This XTAL oscilator was not showing the greater shift. Crystals used was hc69 full size but shift was only 400hz . Very poor shift. I wanted freq shift of few kHz. During reading Internet and practical experience with these Chinese half size xtals, I noticed, that osc requires that feed back capacitance should be low. Earlier I was using 1000pf, 1000pf (c1,c2).So, I replaced them with 100/180 PF. This was the value available with me, nothing particular about it. It clearly showed the shift of one kHz. This shift is good fore CW receiver and transmitter. Body of XTAL metal-can was grounded so due to hand capacitance seen no variations in freq.
Q1 is bc547, Q2 BF494b and Q3 bc547. It is powered from regulated 12v DC but i generally use 5vdc as source. This gives me enough RF to drive mixers, etc.
Earlier i had built the vwn tx. it showed good strength on air but somehow it was not showing the tuning up characteristic as given in the literature of the vwn tx.
Then i made this second transmitter. On dummy load and frequncy counter it shows good heat generations and accurate frequency 7058kc but, one of the days i promised this tx to my friend so putting it on the box and hope it works for him, in atleast AM/CW mode. He likes the cw. Hope this will fill up his logbook.
In the first transmitter there was problem due to the tank- which is a very vital element of this transmitter. I have (as of Jan2014) an LC meter and can verify the design L value and actual L value. Progressing. I will hand over this tx with the request to make the contacts and antenna tune up.
19 Aug 2015 :-
This has given me good signal for my testing the receivers antennas but as of July 2015 I have gifted it to one new ham.. Hope he operates it beautifully. on 7058kc. I will miss it. It was one of the well built vwn.
Introduction: Bring back the nostalgia with this one tube transmitter. The EL84 tube is
still available or can be salvaged from an old radio set. New tubes can be
ordered from http://thetubestore.com.
The circuit is self-explainatory and should always be used
with proper output load. The transmitter
takes about 10W DC in and puts about 5-7W out.
Construction: Mount the nine pin tube socket on the
general purpose board by 1/2" spacers at one end of the board. Keep all
lead lengths as short as possible to avoid losses and parasitic. All resistors
should be 1/2W unless stated on the schematic. The tuning capacitor on the tank
circuit is air variable type. Do not use the common 2J type broadcast receiver
gang condenser. Keep the connecting lead to the tuning condenser short and
thick. Use 35mm film container to wind the tank coil. For link winding use
hookup wire for easy winding. Tape the entire assembly for neatness. Mount the
tank coil close to the output circuit without using long connecting leads.
Tuning: After applying power, give about 30 seconds
for the tube to warm up. Connect a 6V 0.5 Amp lamp as dummy load and press the
key. If Murphy did not visit you, the lamp should light up indicating RF. Tune the
150pf condenser for maximum output, i.e. maximum brightness of the lamp. At full
power the lamp will glow ultra bright. I recommend use of antenna tuner on air.
Note. For AM transmission the code key can be used as PTT.
Close key to transmit.
CAUTION – High voltages
are present in the circuit, which could be fatal. Please take all precautions.
Always use a fuse protected power cord. Make sure the grounding is proper.
Acknowledgement: I'm thankful to the
following HAMs
for their valuable advices on this circuit - Harry Lythall (SM0VPO),
Hans Summer
(G0UPL), Niel Wiegand (W0VLZ), Stan Wilson (AK0B), John Kukla (KB10JM),
Ivica Bogdanovic (YU1QRP) and SWL Anatoly Lisowsky, David (M0DAD), M
Reeves (AB5L)
VWN ckt was not tuning up properly as the inductance given in the design was resonated only upto 6500kc. It was needed to tune it properly. For finding an inductors value, some sort of fast calculator was needed. This is an online calculator. It is wonderful and useful. After this I found out many program, javascript programs for calculating the values. Later on I also bought the VU2PTR L&C meter.
