blood)
money collected by the taxman goes to waste. From what I see the
entire educational system has become a complete farcicle.
- How about sending men to Mars?
- That can be much more beneficial- at least it
- might revive NASA and create some jobs.
- May be...

-wrt- NASA Sending Men to Mars :

How about we spend all that time and money
on 'fixing' our Education System first.

What good is it to send Men to Mars . . .
-if- The People back on Earth can't spell M-a-r-s
-and- Don't know that Mars exists or anything
about it . . .

Why train American engineers when S. Asian engineers are more
cost-effective? *That makes no business sense.

"You want fries with that?"- Hide quoted text -

- Show quoted text -

....not if the potato comes from China !!!

Wonderful discussion! :-)


you just shoot a lot of amps though wire that was NEVER
meant to take the amps, this is obvious by the manufacturer
saying not to run 5 watts though it.

No, I didn't do that. I agree, it might have fried the wire or
magnetized the toroid. The problem was all between the outer shell and
the ground lug-washer on the SO239 side of the device. That contact
was not accessible as it was potted in resin. I had already removed
the magnetics. The 15A flowed only through lug-washer and the outer
conductor.


Isn't there a little factors like cutting the Antenna
Wire to the 'right-length' and having the 'correct
length' of Coax Cable that contribute to a good
"Match" : At least for one SW Band ? ~ RHF

The MLB is meant to give a good-enough, install-and-forget, receive-
only match between a 50 ohm line and a random wire whose Z wildly
gyrates between 30-1000 ohm in and out of the complex field. Any RF
transformer turning 50 ohm into 300 to 600 ohm is vastly superior to a
direct connection.

There are receivers that include exactly that kind of transformer
between the inputs for "50 ohm" and "600 ohm" or "wire". I have seen
such transformers working reasonably well all the way between .1 and
30MHz. The MLB is nothing special but works like that, on a 300/1
bandwidth. The Lowe 124-225-250 etc. contain such a transformer, and
work OK down to 30 (thirty) kHz, a 1000/1 bandwidth. By "working" I
just mean that a given signal from a wire antenna produces
dramatically better results when fed via the transformer than direct
to 50 ohm input. That improvement geverally jibes with the source
being hi-Z.

I've never been able to reproduce such broadband behavior in a toroid
I wound myself. The Palomar Associates MLB clone was OK but weaker on
MF-LF. The ICE ununs come in lower and higher frequency range
versions. I have no idea what the trick is in the transformers used by
Lowe and RF-Systems, but it must be very simple, e.g. a mix that
compromises by having a somewhat higher loss all over or by saturating
at low power levels [over 5W ], but that's just a guess. It has to
be smtg that normal 1:9 ununs made with the usual HF mixes don't do
terribly well.

As for transmission: go on a ship, and if it's old enough you might
still even see a nice chunky metal case with the leftover transformer
matching the MF or low-HF random wire to a coax, complete with anti-
flashover insulator. Every time the radio room was removed from the
wire antenna, it made economic sense to deliver the 100-1000W RF by
standard radio guide (coax) than via a special high-voltage, high-
impedance line made wire suspended inside a large copper pipe.

In the real (professional) world NOBODY in at least the last 30 years
tried to cut MF or HF antennas to resonate on a special frequency.
Broadcasting dipole arrays were ~ 2:1, MW (AM) towers (and even VHF-
UHF antennas in space applications back in the day) are roughly sized
for radiation angle requirements, not for natural resonance. A 5/8
lambda vertical is like that.

Professional broadband dipoles normally "guarantee" a SWR mismatch
under 3:1 over 2-30MHz, and I remember UHF space applications with
1:10 SWR on short coax lines that were compensated at the radio end of
short low power and low loss coax runs. In many applications antenna
mismatch is practically irrelevant as long as it does not multiply
losses in the transmission line.

It's a consideration that corresponds to the cos-phi concern in
electric power transmission. A wild mismatch may generate extra
current or voltage that will cause additional Joule loss in conductor
and dielectric. In power transmission, 50-60Hz wavelength is so large
that you don't really get localized voltage peaks and throughs due to
reflected and direct power interference patterns, but at RF you see
that too, so you get both added losses and extra insulation breakage
risk. But if the run is short, and the power is low, both losses and
overvoltages can be safely ignored, and reflection and Z mismatch can
be addressed at the radio end.

In a long coax run, the huge mismatch of a nonresonant wire to a lo-Z
coax is nontrivial, and a transformer can actually nicely cooperate
with an ATU at the other end.

Today's AUTOMATIC ATUs are now routinely placed at the antenna end.
Not needing human attention, it makes sense to move them over there,
in which case a RF transformer becomes irrelevant. Antenna-side MF
transformers on ships are a thing from the indoor manual ATU and early
automatic ATU era.

But even today, antenna side transformers are the rule in the HF
market. That's what you do to improve match between a generally-high
impedance antenna and a low impedance coax of a broadband dipole. The
few rhombics still in use either have a Z-transforming balun or an
extremely low loss and broadly Z-matched balanced HV line. Ditto for
beverages - you could just connect coax and wire, but it would be
lossy, and nobody does it.

The broadband no-transformer no-ATU alternative exists. In practice,
only the military can afford the metal masses of large HF antennas
that have no clear resonance and reasonably narrow Z range without RF
transformer [and w/o resistor... :-P ], like inverted-cone on ground
plane, double-cone dipole, discone. Also (few) hams use log-periodic
rotatables. An MIT dorm used to have a fixed LP all-wire ham antenna,
never heard of a ham using a fixed "half-LP" vertical wire curtain.
Even with such antennas I'd still leave an automatic ATU in line if
already available. And, not coincidentally, such antennas are
generally sized for 13 MHz. Below that it's mostly broadband wire &
transformer country.


"Toss the piece of cr*p and get/wind something decent ... "

Yes, one can surely do that!

((narrower response or you tell me the simple trick for practicable
300:1 width) and/or (heavy, ground level or masthead commercial unit)
and/or ((buying toroid, casing, connectors, strain-relief, sealant)
and (winding, drilling case, installing strain relief, connectors,
soldering, sealing)))

vs.

(solder, glue, seal, use

On Sep 15, 4:09*pm, dave wrote:
Ian Jackson wrote:

And I can confirm that, with a transmitter-side (shack end)
matcher/tuner, and good, low-loss coax, you can do away with the
transformer.

All that does is match the 50 Ohm transmitter to the 50 Ohm (or less)
transmission line. It doesn't address the mismatch between the
transmission line and the antenna at all.

True, but not necessarily a problem. The battlefield is kept out, on
antenna and transmission line. On the radio side of the coax you do
see a function of the remote mismatch both in terms of wrong impedance
and in terms of a partly reflected wave delayed by the travel time
back and forth and with I/V out of phase due to the reactance at the
other end. What an ATU does is
1- compensating the reactive mismatch so that the power source sees a
resistive load
2- rephasing the incoming reflected wave to match the outgoing
3- providing impedance transformation at the transmitter end.
The result is maximized power transfer, and a clean load from the
p.o.v. of the transmitter, w/ minimized apparent reflection. I think 1
and 2 are mathematicaly dual to each other (please someone confirm!).
Not so sure how 3 fits in but it prolly does.

The price you pay for this is a nice mess along the transmission line,
with power being reflected back and forth in an infinite convergent
series of quickly dropping factors until radiated by the antenna, or
lost en route to heat and line radiation, while minimizing the stress
on the transmitter.

Nodes with higher current and voltage along the way also increase
Joule losses - but, again, this may be the dual of expressing the loss
due to reflection, I am not sure if there is a nonlinearity at work
here.

Having everything matched with the minimum use of concentrated L and C
is beneficial (inside the radio, in the ATU, in the transmission line,
and appended to the antenna), but if the transmisson line is very
efficient and not overly stressed (foam or air insulated, decently
sized conductors and insulator, not overheating nor breaking
insulation) a matching network close to the radio side is bearable.
Quite characteristically, as frequencies rise losses mount. Losses
along the same line at a similar mismatch may be negligible at LF,
acceptable at HF, excessive at V-UHF. This is why this is so often
done in professional applications.

In general. an antenna side matching device is better than radio side,
and no matching network is better than with, but perfection is not
always indidpensable. For example, the advantages of radiating in a
certain geometry (e.g. a Yagi, a nonresonant vertical...) or with
greater radiation resistance, may more than compensate for additional
losses due to a necessary concentrated-reactance matching device.

In message
,
spamhog writes
On Sep 15, 4:09*pm, dave wrote:
Ian Jackson wrote:

And I can confirm that, with a transmitter-side (shack end)
matcher/tuner, and good, low-loss coax, you can do away with the
transformer.

All that does is match the 50 Ohm transmitter to the 50 Ohm (or less)
transmission line. It doesn't address the mismatch between the
transmission line and the antenna at all.

True, but not necessarily a problem. The battlefield is kept out, on
antenna and transmission line. On the radio side of the coax you do
see a function of the remote mismatch both in terms of wrong impedance
and in terms of a partly reflected wave delayed by the travel time
back and forth and with I/V out of phase due to the reactance at the
other end. What an ATU does is
1- compensating the reactive mismatch so that the power source sees a
resistive load
2- rephasing the incoming reflected wave to match the outgoing
3- providing impedance transformation at the transmitter end.
The result is maximized power transfer, and a clean load from the
p.o.v. of the transmitter, w/ minimized apparent reflection. I think 1
and 2 are mathematicaly dual to each other (please someone confirm!).
Not so sure how 3 fits in but it prolly does.

The price you pay for this is a nice mess along the transmission line,
with power being reflected back and forth in an infinite convergent
series of quickly dropping factors until radiated by the antenna, or
lost en route to heat and line radiation, while minimizing the stress
on the transmitter.

Nodes with higher current and voltage along the way also increase
Joule losses - but, again, this may be the dual of expressing the loss
due to reflection, I am not sure if there is a nonlinearity at work
here.

Having everything matched with the minimum use of concentrated L and C
is beneficial (inside the radio, in the ATU, in the transmission line,
and appended to the antenna), but if the transmisson line is very
efficient and not overly stressed (foam or air insulated, decently
sized conductors and insulator, not overheating nor breaking
insulation) a matching network close to the radio side is bearable.
Quite characteristically, as frequencies rise losses mount. Losses
along the same line at a similar mismatch may be negligible at LF,
acceptable at HF, excessive at V-UHF. This is why this is so often
done in professional applications.

In general. an antenna side matching device is better than radio side,
and no matching network is better than with, but perfection is not
always indidpensable. For example, the advantages of radiating in a
certain geometry (e.g. a Yagi, a nonresonant vertical...) or with
greater radiation resistance, may more than compensate for additional
losses due to a necessary concentrated-reactance matching device.

Since Dave's dismissal of my suggestion/confirmation, I started several
draft replies, but each time got bogged down in detail. However, I think
that Spamhog's posting sums up the situation pretty well.

What must be realised is that you are not using the tuner/matcher (at
the radio end of the coaxial feeder) to match into the 50 ohm Zo of the
coax, and then, as an afterthought, connecting a totally mismatched
antenna on the far end. What actually happens is that the antenna feed
impedance is transformed by the electrical length and the Zo of the
feeder (and also its loss), and the tuner/matcher (at the radio end) is
adjusted so that it matches whatever impedance is 'seen' looking into
the feeder. It matches the whole antenna system, ie the antenna plus
feeder.

Admittedly, this arrangement only works well if the feeder losses are
low. Unless the antenna is (fortunately) a good match to the feeder, the
SWR on the feeder will be high, and the losses could be much higher than
if the there was a good match at the antenna end. It follows that, to
minimize the loss, you need to use the lowest loss type of feeder you
can lay your hands on. Nice, chunky CATV trunk cable is a good choice,
if your friendly neighbourhood cable company can be persuaded donate
some to you - especially as fibre optics are rapidly replacing coax.

Note that this is certainly not the 'best' way of doing things. For
receiving, it may - or may not - work better than using a 9:1
transformer at the antenna end. Both arrangements are a compromise.
However, you can certainly transmit with this system and, from what I
understand, at considerably higher powers than you can transmit through
a 9:1 transformer. Low-loss TV coax is probably OK for 100 to 200W,
although, for really high powers, you may need to think about the
implications of high SWR, voltage breakdown, and current burn-out. Of
course, an auto-tuner at the antenna end would be the best, but they
don't work on receive-only.
--
Ian

Ian Jackson wrote:
In message , dave



No. What do you mean by "match"?

The tuner/matcher transforms whatever impedance that is connected to its
'output' to 50 ohms resistive at its 'input'. That way, a transmitter
feeds into a 50 ohm load - which is normally what it will be designed to
feed into.

When receiving, the same applies (although, of course, the signal is
passing through the tuner/matcher from the opposite direction). Its
'input' on transmit is its 'output' on receive, so the output (which
feeds the receiver) is 50 ohms - which is what most communications
receivers are designed to be fed from. In practice, if purely receiving,
you will normally simply twiddle the tuner/matcher for strongest signal
on the receiver (ie maximum smoke). It doesn't really matter too much
whether or not you actually achieve 50 ohms at the matcher 'output' port.

Or have I got things wrong?

You are describing a "transmatch" when used between the generator and
the transmission line. This prevents the VSWR from frying the
transmitter. It does nothing to make the antenna work any better. The
transmitter can feed 50 Ohm co-ax directly. A tuner at the far end of
the transmission line will improve radiation while matching the load to
the transmission line and back to the transmitter. The radiation
improvement may be negligible or more dramatic, depending on the type of
antenna. When receiving you don't worry about frying the transistors
(unless you have a 2001D/2010!) so you just want to make sure you don't
break the hose rule (NO Higher Z generator into Lower Z load). That is
why a 9:1 transformer works OK for receiving. If you transmit through it
the transmitter will see close to a short circuit if the antenna is
resonant.

Ian Jackson wrote:
In message , Geoffrey S.
Mendelson writes



Decent quality RG-6 coax is easy to find at any of the home improvement
type shops, satellite TV dealers, etc. It's a lot better than the RG-59
or RG-59/U that was sold in the past.

If possible, if the coax is fairly long, I'd try and 'acquire' something
a bit less lossy than RG6 (at 50MHz, 5dB/100m, 1.5dB/100'. For cable TV,
RG11 (3.1dm/100m, 0.95dB/100') is sometimes a 'long drop' alternative to
RG6 or RG7. But you can do better than that. A Google should bring up
specs. This site gives a good selection. The CATV trunk cables look
interesting, but will usually be literally a bit 'too hard to handle'.

http://caledonian-cables.com/product/Coaxial%20Cables/coaxial.htm


Davis RF Buryflex is da ****.

Geoffrey S. Mendelson wrote:
Ian Jackson wrote:
If possible, if the coax is fairly long, I'd try and 'acquire' something
a bit less lossy than RG6 (at 50MHz, 5dB/100m, 1.5dB/100'.

Since this is an SWL group, a more meaningful number would be 15 mHz, and
I'm not sure that a loss of 1.5dB is going to noticable. 5dB would, but how
many people have 100m runs of coax?

Geoff.

You'd be surprised. Even at HF, there are QRP applications where a dB or
2 makes a significant difference.

This is a DC to Daylight group.

Ian Jackson wrote:


I'm simply quoting the figures (as given) as a comparison. Any SWL worth
his salt should be able of 'translating' the loss figures from 50 to
15MHz!!

I'm a Dreaded No Code Amateur Extra and I have to look it up.

http://www.soontai.com/cal_rtvswr.html

Are you running the RF gain at maximum? Apart from (usually) being
necessary to obtain the 'correct' S-meter reading, when you are actually
listening, it's a good idea to back it off as far as is necessary to
keep the AGC just working (on SSB, at least). Of course, using the front
end attenuator does allow the AGC to function flat out but, again on
SSB, even with the best of receivers, you still get the inevitable rise
of background noise during gaps in the speech (especially if the gaps
are long). I find this very unpleasant - especially on strong signals.
Somehow, the AGC time constant never seems to be correct - for my ears,
at least.


I wouldn't consider buying a receiver for serious listening if it didn't
have the ability to turn off the AGC completely, and if it din't have an
RF gain control. You can get SSB to sound like FM. Back when GHFS was
happening you could leave it on 11176 USB 24/7 and never hear anything
between the calls except the occasional chirpsounder bloop. If you were
also listening to 8993 on another radio, you'd hear the same bloop a
half second earlier or later, give or take.