开云体育

On August 21, 2018 at 5:48 PM Bo Barry <bobarr@...> wrote:

Needing help from all!
Attached as a .PDF and LibreOffice Spreadsheet.
Please provide input!! Goal is to make it into a club project, simplified as much as possible.
Thanks, Bo W4GHV since '54

I think you omitted 17 meters in that lineup. I am using external filters for CW on those bands and keeping it under 10 watts.

My 2-cents worth, homebrewtestequipment, homebrew test equipment,
or DIYtestequipment? My first choice when using a search engine is the
four words home brew test equipment or three words if you combine homebrew.

Terry - KB8AMZ
Brimfield Twp, OH USA EN91hd
Linux User# 412308, Ubuntu User# 34905, PCARS#78, NAQCC#6668,
QRP-ARCI#8855, SKCC#14195


On Sun, Aug 19, 2018 at 6:10 PM Arv Evans <arvid.evans@...
<mailto:arvid.evans@...>> wrote:

Hello

A few days ago I mentioned an idea for starting a separate
discussion group for
home-brew ham radio test equipment. The idea still seems
interesting but I seem
to be struggling with what to call the group. It needs to be short
enough to type in
easily, and still definitive enough to not be confused with
equipment for testing
pigs or homemade beer, Some possible options that come to mind:

* groups.io/g/hamtest <>
* groups.io/g/homebrewhamtest
<> (probably too long)
* groups.io/g/HBTE <> (*H*ome *B*rew
*T*est *E*quipment)
* or....?

There are probably a myriad of better names. Any ideas?

My Linux NFS File Server has a Test Equipment directory that already
has
several ideas which could be used as a start for this new discussion
group.
I am sure that others have similar card files or computer files
which would be
interesting to the rest of us who like building our own test
equipment. This
does raise questions about how to differentiate hardware test equipment
projects from combination hardware and software based test equipment?

On a slightly different direction........
In the past there have been a few complaints about the amount of
software
discussion here on the BITX20 forum. That raises the question of
possibly
starting a separate discussion group specifically for software that
is relative
to BITX based equipment. Again, if such a forum were established, what
should it be called?

* groups.io/g/BITX-SW <>
* groups.io/g/BIT-SOFT <>
* groups/g/BSoft
* or...?

In the case of Homebrew Test Equipment and a possible new BITX-Software
group we would need a couple of volunteer moderators for each group.

We already have spawned an Antenna discussion group at
groups.io/g/antennas <>
which is working quite well. The moderators are doing a good job
and some
interesting discussion has started.

I can start new discussion groups, but it is possible that someone
else could do
the same. The process involves logging into the "create a group
</creategroup>" page and
filling out the form. The groups.io <> process is
quite easy and straightforward.

It will not hurt my feelings if you want to start one of the above
groups, or another
group. If you have ever envisioned yourself as being the Lord and
King of a
discussion group...Go For It !

Arv K7HKL
_._

It has all been done before over 20 years back.? LT1252. It has essentially infinite input impedance. In this cct it is providing 5K input Z to the wiper of the potentiometer.? This chip can produce 50-60mW out at these voltages and at this load.? In this specific cct it drove the PA in class C to 4W RF.? There is no reason why the PA cannot be replaced by a 2n3866/4227 or any other "2W"? To39 RF? qualified transistor biased class A to produce 600-700 mW into a Trifiilar wound transformer, ie CT for use in a following class B stage.? This comes from a class of Video amps that will drive a +-5V signal into a 150R approx load given a 12V supply.? You can thank the great Dave Benson (SWL) for this cct but frankly a Chap called Breed used it some years before. again as? driver for a class C PA transistor. I respectfully suggest the OPT needs to be on a FB-61-202 core if you want good performance above 10 Mhz.? ? ?Take care with the component values on the schema. The leading decimal point is often meaningless.
Other devices / Sourcing?
An NE592 Will NOT work in such a circuit.? The LT1252 is out of production but still available out of SE Asia.? As Glenn? has pointed out to me the OPA2674 from TI is capable of even MORE and appears to be available on Ebay ex PRC? (but are they white spot chips from out back of the factory bin??).? ?A possible subs for the LT device (ie similar datasheet performance ) is the Max452CPA which Futurlec.com sell.?

?

?

An MMIC between Q90 and RV1 is an easy way to add an extra stage.
/g/BITX20/message/51211
Of course, you still have to adjust the other stages to distribute the
gain properly.
Including those IF amps.
And to really clean stuff up, create a new board layout.
Rapidly becomes way more than most of us want to take on.

I think just operating the uBitx on 20,40,80m with an external LPF (or
cleaned up on-board LPF's)
and with mike levels appropriate for 5 to 10 watts out is acceptable.
We may still have IMD issues, a somewhat unsuppressed suppressed
carrier, some low level out-of-band spurs.
But such operation can meet our legal requirements.

I would not operate the uBitx with an external linear amp to boost power.
Not without a benchfull of gear to monitor the result.

Jerry



On Tue, Aug 21, 2018 at 09:06 AM, Gordon Gibby wrote:

Allison, what about adding an additional stage after the last mixer
in the transmitter lineup? Better choice of transistors (replace Q90
and maybe the other 3904’s)... add (insert) a tiny daughter board
with an additional stage, could that allow for operating the
existing stages at more reasonable gain goals with more negative
feedback?

Further Having intercepted the signal it might also give a point
for bandpass filters to be easily inserted—-

You might laugh at it, but even a single or dual-stage preselecter
with variable capacitor(s) tuning a parallel filter, (like what I
had on my heat kits), once marked for the proper positions for each
band, might significantly clean up most of them except for the 21
MHz debacle. — tune for maximum signal output making sure you’re
near the correct Mark. If too much to ask from one inductor, add
a tap for the higher end

Gordon

If you want to feed it from 12v, then use a resistor of (12v-4v)/60ma = 133 ohms.
You lose some gain, because that 133 ohms is competing with your 50 ohm load at the output
for the available AC output power.? If that matters, add an inductor in series with the 133 ohms.
If running without the inductor, you are much better off feeding it from 12v than from 6v.