Saturday, 11 July 2020

Equipment List

Just a quick update on what I'm using..

  • Yaesu FT-7900 2m/70cm mobile. At home, connected to a 2m dipole in the loft (was in the car, but brought indoors recently).
  • CRT Millenium CB/10m mobile. In the car, with a springer mobile antenna on a Sirio magmount.
  • Yaesu FT-4X(E) 2m/70cm handheld. This is my main handheld radio for analogue FM.
  • Retevis RT8 VHF DMR handheld. Very similar to the TYT MD380 (same firmware and programming software). 
  • Wouxun KG-699E 68-88MHz handheld, covering the 4m amateur band. 
  • SDRPlay RSP1A software defined radio (receiver). Used for all bands, but at the moment it's my only receiver for SSB and data modes, so is often being used for receiving FT-8. 
  • The HF antenna is a dipole in roughly an L shape (no particular length), with one side along the gutter and the other sloping down to the garden fence.

Wednesday, 26 February 2020

Retevis RT-8

Got the VHF version of the Retevis RT-8 DMR handheld for Christmas. There it is alongside my Uniden UBC3500 on a trip to Newcastle last month. 


Tuesday, 17 December 2019

Last 20 QSOs

My last 20 radio contacts
95% FT8

Friday, 6 December 2019

10 Years On

Ten years ago to this day, I sat in the Ashton Under Lyne Travelodge and started this blog which is mostly about my amateur radio activities (well I'd made one post in 2007 with this account but forgotten about it).
Since then, I've discovered quite a few things:
Other digital modes such as JT65/FT8
SDRs - both receive and HF transceiver
Digital voice - I've tried D-Star and DMR (then there's Fusion and even Network Radio, which I've not tried)
The 23cm band - and it was from the Travelodge I ordered a handheld with 23cm.

I'm much less active from portable locations now (it's over 2 years since I did a qualifying SOTA activation), which has also meant I've not had as much to write about.
At the moment I'm mainly doing HF FT-8 and WSPR using 5-10 watts into a dipole that's partly hidden under the gutter, have a Yaesu FT-7900 dual band mobile fitted in the car and a few handheld radios which nearly always come out on walks (even if receive only and not in the hills).

Something has broken in the Comet GP-15 tri-bander on my chimney (probably the coax plug), so here is the temporary loft dipole for 144MHz, connected up when I recently got all the decorations down.

Friday, 5 April 2019

Yaesu FT-4XE

A couple of weeks ago I ordered myself a new dual band handheld, a Yaesu FT-4XE.
For the last 2 years, my main handheld transceiver had been a Baofeng GT-3, which cost only £30 but had some big problems, like being unable to use it anywhere there were other strong signals. On an external antenna at home it was unusable at VHF but even some locations out of doors strong broadcast signals were overloading it.
When Yaesu's new range of cheaper FM only handhelds came out, (FT-65, FT-25, FT-4), I suspected that they could be nothing more than rebadged Baofeng type radios, especially with them having features like FM broadcast reception (but no other wideband coverage of airband etc.). But after reading this review and it being the cheapest 'proper amateur' dual band radio by a long way, I decided to go for it.

It's a small radio, and you could almost call it credit card sized, here it is hiding behind a card.

 and next to the old GT-3
 Only a volume control on top, a tuning dial is one of the things you give up to save money. Using only buttons to move up and down frequency or through the memories is a pain unless you're going to be using the thing on a small number of channels. That and the slow scanning speed (6.5 channels per second, a whole 30% faster than the Baofeng's 5) are probably the things that make it still feel cheap. Some features may be limited by the transceiver on a chip RDA1846 which it shares with the Baofengs though. At least there are 200 memory channels for the radio to take a leisurely stroll through, compared with the Baofeng's 128.

Yes, it does 6.25KHz channels, at least for the 'E' model (the other model may not, there is nothing in the PDF version of the manual about it, with 5 and 10KHz being the minimum in there).

The real test of this radio's performance was connecting it to an outdoor antenna. I knew that the Baofeng could receive nothing on VHF when connected to my 6/2/70 tribander. The FT-4 received just fine, and gave realistic looking s-meter readings. There must be filtering to reject broadcast signals above (DAB) and below the receiver's 136-174MHz range, which is missing from the Baofeng.
S-meter S9 is around -96dBm and S5 is about 10dB lower, giving appoximately 2.5dB per point. There is a 'S10' and 'S11' above this.
The supplied antenna is about 16cm long, similar to other handhelds. For its size, it performed best near to the 144MHz amateur band compared to a few others of the same size I had around. On UHF though, it was actually worse than any other handheld antenna, which is surprising as I've found when testing handheld antennas at 430MHz there isn't very much difference between them, nowhere near as much as there is at VHF, and the higher frequency means a wider bandwidth.
Around 165MHz the antenna was worse than a no-name model of the same length which I paid less than £2 for on AliExpress, but that's going to be the price to pay for more efficiency on frequency, nowhere near as bad as the Alinco DJ-G7's stock antenna though.

Yaesu have made quite a good effort with the memory and tuning features of this radio, with 10 memory banks and 10 programmable band edges. Then there are Yaesu specific features like Automatic Range Transponder System, so obviously not just some other brand being re-badged.
The programming software is free from Yaesu, quite basic, no facility to import/export or sort frequencies, but allows you to organise the memory banks.
I found a video on YouTube showing the wiring of the programming cable (2-wire TTL, using R&S of a 3 pole 2.5mm jack plug) and made up a cable from an old FT-817 USB adaptor and a diode.

So, I wasn't disappointed with this radio, it was clear what it's limits were going to be before buying it (no tuning dial, no extremely wide receive coverage, no digital modes) but it does improve on the £20-£40 range of handhelds which are so common these days.
Unless you were going to use a handheld radio under very limited conditions (a local repeater which could be worked on a short antenna or indoors, monitoring a few channels rather than tying up a more expensive radio etc.), I'd definitely go for this rather than trying to save a few quid.

What about the FT-65? It's about another £25, bigger battery but is the performance going to be the same?

Saturday, 29 December 2018

DATA Socket

I'd been using an FT-847 with a data modes interface to my PC, completely isolated with transformers in both transmit and receive paths and a mechanical relay to switch the PTT. It used the 3.5mm jack on the rear of the FT-847, which is what you must use for transmitting on SSB (the usual 6-pin mini DIN is for FM transmit only).
Everything worked OK on data modes like FT-8 and WSPR, but I noticed that when making a recording of voice, there was something wrong with the frequency response. At first, I thought that this output might be bypassing the de-empasis circuit on FM, but when looking at the frequency response, even on SSB it rolled off below 1KHz.
The transformers I used in the interface were from a 'ground loop isolator' designed for car audio systems, and when tested between the output and input of the PC, showed a response within 2dB down to below 100Hz.
Eventually I thought about the transformers and their impedance. 600 ohms is a common value for them, maybe there was a mismatch between that and the output impedance of the radio.
Checking the schematic for the FT-847, the final op-amp in the 'RX1200' circuit goes to a 100nF capacitor, then this goes through separate 4K7 resistors to both the 3.5mm and DIN sockets.This would explain why there was such a big cut in low frequencies.
At the worst case, driving a short circuit, the 4K7 and 100nF would make a high pass filter with a frequency of about 340Hz. The specification of the data output says a 10K impedance, and with a 10K impedance (which would be in series with the 4K7), the frequency would be around 100Hz. That's fine for any voice or data modes, even 340Hz would be usable.
But the transformer will also create a R-L high pass filter, with its impedance increasing with frequency (DC resistance is about 100 ohms so increasing from that), against the 4K7 resistor. This output is not really suitable for driving an isolating transformer if you want anything like a flat frequency response.
The resistor and capacitor could be replaced with different values (higher capacitance, lower resistance).
I had a look a schematics for other radios made by Yaesu, that had a 6-pin data socket. Although they all used similar op-amps to drive the RX1200 output (NJM2902), 3 radios had 3 different combinations of resistor and capacitor in series.
FT-847 - 4K7 / 100nF
FT-817 - 1K / 1uF
FT-8900 - 220R / 1uF
That's a 20:1 range of output impedances, although every time this is specified as for use with 10K input impedance on whatever equipment is connected. If you're making a direct connection from the radio to the Line In of a PC or amplifier, it probably won't matter as the input impedance will be quite high. But the circuits for most home built and commercial data mode interfaces have isolating transformers, and will affect the frequency response.

Thursday, 22 February 2018


After reading on Twitter that some people were trying the very popular FT8 data mode on 144MHz, I had a go. I don't have anything like a VHF DX station at home, with just a Comet GP15 vertical on the chimney, fed with a bit too much coax.
The frequency for 2m FT8 is 144.174.
I started off using my new SDRPlay receiver and found that I was able to decode a few stations, outside my usual VHF range (G4KUX in IO94 and GM4FVM in IO85).
After connecting up a transceiver, I was able to make some 2-way contacts at this distance, and was even getting reception reports of my signal via PSK Reporter from up to around 300km. This makes the 2m band a bit more interesting, and because data modes software like WSJT-X automatically sends reports to PSK Reporter, even if I'm away from the radio, it's still worth leaving it on all day just in case someone calls CQ.
At the moment, there aren't really any 'lift' conditions on 144MHz, at least not which you would hear if listening to FM or even SSB, and most of the long distance propagation is from reflections off aircraft. Reflections off fast moving objects like aircraft shift the frequency from the doppler effect, and it can be over 100Hz. With FT8, the bandwidth is very narrow, so if there are multiple paths, the same signal can appear on 2 different frequencies. See below for some FT8 activity where there are multiple decodes.

On some days I've received 10 different stations on 144MHz FT8.