More new test gear for the shack

Back in 2012 I wrote about some new test gear that I’d bought for the shack.  Well time doesn’t stand still and it’s always nice to have new toys in the shack, especially if they’re useful.

My miniVNA Pro always did me well but recently I’ve started doing things on higher frequencies, such as building aerials for ADS-B reception and it’s frustrated me that I’ve not been able to fully test them.  With that in mind, earlier this year I bought myself an AAI RF Vector Impedance Analyser N1201SA from Banggood.

AAI RF Vector Impedance Analyser N1201SA

AAI RF Vector Impedance Analyser N1201SA

This is a cracking little piece of kit which covers from 137 MHz up to 2.7 GHz in 1 kHz steps.  It can measure SWR, resistance, reactance and S11. It’s not stupidly expensive either at around £130.  Being battery operated and fairly simple to use, it’s a very good piece of equipment.

The only downside to it is that there’s no way to save the measurements it displays apart from taking a photograph of the screen.  There’s no denying that it looks good though, here’s a plot of my Diamond X510 from earlier today.  It’s also not a full blown VNA so it can’t be used for such things as measuring the performance of filters.

AAI N1201SA scan of my Diamond X510N on 2m

AAI N1201SA scan of my Diamond X510N on 2m

Despite these downsides, if there was an HF version of this analyser, I’d be all over it.

The next logical step for me was an upgrade to my old miniVNA Pro.  It’s a fantastic piece of kit that’s served me very well over the years but I wanted something to cover higher frequencies.  I looked into a number of items and decided that the best thing for me was to change to the newer miniVNA Tiny.  Despite the name sounding as though it’s a downgrade (Pro to Tiny), it’s actually a decent upgrade as it covers from 1 MHz up to 3 GHz which is far higher than I can ever think I’ll need.  It looks quite similar to my old VNA, it’s just a little smaller and has a different connector.

miniVNA Tiny from mini RADIO SOLUTIONS

miniVNA Tiny from mini Radio Solutions

One of the first things I did with this was to test my new Diamond X510N vertical which I put up a couple of weeks ago and here are the results on 2m and 70cms.  It’s encouraging to see that the 2m measurement matches up with the N1201SA image above.

Both these images are clickable for much larger versions.

Diamond X510N 2m SWR measured with miniVNA Tiny

Diamond X510N 2m SWR measured with miniVNA Tiny

Diamond X510N 70cms SWR measured with miniVNA Tiny

Diamond X510N 70cms SWR measured with miniVNA Tiny

Finally I’ve been able to get my hands on something I’ve wanted for quite a long time and it serves multiple purposes.  I’ve wanted an accurate power meter for measuring the output of my WSPR/QRSS transmitters. It’s all very well having a super-duper QRO meter but when trying to measure down to a couple of hundred milliwatts, that’s not exactly suitable.

I bought myself a Yaege FC1-Plus Portable Frequency Counter which covers a massive 10 Hz to 2.6 GHz from 409shop.  Not only is this a frequency counter (which is useful by itself) but it’s also a power meter which is good up to two or three watts.  I wouldn’t want to put any more power into it.

Yaege FC1-Plus Portable Frequency Counter

Yaege FC1-Plus Portable Frequency Counter

If you’re looking to buy one of these, be aware that there are two models.  The FC1 and the FC1-Plus.  If you want the power meter version then you must buy the FC1-Plus.  It’s a little more expensive at around £50 but if you want it as a power meter then it’s worth it.

Here’s the display in frequency counter mode, monitoring my WSPR transmitter.

Yaege FC1-Plus in frequency counter mode

Yaege FC1-Plus in frequency counter mode

This ties up within a few Hz of the frequency I’ve got my GPS based transmitter so I’m happy with the accuracy.

What I was really interested though was power.  I fired up my WSPR transmitter into the meter in power mode.

Yaege FC1-Plus in power mode

Yaege FC1-Plus in power mode

This reads fractionally higher than I was expecting although I am running a higher voltage to the output stage of the U3S transmitter.  I have no reason to disbelieve the accuracy as I’ve been assured from a couple of sources that these meters are pretty much spot on.  Even if it’s only within 10%, I’m still happy but it does mean that I’m probably running a little more power on the lower bands than I thought.

I think that good test equipment in the shack really is essential now – Long gone are the days when we only used an SWR meter to check and align aerials and although a lot of amateurs only use commercial products, it’s still useful to be able to test performance to make sure everything is working properly.  I play around with low power experimental transmitters so this sort of kit is essential really.

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A new record – G to ZL on 60m QRSS

Toward the end of March I ran WSPR and QRSS on the 60m band for a couple of weeks.  I did some experiments on 60m nearly three years ago which gave good results and I was keen to improve that.

I posted on the new Knights QRSS list to announce that I would be active on 60m in the hope that some of the grabbers around the world would switch to 5MHz to listen for my signal and I was very pleased that a number of people happily switched over for a while.  It’s an unusual band because there aren’t that many countries that have a 60m allocation and they don’t always match up around the world.  Of course, anyone is free to receive on the band so that helps.

I was very pleased to receive the following reports.

G6NHU to ON4CDJ on 60m - 208km

G6NHU to ON4CDJ on 60m – 208 km

G6NHU to G3VYZ on 60m - 400km

G6NHU to G3VYZ on 60m – 400 km

G6NHU to VE1VDM on 60m - 4,637km

G6NHU to VE1VDM on 60m – 4,637 km

G6NHU to W4HBK on 60m - 7,293km

G6NHU to W4HBK on 60m – 7,293 km

All very good but no improvement over the tests we did before.  There’s one more though.

G6NHU to ZL2IK on 60m - 18,130km

G6NHU to ZL2IK on 60m – 18,130 km

This is a stacked image and is still quite weak so let’s zoom in a bit.

G6NHU as seen on ZK2IK's 60m QRSS grabber

G6NHU as seen on ZK2IK’s 60m QRSS grabber

Here’s a capture from Pete’s eight hour grabber showing my received signal repeating itself around twelve times between 06:00z and 08:00z on 23rd March 2017.

Eight hour ZL2IK grabber showing G6NHU on 60m QRSS

Eight hour ZL2IK grabber showing G6NHU on 60m QRSS

As far as I’m aware, this is the first time that QRSS signals have been successfully transmitted from G to ZL. I’m using my Hans Summers U3S transmitter with around 250mW output into a random length doublet, just 30ft AGL at the east end, sloping down to 20ft AGL at the west end.  Pete, ZL2IK is using an Icom IC-R75 communications receiver locked to a GPSDO frequency standard (no drift) and a combined 80/40m dipole fed through an ATU to match it to 60m.

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Returning to data modes after an enforced break

My shack computer is an Apple iMac.  For a few years, I’ve operated a lot of data modes and been very successful in data contests.  I’ve always enjoyed data modes and in 2012 I operated GO6NHU to celebrate the London 2012 Olympics exclusively using data.

Back in 2015, Apple released a new operating system called El Capitan and as soon as I upgraded to it, I noticed some problems with fldigi (my favourite data software).  I would switch to transmit, and roughly 60% of the time, the transmitted audio would come out of my iMac internal speakers instead of being sent to the radio.  It was the same with WSPR and any other software I tried which sent audio to the wireless via the USB cable.

My Kenwood TS-590 is connected to the iMac by a single USB cable.  The radio has a built in sound card and fldigi simple recognises that for everything it needs.  Data (CAT control) and audio pass down the same cable and PTT control is via data VOX.

This had worked perfectly for a number of years but broke when I upgraded to El Capitan.  I tried many things to attempt to resolve the problem, software reinstallation, replacement cable, reset the radio and other fixes but nothing worked.  One of the later patches to El Capitan did include a fix for external USB audio devices but that didn’t help either.  I found this article which went some way to explaining what the problem was although there was no recognised fix apart from reverting back to OS X Yosemite.

I simply stopped operating data modes and when Mac OS Sierra was released, I tried again but had no further success.  It was just the same.

Recently I did some more testing, I set up clean installations of both OS X El Capitan and Mac OS Sierra on an external drive to see if I had the same problem – I did.  I then built a clean version of OS X Yosemite on an external drive and it worked perfectly.  My hardware is OK, it’s just the changes to how Apple handle external USB sound cards that is the problem.  Searching the internet found a lot of people with exactly the same problem although frustratingly, it’s not universal.  I know of people with the same model iMac who don’t have any issues.

It was time to finally find a fix.  I decided to bin the USB cable and go the old fashioned way, using an RS-232 interface lead and an audio interface.

The first thing to find was a USB to RS-232 adapter.  I went with a UGreen USB Serial Interface cable based on the PL2303 chipset because it claims to be fully compatible with Mac OS.  I also needed a null modem cable to connect to the back of my Kenwood TS-590 which was simple enough to get hold of.

That completed the CAT side of things and it worked perfectly well.  I had full control over the radio from the computer and the next thing to deal with was the audio.

It’s well documented that to avoid earth loops, hums, audio feedback etc, one should use an audio isolation transformer.  I would need two of these, one each for transmitted and received audio.  There are many of these available for a few pennies on eBay or Amazon but most of them are shipped from overseas with a lead time of weeks.  This wasn’t good enough for me so I drove to the Rapid Online trade counter and bought two Vigortronix VTX-131-001 line matching transformers.  These were mounted on a piece of veroboard and fitted into a small box along with screened cable for the audio in and out.

Home brew interface for data modes using two audio isolation transformers

Home brew interface for data modes using two audio isolation transformers

I considered using a metal box but decided that as all the audio cables were screened and as I’d put decent ferrites at each end, a metal case wasn’t absolutely necessary.  If I get any problems, I can always change the box afterwards.

With this all built and working, I connected one side of the interface to the accessory socket of my radio and the other side to the audio input and output of iMac to test.  It worked perfectly and I was back on the data modes.  However, this wasn’t ideal as it meant that I’d effectively lost all normal sound on the computer and I had to be careful to avoid inadvertently transmitting computer audio!

I did some research to try and find a USB audio device that would work properly with the latest version of the Mac OS and found reports that a fairly cheap card, the Creative Labs Play! 2 was compatible.  I bought one from Amazon because their returns policy is superb and I knew that if this didn’t work, I’d be able to return it. It arrived the next day and as once I’d loaded the drivers, it worked like a dream.

Finally after around two years, I’m fully back and able to work data modes using my iMac.

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Building a Raspberry Pi internet watchdog

I wasn’t sure whether to post this or not as it’s not specifically amateur radio – But there’s a small amount of electronics involved so I figured it might be of interest.

A few days ago while Susan and I were out, I received a text from my son saying “I thought you’d like to know that the wifi isn’t working”.  What this actually meant was that our home internet connection had gone down. I recently changed my ISP and had been warned that for the first couple of weeks, there might be an occasional interruption to the service.  I know the router should automatically connect but sometimes that doesn’t happen.

I spoke to David and quickly determined that this is what had happened but that the router hadn’t automatically reconnected.  All he had to do was switch it off and back on again and it sprung back into life. This got me thinking that perhaps this could be a good use for a Raspberry Pi as a watchdog.

It didn’t take much investigation to find some basic Python code to check for the presence of an internet connection so I grabbed that and then looked into the hardware. I’ve not played with the GPIO before but it all looked pretty straightforward.  I didn’t have a suitable relay so decided to test this with just an LED playing the part of the relay so I could see if it worked.

First version of the Raspberry Pi internet watchdog

First version of the Raspberry Pi internet watchdog

The idea is that if the Raspberry Pi Zero W detects the internet has failed, it will trigger a relay and drop power to the router for a few seconds.  This first version worked perfectly and I tested it by pulling the internet connection from the back of the router.  After a couple of minutes, the LED flashed.  I was very happy with the way this worked and so I ordered a relay.

I wanted things to be a little more sophisticated though and started delving into the code.  I’ve only just started learning Python so this was a nice educational exercise for me.  It wasn’t long before I got things as I wanted.  At regular intervals the Raspberry Pi checks to make sure there’s a good internet connection and if not, it drops power to the router for ten seconds, brings it back up again and then pauses to allow the router to reboot and reconnect before checking again.

The relay I’d ordered turned up and I was able to set it up and prove everything working – Once again, it’s on breadboard and you can see the green ‘OK’ LED along with the red ‘fault’ LED, although that’s disconnected and the relay is in circuit showing that power is passing through.

Raspberry Pi internet watchdog being tested

Raspberry Pi internet watchdog being tested

I made sure to use the normally closed contact on the relay so by default it isn’t energised, it will only activate if there’s a failure so this means I can reboot the Raspberry Pi without killing my internet connection.  However there was a problem – Each time I restarted the Pi, it would click the relay and it took me a while to work out what was happening.  It turned out that my Python script was starting before the WiFi had initialised and connected to my network.  The script was seeing that as an internet error, going into a fail state and triggering the relay.  I resolved that by adding a delay to the cron command which started the script.

I decided to use an official Pi Zero case which has a hole in the top for the camera and to repurpose the hole for the green LED.  Sadly the hole was far too large for a 5mm LED so I picked up some 8mm LEDs.  Of course, the 8mm LED was too large for the hole!

Raspberry Pi Zero W case and 8mm LED

Raspberry Pi Zero W case and 8mm LED

It didn’t take much to enlarge the hole slightly so the LED would fit and before long it was glued in place.

8mm green LED in the Raspberry Pi Zero W case

8mm green LED in the Raspberry Pi Zero W case

While the glue was drying, I built the rest of the watchdog.  I actually used a different Raspberry Pi Zero W to the original one I had been testing with as I didn’t need the entire GPIO header, just needed to solder a few wires straight onto the board.  Here you can see the Pi mounted in the case with the wires for the relay feeding in through the bottom and soldered onto the board.

Raspberry Pi Zero W in the case along with the relay

Raspberry Pi Zero W in the case along with the relay

When the glue had gone off, I wired the LED to the GPIO pins and fitted it all together for final testing.

Finished Raspberry Pi Zero W internet watchdog

Finished Raspberry Pi Zero W internet watchdog

After this it was a simple job to integrate it into my setup.  My router has a standard DC power connector on the back so rather than destroy the manufacturer supplied power brick, I grabbed one of my many power cables, cut the positive wire, fed it through the relay, connected it all up and switched it on.

Raspberry Pi watchdog timer all set up and working

Raspberry Pi watchdog timer all set up and working

You can see I managed to catch it as it flashed the ‘OK’ signal.
The first time I started everything up with the router connected was a good test as it proved everything.  The Pi started before the internet had initialised so it saw a fault condition and rebooted the router, then paused itself for four minutes to allow the router to restart and the internet to connect.  Everything worked perfectly.

I consider this the perfect use for a Raspberry Pi – Think of something for it to do, find a way to do it, tweak as required and then get it working.

This entire project took just three days to complete.  It was conceived on Wednesday afternoon and by Saturday afternoon it was fully implemented and working!

Posted in Construction, Not amateur radio, Raspberry Pi | Tagged , | Leave a comment

New aerials for VHF/UHF (2m/70cms) and 28MHz (10m)

Over the years I’ve used a few different VHF/UHF aerials here and the one I always found the best was my old Diamond X500.  I bought that when I still lived at home with my parents and it moved here with me.  It ran my original AX25 packet radio BBS and then MB7UIV and was only taken down in June 2010.  When it was given away, it was in perfect working order, if just a little dirty.

I replaced it with a beam for 2m and added a Sirio 827 for 28MHz (10m).   Eighteen months or so later, I replaced the Sirio 827 with a Sirio Gain Master and that was destroyed by the wind in February 2014.  My VHF beam was removed after the lightning strike in 2011.

Since then, all I’ve had up for VHF/UHF is a very small aerial on the front of the house and nothing specific for 10m.

Yesterday I fitted brand new aerials to the side of the house – A Diamond X510N and a Sirio 827.  The Diamond is on a 20ft pole making it a little over 100ft above sea level where the Sirio is on a slightly shorter pole of 17ft length putting it around 97ft above sea level.  Here you can see the two aerials along with the very small vertical on the front of the house that I’ve been using for VHF/UHF for the last few years.

Diamond X510N and Sirio 827

Diamond X510N and Sirio 827

Now onto the measurements of the two aerials.  For the Diamond, I used a recent acquisition, an AAI RF Vector Impedance Analyser N1201SA which I bought from Banggood, specifically for the wide frequency coverage from 137MHz up to 2.7GHz.  I can thoroughly recommend this unit except for one thing.  There’s no way to export the graphs it produces so these were taken by photographing the display.

Diamond X510N VSWR on 144MHz (2m)

Diamond X510N VSWR on 144MHz (2m)

Diamond X510N VSWR on 430MHz (70cm).jpg

Diamond X510N VSWR on 430MHz (70cm).jpg

The VSWR on 2m is superb, below 1.4 over the whole band and very nice at just below 1.2:1 on 145.500MHz  (S20), the UK calling frequency.  It’s a little higher on 70cms at just above 1.4:1 on the calling frequency of 433.500MHz (SU20) and rising to about 1.8:1 at the top end of the band but considering the band is 10MHz wide, that’s not surprising and perfectly acceptable.

I’ve already made simplex QSOs on 70cms out to around forty miles and been able to access repeaters on 2m as far as fifty miles away so my initial impressions are that it’s working well.  I’m feeding it with around fifteen metres of EcoFlex 15 coaxial cable which gives me just 0.5dB loss on 2m and 0.9dB loss on 70cms.

For the Sirio on 10m, I used my trusty miniVNA Pro analyser.

Sirio 827 SWR on 28MHz (10m)

Sirio 827 SWR on 28MHz (10m)

The Sirio 827 is adjusted by the top section, the further in it is, the higher the resonant frequency of the aerial. I had the top section in as far as it will go but seeing as this is sold as a CB aerial, the resonant point is only a short distance into our very wide 10m band.  As can be seen, it’s perfectly useable in the CW/SSB segment of 10m but the SWR does raise to nearly 2.2:1 on 29.600MHz, the FM calling and working frequency. It’s a bit windier today so I don’t plan on lowering the aerial but if I get a chance in the coming weeks, I’ll drop it down and try and reduce the overall length just a little further.  I’m feeding the Sirio with seventeen metres of RG213/U which gives me around 0.6dB loss on 28MHz.

Overall it was a very successful days work and I’m very happy with the results.

Posted in Amateur radio, HF, UHF, VHF | Tagged , , | Leave a comment

How to replace the noisy fan in an Icom ID-5100 with a much quieter one

I’m a happy owner of two Icom ID-5100 radios, one is mounted in the car and I use the other one in the shack on low power for working the local repeaters.  It doesn’t get much use but I’m monitoring GB3CL and GB7TE most of the time.

About the only thing which I don’t like about this radio is the cooling fan.  When it kicks in, it sounds like a jet aircraft taking off.  I checked and it’s a Delta fan and they have a reputation for being loud.  You can see the exact specifications of the factory fan here and at 9,000rpm, it’s no surprise it’s noisy.   In the car that’s not a problem but it’s a big issue in the shack.

I did some searching and discovered that Andy, MW0MWZ had found a suitable replacement fan and written about it on his blog.  As this was written well over a year ago I contacted Andy to see if he was still happy with this replacement fan and he replied that he was but with one caveat.  He only uses the radio at 5W output and it’s perfectly good for that.  He does question whether the fan will be man enough for the job if it’s running 50W for long chats.  I don’t do that, mine never goes above the low power setting so I decided to do the same mod.

If you want to see the video comparing the audio levels before and after this mod, either scroll down to the bottom of this post or click here to see it on YouTube.

I ordered the suggested fan, a Scythe Mini Kaze Ultra SY124020L from Amazon and it dutifully arrived two days later in a nice package.

Scythe Mini Kaze Ultra SY124020L

Scythe Mini Kaze Ultra SY124020L

First thing to do was remove these four screws.

Back of the ID-5100 showing the fan about to be removed

Back of the ID-5100 showing the fan about to be removed

The screws were very tight to remove, I suspect there was some kind of screw-lock involved to stop them from turning.  Having a decent screwdriver helps here, be careful not to burr the screw heads.

ID-5100 with the fan cover off and the fan loose

ID-5100 with the fan cover off and the fan loose

It was very obvious that the length of the wire on the fan wasn’t going to be enough for me to easily get in there with a soldering iron to fit the new fan.

Not much wire to work with

Not much wire to work with

I hoped that the wire going to the fan would be actually plugged into the board inside the wireless so I carefully removed all the screws on the bottom cover of the Icom ID-5100 to see.  Oh yes, life is good!

Inside of the ID-5100 showing the fan connection

Inside of the ID-5100 showing the fan connection

I did hope that the connector on the wire with the replacement fan would be the same but it’s much larger so I would have to get the soldering iron warmed up.  I was expecting to do this anyway so it wasn’t a problem.

It was a simple matter to unsolder the cable from the original fan, remove the label from the new fan, unsolder the cable, solder the cable from the factory fan onto the now exposed connections and stick the label back on.  It probably took longer to type that sentence than it did to actually do it.

New fan with power cable attached

New fan with power cable attached

With that all done I just had to plug it in, mount the fan back in place and check it all worked.  I did this before I screwed the fan back on and replaced the bottom cover, being careful not to catch the power cable on the case frame or against the fan blades.

Inside of the Icom ID-5100 showing the new fan in place

Inside of the Icom ID-5100 showing the new fan in place

With the bottom cover replaced and the fan screwed securely back in place.

Icom ID-5100 all back together with the replacement fan fitted

Icom ID-5100 all back together with the replacement fan fitted

And onto the full test – What better way to demonstrate the difference between the old and the new fan than to produce a video and that’s what I’ve done.  You can see it directly here or use this link to watch it on YouTube in full HD quality.

Checking the specifications of the two fans, it’s really obvious why there’s such a difference in noise between the two.  The Delta is rated at 9,000 RPM compared with 3,500 RPM for the replacement and the measured sound level of the Delta is 36dBA compared to 19.5dBA for the replacement.  Of course the airflow on the new fan is significantly lower on the new fan at 4.86CFM as opposed to 10.1CFM for the Delta.

I cannot say enough that you do this at your own risk.  If you regularly use the radio on high power, I can’t recommend this modification as you’ll probably fry your radio.  If you only use it on low power though, I think it’s worthwhile.

I take no responsibility for any damage caused to your radio if you do this modification.  In other words, if you do it and your wireless catches fire due to overheating, don’t blame me.

Posted in Amateur radio, Construction, D-STAR, FM, VHF | Tagged , , , , , , , | Leave a comment

5B4AGN bandpass filters – The measurements

I’ve been moving some boxes around recently and I unpacked the bandpass filters I built for one of the Martello Tower Group DXpeditions and successfully used again during our activation of the MV Ross Revenge in August 2016.

It struck me that I’d never produced a full set of figures showing rejection on each band, insertion loss and SWR for them so today I’ve corrected that.

My filters were designed by Bob Henderson, 5B4AGN who helps set up group purchases once a year of so of all the parts required to build them.  Everything is done through a Yahoo Group so if you’re interested, head over there to find out more.

Although I bought all the parts to build six filters, I didn’t make the one for 160m so I have a set of five filters for 80m, 40m, 20m, 15m and 10m.  Without these filters it wouldn’t have been possible for us to have three stations running simultaneously while on Herm and two stations sitting next to each other on the Ross Revenge.

To measure the performance of these filters I used my miniVNA PRO and my homebrew dummy load.  Even though the filters aren’t designed for rejection specifically on the WARC bands, I measured them on those bands as well for completeness.  I believe that Bob has produced some newer design filters with higher rejection since I built these and they cope much better with the WARC bands.

For each filter, I connected it to the VNA and measured the rejection per band along with the insertion loss on the primary band.  I then disconnected one side of the filter, connected it to my dummy load and measured the SWR.

5B4AGN Bandpass filter performance measurements

5B4AGN Bandpass filter performance measurements

The important frequencies are the multiples of the primaries so for 80m we’re mainly interested in 40m, 20m and perhaps 10m.  For 40m, we’re interested in 20m, 15m and 10m etc.  The ‘next-door’ bands and the WARC band aren’t really important so it’s no surprise to see that the 20m filter only gives 14dB of rejection on 17m or the 10m filter only gives 10dB of rejection on 12m.

It’s interesting to see that compared to the very popular Dunestar filters, the 5B4AGN TXBPF are superior in performance overall and at a much cheaper cost.  I seem to remember these worked out at about £40 each to build.

Of note is the exceptionally good insertion loss figures on these filters, varying from 0.19dB to just 0.31dB which compares very favourably with all the commercial filters I’ve seen.

Apart from the chart, I also plotted rejection/insertion loss against SWR for each filter.  Each image can be clicked to see a higher resolution version.

5B4AGN 80m bandpass filter performance plot

5B4AGN 80m bandpass filter performance plot

5B4AGN 40m bandpass filter performance plot

5B4AGN 40m bandpass filter performance plot

5B4AGN 20m bandpass filter performance plot

5B4AGN 20m bandpass filter performance plot

5B4AGN 15m bandpass filter performance plot

5B4AGN 15m bandpass filter performance plot

5B4AGN 10m bandpass filter performance plot

5B4AGN 10m bandpass filter performance plot

I built these as individual filters in their own boxes rather than having them all together and switchable for the simple reason that for a multi radio station, if the filters had been all boxed together then I would have had to build two or perhaps three sets at the additional cost and time.  I never expect to have two or more stations operating on the same band so therefore one set of filters is enough.  The rejection figures really do talk for themselves and once you’ve used bandpass filters on multi-station setups, you won’t want to operate without them.

If you run any kind of special event station, DXpedition or contest where you have multiple stations running, I really can’t recommend enough that you have a set of bandpass filters to hand.  There are a few different types of commercial filters with different levels of performance but it’s a great feeling to have built your own which perform better than the majority of commercial products at a cheaper price.

(I have no connection with Bob, 5B4AGN except for being a satisfied customer)

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