Saturday, 29 December 2012


Having registered for and downloaded my 472kHz band NoV I am currently looking for parts to use on this MF band when it opens for 'service' on the 1January.
I had originally planned to use a G3XBM transmit converter with my FT817. I have ordered a pack of ten 3.2MHz crystals on EBAY. However, they have not yet appeared, probably due to the Christmas post backlog.

In the meantime I have been looking at alternative methods of accessing the band, including transverting ( both transmit and receive) using my K3 which will not receive directly on 472kHz due to not having the wideband RF bandpass filter fitted. I am still considering this approach.

Meanwhile I have been fortunate to obtain a 50W RF output, Class B, switching FET power amplifier. This was originally designed for use at 470kHz! Its high gain means it can be driven direcly from a mixer output.

It would have been fairly easy to make a switching MOSFET amplifier, but as I am only dabbling at this stage and have lots of other projects on the go, I wanted to minimise the amount of building I would need to do.

I am still learning a lot about antennas at MF and what may and may not work.


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Sunday, 16 December 2012

13cm back on

I put the 13cm terrestrial system back on and can see 2dB of cold sky to ground. That is about right for the system as it is currently configured.
Sadly, no sign of GB3ANT/B. I am beginning to suspect that the beacon may well be a down a bit on normal. However, I will continue looking for it.
That's the 13cm 67 element yagi on the top of the mast.


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Saturday, 15 December 2012

13cm update

I investigated a fault on my 13cm masthead preamp some months ago. I didn't find any fault, but the system sensitivity was definitely low. I put it all back a few weeks ago, meaning to look at it again sometime. It still worked ( sort of) and that is better than not having any 13cm capability at all.

Normally I can hear GB3ANT/B , located near Norwich, all the time. Since the summer reception of the beacon has been poor. G3LQR reports hearing the beacon as normal so I have to assume the worst, hence the tests on the masthead.

Today I decided to have another go. With the masthead preamp in the shack a visual investigation revealed the preamp (VLNA13 - original Issue 1 board but with the current build standard) input SMA connector was starting to break away from the tinplate box. I had obviously missed this the first time! The preamp still worked, but the noise match was totally shot.

I replaced the preamp input 2- hole female SMA connector with a four-hole male SMA. With this arrangement I was able to connect the input of the VLNA direct to a bulkhead SMA female-female connector.

Now, on test, the masthead preamp measures 0.5dB noise figure and 24dB gain. As this is with a short SMA to SMA lead from the bulkhead Connector to the relay receive port, N to SMA adapters on two ports and a home made bias Tee to extract the 28v from the receive coax to the 12V regulator in the box, I regard this as quite good and certainly far better than I managed previously.
I hope to put the masthead box back on the tower tomorrow. It will be interesting to see how well the system works now!


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Wednesday, 12 December 2012

EME doings

A VLNA23 recently built-up for a well-known European EME operator.
I hope to see that he and his EME partner get even better results on 23cm than they have done so far ( and they are pretty good!) with an older design of preamplifier in use.

This one has an N type female output connector in place of the usual SMA female connector.

The photo below shows independent results, measured by a well-respected American amateur, of one of my VLNA23 preamps on test.

He is continuing with his tests, seeking to quantify results with a number of input connector types and materials. With his permission, I will bring you some results later.

Work continues to further improve the VLNA preamplifier range!


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Location:Falkenham Road,Kirton,United Kingdom

Wednesday, 28 November 2012

Won't be QRV

Unfortunately a family emergency means I won't now be QRV in the EME contest at the weekend. I will be in GI until Sunday.

73 de Sam

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Tuesday, 27 November 2012

Some results of tests with isolator and relays

Prior to putting my 23cm EME system back on-air I thought I would check out some isolators and relays I had used previously.
I had thought about using the Totsu CX600N at the output of the TS2000X, but the results show this is not a good idea. That relay is just OK at 432MHz, but definitely not at 1296MHz!
I have two identical 1200Mhz range isolators. The 'black' one shows the best results at 1296MHz, so will be used for the TS2000X transmitter 'protection'.
The isolator gives 0.33dB insertion loss ( forward) and 23.9dB reverse loss with reverse return loss of 16.3dB
CX600N @1296MHz
Insertion loss common to NC with other port terminated in 50R
Insertion loss common to NO ( relay operated) =0.19dB
Isolation common to NO 20.25dB
NC to NO isolation = 19.9dB
RLC electronics relay @1296MHz
Insertion loss common to NC or NO with other port terminated
= <0.1dB
Isolation common to NC or NO = ~85dB
NC to NO isolation = ~90dB
Not shown is the Relcomm RDL-SR006 relay used for preamp isolation
The main parameter here is insertion loss. This measured <0.1dB ( 0.06dB measured but there are uncertainties of the same order!).
I need to confirm the isolation figures again. But they were good.

More later.
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Sunday, 25 November 2012

A purpose in life!

My current thoughts are that I will write about my EME actvities, in the main, although there will be other stuff as well.
With the final part of the ARRL EME contest next weekend there is obviously a lot of interest, judging from the number of requests I am getting for preamps and spare parts for VLNA preamps!
I am going to try and get my own 23cm system up and running for next weekend and will aim to have a few QSOs.
I was active on receive only in the 50-1296MHz section at the beginning of this month. There were a lot of stations visible on my Spectravue screen. Unfortunately MAP65 performed rather poorly and only the bigger stations decoded. Changing to JT65C, decodes were close to 100% on all but the weakest stations.
As far as I can tell, there has been no wind damage to the dish or mast ( luffed over from the previous wind storm, last week) from last night's storm, at my QTH. Lots of branches down on surrounding country roads and lanes.
73 de Sam

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Location:Falkenham Road,Kirton,United Kingdom

Friday, 23 November 2012

A relaunch

After an almost two year hiatus I have decided to re-launch my blog. Now I no longer write the GHz Bands column for Radcom I need a new canvas to lay out my thoughts, current interests and project progress. Where better than a blog? Facebook and Twitter are too limiting.

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