It’s been a long slow process but today I finally finished installing the G4DDK 23cms VLNA at the masthead. The extended timeline was partly due to some other improvements that needed to be done to the 2m EME setup and the availability of some reasonably priced right-angle N-type connectors for LDF4-50. With the assistance of Roger, EI8KN I was able to complete this initial work.

Ideally to minimise the losses the box housing the VLNA and TX/RX relay would be mounted right at the driven element (DE) on the Wimo 67 element long yagi. I know of one EME station that has done this but a lot of extra support was needed to keep the yagi boom straight and to not have the antenna break in strong winds.

My solution has been to mount the box on the support brace and have a 2.15m length of LDF4-50 between the relay and DE. To keep the losses to a minimum the LDF4-50 passes through the wall of the box and connects directly to the relay also the input to the VLNA connects directly to the relay using a high quality SMA<>N-type adapter. The calculated loss for this arrangement is ~0.6dB. I used a large (25mm) plastic cable-gland to weatherproof the entry of the LDF4-50 into the box. This has the advantage that the N-type connector will pass through the internal securing nut which allows the complete VLNA box to be removed from the mast for servicing.

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The VLNA box is secured to the 15mm square section brace with two short lengths of aluminium angle that sit either side of the brace.

The system uses separate TX and RX feeders. Currently Ecoflex 15 is used for the loop round the rotator and down to the base of the mast. I’m not sure on the use of this foil+braid type of cable for this part of the system and only time will tell.

The challenge to try EME on another band was made much easier when I heard about the SG-Lab TR1300 transverter. I could see that this could be fairly easily integrated into my existing 2m setup.

Things have and continue to move slowly on this new project. Having never operated before on any band above 70cms this is a whole new challenge especially with the intention of jumping straight to EME.

23cms EME Initials Worked

Initial  Date        Time    Call      Grid    Rpt    My Rpt Setup
  1      30/04/2017  12:55   PI9CAM    JO32    -15             1
  2      01/05/2017  12:47   HB9Q      JN47    -12     -25     1
  3      12/08/2018  12:08   I1NDP     JN45    -21     -27     1

Having recently completed the ~20W PA for 23cms I was looking for some activity on the band to see what difference the extra few watts would make. Unfortunately I had just missed the monthly UKAC session. Reading the UKMicrowave Digest I came across a posting advising that PI9CAM would be active on 23cms Moonbounce (EME) on Sunday 30^th May. 🙂

The very small setup here on 23cms is still suboptimal in terms of receive and it’s definitely QRPp (very low power in 23cms EME terms). However, I have been decoding several stations that were using ~3m dishes so PI9CAM with their 25m dish (i.e. BIG Ears 🙂 ) might just be workable… right?

It was around lunchtime that I noticed PI9CAM on the MAP65 display, they were -14dB with me. Checking on the HB9Q chatroom others were giving reports around -4dB or -5dB. I decided that I’d try calling, if nothing else it would be a good stress test of the system. 🙂 Then another challenge hit me, Doppler! What frequency do I set the Transmit to? Is my potential QSO partner where they think they should be? What’s their receive bandwidth etc. I tried calling for several periods without success but then the penny dropped, Doh… I’d applied the TX Doppler shift the wrong way!!! Once this was corrected I called again and after 2 or 3 periods of calling I got my first “OOO” report back!

I responded with “RO” and waited for a “RRR”, the trace was bright but it wasn’t “RRR”, I got an “RO”. So I responded with a second “RO” and then the magic “RRR” was returned which I followed with the customary “73”. My first 23cms EME Initial was in the log.

The challenge was on, HB9Q was my next goal. Unfortunately I didn’t see Dan on 23cms on Sunday. However, he was QRV the next day.

Having left the gear monitoring 23cms and 2m EME I spotted that Dan, HB9Q was active. I made sure I got the Doppler set correctly and called. After a few calls, Bingo! I decoded my second “OOO” and we completed quickly. Dan gave me a -25dB report which was a great surprise.

It was great to have two new random contacts in the EME log. It has to be said though that all credit goes to both of these outstanding EME stations, and my thanks go to the Team CAM, PI9CAM and Dan, HB9Q. I’m certain my next EME contact on this band will not be quite so easy, but then that’s the challenge and the fun.  😉  I’m totally hooked now on the GHz bands and would encourage anyone to give 23cms and above a go.

My setup was a single 67 element yagi, G4DDK VLNA, 20W PA  (~8W at the antenna), SG-Lab TR1300 TVTR >> Anglian TVTR >> K3 and FCDPP + Linrad + MAP65

For interest here are a few other screen captures of various stations decoded via the Moon.

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What’s next? The VLNA needs to be moved as close as possible to the antenna driven-element and the number of N-type connectors reduced plus more power on TX!!!

My plan to be QRV on 23cms EME continues to move forward albeit at a rather different pace to what I’d originally envisaged. After a period of many weeks where little progress was made I’ve focussed my mind on getting a small 23cms PA going, possibly inspired by my recent visit to the Martlesham Microwave Round Table 🙂

My goal is to have somewhere in the region of 120W at the antenna from a SSPA. To overcome the inherent losses in a long coax cable run on 23cms the SSPA needs to be as close to the antenna system as possible. The SG-Lab TR1300 produces approximately 2.5W output so depending on where the transverter and PA are eventually situated another small SSPA is possibly going to be needed.

I was very fortunate to be offered a complete kit of parts for a ~20W PA that’s based on a Mitsubishi M57762 Power Amplifier module. I initially thought that I would combine this new PA with the TR1300 in one neat enclosure but decided it would be better to keep things modular so there was flexibility in what went where, and for ease of repair should things fail.

The following photos show the build stages of this small PA.

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Those of you that have a keen eye may have noticed that the original kit came complete with a two-part enclosure. But like the majority of my smaller projects this PA has ended up in my preferred aluminium die-cast box. 🙂

The construction centred mainly on metal-bashing, not the part I generally enjoy. Strangely though this project was different, I really enjoyed the drilling and tapping of the heatsink, something I’d not done for probably 30+ years! Maybe one day I will find some enjoyment in spray-painting and my projects will not have the natural aluminium look finish… 😉

So far the PA is working as expected, with an attenuator between the TR1300 and the input to of the PA both sit side-by-side in the shack and the PA produces 18 – 20W (JT65). The TX coax run to the EME antennas (2m & 23cms) has a loss of ~3.6dB at 23cms so should I choose to place this small PA at the antennas there should still be sufficient drive from the shack to produce ~18W output.

The next step is to tidy up the transverter, band pass filter and switching.

The SG-Lab TR1300 transverter continues to impress me. My current setup on 1.3GHz is the TR1300 with Sam, G4DDK’s VLNA and a single 67 element long yagi. The Anglian transverter is used on the 144MHz IF side, both transverters are locked to a 10MHz GPSDO. Unless EME conditions are really poor, it’s unusual for the ON0EME  beacon not to be seen on the screen, albeit rather faint at times.

The TR1300 can be used with a single (SMA) antenna connection, with internal changeover switching, or by removing a SMD zero ohm resistor separate receive and transmit antenna connections can be used. To connect the VLNA and prepare for the planned SSPA I did the modification and split the antenna connections. The antenna switching is now done by an external 12V high power relay that offers ~80dB of isolation and will easily handle the planned 150W power output.

The one observation after doing this modification is that the receive path no longer has the same filtering on the input. Now this wasn’t an issue when the antenna was pointing up at The Moon but with the antenna horizontal in certain directions the band was unusable due to interference / intermodulation from strong out of band signals, due I suspect to mobile phone transmissions originating from a local base station. A search on the Internet / Microwave forums suggests this to be a fairly common problem when operating on 1.3GHz with nearby mobile phone / TV transmitters. Some additional external filtering was going to be needed.

Constructing an interdigital filter was considered, but whilst the mechanical side was doable with my (limited) workshop facilities I certainly would not have the necessary test gear to tune and measure the performance of the filter. Another local station had been experiencing a similar issue and solved it by using the KUHNE Electronic 1296 interdigital filter (MKU BPF 1.3) . This sounded as if it might work for me. So for Christmas my XYL  bought me a MKU BPF 1.3 filter … 🙂

The filter is now installed (between the VLNA and transverter RX port) and the results have met my expectations.  There is no obvious interference when looking at the band on an SDR display… and I can still “see” the ON0EME EME beacon 🙂

The following two photos show the SDR display and give an indication of the band before and after the filter was installed.

23cms before filter, heading-127deg

23cms after fitting filter, heading-127deg