Wednesday, 29 January 2014

6m receiver sensitivity, or increasing noise levels

Are noise levels creeping up or are operators not taking notice of how deaf some commercial multiband rigs can be?
I operated for a while last night and heard dozens of UK stations calling on 6m. More than 25% of the stations I called with my 100W to 5 element yagi seemed not to hear me? Not even a QRZ!
I know that beaming north of west through north East from here on 6m the noise level rises by more than 10dB. I can see this quite clearly on my P3 display attached to my K3. This broadband noise is not so obvious just listening on the K3, but is easily seen on the display.
More worrying is that stations in a southerly direction from here, including Kent, were also having problems hearing me.
Now, I can see the signal levels on 6m on the display, I know the bandwidth so I know when a station similarly equipped to myself should hear me on a quiet band. Unless these 'deaf' stations are running considerably more than the UK legal limit, then they should be hearing me.
I should add that I have a low noise preamp on the K3 input ( not an ideal place for it, but it makes a noticeable difference).
So, is it that a lot of stations are actually 'deaf' on 6m or is the 6m noise level now getting so high that it is impacting our ability to work at typical terrestrial distances? SpE signal levels are generally so high that a 'deaf' receiver doesn't matter too much. Good performance on SpE is not really a good indicator of receiver performance.
In case you think this problem is limited to myself, I have discussed the observation with some other 6m operators and they seem to have the same complaint.
So, what is it ? Lack of attention to receiver sensitivity or increasing noise levels ( or both) ?


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Sunday, 26 January 2014

Nacton update

A little more info on progress with the Nacton transverter.
Around 35 Four metre kits have been shipped plus a number built by myself and by my Beta testers. No major problems have been identified but one or two tips to aid construction have been made.

Several 2m versions of the Nacton have been built and a number of issues identified that must be addressed before 2m kits can be shipped.

Thanks to the efforts of G4SWX the 2m filters have been redesigned for much improved performance. During the ongoing development of the transverter a few other areas requiring attention were identified and have been addressed. The PIN switches have been improved and an embarrassing problem identified and corrected...... Non saturated switching led to noise injection that raised the transverter noise floor.

John also suggested an alternative post mixer amplifier with a much higher intercept. These changes have produced a 2m transverter with an exceptionally good dynamic range.

These changes will be incorporated into a new PCB.

The good news is that several of these changes will also be incorporated into the next version of the 4m transverter.

Existing 4m Nacton transverters can be upgraded with simple cut and strap and a few component changes. Only the post mixer amplifier will require any significant change ( it uses a different package) but it can still be accommodated on the existing PCB. Since the background noise on 4m is much higher than on 2m the improved noise figure is of less consequence and the MAV11 can be retained if required. The slightly higher dynamic range that the new post mixer amplifier gives may not be too important. If it is felt to be important then it too can be changed.

I still don't know when the new Nacton kits will be available, but my hope is still in the next month or so. Due to significant delivery times for some parts and the cost of purchasing quantities, I will not have large stocks of the new kits, right away. At present I am keeping a list of requests and I'll let those on the list know when kits are available.


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Location:Falkenham Road,Ipswich,United Kingdom

Tuesday, 21 January 2014

Back to the Nacton

I have spent much of the last few days, after returning from Heelweg, making measurements on Nacton 2m transverters. John, G4SWX, has identified some problems with the original filter designs and advised on some improvements. These in turn showed up some other areas for improvement including the diode switch in the receive path between the RF front end and the band pass filter. It looks like new switching diodes are in order!

Initial measurements with the new filters and an alternative PIN diode show a big improvement in dynamic range.

John has also provided some new and possibly better post mixer amplifier devices. I will be trying one of these devices over the next few days, together with some other changes.

IF all this works, as it should, then the result could be an outstanding performance from a small, low cost, 144/28MHz transverter.

One further item of news. The scaffolding, that has prevented my use of the 2.3m dish, has been removed as next door's extension comes towards completion. At last I can get back on 23cm EME. Weather permitting of course.......!


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Location:The shack

Monday, 20 January 2014

Heelweg 2014

I have just arrived home from the Harwich/Hoek van Holland ferry and want to pass on my thanks to the organisers of the Dutch Heelweg microwave meeting.

It was a most enjoyable meeting, with lots going on and many European EME ops in attendance to chat to and make plans.

What makes this meeting so special is that it is all about practical things. Lots of measurement bays to get all manner of items tested and lots of small ' traders' selling all manner of VHF and microwave gear. Being part of the Cafe VOS, food and drink was available all day. Great! And the after-meeting Chinese meal in nearby Varsseveld sees more tables occupied each year. This is a celebration of all things amateur VHF/UHF and microwave radio.

My thanks to the organisers, to Hans and Ruud for looking after us on Sunday and not least to my travel companions, Dave and John.



Tuesday, 14 January 2014


I recently ordered a ZLPLL from Wayne, ZL2BKC, in New Zealand.
This is a ADF4351 based source board, capable of generating a signal between 31 and 4400MHz from an on-board 26MHz OCXO or external 10MHz reference. Wayne supplies a detailed manual for the ZLPLL, in PDF format, on his web page.

The ZLPLL turned up, safely, in this morning's post.

I wanted the ZLPLL to use with my 144MHz Nacton transverter, to be used where carrier stability was important, such as with digital modes like JT65B and when onward transverting to the microwave bands, where the LO of the transverter would also be locked to the shack 10MHz standard (GPS or Rubidium). This ZLPLL has already been programmed for me to give a (switchable) 116 or 115MHz output.

The Nacton 2m has provision for an external 116MHz input, if required.
On initial inspection the ZLPLL looks excellent.

I will probably give it a proper set of tests ( especially to check if it meets my phase noise needs) after this coming weekend's Heelweg trip is over. Right now I'm still getting things ready to take to the meeting.

My thanks to Wayne for his prompt attention to my order and congratulations on a fine piece of kit.


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Thursday, 9 January 2014

K3 update

Last May, at the Dayton Hamfest I bought a few 'accessories' for my K3. I was keen to try the bigger screen available by adding an SVGAP3 adapter to my P3. This meant updating the K3 +12v output via the switchable phono socket on the back of the rig. The parts to do this ( updated polyfuse and bigger choke) were provided with the SVGAP3 card. However, I had not got round to fitting these parts as I still hadn't ( still haven't!) fitted the SVGAP3 card inside the P3. There is a good reason for this, but I won't bore you with it now. That's for another blog.
Last week I received a PR6-10 preamp to increase the sensitivity of the K3 on these two bands. This preamp is also powered from the same +12v output as the P3 and whilst there was probably enough to power these two items, I wanted to add the SVGAP3 card soon, so decided to do the mod to the +12v supply.
This turned out to be a bit more involved than I expected, necessitating removing the top and bottom covers and the 100W PA. After that it was quite straightforward!
Whilst I had the covers off I thought I would fit the other accessory I'd bought at Dayton. The general coverage BPF. Again, more dismantling. The KBPF3 fits on top of the K3 ham band filter bank, but it necessitates removing the internal 2m transverter.
With the transverter removed the KBPF3 fitted easily.

With everything back together it all seemed to work OK, so the next job is to fit the SVGAP3 card in the P3 and see it it works as it should.

More about the preamp and results as well as how the SVGA
3 works in a later blog when I've had a chance to test the preamp and fitted the P3 card.


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Sunday, 5 January 2014

70cm Nacton trials

I have been spending a bit of time looking at the possibilities of putting the Nacton transverter on 70cm. The first problem to solve is the local oscillator. Using a 101MHz crystal removed from an old MM receive converter I'm pleased to say that I can achieve at least +13dBm on 404MHz, which is encouraging. I need to add a bit more filtering as 202MHz is only about 13dB down. Also 606MHz is a bit higher than I would like.
I am playing with extra filtering to clean up the LO spectrum.

Next will come the RF band pass filter. Can I achieve a good enough filter at 432MHz within the filter space constraints of the existing board? I think so, but it may involve a few PCB 'hacks'.

Even if the results are successful, I don't think that I will make a 432MHz 'Nacton' available, but I'll publish my results on my web page for anyone who feels like having a go. This all assumes I can get it to work to my satisfaction! If I can achieve a better performance than my TS2000 does on 432Mhz, I will be happy.........

I won't be giving any priority to this work, so don't expect results any time soon. The new PCB design for the Nacton comes first. 432MHz is just an idea at present.

73 de Sam

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Thursday, 2 January 2014


I'm not sure how I missed Dayton off my list of events attended last year!

This was far more a social event for me than one where I go to buy a rig or accessories. Having said that I did buy some bits for my Elecraft K3 inc. an SVGA card for the P3 display and the general coverage filter card.
To add to that I have a 10/6m preamp somewhere in transit from the USA, as a Christmas present to myself. Where oh where is it?!!!!!!!!!according to USPS it reached the UK on the 27th December, so maybe tomorrow.

I spent some time with Lloyd, NE8I, at Dayton. Lloyd was taken seriously Ill shortly after he got back home to Michigan. I'm pleased I did spend that time with him as he is unlikely to attend Dayton again, anytime soon. Get well, Lloyd.

I did blog about my Dayton trip in an earlier blog on here, if you really want to read more! Really?.........


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