Tuesday, 27 March 2018

New Antenna Mast from MM0CUG

My original antenna mast consisted of a 21 foot scaffold pole attached the side of the bungalow via T&K brackets however over winter I noticed that this was causing some damage to the brickwork and so I decided to replace it with a free standing mast from MM0CUG in Aberdeen.

The new mast is 8.5 metres tall however 1 metre is buried in a large block of concrete so 7.5 metres in total and is approximately 1 metre taller than the original scaffold pole.   It's a telescope design raised and lowered by a heavy duty winch triggered by a remote control, so no going outside in bad weather to raise and lower it.

The winch is powered by a battery which is a kept topped up using a 2.5W solar panel.

The guys from MM0CUG kindly took down the scaffold pole for me and moved my antenna to the new mast all within a day.   I still need to do a little tidying up regards cable routing etc ... but overall a stress free project.

Below is a few pictures taken on the day again from the luxury of my living room.

The initial hole cut in the decking
Digging a hole
Mast stub concreted and mast inserted
Getting ready to attach the rotator and antenna's
The new mast in the lowered position.

The mast extended.

Monday, 26 March 2018

Kuhne Electronics IC7300 IF Transverter Mod Board

While building the Iceni 70cm transverter I thought of combining the separate TX and RX IF's with either a simple resistive Wilkinson combiner or using a lumped component Wilkinson.

But the guys at Kuhne Electronics however do a simple mod board consisting of a couple of relays and diodes and a single resistor which will give separate TX and RX IF outputs so I bought the mod board to try it out.  The beauty of this method is there will be no attenuation loss in the RX path.

The supplied PCB looks to be good quality though the connectors are RCA phono sockets and it would have been nice to have BNC's instead, the only other thing that would have been nice is an adjustable attenuator on the IF out as according the Kuhne the IF output will be about 25dBm and Sam's transverters require 0dBm.

The board itself took 10 minutes to construct having so few components.   I've yet to fit it but that just involves making a couple of coax tails made out of 35ohm 3.6mm rigid coax which plugs into the IC7300 RF unit and then soldered to the Kuhne IF board once the right length has been determined.

The board sits between the RF PCB and PA PCB.  When the mod board is activated it provides a 50ohm load on the PA input while passing the feeds from the RF PCB out to the transverter.

The board operates by supplying 12V to switch the relays.   I'll update the blog once I tried the board out.

Kuhne Electronic IC7300 IF break out board.

The day I was featured member on QRZ.com

Well I got up this morning and found I was the featured member on QRZ.com

M0WGF Featured Member 26th March 2018
Now I'm not sure what to make of that other than,  one I wished I had a better photo up of the shack and two what is all this web contact book all about?  Anyway funny to have been featured member for 5 minutes. ;-))

Friday, 23 March 2018

Iceni 70cm Transverter from G4DDK - Part 2

I've finally finished the G4DDK Iceni 70cm transverter module.

The unit seemed checkout the initial tests as specified in the build document however when I attached the module to my spectrum analyser I had no output from the oscillator.   I checked the voltages on the the couple of transistors in the oscillator circuit all of which seemed to be correct the ball park I emailed Sam for suggestions.

Sam suggested making sure all the components were correctly soldered to the ground plane which to my eyesight seemed they were so Sam kindly offered to take a look at the unit for me.

Sam very kindly not only fixed the couple of bad solder joints I had on the unit, which he suggested was down to the iron not being hot enough and so not conducting enough heat into the ground plane, he also aligned the unit for me.  Strangely he found one inductor which was open circuit and I have no idea as to how that could have happened.

He also commented on how well the unit was constructed which was a nice vote of confidence in my ability with SMD components being only the second project undertaken with these minute components the MMIC's are particularly tricky as detailed in the last post on the Iceni.

To say I'm impressed with Sam's product and assistance is an under statement to the point I've just ordered the Anglian 3L and 8W short PA from him as well.

So with the Iceni built and up and running I fitted a Kuhne QH40A crystal heater for added stability.

The total amount of man hours to complete the unit was around nine hours from start to finished including the fabrication of the housing.

I've now ordered a 7W PA from mini-kits in Australia, so once that has arrived and is constructed I get on with sorting out the power supply and a nice box for it all.

The finished Iceni transverter

Wednesday, 14 March 2018

Cheap Chinese 70cm 100W Linear Amplifier - Part 2

I finally got my VNWA back from sdr-kits after receiving a DOA unit and then I found I had a faulty calibration cable as well, all of which was resolved quickly with no aggravations, so I had another look at the 70cm PA's LPF.

Though the original filter looked good on the old VNWA but I thought I'd better check with the new one just to be certain of the results.

Though the filter still looked fairly good I decided to adjust the inductor size slightly.  The original designed called for each coil to be wound on a 3mm mandrel for two turns so I increased the mandrel size to 3.2mm which yielded worse results but gave me some adjustment in the coils unlike the original.

The insertion loss stayed almost the same at 0.43dB but the return loss was improved by almost 10dB and the second harmonic was also improved by almost 10dB.    So the VSWR is now around 1.07:1 down from 1.2:1 originally.

LPF with increased coil diameters.
Now I just need to arrange to take the unit over to my friends with the spectrum analyser and see how the modifications have worked. 

Part Three coming soon. 

Monday, 12 March 2018

Iceni 70cm Transverter from G4DDK - Part 1

I have plunged myself into the world of transverters by buying the 70cm Iceni from Sam Jewell G4DDK.

Here's a list of specifications from Sam's website.

Parameter Measured Comments
RX noise figure 2.0dB Usual uncertainties apply
RX gain 21dB +/-1dB Fixed Gain
RX maximum input 0dBm Max non-damage level
RX IIP3 -10dBm +/-1dB Measured at -37dBm/tone
RX bandwidth 8.5MHz 3dB bandwidth
TX gain 16.5dB +/-0.5dB Tx attenuator at minimum
TX IF input level 0dBm Max +6dBm at attenuator minimum
TX output power +20dBm At +6dBm IF input. 0dBm max IF input recommended
TX IMD -50dBc/-38dBc +7dBm/+10dBm per tone at output
TX spurious <-60dbc Except second harmonic -53dBc at +16.5dBm output

The kit doesn't on the face of it look too complicated, but care must be taken when assembling.   All the problems I encountered were all RTFM issues.

Sam suggested to mark and drill the tin enclosure first which went quite well until I had scribed the first few line on the box only to realise what I considered to be the top of the PCB was in fact the bottom, again an RTFM problem on my part.  Make sure you have sharp drill bits tin isn't the easiest material to drill though.  It took about 45 minutes to mark up and 10 minutes to drill.

Tin box marked and drilled.

To assemble the PCB you do need a good pair of tweezers, a decent eye glass and a fine tipped iron.  Sam  recommended using 0.8mm tin/lead mix solder but I went for solder paste instead, dabbing the correct amount on the pads using a cocktail stick, which was recommended to me by a friend.  The jury is still out on which way is best when the solder paste flowed correctly it was much easier and gave a good looking joint but you do need to keep the board clean and not apply to much paste.

I washed the board after fitting the resistors by soaking in a bath of isopropyl for an hour then agitating with a toothbrush to remove any small solder balls and left over paste.  Once the wash has been completed go over the joints with the eye glass checking that the paste hasn't just blobbed up onto the end the component and has in fact made a good joint.   I washed the board after fitting each set of components but omitted devices like the variable capacitors, electrolytic caps, variable inductors and the ADE-13 mixer all of which wouldn't take kindly to the ingress of solder paste.

If I was going to build another one I'd actually fit the ceramic caps first as most are coupling caps and so could easily be tested for shorts which wasn't the case once I had fitted the resistors.

The only device I had real trouble with was fitting the PSA4-5043 MMIC amps they're damn fiddlely to fit.  Now that I tried fitting them I'd have done it differently by fitting the main ground leg by using the 0.8mm solder to apply a blob on the ground pad and then using the tweezers slide the device into place while keeping the solder blob molten.    I found when using the paste as I couldn't see the solder pads getting the orientation wrong was all too easy.   I'm now awaiting for two replacements from Sam as I ended up damaging two of the devices trying to remove them due to the orientation issue.

You can see in the picture below how small the MMIC amps, circled in red, really are.  The markings on the green background are 1cm squares.

The Iceni with an MMIC encircled in red 
I had a couple of parts go awol in the construction which Sam has very kindly replaced gratis he did however charge me for the additional two MMIC's at three pounds each plus postage which is very fair.

Once the new parts arrive I'll need to fit the parts and then finally the MX1 and inductors I can then move onto the fitting the PCB into the tin box.

Part two coming soon.

Odd quarter wave coaxial transmission line myth.

I've heard from a number of Amateurs on the bands that I will get much better performance if I cut the feeders for my 2m and 70cm beams in odd multiples of a quarter-wave.

Not being someone who believes all that I'm told on face value I thought I'd investigate further.

A quick caveat - I'm ignoring line losses here so remember to take that into account.  Ecoflex 10 at 200MHz has a loss of nearly 6dB per 100 metres meaning a quarter of the generated power will be lost.

The RSGB Full Licence Manual states the following regards standing waves - "If the line is terminated in a resistor of value Zo, it's characteristic impedance, the resistor will absorb all the power."

So in which case as long as the load we are transmitting into is of the same impedance as both the generator and feeder we will radiate all the power.

Now to double check lets check what the current ARRL handbook says, section 20.1.2 has the following to say - "In a matched transmission line, energy travels along the line until it reaches the load, where it's completely absorbed (or radiated if the load is an antenna)."

So again this indicates that as long as the transmission line is matched to both the generator and load we will radiate the maximum amount of power, which is exactly what Ohm's law states as well.

Lets triple check just so we know 100% what we have read is correct.  

Foundations of Wireless by M. G. Scroggie (1958) Pages 180 says the following - "In accordance to ohms law, the power going into the line during this transient state is a maximum if Zo is equal to the generator and load resistance."

This would indicate that it doesn't make any difference if we have an odd quarter-wave of coax feeding our antennas whatsoever as long as the characteristic impedance equals both the generator and the load.

I think where people are getting this myth from is confusing feeder with quarter-wave transformers used to match unequal loads, where the unequal load does cause an impedance and phase transformation.

Sunday, 11 March 2018

Setting the Yaesu FT991 microphone gain for sideband operation

I've had a number of conversations recently with owners of the Yaesu FT991 regarding setting the microphone gain.   I've seen Youtube videos showing the operator setting the microphone gain so that the ALC is going the full range of the ALC scale.  The problem with this isn't just wrong you will also be over driving the PA causing splatter across the band.

The manual states the following on page 59 section 5, "In SSB mode, touch [MIC GAIN] and then adjust MULTI knob so that the ALC meter stays within the ALC zone of the meter (up to half scale deflection) on voice peaks."

Now the problem is that the manual is a little ambiguous in regards to what half scale deflection means and in fact the image supplied doesn't even show the ALC meter.

Default image shown in the FT991 Manual.

What is considered half scale deflection?  If we look at the actual ALC meter, shown below, is half scale halfway along the blue ALC zone or halfway along the 0 - +60dB scale?

ALC meter display

Well consider this the 0 - +60dB scale is for the S meter not the ALC, the full range of the ALC meter is within the blue zone only.   After a number of friendly arguments about this I called Yaesu UK and confirmed the blue zone is the full range of the ALC meter.

So if the ALC is peaking at the red line on the image below then you'll be over driving the amplifier.

Red line showing excessive level

If you keep voice peaks to within the green line on the image below you should be good to go, and will keep other operators within you vicinity from moaning at you.

Green line showing correct level

Just remember adjusting the drive level so you have maximum output isn't the right thing to do.  The difference between output say 40W or 50W to the other station won't even be noticeable, so keep you transmissions clean.

One other point if possible adjust the microphone gain while transmitting into a dummy load and adjust the ALC so voice peaks actually come a little bit lower than the green line this will help take into account the fact your antenna is almost certainly not presenting an impedance of 50ohms across the entire band.

In my next post on the FT991 I'll take a look at setting the compression level to be within parameters.

Saturday, 3 March 2018

Cheap Chinese 70cm 100W Linear Amplifier - Part 1

Wanting to dip my toes deeper into 70cm I decided in December I could do with a little more power than the 50W my Yaesu FT991 puts out and decided a 100W linear was the order of the day.

After looking around on the Internet and various UK suppliers I headed to the drinks cabinet for a stiff whisky after balking at the £400+ price tags and decided a homebrew amp was in order.

A quick Google later and I came across an A/B class linear on eBay, from our friendly cousins in China, based on the Motorola MRF186 for £28.99 inc P&P and promptly ordered the kit, which according the advertisement was 100% brand new.  Two weeks later the kit dropped through the door to say I was impressed is an understatement.

Opening the package up I found a good quality PCB and assorted components however upon closer inspection found the MRF186 was actually second hand along with the High Q capacitors, but otherwise everything looked OK.

70cm kit as supplied
70cm kit as supplied.
Now the fun began as I had never used SMD components before and in fact this was part of the reason for buying such a cheap kit on the basis if I buggered it up I wouldn't have lost much.   Using the much referenced Google again I found the most suggested way to solder the SMD components was to place a blob of solder on one of the pads then using tweezers slide the component into the molten blob then solder the opposite side and hey presto jobs a goodun.

The only major problem was most of the components aren't marked so you need an inductance meter and DVM to determine the sizes.

It took about 45 minutes to complete the kit not including the matching lines, air cored inductors or soldering the MRF in place.

I decided at this point just to check the biasing circuit worked, supplying 24V to the circuit I varied the bias pot and found I got slightly less than 2.5V and not the 5V I was expecting after looking at the schematic.

70cm PA Schematic
70cm Schematic
After much heading scratching and poking around with the voltmeter I found the supposed 5K pot was in fact only 2.5K aggghhh, so it was off to RS for a replacement.

In the mean time I started to wind the required inductors from the supplied 18SWG wire.  The drain chokes went well however the inductors for the LPF didn't, the wire was extremely hard to bend around a 3mm mandrel and in fact I ran out of the supplied wire while trying.  I found some polyurethane coated wire of the same size in my bits box and finally managed to get the LPF coils wound and installed.

Next up was to cut and fix the matching lines which according to the board needed to be 10cm long which were duly cut and soldered to the board.

With the new 5k pot from RS in hand I needed to remove the original 2.5k pot from the board, which without a reflow iron was a pain in the backside.  I found the best way was to use an old pair of side cutters to remove the top of the pot and then split the side of the pot which then meant I could remove the old pot in pieces.   With the new pot soldered in I got a voltage swing of 0 - 4.8V over the full range of the pot.

Next I fixed the PCB to a heatsink and soldered the MRF186 to the board as well as adding a connecting wire so that both drains had access to the power supply.

The completed amplifier
The completed amplifier.

Next I need a 24V 7A power supply so I headed back to eBay and found an LED lighting supply which suited the job and was only £15, be careful with what you order here as some LED lighting supplies are constant current.

According the MRF186 data sheet the idq needs to be set to around 800mA at 900MHz so I set mine to 700mA on the assumption running the MRF186 at 432MHz would possibly result in more gain.

With a dummy load connected to the amp and set my rig to 5W I got 70W out, lucky for me my FT991 has a inbuilt VSWR meter and which showed an VSWR 5.1:1 so I immediately stopped testing, lucky for me both the FT991 an MRF186 can handle a high VSWR for short periods.

The input matching lines looked to be RG316 which with a velocity factor of 0.7 gave me a matching line of 12.2cm at 432MHz, two centimetres longer than the stated 10cm on the PCB so I furnished another line and fitted it and then tested the board again.  The VSWR had fallen to a much more respectable 1.2:1 so I replaced the output matching line as well.

Now when I supplied the 5W of drive I got 80W out and with a quick turn of the gate trimmer brought the output up to 100W, hoorah!

One thing that did cross my mind was the performance of the 7 pole Chebyshev LPF.   The PCB nor the schematic gave a value for the coils so I tested them with my LCR meter, which isn't that accurate below 1mH,  which gave a reading of 20nH.  I modelled the filter in Elsie with a variance of 20% inductance and it looked though the filter would work fine showing the second and third harmonics down 50dB and 70dB respectively.

Low Pass Filter Modelled
LPF modelled in Elsie 20nH inductors

With the amplifier finished I took it an acquaintance of mine who has a Rhode & Schwarz spectrum analyser and measured the spurious emissions which showed that though the third harmonic was -53dBc while the second was only -40dBc with 5W of drive and 100W out.

The UK regulations state that the harmonics in the spurious domain should be at least -70dBc at frequencies above 30MHz, so the amplifier appeared in it's present state not to be suitable for use in the UK.

Once home my friend had sent me an email pointing to an article by Jon Joyce GM4JTJ who had bought the same amplifier.   After reading Jon's article I found he had a similar experience to myself with the matching lines and so I popped him an email seeing if he had also had the same problem with spurious emissions.  Jon sent back a nice email saying he had sold the amplifier awhile ago but from memory had the same results when running at a lower out power of 88W.  He had never got around to cleaning the amp itself up but had used 1/4 wave coax notch filters to remove the unwanted harmonics.

I tested the LPF with my new sdr-kits VNWA.

Yes I know I was trying to save hundreds of pounds by not buying an amplifier only for me to then spend hundreds buying the VNWA but the VNWA is good value and has multiple uses anyway I digress.

The filter looks to be in the right ball park the return loss was horrendous only -12.5dB yielding a VSWR of 1.8:1 or a reflected power of 8.2%.

7 Pole Chebyshev LPF Original Component Values
Original LPF Response

I swapped the capacitors for the first and last poles from 6.8pF to two 3.9pF in parallel and happy days the got a much better return loss of 20.06dB a VSWR of 1.2:1 or a reflected power of 0.8%.

7 Pole Chebyshev LPF Modified First and Last Pole Caps
LPF response with an extra 1pF added to 1st & 7th poles

The data sheet for the MRF186 stated that the device should be run at 28V and not the 24V.  This was a problem as I only had the 24V supply from eBay, but upon closer inspection remembered there was a small pot to adjust the voltage level so with voltmeter in hand I tried the adjustment and low and behold managed to gain the extra 4V.

I measured the 1dB compression point at both voltages and found at 24V and an idq of 700mA the 1dB compression point was 80W for 5W of drive while at 28V and an idq of 800mA it was 110W with 7W of drive so I'll stick with 28V.  The amplifier gives an efficiency of 63% which is about right for a A/B class amplifier.

The next thing to do is test it again on the spectrum analyser but since my friend is on holiday that will need to wait a few weeks.

Part Two coming soon.