I purchased two inexpensive Baofeng BF-T1 UHF portables (hand-helds) for use around the yard.
- LiIon pouch single cell battery that may be obtainable longer than proprietary batteries;
- micro USB charger interface, internal charge / battery management;
- programmable with CHIRP (channel table only);
- chanellised operation, lockable keypad;
- CTCSS support;
- integrated antenna;
- small and lightweight (110g with belt clip);
The radio has been in the market for more than three years, so one might hope that design issues have been fixed in ‘mature’ product. Continue reading Baofeng BF-T1 (BF-9100) – initial impressions
This article documents a station for propagation observations on 144MHz, in this case the antenna system part of the entire system.
Above, the antenna is a 4 element Yagi with Gamma match. Continue reading 144MHz propagation experiment – antenna
At AIM4170 – de-embedding the feed line in remote measurement a set of measurements of a monoband antenna looking from the transmitter were analysed to de-embed the feed line and arrive at the indicated feed point impedance.
This article explores a simple series match to improve the load seen by the transmitter.
In the Simsmith model above, the estimated feed point impedance is imported into element L, then a series section of lossless 50Ω line to represent the coax in the common mode choke (balun), then a series section of lossless 75Ω to perform the impedance transformation, then a section of 50Ω lossless line to make up the required length to the transmitter. Continue reading AIM4170 – de-embedding the feed line in remote measurement – a simple match
At nanoVNA-H – de-embedding the feed line in remote measurement I recently wrote on a procedure that can be very useful to refer measurements made at the transmitter end of a feed line to the antenna feed point.
A correspondent recently shared an AIM 4170 scan file of his 40m half wave dipole antenna system taken from the transmitter end of the coax and maintaining the common mode current path by bonding the shield of the coax connector to normal connection point on the transmitter.
Above is his graphic of the measurement looking into around 23m of RG58 feed line.
It shows the VSWR curve is quite classic in shape, the frequency of minimum VSWR is a little low, and the minimum VSWR is 1.478 which is quite within expectations of such an antenna. Continue reading AIM4170 – de-embedding the feed line in remote measurement
I have a nanoVNA-H which has had many hardware problems, some designed in,but mostly sub-standard / faulty components.
Above, the latest repair. A new battery socket to replace the original that crumbled apart… sub-standard plastic from all appearances. This was from a reputable supplier, so it is probably a genuine Molex Picoblade part rather than some cheap Chinese knock off.
The blue wire is part of a mod to invoke the bootloader on power up, R5 was also changed to something small, 1k IIRC.
PS: a word of warning… always check polarity when fitting a battery, there is not rigid standardisation of connectors on LIPO batteries.
At nanoVNA-H – Port 2 attenuator for improved Return Loss I explained the reasons for essentially permanent attachment of a 10dB attenuator to Port 2 (Ch 1 in nanoVNA speak).
Above, the 10dB attenuator is semi permanently attached to Port 2 principally to improve the Return Loss (or impedance match) of Port 2, a parameter that becomes quite important when testing some types of networks than depend on proper termination (eg many filters). I should remind readers that the improvement in Port 2 Return Loss comes at a cost, the dynamic range of Port 2 is reduced by 10dB. Continue reading nanoVNA-H – Port 1 attenuator for improved what???
A friend wrote saying “I thought the nanoVNA display was smaller than this”.
I make the index finger nail width exactly the same as the round part of the SMA nut which is 7.6mm. That is a very tiny hand… or the image is a composite fraudulently not to scale. Continue reading nanoVNA – promotion by cheats
There is little doubt that the nanoVNA has made VNAs very popular in the ham community, possibly more so that any other device.
Eager owners are trying to apply them to solve lots of problems, often without sufficient knowledge or experience to properly inform the measurements.
An example that has a appeared a few times on online forums in the last weeks is measuring the matched line loss (MLL) of a section of RG6 coax… to inform a decision to discard it or keep it.
The common approach is to use a measurement of |s11| and to calculate Return Loss and infer the MLL.
For discussion, lets consider an example of 30′ of Belden 1694A RG6 solved in Simsmith. We should note that unlike most RG6 in the market today, this uses a solid copper centre conductor.
Short circuit termination
Some authors insist that the half return loss method is to be performed using a short circuit test section. Bird does this in their Bird 43 manual.
Above is a plot of calculated |s11| (-ReturnLoss) from 1 to 20MHz for the test section. The three plots are of |s11| wrt 50Ω, 75Ω and frequency dependent actual Zo (as calculated for the model). The cursor shows that the actual |s11| is -0.37474dB (ReturnLoss=0.37474dB). Using the half return loss method MLL=ReturnLoss/2=0.37474=0.187dB/m. Continue reading nanoVNA-H – woolly thinking on MLL measurement
A question was asked in an online forum specific to nanoVNA as to how the use the nanoVNA to
check the attenuation loss in some old & weathered RG-6 (75 ohm) cables for the TV signal frequencies. Excuse the term
attenuation loss, lets assume the poster is asking for matched line loss (MLL).
The assembled experts are offering solutions to transform the ports to 75Ω and make a measurement, deducting the loss of the transformation (minimum loss pads were suggested).
There is a very simple solution that should be quite practical for the scenario described. Let’s work through two examples using 35.5m of unbranded quad shield RG6 with CCS centre conductor (of unknown quality) for the DUT. Continue reading nanoVNA-H – thinking laterally
Users of some ATUs may have noticed particular sensitivity to hands on the capacitor adjustment knobs. It is a common problem with cheap implementations of the T match as the capacitor rotor is usually at high RF voltage and if that shaft is extended to the adjustment knob, under certain circumstances tuning becomes very sensitive to hands on the knobs.
In some of these implementations, if the users hand touches the metal grub screw in the knob, or the metal panel bushing behind the knob they may get a significant RF burn.
Let’s use the MFJ-949E as a discussion example. It is a T match, and the metal capacitor shafts in the knobs and panel bushings carry RF voltages.
So why is this only sometimes a problem?
The RF voltage across the coil, and impressed on the capacitor shafts can be extremely high when using loads with small resistance and large negative reactance, more so on the lower bands. Continue reading MFJ ATU hand effects on capacitor knobs