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Old 13th Jan 2023, 2:29 am   #41
AdrianH
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Default Re: Some times I start something without any real plans.

Well I decided to start on the case, this is where I really found out how bad my chassis was, I am using 1mm steel plate that one can get from B&Q, the Vice mounted Clarke folder can only just deal with it when doing parts over 6 inch, this is why my chassis have rounded corners.

As my steel is in 500mm lengths, and I needed 630mm it meant I had to stick two bits together. No problem I thought, get the TIG welder out, soon have it done.
What a mess I made. I forgot to clean the protective oil off the steel and it made a real mess of the joint. Still nothing that a bit of primer and paint will not hide.

Started to do a dry fit up minus the valves in place s I do not break them, a real concoction of knobs being used.
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Have a 1/4" slow motion ball drive on order for the VFO.

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Old 15th Jan 2023, 12:10 am   #42
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Default Re: Some times I start something without any real plans.

Major problem today, the meter used for the Anode current failed, the indicator dropped to one side and when I took it out one of the locating screws for the central movement was loose and the whole movement had shifted.

After working on it for some hours the movement is now back in but it will no longer read correctly, so I must have done some damage to it, it now reads less than half display and I'm not convinced it is linear any more. So on the look out for a replacement.

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Old 15th Jan 2023, 12:35 am   #43
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Default Re: Some times I start something without any real plans.

You're too harsh on yourself Adrian. I've seen far worse. What range of meter are you looking for?

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Old 15th Jan 2023, 12:40 am   #44
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Default Re: Some times I start something without any real plans.

I have started a wanted post to try and find the same type, other then that I will go Ebay and order generic 1mA or 50 mA meters and redrill the panel. It is just annoying I guess.

I had the TX in a dummy load and acting as a Pantry transmitter today, sounds OK, so I definitely need to loose some top end response.

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Old 16th Jan 2023, 11:45 am   #45
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Default Re: Some times I start something without any real plans.

I have had some success with the original meter, it is I think damaged. Originally the coil resistance was around 50 Ohms and now it is 104 Ohms. I believe that the moving coil to be wound with two sets of windings, if both done in parallel then I got the 50 Ohms and a 1 mA movement, I believe they could also have been wound in series to give a 200'ish Ohms and 500 uA movement. But one of the windings has now gone open circuit leaving me with the 104 Ohms and 2 mA movement. This was a bit out but could be adjusted with a moving magnetic shunt to the bottom of the movement.

So I did a new shunt to give me a 50mA meter and use the magnetic shunt to get it as near as possible accurate. I am not sure how long the meter would last like this so I am still looking for a meter movement that would fit the same hole.

As I already have the 46mm hole it becomes difficult to enlarge the metal with a typical hole saw as these need a centre drill to keep it in position. I am also quite fixed on position already.
So I am on Ebay asking some of the merchants questions about some of the cheap meters.

Still awaiting the slow motion drive in the post for the VFO, (Far left knob), and answers for a new transformer, but at least for now the old TV powers supply is doing a wonderful job. Perforated metal has been used on the top and base to allow air to circulate and me to keep my fingers safe.

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The home made pointer below the meter should have a back scale and is the PA tuning. the knob to the very right being loading.

I did a dropper resistor and cap in the PA side of the autotransformer, which gave me a very slight increased depth of modulation at the cost of a few HT volts but not really that noticeable.

Cheers

Adrian

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Old 30th Jan 2023, 1:05 pm   #46
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Default Re: Some times I start something without any real plans.

Had a week or so away from the transmitter and did other things. went to Lincoln Rally yesterday, managed to pick up a few items that will be used, but noticed the days of old gear to be picked over seems to have gone, quite a few computers for sale, laptops, security gear, etc.

Anyway the AM/CW switching is fitted, awaiting a CW key socket to arrive this week and have ordered a Jones connector to allow the PSU to be disconnected.

Had a listen this morning on 80m AM and a few comments about valves and old gear/amps mentioned, so I guess a few on air are also on here.

Time for a walk while the weather permits.

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Old 21st Feb 2023, 11:20 am   #47
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Default Re: Some times I start something without any real plans.

Back at it, a decision has been made to go purely 80m, I am enquiring about crystal costs but await an answer on that from Belgium.

Decided to change the VFO over to 3.5 to 3.8 MHz, initial tests just changing the coil were a bit poor on stability, so had a rethink on how I was going about it.

So I sat down with the circuit diagram and worked out the reactance's for the various capacitors around the VFO, then calculated what values would give me the same Xc value or close to it at 3.65 MHz and I ended up with something like this :-
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C1 is 66pf in series with 59pf
C2 is 1nF
C3 is 130pF
C4 & C5 together are 140pF fixed
C6 still 100pF
In addition the resistors
R1 47K
R2 33K
R3 15K

This was built up on copper clad, a new coil wound to give me the required frequency and finally a 30 pF ceramic trimmer was placed across C1 the 66pf Variable.

R2 and R3 were changed to bring the output of the stage back up to a reasonable level of around 15 to 18 Volts p-p output at 3.6 MHz. The Screen now running at 83 Volts 2.5mA and the anode 63 Volts 4.2 mA, both well within limits of the valve.

It seemed to be very stable and after initial warm up and drift was low. So the changes were then applied to the main chassis.

I could still get a few watts from the PA valve but drive it with any modulation and the thing would splatter, showing up as a terrible waveform on the scope. A check of the PA grid valve showed little drive with only around -9 Volts on the grid, not the - 20 odd Volts previously. So the EF80 buffer is not doing a great job at it's new input frequency. This was still with the resistor type 2.5mH choke on the anode. So back out with the variable inductance instead of the choke and peak for max grid volts and it is best around 90 to 100 uH, bringing the anode circuit into resonance, suggesting that the Valve anode to PA grid and stray capacitance around the stage is approx 20pF.

The PA grid voltage now reaching in excess of - 70 Volts.

So now at the stage of making another coil up to replace the variable one and will give it a test before moving on to the PA tank coil which will need some turns removing or just remaking.

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Old 22nd Feb 2023, 11:53 pm   #48
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Default Re: Some times I start something without any real plans.

Another quick update.

The new power transformer has arrived so I can make a smaller PSU, I also have one of the 12 Volt to HT SMPS units that will do 40 Watts i could use?

A new Tank coil was made and fitted at around 15uH, this allows it to tune up OK into 50 Ohms and 2300 Ohms OK, well I believe the small lamp I use is around that area.

I got a cost back for a HC6U/48U crystal at 3615 kHz and it came in at 110 euro, so I do not think I will be going down that route. If I ever need to I will go for a DDS system from around £35 to £45, cheating I know.

I also have a 3550kHz crystal I could always try thinning down! But for now the new VFO may be OK for a while.

One of the items on my todoo list will be a loop tuner for an aerial.

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Old 23rd Feb 2023, 9:53 am   #49
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Default Re: Some times I start something without any real plans.

Adrian, at that price for a crystal, you could join VMARS for £28 , get a new crystal for £12.50 and have plenty of change. Still, you seem to have a nice VFO.

Cheers

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Old 23rd Feb 2023, 1:45 pm   #50
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Default Re: Some times I start something without any real plans.

The thing is although I have some military kit around, it is not my main interest, I do not collect the gear, what I have was to initially strip for parts when I started back with valves.
I have two RX's a R210 and a Racal R17, these are items I used to have when in late teens so thought it nice to have them again.

I picked up a few frequency meters one for £5 and another for £10 and scrap power supplies for under £10. The likes of the 19 set, C11 etc I tend to think are out of my price range. So me joining VMARS for a crystal would seem to be a bit cheeky as the crystal would be the only reason for it.

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Old 23rd Feb 2023, 6:42 pm   #51
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Default Re: Some times I start something without any real plans.

Understood Adrian. I'm not particularly interested in military gear either, having built my own AM transmitters. It's mainly the AM interest. When VMARS first started, in 1999, I was amazed to find I could use AM on 80 metres, years after SSB had taken over the HF bands ( except CW of course).

All the best

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Old 23rd Feb 2023, 7:09 pm   #52
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Default Re: Some times I start something without any real plans.

I still have to come up with an 80 metre antenna yet. Now it is typically FT8 I can hear droning away on the bands all the time. Hope to contact you some point on 80 AM. Have fun.

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Old 28th Feb 2023, 8:22 pm   #53
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Default Re: Some times I start something without any real plans.

Another change to the transmitter, I did another modulation transformer/autotransformer this time winding more turns on the RF PA side as it would be with a 0-110-240 volt auto transformer.

I can now easily hit 90% mod on peaks, trough is still around the 25 to 30% mod, this is without the extra resistor and cap in series with the PA HT feed. more as the actual Codar. I think I have gained a few percent overall.
No mod
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with mod
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Just playing.

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Old 13th Apr 2023, 2:46 pm   #54
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Default Re: Some times I start something without any real plans.

I am still laying with this. I built up the smaller power supply and stuck a voltage doubler on the heater 6.3 Volt winding and can get over 12 Volts, this now goes via ta switch and Jones connector to the transmitter to supply all the volts and a switch over relay for the antenna. I picked up 10 of the magnetic devices, (ex Pye style) relays for £13.

The Fat5 modulator in a box and that is driven from a basic PC type desk mic and goes into the transmitter. The receiver is the R210 I have.

Click image for larger version

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For an aerial I had a play at making a loop antenna using some LDF12-50 cable, I have approx 13.3 metres of it, being a bit too big to support I have tried it on the end wall of the garage, it goes up under the 'bargeboards?' and the finishes in a simple home made loop tuner, (caps) and via some RG58 to my room. I do believe there is too much metal work around especially on the other side of the wall as I have steel benches, 19 inch rack, lathe etc. as well as the dish on the outside. So believe it is effecting the resonance and SWR of the antenna.

Click image for larger version

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I did try to contact the VMARS net the other morning without success, so it looks as though the 10 watts output and antenna is not making the distance, mainly to the South East of me where many of the members appear to be.

When the weather improves I will try a smaller loop with say a 3 metre diameter, perhaps I could support it with plastic pipe and get it away from the wall, it may make a difference.

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Old 14th Apr 2023, 7:11 pm   #55
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Default Re: Some times I start something without any real plans.

I'd be worried about the proximity of the brickwork to your 'loop'.

Methinks your loop is really behaving more like a tuned dummy-load, specially if the brickwork is in any way damp! [as it's bound to be given that we've had a March with well-over the average rainfall for the month!]
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Old 14th Apr 2023, 7:36 pm   #56
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Default Re: Some times I start something without any real plans.

I think it is called the joys of trying to have a stealth antenna and no way could I support 13.3 metres of co-ax,.

OK on the wet walls yes that could well be an issue, but there is also a lot of metal on the other side of that wall. When things improve weather wise I will try for a smaller loop as said, I should then be able to bring it away from the wall.

I also think there is some interaction between the feeder length and the aerial as it does make a difference how the feeder is run, at the moment 10.6 metres just along the ground and up a wall.

Here are a few pics taken from my small VNA. First two are with a band spread of 2.5 to 4.5 MHz the second when I take it out to 20 MHz there are reasonable SWR's that I would not expect to see that suggests it is not acting correctly, but with my first play with these types of antennas I am not really sure.
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Old 18th Apr 2023, 9:13 am   #57
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Default Re: Some times I start something without any real plans.

Just an update to say I have managed to make a few contacts with the radio. I have, all be it with a week
signal got into the VMARS net two times now with my signal getting from the NW to the South. So I will call the little project complete and see what else I can get up to.

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