Hi Farhan,
You can see in the schema's in the Files box under PE2BS or in the
Photos box how I used the trifilair transformers. The first trifilair
transformer (13 wdg on an T37-43 lookalike) is the output of the
driverstage and is placed on its "print". The last trifilair
transformer is made of 14 wdg trifilair on an T50-6. Like I wrote to
Ron it is difficult to say what exactly solved the problem but I got
rid of all the oscilations after the shielding AND the trifilair
transformers.
73
Ruud.
PE2BS
--- In BITX20@..., "ashhar_farhan" <farhan@p...> wrote:
hi all,
looks like the instability problem has something to do with the
phase
of the input to the IRF510 too.
can those who have tried the trifilar windings also suggest the
phase
used in the transformer?
- farhan
--- In BITX20@..., "Ruud Jongeling" <pe2bs@t...> wrote:
Hi Ron,
I just read your message. There is something in the message I
recognize: 'Found that the IRF510 has a tendency to start
oscillating
when set at a higher bias-level.' I had that problem too. In mine
BITX-PSK it was not enough to lower the bias-level. The PA seems
to
work OK when I was tuning from the computer and there was no
output
when there was no modulation. Unfortunately the PA worked in
class C.
The whole problem turned out to be an instability in the
driver==>PA==>antenna system. I solved it the way I discribed in
my message a few weeks ago:
First I biased the IRF 510: with no modulation and carrier nulled
by
the trimpot of the balanced modulator, the Id should be about 80
mA.
(from: "A simple SSB tranceiver" by Ashar Farhan
www.antentop.bel.ru/)
Second: a lot of decoupling.
Third: shielding the driver stage (see picture in the picture box
PE2BS)
Fourth: change the impedance matching between driverstage and PA
and
between the PA and the pi filter. Make it trifilair instead of
bifilair (see the remarks of Chris in the filebox Modifications).
The
result is also more watts RF.
Now the rig is working OK. When there is no modulation, there is
no
output in the SWR meter and a little on the spectrumanalyzer.
Even
with mismatching the system to the antenna the PA does not
generate.
It is the first HF-QRP rig I build and the results are amazing.
In CW
(Hamscope and CWget on the computer) and only 5 watt I worked
UA3,
YO, ER, HA!
Succes and like to hear from you.
73
Ruud
PE2BS
--- In BITX20@..., Ron Brink <pa2rf@y...> wrote:
Thanks for reply Chris,
Ja in de Zoetermeerse polder waren (kei) harde signalen in de
17 m
band te horen!
I think your 6 Watts RF should be fine for digimode use. Or am
i
wrong?
I hope to experience this myself on short notice. Yesterday did
first trials with the IRF510 endstage. I had 4 Watts RF out with
a
RTTY test signal connected. Hope to increase output level with a
few
Watts (increase supply voltage and adjust pi-filter) and do some
real
trials (hopefully 2-way comms) this weekend. Found that the
IRF510
has a tendency to start oscillating when set at a higher bias-
level.
Should fix that too. Also found that my (bureau) desk-light when
30
cm above the VFO gets this VFO change frequency; but when Huff
and
Puff circuit is connected, VFO frequency is corrected in a quick
and
fine way..
My appreciation for the BITX is growing ...
Bye
Ron 73
PA2RF
vdberghak <vdberghak@z...> wrote:
Hi,
responding to the messages below:
- Ron, in the Netherlands, I heard also several stations with
very
strong signals, form Russia but also from the States.
However, the 6 watt I have on 17 mtr is a bit little in
combination
with my sloping dipole. Stations in (for example) Bulgaria are
answering: 'only outside Europe'....
- Rahul, I use a small 8 Ohm speaker (removed from an old
transistor
radio). When I connect the antenna, a loud noise is comming out
of
the speaker. When I receive a weak station, it is just above
the
noise but at the moment a strong station enters, I really have
to
turn down the volume potmeter immidiatly!
In fact, the volume is never on its maximum.
By the way, I use the real, original BC107, metal can ;-) For
the
stage before the LM386 I use a BC109.
Best regards,
Chris.
Interesting are you using a speaker or heaphone. Secondly
what
transistors are you usingBC547s or 2n3904s
73
Rahul VU3WJM
Bye the way, RX signals on 17m were fine this afternoon,
heard
ssb
voice, rtty, psk31 and cw. With a one-lambda (17 m) long-wire
antenna
connected. Some signals clear enough to decode...
Does anybody have experience with one wave-length antennas
(up
till
now I have only used half or quarter lambda ant's..)
Bye bye and have a good Easter weekend (for what's left)
Ron
PA2RF
Yahoo! Groups SponsorADVERTISEMENT
---------------------------------
Yahoo! Groups Links
To visit your group on the web, go to:
To unsubscribe from this group, send an email to:
BITX20-unsubscribe@...
Your use of Yahoo! Groups is subject to the Yahoo! Terms of
Service.
__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
