Saturday, 30 May 2015

4m transverter

Although I haven't advertised them, I have been making 4m versions of the Anglian kit available.
Since getting back from Dayton I was determined to finish a new 4m transverter incorporating the Anglian module with one of the 30W Mitsubishi blocks. This is destined for a customer of mine.
I finished the transverter last night, just in time to take it to the Codgers breakfast this morning.

After a few tweeks to the grounding around the module and replacing the cheap Chinese power lead ( it came with a moulded plug and socket) I am now seeing over 50W saturated output. At 30W PEP the output IMD seems to be quite acceptable.

Unfortunately my QTH seems to suffer an abnormally high noise level on 4m. It is far worse on 4 than on either 6 or 2m. The noise level increases over 10dB in all directions away from due south.
I think it is time to do some serious investigating as I really would like to get back on 4m myself and I still have one of my original Nacton 4m transverters and a 150W SSPA. Nice!

Sam

Wednesday, 27 May 2015

PCB made

Well, I etched my first PCB in several years. I'm pleased to say that it was a very clean etch in spite of some reservations I had about the old sensitized Photoboard 2 (6 years old!) I had used and the two year old developer. That developer has now been ditched and a new batch made up. I' e also bought new sensitized board.

Tomorrow I intend making up the 4m 30W PA. my plan is to finish the transverter by this weekend as I want to use it in the present good ES conditions.

I had a disappointment with the Magnetic Devices 951 relay I had intended to use in the transverter. It turned out to be a 24V rather than a 12v coil............the 700R coil should have told me that!


To overcome this problem I started to look for a suitable circuit to drive the 24v relay coil from the transverter 12v supply. I did not want to use a voltage converter as there is a potential for audio frequency spikes causing interference. 
An alternative solution is to use a circuit like the K04BB all-DC circuit. This circuit charges a rather large value electrolytic capacitor to 12v. When you want the relay to operate, the charged capacitor is placed in series with the 12v supply to give 24v. Although the capacitor will discharge rather quickly as the relay is operated, the remining 12v is sufficient to hold the relay operated. 

The disadvantage of this circuit, as shown, is that it is not possible to operate the relay with a press to talk ground connection. Usually an isolated relay contact is used to apply a positive voltage to the 'trigger' input.
I didn't want to use a relay so I thought it might be possible to use an Infineon high side switch MOSFET to do the same thing, but with a ground PTT input.
I am pleased to say that this worked extremely well. I was wary that under certain conditions it might be possible to defeat the circuit by rapidly switching between on and off. I'm pleased to say that with the relay and circuit component  values that I used it was not possible to defeat the circuit!
I'll publish the circuit on my web page.
I will be making a printed circuit board for the relay circuit as my first new PCB with the resurrected PCB facility. I see this could be a very useful board for all sorts of uses!

Sam




Tuesday, 26 May 2015

PCB manufacture

Since I had an 'accident' with my etching tank around 2 years ago I have not etched any PCBs, choosing instead to have boards manufactured for me. This has been very successful but it can be expensive since it can often take three tries to get a PCB just right. Or more!

Needing a single 70MHz 30W PA board for a transverter I'm building around an Anglian transverter module I decided to ask if anyone local had a larger PA board that they weren't using. Whilst no boards were forthcoming there were several offers to etch boards for me.

However, I have decided to resurrect my own PCB-making facility. I have bought (from Rapid Electronics- surprise, everything was in stock, unlike last time I tried to order PCB materials!) a new batch of clear crystal etchant ( I hate Ferric Cloride) - too messy), sensitised board and developer crystals. I've cleaned out the etching tank and bought more chemical trays.

Tomorrow I will find out if the old magic is still there!

Among the projects I plan to have a go at are the long-talked-about 432>28MHz transverter. 
It is unlikely I will offer any of these transverters as kits ( assuming it is successful) but may well offer PCBs and a few of the more difficult to obtain parts. Please don't ask 'when?' as it is not an immediate project, but I do have a personal need for one and that often acts as the catalyst!

Sam




Monday, 11 May 2015

Dayton 2015

Getting ready to travel to Dayton later this week.
I'm travelling via Virginia, with WA1ZMS. 500 miles across the Appalachians and W Virginia before the flatlands of Ohio. 
Whahooo! one more state ticked off on my list. Virginia. That makes 36 states, I think.

I will tweet progress on my @DXing Twitter account.

I plan to spend much of my time in the fleamarket, either on WA5VJB's or WA1ZMS' stands.

Sam